LTC1992 Family
1
1992fb
TYPICAL APPLICATION
FEATURES DESCRIPTION
Low Power, Fully Differential
Input/Output
Amplifier/Driver Family
The LTC
®
1992 product family consists of five fully differen-
tial, low power amplifiers. The LTC1992 is an unconstrained
fully differential amplifier. The LTC1992-1, LTC1992-2,
LTC1992-5 and LTC1992-10 are fixed gain blocks (with
gains of 1, 2, 5 and 10 respectively) featuring precision
on-chip resistors for accurate and ultrastable gain. All of
the LTC1992 parts have a separate internal common mode
feedback path for outstanding output phase balancing
and reduced second order harmonics. The VOCM pin sets
the output common mode level independent of the input
common mode level. This feature makes level shifting of
signals easy.
The amplifiers’ differential inputs operate with signals
ranging from rail-to-rail with a common mode level from
the negative supply up to 1.3V from the positive supply.
The differential input DC offset is typically 250μV. The
rail-to-rail outputs sink and source 10mA. The LTC1992
is stable for all capacitive loads up to 10,000pF.
The LTC1992 can be used in single supply applications
with supply voltages as low as 2.7V. It can also be used
with dual supplies up to ±5V. The LTC1992 is available in
an 8-pin MSOP package.
Single-Supply, Single-Ended to Differential Conversion
APPLICATIONS
n Available with Adjustable Gain or Fixed Gain of 1,
2, 5 or 10
n ±0.3% (Max) Gain Error from –40°C to 85°C
n 3.5ppm/°C Gain Temperature Coefficient
n 5ppm Gain Long Term Stability
n Fully Differential Input and Output
n C
LOAD Stable up to 10,000pF
n Adjustable Output Common Mode Voltage
n Rail-to-Rail Output Swing
n Low Supply Current: 1mA (Max)
n High Output Current: 10mA (Min)
n Specified on a Single 2.7V to ±5V Supply
n DC Offset Voltage <2.5mV (Max)
n Available in 8-Lead MSOP Package
n Differential Driver/Receiver
n Differential Amplification
n Single-Ended to Differential Conversion
n Level Shifting
n Trimmed Phase Response for Multichannel Systems
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
–
–
+
+
5V
5V
LTC1992
3
6
VOCM
VMID 0V
2.5V
0V
VIN
0.01μF
1992 TA01a
4
5
2
7
8
1
10k
10k
10k
10k
5V
0V
5V
–5V
2.5V
INPUT SIGNAL
FROM A
±5V SYSTEM
OUTPUT SIGNAL
FROM A
SINGLE-SUPPLY SYSTEM
VIN
(5V/DIV)
+OUT
–OUT
(2V/DIV)
5V
0V
–5V
5V
0V
1992 TA01b
LTC1992 Family
2
1992fb
ABSOLUTE MAXIMUM RATINGS
Total Supply Voltage (+VS to –VS) ............................. 12V
Maximum Voltage
on any Pin ................ (–VS – 0.3V) ≤ VPIN ≤ (+VS + 0.3V)
Output Short-Circuit Duration (Note 3) ............ Indefinite
Operating Temperature Range (Note 5)
LTC1992CMS8/LTC1992-XCMS8/
LTC1992IMS8/LTC1992-XIMS8 ...........–40°C to 85°C
LTC1992HMS8/LTC1992-XHMS8 ...... –40°C to 125°C
(Note 1)
PIN CONFIGURATION
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE
LTC1992CMS8#PBF LTC1992CMS8#TRPBF LTYU 8-Lead Plastic MSOP 0°C to 70°C
LTC1992IMS8#PBF LTC1992IMS8#TRPBF LTYU 8-Lead Plastic MSOP –40°C to 85°C
LTC1992HMS8#PBF LTC1992HMS8#TRPBF LTYU 8-Lead Plastic MSOP –40°C to 125°C
LTC1992-1CMS8#PBF LTC1992-1CMS8#TRPBF LTACJ 8-Lead Plastic MSOP 0°C to 70°C
LTC1992-1IMS8#PBF LTC1992-1IMS8#TRPBF LTACJ 8-Lead Plastic MSOP –40°C to 85°C
LTC1992-1HMS8#PBF LTC1992-1HMS8#TRPBF LTACJ 8-Lead Plastic MSOP –40°C to 125°C
LTC1992-2CMS8#PBF LTC1992-2CMS8#TRPBF LTYV 8-Lead Plastic MSOP 0°C to 70°C
LTC1992-2IMS8#PBF LTC1992-2IMS8#TRPBF LTYV 8-Lead Plastic MSOP –40°C to 85°C
LTC1992-2HMS8#PBF LTC1992-2HMS8#TRPBF LTYV 8-Lead Plastic MSOP –40°C to 125°C
LTC1992-5CMS8#PBF LTC1992-5CMS8#TRPBF LTACK 8-Lead Plastic MSOP 0°C to 70°C
LTC1992-5IMS8#PBF LTC1992-5IMS8#TRPBF LTACK 8-Lead Plastic MSOP –40°C to 85°C
LTC1992-5HMS8#PBF LTC1992-5HMS8#TRPBF LTACK 8-Lead Plastic MSOP –40°C to 125°C
LTC1992-10CMS8#PBF LTC1992-10CMS8#TRPBF LTACL 8-Lead Plastic MSOP 0°C to 70°C
LTC1992-10IMS8#PBF LTC1992-10IMS8#TRPBF LTACL 8-Lead Plastic MSOP –40°C to 85°C
LTC1992-10HMS8#PBF LTC1992-10HMS8#TRPBF LTACL 8-Lead Plastic MSOP –40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
Specified Temperature Range (Note 6)
LTC1992CMS8/LTC1992-XCMS8 ............. 0°C to 70°C
LTC1992IMS8/LTC1992-XIMS8 ...........–40°C to 85°C
LTC1992HMS8/LTC1992-XHMS8 ...... –40°C to 125°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec) ...................300°C
LTC1992 LTC1992-X
1
2
3
4
–IN
VOCM
+VS
+OUT
8
7
6
5
+IN
VMID
–VS
–OUT
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
+
+
–
–
TJMAX = 150°C, θJA = 250°C/W
1
2
3
4
–IN
VOCM
+VS
+OUT
8
7
6
5
+IN
VMID
–VS
–OUT
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
+
+
–
–
TJMAX = 150°C, θJA = 250°C/W
LTC1992 Family
3
1992fb
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise
noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is
defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Specifications applicable to all parts in the LTC1992 family.
SYMBOL PARAMETER CONDITIONS
ALL C AND I GRADE ALL H GRADE
UNITSMIN TYP MAX MIN TYP MAX
VSSupply Voltage Range l2.7 11 2.7 11 V
ISSupply Current VS = 2.7V to 5V
VS = ±5V
l
l
0.65
0.75
0.7
0.8
1.0
1.2
1.2
1.5
0.65
0.8
0.7
0.9
1.0
1.5
1.2
1.8
mA
mA
mA
mA
VOSDIFF Differential Offset Voltage
(Input Referred) (Note 7)
VS = 2.7V
VS = 5V
VS = ±5V
l
l
l
±0.25
±0.25
±0.25
±2.5
±2.5
±2.5
±0.25
±0.25
±0.25
±4
±4
±4
mV
mV
mV
ΔVOSDIFF/ΔT Differential Offset Voltage Drift
(Input Referred) (Note 7)
VS = 2.7V
VS = 5V
VS = ±5V
l
l
l
10
10
10
10
10
10
μV/°C
μV/°C
μV/°C
PSRR Power Supply Rejection Ratio
(Input Referred) (Note 7)
VS = 2.7V to ±5V l75 80 72 80 dB
GCM Common Mode Gain(VOUTCM/VOCM)
Common Mode Gain Error
Output Balance (ΔVOUTCM/(ΔVOUTDIFF)V
OUTDIFF = –2V to +2V
l
l
l
1
±0.1
–85
±0.3
–60
1
±0.1
–85
±0.35
–60
%
dB
VOSCM Common Mode Offset Voltage
(VOUTCM – VOCM)
VS = 2.7V
VS = 5V
VS = ±5V
l
l
l
±0.5
±1
±2
±12
±15
±18
±0.5
±1
±2
±15
±17
±20
mV
mV
mV
ΔVOSCM/ΔT Common Mode Offset Voltage Drift VS = 2.7V
VS = 5V
VS = ±5V
l
l
l
10
10
10
10
10
10
μV/°C
μV/°C
μV/°C
VOUTCMR Output Signal Common Mode Range
(Voltage Range for the VOCM Pin)
l(–VS) + 0.5V (+VS) – 1.3V (–VS) + 0.5V (+VS) – 1.3V V
RINVOCM Input Resistance, VOCM Pin l500 500 MΩ
IBVOCM Input Bias Current, VOCM Pin VS = 2.7V to ±5V l±2 ±2 pA
VMID Voltage at the VMID Pin l2.44 2.50 2.56 2.43 2.50 2.57 V
VOUT Output Voltage, High
(Note 2)
VS = 2.7V, Load = 10k
VS = 2.7V, Load = 5mA
VS = 2.7V, Load = 10mA
l
l
l
2.60
2.50
2.29
2.69
2.61
2.52
2.60
2.50
2.29
2.69
2.61
2.52
V
V
V
Output Voltage, Low
(Note 2)
VS = 2.7V, Load = 10k
VS = 2.7V, Load = 5mA
VS = 2.7V, Load = 10mA
l
l
l
0.02
0.10
0.20
0.10
0.25
0.35
0.02
0.10
0.20
0.10
0.25
0.41
V
V
V
Output Voltage, High
(Note 2)
VS = 5V, Load = 10k
VS = 5V, Load = 5mA
VS = 5V, Load = 10mA
l
l
l
4.90
4.85
4.75
4.99
4.90
4.81
4.90
4.80
4.70
4.99
4.90
4.81
V
V
V
Output Voltage, Low
(Note 2)
VS = 5V, Load = 10k
VS = 5V, Load = 5mA
VS = 5V, Load = 10mA
l
l
l
0.02
0.10
0.20
0.10
0.25
0.35
0.02
0.10
0.20
0.10
0.30
0.42
V
V
V
Output Voltage, High
(Note 2)
VS = ±5V, Load = 10k
VS = ±5V, Load = 5mA
VS = ±5V, Load = 10mA
l
l
l
4.90
4.85
4.65
4.99
4.89
4.80
4.85
4.80
4.60
4.99
4.89
4.80
V
V
V
Output Voltage, Low
(Note 2)
VS = ±5V, Load = 10k
VS = ±5V, Load = 5mA
VS = ±5V, Load = 10mA
l
l
l
–4.99
–4.90
–4.80
–4.90
–4.75
–4.65
–4.98
–4.90
–4.80
–4.85
–4.75
–4.55
V
V
V
LTC1992 Family
4
1992fb
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise
noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is
defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Specifications applicable to all parts in the LTC1992 family.
SYMBOL PARAMETER CONDITIONS
ALL C AND I GRADE ALL H GRADE
UNITSMIN TYP MAX MIN TYP MAX
ISC Output Short-Circuit Current
Sourcing (Notes 2,3)
VS = 2.7V, VOUT =1.35V
VS = 5V, VOUT = 2.5V
VS = ±5V, VOUT = 0V
l
l
l
20
20
20
30
30
30
20
20
20
30
30
30
mA
mA
mA
Output Short-Circuit Current Sinking
(Notes 2,3)
VS = 2.7V, VOUT =1.35V
VS = 5V, VOUT = 2.5V
VS = ±5V, VOUT = 0V
l
l
l
13
13
13
30
30
30
13
13
13
30
30
30
mA
mA
mA
AVOL Large-Signal Voltage Gain l80 80 dB
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
+VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined
as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT).
Specifications applicable to the LTC1992 only.
SYMBOL PARAMETER CONDITIONS
LTC1992CMS8
LTC1992ISM8 LTC1992HMS8
UNITSMIN TYP MAX MIN TYP MAX
IBInput Bias Current VS = 2.7V to ±5V l2 250 2 400 pA
IOS Input Offset Current VS = 2.7V to ±5V l0.1 100 0.1 150 pA
RIN Input Resistance l500 500 MΩ
CIN Input Capacitance l33pF
enInput Referred Noise Voltage Density f = 1kHz 35 35 nV/√Hz
inInput Noise Current Density f = 1kHz 1 1 fA/√Hz
VINCMR Input Signal Common Mode Range l(–VS) – 0.1V (+VS) – 1.3V (–VS) – 0.1V (+VS) – 1.3V V
CMRR Common Mode Rejection Ratio
(Input Referred)
VINCM = –0.1V to 3.7V l69 90 69 90 dB
SR Slew Rate (Note 4) l0.5 1.5 0.5 1.5 V/μs
GBW Gain-Bandwidth Product
(fTEST = 100kHz)
TA = 25°C
LTC1992CMS8
LTC1992IMS8/
LTC1992HMS8
l
l
3.0
2.5
1.9
3.2
3.0
3.5
4.0
4.0
3.0
1.9
3.2 3.5
4.0
MHz
MHz
MHz
LTC1992 Family
5
1992fb
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise
noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is
defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Typical values are at TA = 25°C. Specifications apply to the
LTC1992-1 only.
SYMBOL PARAMETER CONDITIONS
LTC1992-1CMS8
LTC1992-1ISM8 LTC1992-1HMS8
UNITSMIN TYP MAX MIN TYP MAX
GDIFF Differential Gain
Differential Gain Error
Differential Gain Nonlinearity
Differential Gain Temperature Coefficient
l
l
1
±0.1
50
3.5
±0.3
1
±0.1
50
3.5
±0.35
V/V
%
ppm
ppm/°C
enInput Referred Noise Voltage Density (Note 7) f = 1kHz 45 45 nV/√Hz
RIN Input Resistance, Single-Ended +IN, –IN Pins l22.5 30 37.5 22 30 38 kΩ
VINCMR Input Signal Common Mode Range VS = 5V –0.1V to 4.9V –0.1V to 4.9V V
CMRR Common Mode Rejection Ratio
(Amplifier Input Referred) (Note 7)
VINCM = –0.1V to 3.7V l55 60 55 60 dB
SR Slew Rate (Note 4) l0.5 1.5 0.5 1.5 V/μs
GBW Gain-Bandwidth Product fTEST = 180kHz 3 3 MHz
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
+VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined
as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT).
Typical values are at TA = 25°C. Specifications apply to the LTC1992-2 only.
SYMBOL PARAMETER CONDITIONS
LTC1992-2CMS8
LTC1992-2ISM8 LTC1992-2HMS8
UNITSMIN TYP MAX MIN TYP MAX
GDIFF Differential Gain
Differential Gain Error
Differential Gain Nonlinearity
Differential Gain Temperature Coefficient
l
l
2
±0.1
50
3.5
±0.3
2
±0.1
50
3.5
±0.35
V/V
%
ppm
ppm/°C
enInput Referred Noise Voltage Density (Note 7) f = 1kHz 45 45 nV/√Hz
RIN Input Resistance, Single-Ended +IN, –IN Pins l22.5 30 37.5 22 30 38 kΩ
VINCMR Input Signal Common Mode Range VS = 5V –0.1V to 4.9V –0.1V to 4.9V V
CMRR Common Mode Rejection Ratio
(Amplifier Input Referred) (Note 7)
VINCM = –0.1V to 3.7V l55 60 55 60 dB
SR Slew Rate (Note 4) l0.7 2 0.7 2 V/μs
GBW Gain-Bandwidth Product fTEST = 180kHz 4 4 MHz
LTC1992 Family
6
1992fb
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise
noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is
defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Typical values are at TA = 25°C. Specifications apply to the
LTC1992-5 only.
SYMBOL PARAMETER CONDITIONS
LTC1992-5CMS8
LTC1992-5ISM8 LTC1992-5HMS8
UNITSMIN TYP MAX MIN TYP MAX
GDIFF Differential Gain
Differential Gain Error
Differential Gain Nonlinearity
Differential Gain Temperature Coefficient
l
l
5
±0.1
50
3.5
±0.3
5
±0.1
50
3.5
±0.35
V/V
%
ppm
ppm/°C
enInput Referred Noise Voltage Density (Note 7) f = 1kHz 45 45 nV/√Hz
RIN Input Resistance, Single-Ended +IN, –IN Pins l22.5 30 37.5 22 30 38 kΩ
VINCMR Input Signal Common Mode Range VS = 5V –0.1V to 3.9V –0.1V to 3.9V V
CMRR Common Mode Rejection Ratio
(Amplifier Input Referred) (Note 7)
VINCM = –0.1V to 3.7V l55 60 55 60 dB
SR Slew Rate (Note 4) l0.7 2 0.7 2 V/μs
GBW Gain-Bandwidth Product fTEST = 180kHz 4 4 MHz
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
+VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined
as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT).
Typical values are at TA = 25°C. Specifications apply to the LTC1992-10 only.
SYMBOL PARAMETER CONDITIONS
LTC1992-10CMS8
LTC1992-10ISM8 LTC1992-10HMS8
UNITSMIN TYP MAX MIN TYP MAX
GDIFF Differential Gain
Differential Gain Error
Differential Gain Nonlinearity
Differential Gain Temperature Coefficient
l
l
10
±0.1
50
3.5
±0.3
10
±0.1
50
3.5
±0.35
V/V
%
ppm
ppm/°C
enInput Referred Noise Voltage Density (Note 7) f = 1kHz 45 45 nV/√Hz
RIN Input Resistance, Single-Ended +IN, –IN Pins l11.3 15 18.8 11 15 19 kΩ
VINCMR Input Signal Common Mode Range VS = 5V –0.1V to 3.8V –0.1V to 3.8V V
CMRR Common Mode Rejection Ratio
(Amplifier Input Referred) (Note 7)
VINCM = –0.1V to 3.7V l55 60 55 60 dB
SR Slew Rate (Note 4) l0.7 2 0.7 2 V/μs
GBW Gain-Bandwidth Product fTEST = 180kHz 4 4 MHz
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: Output load is connected to the midpoint of the +VS and –VS
potentials. Measurement is taken single-ended, one output loaded at a
time.
Note 3: A heat sink may be required to keep the junction temperature
below the absolute maximum when the output is shorted indefinitely.
Note 4: Differential output slew rate. Slew rate is measured single ended
and doubled to get the listed numbers.
Note 5: The LTC1992C/LTC1992-XC/LTC1992I/LTC1992-XI are guaranteed
functional over an operating temperature of –40°C to 85°C. The
LTC1992H/LTC1992-XH are guaranteed functional over the extended
operating temperature of –40°C to 125°C.
Note 6: The LTC1992C/LTC1992-XC are guaranteed to meet the specified
performance limits over the 0°C to 70°C temperature range and are
designed, characterized and expected to meet the specified performance
limits over the –40°C to 85°C temperature range but are not tested or QA
sampled at these temperatures. The LTC1992I/LTC1992-XI are guaranteed
to meet the specified performance limits over the –40°C to 85°C
temperature range. The LTC1992H/LTC1992-XH are guaranteed to meet the
specified performance limits over the –40°C to 125°C temperature range.
Note 7: Differential offset voltage, differential offset voltage drift, CMRR,
noise voltage density and PSRR are referred to the internal amplifier’s
input to allow for direct comparison of gain blocks with discrete amplifiers.
LTC1992 Family
7
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Common Mode Offset Voltage
vs VOCM Voltage
Common Mode Offset Voltage
vs VOCM Voltage
Common Mode Offset Voltage
vs VOCM Voltage
Output Voltage Swing
vs Output Load, VS = 2.7V
Output Voltage Swing
vs Output Load, VS = 5V
Supply Current vs Supply Voltage
Differential Input Offset Voltage
vs Temperature (Note 7)
Common Mode Offset Voltage
vs Temperature
Applicable to all parts in the LTC1992 family.
TOTAL SUPPLY VOLTAGE (V)
0
SUPPLY CURRENT (mA)
0.6
0.8
1.0
8
1992 G01
0.4
0.2
0.5
0.7
0.9
0.3
0.1
021 43 67 9
510
125°C
85°C
25°C
–40°C
TEMPERATURE (°C)
–40
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
1992 G02
25 85 125
DIFFERENTIAL VOS (mV)
VINCM = 0V
VOCM = 0V
VS = ±1.35V
VS = ±2.5V
VS = ±5V
TEMPERATURE (°C)
–40
–5
COMMON MODE VOS (mV)
–4
–2
–1
0
85
4
1992 G03
–3
25 125
1
2
3
VINCM = 0V
VOCM = 0V
VS = ±5V
VS = ±1.35V
VS = ±2.5V
VOCM VOLTAGE (V)
0
–20
VOCM VOS (mV)
–15
–5
0
5
0.6 1.2 1.5 2.7
1992 G04
–10
0.3 0.9 1.8 2.1 2.4
125°C
85°C
25°C
–40°C
+VS = 2.7V
–VS = 0V
VINCM = 1.35V
VOCM VOLTAGE (V)
0
VOCM VOS (mV)
–5
0
5
4
1992 G05
–10
–15
–20 0.5 1 1.5 2 2.5 3 3.5 4.5 5
+VS = 5V
–VS = 0V
VINCM = 2.5V
125°C
85°C
25°C
–40°C
VOCM VOLTAGE (V)
–5
VOCM VOS (mV)
–5
0
5
3
1992 G06
–10
–15
–20 –4 –3 –2 –1 0 12 45
+VS = 5V
–VS = –5V
VINCM = 0V
125°C
85°C
25°C
–40°C
LOAD CURRENT (mA)
–20
+SWING (V)
–SWING (V)
2.50
2.60
20
1992 G07
2.40
2.30 –10 010
–15 –5 515
2.70
2.45
2.55
2.35
2.65
0.4
0.6
0.2
0
0.8
0.3
0.5
0.1
0.7
–40°C
–40°C
125°C
125°C
25°C
85°C
85°C
25°C
LOAD CURRENT (mA)
–20 20
4.50
+SWING (V)
–SWING (V)
4.55
4.65
4.70
4.75
5.00
4.85
–10 0
1992 G08
4.60
4.90
4.95
4.80
0
0.1
0.3
0.4
0.5
1.0
0.7
0.2
0.8
0.9
0.6
10 15
–15 –5 5
–40°C
–40°C
125°C
125°C
85°C
85°C
25°C
25°C
LTC1992 Family
8
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Differential Gain vs Time
(Normalized to t = 0)
Input Common Mode Overdrive
Recovery (Expanded View)
Input Common Mode Overdrive
Recovery (Detailed View)
Output Overdrive Recovery
(Expanded View)
Output Overdrive Recovery
(Detailed View)
Output Voltage Swing
vs Output Load, VS = ±5V
VOCM Input Bias Current
vs VOCM Voltage
Differential Input Offset Voltage
vs Time (Normalized to t = 0)
Applicable to all parts in the LTC1992 family.
LOAD CURRENT (mA)
–20
4.4
+SWING (V)
–SWING (V)
4.5
4.6
4.7
4.8
–10 0 10 20–15 –5 515
1992 G09
4.9
5.0
–5.0
–4.8
–4.6
–4.4
–4.2
–4.0
–3.8
–40°C
–40°C
125°C
125°C
85°C
25°C
85°C
25°C
VOCM VOLTAGE (V)
0 0.5 1
VOCM INPUT BIAS CURRENT (A)
1.5 2 2.5 3 3.5 4 4.5 5
1992 G10
100E-15
10E-9
1E-9
100E-12
10E-12
1E-12 +VS = 5V
–VS = 0V
VINCM = 2.5V
125°C
85°C
25°C
–40°C
TIME (HOURS)
100
80
60
40
20
0
–20
–40
–60
–80
–100
DELTA VOS (μV)
1992 G11
0 400 800 1200 1600 2000
TEMP = 35°C
TIME (HOURS)
10
8
6
4
2
0
–2
–4
–6
–8
–10
DELTA GAIN (ppm)
1992 G12
0 400 800 1200 1600 2000
TEMP = 35°C
50μs/DIV
1V/DIV
1992 G13
BOTH INPUTS
(INPUTS TIED
TOGETHER)
OUTPUTS
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
LTC1992-10 SHOWN
FOR REFERENCE
1μs/DIV
1V/DIV
1992 G14
BOTH INPUTS
(INPUTS TIED TOGETHER)
OUTPUTS
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
LTC1992-10 SHOWN
FOR REFERENCE
50μs/DIV
1V/DIV
1992 G15
+VS = 2.5V, –VS = –2.5V, VOCM = 0V
OUTPUTSINPUTS
LTC1992-2 SHOWN FOR REFERENCE
5μs/DIV
1V/DIV
1992 G16
INPUTS OUTPUTS
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
LTC1992-2 SHOWN
FOR REFERENCE
LTC1992 Family
9
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
Common Mode Rejection Ratio
vs Frequency (Note 7)
Power Supply Rejection Ratio
vs Frequency (Note 7) Output Balance vs Frequency
Differential Input Differential
Gain vs Frequency, VS = ±2.5V
Single-Ended Input Differential
Gain vs Frequency, VS = ±2.5V
Differential Phase Response
vs Frequency
Applicable to the LTC1992 only.
FREQUENCY (kHz)
10
–24
GAIN (dB)
–18
–12
–6
0
100 1000 10000
1992 G17
–30
–36
–42
–66
–60
–54
–48
6
12
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
RIN = RFB = 10k
FREQUENCY (kHz)
10
–24
GAIN (dB)
–18
–12
–6
0
100 1000 10000
1992 G18
–30
–36
–42
–66
–60
–54
–48
6
12
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
RIN = RFB = 10k
FREQUENCY (kHz)
10
PHASE (DEG)
0
–20
–40
–60
–80
–100
–120
–140
–160
–180 100 1000
1992 G37
CLOAD =
10pF
50pF
100pF
500pF
1000pF
5000pF
10000pF
RIN = RFB = 10k
COMMON MODE VOLTAGE (V)
0
DIFFERENTIAL VOS (mV)
1922 G20
0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
125°C
–40°C
25°C 85°C
+VS = 2.7V
–VS = 0V
VOCM = 1.35V
COMMON MODE VOLTAGE (V)
0 4.0
1922 G21
1.00.5 1.5 2.5 3.5 4.5
2.0 3.0 5.0
125°C
–40°C
85°C
25°C
DIFFERENTIAL VOS (mV)
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
+VS = 5V
–VS = 0V
VOCM = 2.5V
COMMON MODE VOLTAGE (V)
–5 3
1922 G22
–3–4 –2 0 2 4
–1 15
125°C
–40°C
85°C
DIFFERENTIAL VOS (mV)
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
25°C
+VS = 5V
–VS = –5V
VOCM = 0V
FREQUENCY (Hz)
40
CMRR (dB)
80
120
20
60
100
100 10k 100k 1M
1992 G23
01k
ΔVAMPCM
ΔVAMPDIFF
FREQUENCY (Hz)
10
40
PSRR (dB)
50
60
70
80
100 1k 10k 100k 1M
1992 G24
30
20
10
0
90
100
–VS
+VS
ΔVS
ΔVAMPDIFF
FREQUENCY (Hz)
110
–40
OUTPUT BALANCE (dB)
–60
–80
100 1k 10k 100k 1M
1992 G25
–20
0
–100
ΔVOUTCM
ΔVOUTDIFF
LTC1992 Family
10
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Single-Ended Input Large-Signal
Step Response
Single-Ended Input Large-Signal
Step Response
Differential Input Small-Signal
Step Response
Differential Input Small-Signal
Step Response
Differential Input Large-Signal
Step Response
Differential Input Large-Signal
Step Response
Applicable to the LTC1992 only.
2μs/DIV
VOUTDIFF (1V/DIV)
1992 G26
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±1.5V
–VIN = 1.5V
CLOAD = 0pF
GAIN = 1
0V
±
20μs/DIV 1992 G27
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±1.5V
–VIN = 1.5V
GAIN = 1
CLOAD = 10000pF
CLOAD = 1000pF
VOUTDIFF (1V/DIV)
0V
±
2μs/DIV
VOUTDIFF (1V/DIV)
1992 G28
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 4V
–VIN = 2V
CLOAD = 0pF
GAIN = 1
2.5V
20μs/DIV
VOUTDIFF (1V/DIV)
1992 G29
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 4V
–VIN = 2V
GAIN = 1
CLOAD = 10000pF
CLOAD = 1000pF
2.5V
1μs/DIV
VOUTDIFF (50mV/DIV)
1992 G30
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±50mV
–VIN = 50mV
CLOAD = 0pF
GAIN = 1
0V
±
10μs/DIV
VOUTDIFF (50mV/DIV)
1992 G31
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±50mV
–VIN = 50mV
GAIN = 1
CLOAD = 10000pF
CLOAD = 1000pF
0V
±
LTC1992 Family
11
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
THD + Noise vs Frequency THD + Noise vs Amplitude
Differential Noise Voltage Density
vs Frequency
VOCM Gain vs Frequency,
VS = ±2.5V
Single-Ended Input Small-Signal
Step Response
Single-Ended Input Small-Signal
Step Response
Applicable to the LTC1992 only.
FREQUENCY (kHz)
10
–15
GAIN (dB)
–5
5
100 1000 10000
1992 G19
–25
–20
–10
0
–30
–35
CLOAD = 10pF TO 10000pF
1μs/DIV
VOUTDIFF (50mV/DIV)
1992 G32
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 200mV
–VIN = 100mV
CLOAD = 0pF
GAIN = 1
2.5V
10μs/DIV
VOUTDIFF (50mV/DIV)
1992 G33
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 200mV
–VIN = 100mV
GAIN = 1
CLOAD = 10000pF
CLOAD = 1000pF
2.5V
FREQUENCY (Hz)
100
–100
THD + NOISE (dB)
–60
–50
–40
1k 10k 50k
1992 G34
–70
–80
–90
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–VS = –5V
VOCM = 0V
VOUT = 1VP-PDIFF
VOUT = 2VP-PDIFF
VOUT = 10VP-PDIFF
VOUT = 5VP-PDIFF
INPUT SIGNAL AMPLITUDE (VP-PDIFF)
0.1
–100
THD + NOISE (dB)
–90
–80
–70
–60
–40
11020
1992 G35
–50
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–VS = –5V
VOCM = 0V
50kHz
20kHz
10kHz
5kHz
2kHz 1kHz
FREQUENCY (Hz)
INPUT REFERRED NOISE (nV√Hz)
1000
100
10 100 1000 10000
1922 G36
10
LTC1992 Family
12
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Gain Error
vs Temperature VOCM Gain vs Frequency
Differential Input Differential
Gain vs Frequency, VS = ±2.5V
Single-Ended Input Differential
Gain vs Frequency, VS = ±2.5V
Differential Phase Response
vs Frequency
Applicable to the LTC1992-1 only.
FREQUENCY (kHz)
10
–24
GAIN (dB)
–18
–12
–6
0
100 1000 10000
1992 G38
–30
–36
–42
–66
–60
–54
–48
6
12
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
FREQUENCY (kHz)
10
–24
GAIN (dB)
–18
–12
–6
0
100 1000 10000
1992 G39
–30
–36
–42
–66
–60
–54
–48
6
12
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
FREQUENCY (kHz)
10
PHASE (DEG)
0
–20
–40
–60
–80
–100
–120
–140
–160
–180 100 1000
1992 G40
CLOAD =
10pF
50pF
100pF
500pF
1000pF
5000pF
10000pF
TEMPERATURE (°C)
–50
GAIN ERROR (%)
0.025
0.020
0.015
0.010
0.005
0
–0.005
–0.010
–0.015
–0.020
–0.025 050 75
1992 G41
–25 25 100 125
FREQUENCY (kHz)
10
–15
GAIN (dB)
–5
5
100 1000 10000
1992 G42
–25
–20
–10
0
–30
–35
CLOAD = 10pF TO 10000pF
COMMON MODE VOLTAGE (V)
0
DIFFERENTIAL VOS (mV)
1922 G43
0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7
5
4
3
2
1
0
–1
–2
–3
–4
–5
125°C
–40°C
85°C
25°C
+VS = 2.7V
–VS = 0V
VOCM = 1.35V
COMMON MODE VOLTAGE (V)
0
1922 G44
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
125°C
–40°C
85°C
25°C
DIFFERENTIAL VOS (mV)
5
4
3
2
1
0
–1
–2
–3
–4
–5
+VS = 5V
–VS = 0V
VOCM = 2.5V
COMMON MODE VOLTAGE (V)
–5
1922 G45
–4 –3 –2 –1 0 1 2 3 4 5
125°C
–40°C 85°C
25°C
DIFFERENTIAL VOS (mV)
5
4
3
2
1
0
–1
–2
–3
–4
–5
+VS = 5V
–VS = –5V
VOCM = 0V
LTC1992 Family
13
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Single-Ended Input Large-Signal
Step Response
Single-Ended Input Large-Signal
Step Response
Power Supply Rejection Ratio
vs Frequency
Differential Input Small-Signal
Step Response
Differential Input Small-Signal
Step Response Output Balance vs Frequency
Differential Input Large-Signal
Step Response
Differential Input Large-Signal
Step Response
Common Mode Rejection Ratio
vs Frequency
Applicable to the LTC1992-1 only.
2μs/DIV
VOUTDIFF (1V/DIV)
1992 G46
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±1.5V
–VIN = 1.5V
CLOAD = 0pF
0V
±
20μs/DIV
VOUTDIFF (1V/DIV)
1992 G47
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±1.5V
–VIN = 1.5V
CLOAD = 10000pF
CLOAD = 1000pF
0V
±
FREQUENCY (Hz)
30
CMRR (dB)
90
100
20
10
80
50
70
60
40
100 10k 100k 1M
1992 G48
01k
ΔVAMPCM
ΔVAMPDIFF
2μs/DIV
VOUTDIFF (1V/DIV)
1992 G49
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 4V
–VIN = 2V
CLOAD = 0pF
2.5V
20μs/DIV
VOUTDIFF (1V/DIV)
1992 G50
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 4V
–VIN = 2V
CLOAD = 10000pF
CLOAD = 1000pF
2.5V
FREQUENCY (Hz)
10
40
PSRR (dB)
50
60
70
80
100 1k 10k 100k 1M
1992 G51
30
20
10
0
90
100
–VS
+VS
ΔVS
ΔVAMPDIFF
1μs/DIV
VOUTDIFF (50mV/DIV)
1992 G52
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±50mV
–VIN = 50mV
CLOAD = 0pF
0V
±
10μs/DIV
VOUTDIFF (50mV/DIV)
1992 G53
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±50mV
–VIN = 50mV
CLOAD = 10000pF
CLOAD = 1000pF
0V
±
FREQUENCY (Hz)
110
–40
OUTPUT BALANCE (dB)
–60
–80
100 1k 10k 100k 1M
1992 G54
–20
0
–100
ΔVOUTCM
ΔVOUTDIFF
LTC1992 Family
14
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Single-Ended Input Small-Signal
Step Response
Single-Ended Input Small-Signal
Step Response
Differential Noise Voltage Density
vs Frequency
THD + Noise vs Frequency THD + Noise vs Amplitude
Applicable to the LTC1992-1 only.
1μs/DIV
VOUTDIFF (50mV/DIV)
1992 G55
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 200mV
–VIN = 100mV
CLOAD = 0pF
2.5V
10μs/DIV
VOUTDIFF (50mV/DIV)
1992 G56
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 200mV
–VIN = 100mV
CLOAD = 10000pF
CLOAD = 1000pF
2.5V
FREQUENCY (Hz)
100 1000 10000
1922 G57
10
INPUT REFERRED NOISE (nV√Hz)
1000
100
10
FREQUENCY (Hz)
100
–100
THD + NOISE (dB)
–60
–50
–40
1k 10k 50k
1992 G58
–70
–80
–90
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–VS = –5V
VOCM = 0V
VOUT = 1VP-PDIFF
VOUT = 2VP-PDIFF
VOUT = 10VP-PDIFF
VOUT = 5VP-PDIFF
INPUT SIGNAL AMPLITUDE (VP-PDIFF)
0.1
–100
THD + NOISE (dB)
–90
–80
–70
–60
–40
11020
1992 G59
–50
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–VS = –5V
VOCM = 0V
50kHz
20kHz
10kHz
5kHz
2kHz 1kHz
LTC1992 Family
15
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Differential Gain Error
vs Temperature
VOCM Gain vs Frequency,
VS = ±2.5V
Differential Input Offset Voltage
vs Input Common Mode Voltage
(Note 7)
Differential Input Offset Voltage
vs Input Common Mode Voltage
(Note 7)
Differential Input Offset Voltage
vs Input Common Mode Voltage
(Note 7)
Differential Input Differential
Gain vs Frequency, VS = ±2.5V
Single-Ended Input Differential
Gain vs Frequency, VS = ±2.5V
Differential Phase Response
vs Frequency
Applicable to the LTC1992-2 only.
FREQUENCY (kHz)
10
–24
GAIN (dB)
–18
–12
–6
0
100 1000 10000
1992 G60
–30
–36
–42
–66
–60
–54
–48
6
18
12
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
FREQUENCY (kHz)
10
–24
GAIN (dB)
–18
–12
–6
0
100 1000 10000
1992 G61
–30
–36
–42
–66
–60
–54
–48
6
18
12
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
FREQUENCY (kHz)
10
PHASE (DEG)
0
–20
–40
–60
–80
–100
–120
–140
–160
–180 100 1000
1992 G62
CLOAD =
10pF
50pF
100pF
500pF
1000pF
5000pF
10000pF
TEMPERATURE (°C)
–50
GAIN ERROR (%)
0.05
0.04
0.03
0.02
0.01
0
–0.01
–0.02
–0.03
–0.04
–0.05 050 75
1992 G63
–25 25 100 125
FREQUENCY (kHz)
10
–10
GAIN (dB)
–5
0
5
100 1000 10000
1992 G64
–15
–20
–25
–30
CLOAD = 10pF TO 10000pF
COMMON MODE VOLTAGE (V)
0
DIFFERENTIAL VOS (mV)
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0 4.0
1992 G66
1.0 2.0 3.0 5.03.50.5 1.5 2.5 4.5
–40°C
125°C
25°C
85°C
+VS = 5V
–VS = 0V
VOCM = 2.5V
COMMON MODE VOLTAGE (V)
0
DIFFERENTIAL VOS (mV)
0
0.5
1.0
2.4
1992 G65
–0.5
–1.0
–2.0 0.6 1.2 1.8
0.3 2.7
0.9 1.5 2.1
–1.5
1.5
2.0 +VS = 2.7V
–VS = 0V
VOCM = 1.35V
–40°C
25°C
125°C
85°C
COMMON MODE VOLTAGE (V)
–5
DIFFERENTIAL VOS (mV)
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0 3
1992 G67
–3 –1 1 52–4 –2 0 4
–40°C
125°C
25°C
+VS = 5V
–VS = –5V
VOCM = 0V
85°C
LTC1992 Family
16
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Applicable to the LTC1992-2 only.
Single-Ended Input Large-Signal
Step Response
Single-Ended Input Large-Signal
Step Response
Power Supply Rejection Ratio
vs Frequency (Note 7)
Differential Input Small-Signal
Step Response
Differential Input Small-Signal
Step Response Output Balance vs Frequency
Differential Input Large-Signal
Step Response
Differential Input Large-Signal
Step Response
Common Mode Rejection Ratio
vs Frequency (Note 7)
2μs/DIV 1992 G68
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±750mV
–VIN = 750mV
CLOAD = 0pF
VOUTDIFF (1V/DIV)
0V
±
20μs/DIV 1992 G69
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±750mV
–VIN = 750mV
CLOAD = 10000pF
CLOAD = 1000pF
VOUTDIFF (1V/DIV)
0V
±
FREQUENCY (Hz)
30
CMRR (dB)
90
100
20
10
80
50
70
60
40
100 10k 100k 1M
1992 G70
01k
ΔVAMPCM
ΔVAMPDIFF
2μs/DIV 1992 G71
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 2V
–VIN = 1V
CLOAD = 0pF
VOUTDIFF (1V/DIV)
2.5V
20μs/DIV
VOUTDIFF (1V/DIV)
1992 G72
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 2V
–VIN = 1V
CLOAD = 10000pF
CLOAD = 1000pF
2.5V
FREQUENCY (Hz)
10
40
PSRR (dB)
50
60
70
80
100 1k 10k 100k 1M
1992 G73
30
20
10
0
90
100
–VS
+VS
ΔVS
ΔVAMPDIFF
2μs/DIV
VOUTDIFF (50mV/DIV)
1992 G74
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±25mV
–VIN = 25mV
CLOAD = 0pF
0V
±
20μs/DIV
VOUTDIFF (50mV/DIV)
1992 G75
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±25mV
–VIN = 25mV
CLOAD = 10000pF
CLOAD = 1000pF
0V
±
FREQUENCY (Hz)
110
–40
OUTPUT BALANCE (dB)
–60
–80
100 1k 10k 100k 1M
1992 G76
–20
0
–100
ΔVOUTCM
ΔVOUTDIFF
LTC1992 Family
17
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Single-Ended Input Small-Signal
Step Response
Single-Ended Input Small-Signal
Step Response
Differential Noise Voltage Density
vs Frequency
THD + Noise vs Frequency THD + Noise vs Amplitude
Applicable to the LTC1992-2 only.
2μs/DIV
VOUTDIFF (50mV/DIV)
1992 G77
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 100mV
–VIN = 50mV
CLOAD = 0pF
2.5V
20μs/DIV
VOUTDIFF (50mV/DIV)
1992 G78
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 100mV
–VIN = 50mV
CLOAD = 10000pF
CLOAD = 1000pF
2.5V
FREQUENCY (Hz)
100 1000 10000
1922 G79
10
INPUT REFERRED NOISE (nV√Hz)
1000
100
10
FREQUENCY (Hz)
100
–100
THD + NOISE (dB)
–60
–50
–40
1k 10k 50k
1992 G80
–70
–80
–90
VOUT = 1VP-PDIFF
VOUT = 2VP-PDIFF
VOUT = 10VP-PDIFF
VOUT = 5VP-PDIFF
INPUT SIGNAL AMPLITUDE (VP-PDIFF)
0.1
–100
THD + NOISE (dB)
–90
–80
–70
–60
–40
110
1992 G81
–50
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–VS = –5V
VOCM = 0V 50kHz
20kHz
10kHz
5kHz
2kHz
1kHz
LTC1992 Family
18
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Differential Gain Error
vs Temperature VOCM Gain vs Frequency
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Differential
Gain vs Frequency, VS = ±2.5V
Single-Ended Input Differential
Gain vs Frequency, VS = ±2.5V
Differential Phase Response
vs Frequency
Applicable to the LTC1992-5 only.
FREQUENCY (kHz)
10
–24
GAIN (dB)
–18
–12
–6
0
100 1000 10000
1992 G82
–30
–36
–42
–60
–54
–48
6
24
12
30
18
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
FREQUENCY (kHz)
10
–24
GAIN (dB)
–18
–12
–6
0
100 1000 10000
1992 G83
–30
–36
–42
–60
–54
–48
6
24
12
30
18
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
FREQUENCY (kHz)
10
PHASE (DEG)
0
–20
–40
–60
–80
–100
–120
–140
–160
–180 100 1000
1992 G84
10pF
50pF
100pF
500pF
1000pF
5000pF
10000pF
CLOAD =
TEMPERATURE (°C)
–50
GAIN ERROR (%)
0.050
0.025
0
–0.025
–0.050
–0.075
–0.100
–0.125
–01.50 050 75
1992 G85
–25 25 100 125
COMMON MODE VOLTAGE (V)
0
DIFFERENTIAL VOS (mV)
1922 G87
0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
125°C
–40°C
85°C
25°C
+VS = 2.7V
–VS = 0V
VOCM = 1.35V
FREQUENCY (kHz)
10
–10
GAIN (dB)
–5
0
5
100 1000 10000
1992 G86
–15
–20
–25
–30
CLOAD = 10pF TO 10000pF
COMMON MODE VOLTAGE (V)
0
1922 G88
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
125°C
–40°C
85°C
25°C
DIFFERENTIAL VOS (mV)
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
+VS = 5V
–VS = 0V
VOCM = 2.5V
COMMON MODE VOLTAGE (V)
–5
1922 G89
–4 –3 –2 –1 0 1 2 3 4 5
125°C
–40°C
25°C
85°C
DIFFERENTIAL VOS (mV)
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
+VS = 5V
–VS = –5V
VOCM = 0V
LTC1992 Family
19
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Applicable to the LTC1992-5 only.
Single-Ended Input Large-Signal
Step Response
Single-Ended Input Large-Signal
Step Response
Power Supply Rejection Ratio
vs Frequency (Note 7)
Differential Input Small-Signal
Step Response
Differential Input Small-Signal
Step Response Output Balance vs Frequency
Differential Input Large-Signal
Step Response
Differential Input Large-Signal
Step Response
Common Mode Rejection Ratio
vs Frequency (Note 7)
2μs/DIV
VOUTDIFF (1V/DIV)
1992 G90
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ± 300mV
–VIN = 300mV
CLOAD = 0pF
0V
±
20μs/DIV 1992 G91
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ± 300mV
–VIN = 300mV
CLOAD = 10000pF
CLOAD = 1000pF
VOUTDIFF (1V/DIV)
0V
±
FREQUENCY (Hz)
30
CMRR (dB)
90
100
20
10
80
50
70
60
40
100 10k 100k 1M
1992 G92
01k
ΔVAMPCM
ΔVAMPDIFF
2μs/DIV
VOUTDIFF (1V/DIV)
1992 G93
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 800mV
–VIN = 400mV
CLOAD = 0pF
2.5V
20μs/DIV 1992 G94
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 800mV
–VIN = 400mV
CLOAD = 10000pF
CLOAD = 1000pF
VOUTDIFF (1V/DIV)
2.5V
FREQUENCY (Hz)
10
40
PSRR (dB)
50
60
70
80
100 10k 100k1k 1M
1992 G95
30
20
10
0
90
100
+VS
–VS
ΔVS
ΔVAMPDIFF
5μs/DIV
VOUTDIFF (50mV/DIV)
1992 G96
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±10mV
–VIN = 10mV
CLOAD = 0pF
0V
±
50μs/DIV
VOUTDIFF (50mV/DIV)
1992 G97
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±10mV
–VIN = 10mV
CLOAD = 10000pF
CLOAD = 1000pF
0V
±
FREQUENCY (Hz)
110
–40
OUTPUT BALANCE (dB)
–60
–80
100 1k 10k 100k 1M
1992 G98
–20
0
–100
ΔVOUTCM
ΔVOUTDIFF
LTC1992 Family
20
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Single-Ended Input Small-Signal
Step Response
Single-Ended Input Small-Signal
Step Response
Differential Noise Voltage Density
vs Frequency
THD + Noise vs Frequency THD + Noise vs Amplitude
5μs/DIV
VOUTDIFF (50mV/DIV)
1992 G99
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 40mV
–VIN = 20mV
CLOAD = 0pF
2.5V
50μs/DIV 1992 G100
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 40mV
–VIN = 20mV
CLOAD = 10000pF
CLOAD = 1000pF
VOUTDIFF (50mV/DIV)
2.5V
FREQUENCY (Hz)
100 1000 10000
1922 G101
10
INPUT REFERRED NOISE (nV√Hz)
1000
100
10
FREQUENCY (Hz)
100
–100
THD + NOISE (dB)
–60
–50
–40
1k 10k 50k
1992 G102
–70
–80
–90
VOUT = 1VP-PDIFF
VOUT = 2VP-PDIFF
VOUT = 10VP-PDIFF
VOUT = 5VP-PDIFF
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–VS = –5V
VOCM = 0V
INPUT SIGNAL AMPLITUDE (VP-PDIFF)
0.1
–100
THD + NOISE (dB)
–90
–80
–70
–60
–40
15
1992 G103
–50
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–VS = –5V
VOCM = 0V 50kHz
20kHz
10kHz
5kHz
2kHz
1kHz
Applicable to the LTC1992-5 only.
LTC1992 Family
21
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Applicable to the LTC1992-10 only.
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Gain Error
vs Temperature VOCM Gain vs Frequency
Differential Input Differential
Gain vs Frequency, VS = ±2.5V
Single-Ended Input Differential
Gain vs Frequency, VS = ±2.5V
Differential Phase Response
vs Frequency
FREQUENCY (kHz)
10
–30
GAIN (dB)
–20
–10
0
10
100 1000 10000
1992 G104
–40
–50
–60
20
30
40
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
FREQUENCY (kHz)
10
–30
GAIN (dB)
–20
–10
0
10
100 1000 10000
1992 G105
–40
–50
–60
20
30
40
CLOAD = 10000pF
CLOAD = 5000pF
CLOAD = 1000pF
CLOAD = 500pF
CLOAD = 100pF
CLOAD = 50pF
CLOAD = 10pF
FREQUENCY (kHz)
10
PHASE (DEG)
0
–20
–40
–60
–80
–100
–120
–140
–160
–180 100 1000
1992 G106
10pF
50pF
100pF
500pF
1000pF
5000pF
10000pF
CLOAD =
TEMPERATURE (°C)
–50
GAIN ERROR (%)
0.050
0.025
0
–0.025
–0.050
–0.075
–0.100
–0.125
–0.150
–0.175
–0.200 050 75
1992 G107
–25 25 100 125
FREQUENCY (kHz)
10
–10
GAIN (dB)
–5
0
5
100 1000 10000
1992 G108
–15
–20
–25
–30
CLOAD = 10pF TO 10000pF
COMMON MODE VOLTAGE (V)
0
1922 G109
0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7
125°C
–40°C
85°C
25°C
DIFFERENTIAL VOS (mV)
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
+VS = 2.7V
–VS = 0V
VOCM = 1.35V
COMMON MODE VOLTAGE (V)
0
1922 G110
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
125°C
–40°C
85°C
25°C
DIFFERENTIAL VOS (mV)
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
+VS = 5V
–VS = 0V
VOCM = 2.5V
COMMON MODE VOLTAGE (V)
–5
1922 G111
–4 –3 –2 –1 0 1 2 3 4 5
125°C
–40°C
85°C
25°C
DIFFERENTIAL VOS (mV)
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
+VS = 5V
–VS = –5V
VOCM = 0V
LTC1992 Family
22
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Applicable to the LTC1992-10 only.
Single-Ended Input Large-Signal
Step Response
Single-Ended Input Large-Signal
Step Response
Power Supply Rejection Ratio
vs Frequency (Note 7)
Differential Input Small-Signal
Step Response
Differential Input Small-Signal
Step Response Output Balance vs Frequency
Differential Input Large-Signal
Step Response
Differential Input Large-Signal
Step Response
Common Mode Rejection Ratio
vs Frequency (Note 7)
2μs/DIV 1992 G112
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±150mV
–VIN = 150mV
CLOAD = 0pF
VOUTDIFF (1V/DIV)
0V
±
20μs/DIV
VOUTDIFF (1V/DIV)
1992 G113
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±150mV
–VIN = 150mV
CLOAD = 10000pF
CLOAD = 1000pF
0V
±
FREQUENCY (Hz)
30
CMRR (dB)
90
100
20
10
80
50
70
60
40
100 10k 100k 1M
1992 G114
01k
ΔVAMPCM
ΔVAMPDIFF
2μs/DIV 1992 G115
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 400mV
–VIN = 200mV
CLOAD = 0pF
VOUTDIFF (1V/DIV)
2.5V
20μs/DIV
VOUTDIFF (1V/DIV)
1992 G116
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 400mV
–VIN = 200mV
CLOAD = 10000pF
CLOAD = 1000pF
2.5V
FREQUENCY (Hz)
10
40
PSRR (dB)
50
60
70
80
100 10k 100k1k 1M
1992 G117
30
20
10
0
90
100
+VS
–VS
ΔVS
ΔVAMPDIFF
10μs/DIV 1992 G118
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±5mV
–VIN = 5mV
CLOAD = 0pF
VOUTDIFF (50mV/DIV)
0V
±
100μs/DIV
VOUTDIFF (50mV/DIV)
1992 G119
+VS = 2.5V
–VS = –2.5V
VOCM = 0V
+VIN = ±5mV
–VIN = 5mV
CLOAD = 10000pF
CLOAD = 1000pF
0V
±
FREQUENCY (Hz)
110
–60
OUTPUT BALANCE (dB)
100 1k 10k 100k 1M
1992 G120
–40
–20
0
–80
–100
–120
ΔVOUTCM
ΔVOUTDIFF
LTC1992 Family
23
1992fb
TYPICAL PERFORMANCE CHARACTERISTICS
Applicable to the LTC1992-10 only.
Single-Ended Input Small-Signal
Step Response
Single-Ended Input Small-Signal
Step Response
Differential Noise Voltage Density
vs Frequency
THD + Noise vs Frequency THD + Noise vs Amplitude
10μs/DIV 1992 G121
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 20mV
–VIN = 10mV
CLOAD = 0pF
VOUTDIFF (50mV/DIV)
2.5V
100μs/DIV
VOUTDIFF (50mV/DIV)
1992 G122
+VS = 5V
–VS = 0V
VOCM = 2.5V
+VIN = 0V TO 20mV
–VIN = 10mV
CLOAD = 10000pF
CLOAD = 1000pF
2.5V
FREQUENCY (Hz)
100 1000 10000
1922 G123
10
INPUT REFERRED NOISE (nV√Hz)
1000
100
10
FREQUENCY (Hz)
100
–100
THD + NOISE (dB)
–60
–50
–40
1k 10k 50k
1992 G124
–70
–80
–90
VOUT = 1VP-PDIFF
VOUT = 2VP-PDIFF
VOUT = 5VP-PDIFF
500kHz MEASUREMENT BANDWIDTH
+VS = 5V
–VS = –5V
VOCM = 0V
INPUT SIGNAL AMPLITUDE (VP-PDIFF)
0.1
–100
THD + NOISE (dB)
–90
–80
–70
–60
–40
12
1992 G125
–50 50kHz
20kHz
10kHz
5kHz
2kHz
1kHz
LTC1992 Family
24
1992fb
PIN FUNCTIONS
–IN, +IN (Pins 1, 8): Inverting and Noninverting Inputs
of the Amplifier. For the LTC1992 part, these pins are
connected directly to the amplifier’s P-channel MOSFET
input devices. The fixed gain LTC1992-X parts have preci-
sion, on-chip gain setting resistors. The input resistors
are nominally 30k for the LTC1992-1, LTC1992-2 and
LTC1992-5 parts. The input resistors are nominally 15k
for the LTC1992-10 part.
VOCM (Pin 2): Output Common Mode Voltage Set Pin.
The voltage on this pin sets the output signal’s common
mode voltage level. The output common mode level is set
independent of the input common mode level. This is a
high impedance input and must be connected to a known
and controlled voltage. It must never be left floating.
+VS, –VS (Pins 3, 6): The +VS and –VS power supply pins
should be bypassed with 0.1μF capacitors to an adequate ana-
log ground or ground plane. The bypass capacitors should
be located as closely as possible to the supply pins.
+OUT, –OUT (Pins 4, 5): The Positive and Negative
Outputs of the Amplifier. These rail-to-rail outputs are
designed to drive capacitive loads as high as 10,000pF.
VMID (Pin 7): Mid-Supply Reference. This pin is connected
to an on-chip resistive voltage divider to provide a mid-
supply reference. This provides a convenient way to set
the output common mode level at half-supply. If used for
this purpose, Pin 2 will be shorted to Pin 7, Pin 7 should
be bypassed with a 0.1μF capacitor to ground. If this refer-
ence voltage is not used, leave the pin floating.
BLOCK DIAGRAMS
(1992)
+
–
1
7
2
6
3
8
5
4
+
–
200k
200k
+VS
–VS
V+
V–
30k
30k
A1
+
+
+
–
A2
+OUT
1992 BD
–IN
VMID
VOCM
+IN
–OUT
+VS
–VS
+VS
–VS
LTC1992 Family
25
1992fb
BLOCK DIAGRAMS
(1992-X)
–
–
+
+
+VS
+VS
–IN
VMID
+IN
–VS
+VS
–VS
–VS
+OUT
–OUT
VOCM
200k
200k
RIN RFB
RIN RFB
4
5
26
1
3
7
8
1992-X BD
PART
LTC1992-1
LTC1992-2
LTC1992-5
LTC1992-10
RIN
30k
30k
30k
15k
RFB
30k
60k
150k
150k
APPLICATIONS INFORMATION
Theory of Operation
The LTC1992 family consists of five fully differential, low
power amplifiers. The LTC1992 is an unconstrained fully
differential amplifier. The LTC1992-1, LTC1992-2, LTC1992-
5 and LTC1992-10 are fixed gain blocks (with gains of
1, 2, 5 and 10 respectively) featuring precision on-chip
resistors for accurate and ultra stable gain.
In many ways, a fully differential amplifier functions much
like the familiar, ubiquitous op amp. However, there are
several key areas where the two differ. Referring to Figure 1,
an op amp has a differential input, a high open-loop gain
and utilizes negative feedback (through resistors) to set
the closed-loop gain and thus control the amplifier’s gain
with great precision. A fully differential amplifier has all of
these features plus an additional input and a complemen-
tary output. The complementary output reacts to the input
signal in the same manner as the other output, but in the
opposite direction. Two outputs changing in an equal but
opposite manner require a common reference point (i.e.,
opposite relative to what?). The additional input, the VOCM
pin, sets this reference point. The voltage on the VOCM input
directly sets the output signal’s common mode voltage and
allows the output signal’s common mode voltage to be
set completely independent of the input signal’s common
mode voltage. Uncoupling the input and output common
mode voltages makes signal level shifting easy.
For a better understanding of the operation of a fully dif-
ferential amplifier, refer to Figure 2. Here, the LTC1992
functional block diagram adds external resistors to real-
ize a basic gain block. Note that the LTC1992 functional
block diagram is not an exact replica of the LTC1992
circuitry. However, the Block Diagram is correct and is
a very good tool for understanding the operation of fully
differential amplifier circuits. Basic op amp fundamentals
together with this block diagram provide all of the tools
needed for understanding fully differential amplifier circuit
applications.
The LTC1992 Block Diagram has two op amps, two sum-
ming blocks (pay close attention the signs) and four resis-
tors. Two resistors, RMID1 and RMID2, connect directly to
the VMID pin and simply provide a convenient mid-supply
reference. Its use is optional and it is not involved in the
operation of the LTC1992’s amplifier. The LTC1992 functions
through the use of two servo networks each employing
LTC1992 Family
26
1992fb
APPLICATIONS INFORMATION
Figure 1. Comparison of an Op Amp and a Fully Differential Amplifier
Figure 2. LTC1992 Functional Block Diagram with External Gain Setting Resistors
–
–
+
+
–
–
+
+
1992 F01
RIN
RIN
RFB
RFB
Fully Differential Amplifier with Negative Feedback
Fully Differential Amplifier
–VIN
+VIN
VOCM
VOCM
VOCM
–VOUT
+VOUT
–
+
RIN
RFB
Op Amp with Negative Feedback
VIN
VOUT
RFB
RIN
GAIN = –
RFB
RIN
GAIN = –
+OUT
• DIFFERENTIAL INPUT
• HIGH OPEN-LOOP GAIN
• DIFFERENTIAL OUTPUT
• VOCM INPUT SETS OUTPUT
COMMON MODE LEVEL
–OUT
–IN
+IN
VOCM
–
+
Op Amp
OUT
LTC1992
AO
LTC1992
AO
LTC1992LTC1992
• DIFFERENTIAL INPUT
• HIGH OPEN-LOOP GAIN
• SINGLE-ENDED OUTPUT
–IN
+IN
+
–
7
2
6
3
+
–
RMID1
200k
RMID2
200k
INP
INM
V+
V–
RCMP
30k
RCMM
30k
A1
SP
LTC1992
SM
+
+
+
–
A2
+OUT
1992 F02
–IN
+VIN
–VIN
RIN
RFB
RIN
VMID
VOCM
+IN
–OUT –VOUT
+VOUT
+VS
–VS
5
4
RFB
1
8
LTC1992 Family
27
1992fb
APPLICATIONS INFORMATION
negative feedback and using an op amp’s differential input
to create the servo’s summing junction.
One servo controls the signal gain path. The differential
input of op amp A1 creates the summing junction of this
servo. Any voltage present at the input of A1 is amplified (by
the op amp’s large open-loop gain), sent to the summing
blocks and then onto the outputs. Taking note of the signs on
the summing blocks, op amp A1’s output moves +OUT and
–OUT in opposite directions. Applying a voltage step at
the INM node increases the +OUT voltage while the –OUT
voltage decreases. The RFB resistors connect the outputs
to the appropriate inputs establishing negative feedback and
closing the servo’s loop. Any servo loop always attempts
to drive its error voltage to zero. In this servo, the error
voltage is the voltage between the INM and INP nodes,
thus A1 will force the voltages on the INP and INM nodes
to be equal (within the part’s DC offset, open loop gain
and bandwidth limits). The “virtual short” between the
two inputs is conceptually the same as that for op amps
and is critical to understanding fully differential amplifier
applications.
The other servo controls the output common mode level.
The differential input of op amp A2 creates the summing
junction of this servo. Similar to the signal gain servo
above, any voltage present at the input of A2 is amplified,
sent to the summing blocks and then onto the outputs.
However, in this case, both outputs move in the same direc-
tion. The resistors RCMP and RCMM connect the +OUT and
–OUT outputs to A2’s inverting input establishing negative
feedback and closing the servo’s loop. The midpoint of
resistors RCMP and RCMM derives the output’s common
mode level (i.e., its average). This measure of the output’s
common mode level connects to A2’s inverting input while
A2’s noninverting input connects directly to the VOCM pin.
A2 forces the voltages on its inverting and noninverting
inputs to be equal. In other words, it forces the output
common mode voltage to be equal to the voltage on the
VOCM input pin.
For any fully differential amplifier application to function
properly both the signal gain servo and the common mode
level servo must be satisfied. When analyzing an applica-
tions circuit, the INP node voltage must equal the INM node
voltage and the output common mode voltage must equal
the VOCM voltage. If either of these servos is taken out of
the specified areas of operation (e.g., inputs taken beyond
the common mode range specifications, outputs hitting the
supply rails or input signals varying faster than the part
can track), the circuit will not function properly.
Fully Differential Amplifier Signal Conventions
Fully differential amplifiers have a multitude of signals and
signal ranges to consider. To maintain proper operation
with conventional op amps, the op amp’s inputs and its
output must not hit the supply rails and the input signal’s
common mode level must also be within the part’s speci-
fied limits. These considerations also apply to fully dif-
ferential amplifiers, but here there is an additional output
to consider and common mode level shifting complicates
matters. Figure 3 provides a list of the many signals and
specifications as well as the naming convention. The
phrase “common mode” appears in many places and often
leads to confusion. The fully differential amplifier’s ability
to uncouple input and output common mode levels yields
great design flexibility, but also complicates matters some.
For simplicity, the equations in Figure 3 also assume an
ideal amplifier and perfect resistor matching. For a detailed
analysis, consult the fully differential amplifier applications
circuit analysis section.
Basic Applications Circuits
Most fully differential amplifier applications circuits employ
symmetrical feedback networks and are familiar territory
for op amp users. Symmetrical feedback networks require
that the –VIN/+VOUT network is a mirror image duplicate of
the +VIN/–VOUT network. Each of these half circuits is basi-
cally just a standard inverting gain op amp circuit. Figure 4
shows three basic inverting gain op amp circuits and their
corresponding fully differential amplifier cousins. The vast
majority of fully differential amplifier circuits derive from
old tried and true inverting op amp circuits. To create a
fully differential amplifier circuit from an inverting op amp
circuit, first simply transfer the op amp’s VIN/VOUT network
to the fully differential amplifier’s –VIN/+VOUT nodes. Then,
take a mirror image duplicate of the network and apply it
to the fully differential amplifier’s +VIN/–VOUT nodes. Op
amp users can comfortably transfer any inverting op amp
circuit to a fully differential amplifier in this manner.
LTC1992 Family
28
1992fb
Single-Ended to Differential Conversion
One of the most important applications of fully differential
amplifiers is single-ended signaling to differential signaling
conversion. Many systems have a single-ended signal that
must connect to an ADC with a differential input. The ADC
could be run in a single-ended manner, but performance
usually degrades. Fortunately, all of basic applications
circuits shown in Figure 4, as well as all of the fixed gain
LTC1992-X parts, are equally suitable for both differential
and single-ended input signals. For single-ended input
signals, connect one of the inputs to a reference voltage
(e.g., ground or mid-supply) and connect the other to
the signal path. There are no tradeoffs here as the part’s
performance is the same with single-ended or differential
input signals. Which input is used for the signal path only
affects the polarity of the differential output signal.
Signal Level Shifting
Another important application of fully differential ampli-
fier is signal level shifting. Single-ended to differential
conversion accompanied by a signal level shift is very
commonplace when driving ADCs. As noted in the theory of
operation section, fully differential amplifiers have a com-
mon mode level servo that determines the output common
mode level independent of the input common mode level.
To set the output common mode level, simply apply the
desired voltage to the VOCM input pin. The voltage range
on the VOCM pin is from (–VS + 0.5V) to (+VS – 1.3V).
Figure 3. Fully Differential Amplifier Signal Conventions (Ideal Amplifier and Perfect Resistor Matching is Assumed)
–
–
+
+
1992 F03
RIN
RIN
RFB
VOCM
VOCM
RFB
B
B
–B
–B
–VIN
–A
–A
VINCM VOUTCM
VINDIFF
4AVP-PDIFF A
A
+VIN
2AVP-P
2AVP-P
= VINDIFF = +VIN – –VIN
2BVP-P
2BVP-P
DIFFERENTIAL
INPUT VOLTAGE
= VINCM =
INPUT COMMON
MODE VOLTAGE
+VOUT = • • + VOCM ; VOSCM = 0V +VIN – –VIN
+VIN + –VIN
2
= VOUTDIFF = +VOUT – –VOUT
DIFFERENTIAL
OUTPUT VOLTAGE
–VOUT
+VOUT
LTC1992 VOUTDIFF
4BVP-PDIFF
1
2
RFB
RIN
= VOUTCM =
OUTPUT COMMON
MODE VOLTAGE
+VOUT + –VOUT
2
()
–VOUT = • • + VOCM ; VOSCM = 0V –VIN – +VIN 1
2
RFB
RIN
VOUTDIFF = VINDIFF • RFB
RIN
rN ≈ (0.13nV/√Hz)
VAMPCM = VINP + VINM
2
CMRR = ; +VIN = –VIN
ΔVAMPCM
ΔVAMPDIFF
OUTPUT BALANCE = ΔVOUTCM
ΔVOUTDIFF
eNOUT = WHERE: eNOUT = OUTPUT REFERRED NOISE VOLTAGE DENSITY
e
NIN = INPUT REFERRED NOISE VOLTAGE DENSITY
(RESISTIVE NOISE IS ALREADY INCLUDED IN THE
SPECIFICATIONS FOR THE FIXED GAIN LTC1992-X PARTS)
+ 1
RFB
RIN
VOUTCM = VOCM
VAMPDIFF = VINP – VINM
VOSCM = VOUTCM – VOCM
()
()
VOSDIFFOUT = VOSDIFFIN • + 1
RFB
RIN
()
INM
INP
RIN • RFB
RIN + RFB
()
• √eNIN2 + rN2
APPLICATIONS INFORMATION
LTC1992 Family
29
1992fb
APPLICATIONS INFORMATION
Figure 4. Basic Fully Differential Amplifier Application Circuits (Note: Single-Ended to Differential Conversion is
Easily Accomplished by Connecting One of the Input Nodes, +VIN or –VIN, to a DC Reference Level (e.g., Ground))
–
–
+
+
RIN
RIN
RFB
RFB
Gain Block
–VIN
+VIN
VOCM
–VOUT
+VOUT
–
+
RIN
VIN
RFB
VOUT
RFB
RIN
GAIN =
LTC1992
–
–
+
+
RIN
RIN
RFB
RFB
AC Coupled Gain Block
–VIN
+VIN
VOCM
–VOUT
+VOUT
–
+
RIN
CIN CIN
CIN
VIN
RFB
VOUT LTC1992
–
–
+
+
RIN
RIN
RFB
RFB
Single Pole Lowpass Filter
–VIN
+VIN
RFB
RIN
WP
S + WP
; WP =
VOCM
–VOUT
+VOUT
–
+
RIN
VIN
RFB
C
VOUT
H(S) = HO •
WHERE HO =
LTC1992
C
C
1
RFB • C
–
–
+
+
R1 R3
R3
R4
R4R1
R2
R2
3-Pole Lowpass Filter
–VIN
+VIN
R2
R1 ; WP =; WO =
VOCM
–VOUT
1992 F04
+VOUT
–
+
R1 R3
R4
R2
C1
C2 VOUT
WHERE HO =
LTC1992
C3
C1
C1
1
R4C3
1
R2R3C1C2
C2
2
C3
2
WP
S + WP
H(S) = HO
()
WO2
S2 + S +
WO
QWO2
()
VIN
RFB
RIN ; WP =
HO = 1
RIN • CIN
S
S + WP
H(S) = HO •
C2
C1
R1 • √R2R3
R1 R2 + R1 R2 + R2 R3 •
Q =
LTC1992 Family
30
1992fb
APPLICATIONS INFORMATION
The VOCM input pin has a very high input impedance and
is easily driven by even the weakest of sources. Many
ADCs provide a voltage reference output that defines
either its common mode level or its full-scale level. Apply
the ADC’s reference potential either directly to the VOCM
pin or through a resistive voltage divider depending on
the reference voltage’s definition. When controlling the
VOCM pin by a high impedance source, connect a bypass
capacitor (1000pF to 0.1μF) from the VOCM pin to ground
to lower the high frequency impedance and limit external
noise coupling. Other applications will want the output
biased at a midpoint of the power supplies for maximum
output voltage swing. For these applications, the LTC1992
provides a mid-supply potential at the VMID pin. The VMID
pin connects to a simple resistive voltage divider with
two 200k resistors connected between the supply pins.
To use this feature, connect the VMID pin to the VOCM pin
and bypass this node with a capacitor.
One undesired effect of utilizing the level shifting function
is an increase in the differential output offset voltage due to
gain setting resistor mismatch. The offset is approximately
the amount of level shift (VOUTCM – VINCM) multiplied by the
amount of resistor mismatch. For example, a 2V level shift
with 0.1% resistors will give around 2mV of output offset
(2 • 0.1% = 2mV). The exact amount of offset is dependent
on the application’s gain and the resistor mismatch. For a
detail description, consult the Fully Differential Amplifier
Applications Circuit Analysis section.
CMRR and Output Balance
One common misconception of fully differential amplifiers
is that the common mode level servo guarantees an infinite
common mode rejection ratio (CMRR). This is not true. The
common mode level servo does, however, force the two
outputs to be truly complementary (i.e., exactly opposite
or 180 degrees out of phase). Output balance is a measure
of how complementary the two outputs are.
At low frequencies, CMRR is primarily determined by the
matching of the gain setting resistors. Like any op amp, the
LTC1992 does not have infinite CMRR, however resistor
mismatching of only 0.018%, halves the circuit’s CMRR.
Standard 1% tolerance resistors yield a CMRR of about
40dB. For most applications, resistor matching dominates
low frequency CMRR performance. The specifications for
the fixed gain LTC1992-X parts include the on-chip resistor
matching effects. Also, note that an input common mode
signal appears as a differential output signal reduced by the
CMRR. As with op amps, at higher frequencies the CMRR
degrades. Refer to the Typical Performance plots for the
details of the CMRR performance over frequency.
At low frequencies, the output balance specification is
determined by the matching of the on-chip RCMM and
RCMP resistors. At higher frequencies, the output bal-
ance degrades. Refer to the typical performance plots
for the details of the output balance performance over
frequency.
Input Impedance
The input impedance for a fully differential amplifier ap-
plication circuit is similar to that of a standard op amp
inverting amplifier. One major difference is that the input
impedance is different for differential input signals and
single-ended signals. Referring to Figure 3, for differential
input signals the input impedance is expressed by the
following expression:
R
INDIFF = 2 • RIN
For single-ended signals, the input impedance is expressed
by the following expression:
RINS-E =RIN
1– RFB
2• R
IN +RFB
()
The input impedance for single-ended signals is slightly
higher than the RIN value since some of the input signal
is fed back and appears as the amplifier’s input common
mode level. This small amount of positive feedback in-
creases the input impedance.
Driving Capacitive Loads
The LTC1992 family of parts is stable for all capacitive loads
up to at least 10,000pF. While stability is guaranteed, the
part’s performance is not unaffected by capacitive load-
ing. Large capacitive loads increase output step response
ringing and settling time, decrease the bandwidth and
increase the frequency response peaking. Refer to the
LTC1992 Family
31
1992fb
APPLICATIONS INFORMATION
Typical Performance plots for small-signal step response,
large-signal step response and gain over frequency to
appraise the effects of capacitive loading. While the con-
sequences are minor in most instances, consider these
effects when designing application circuits with large
capacitive loads.
Input Signal Amplitude Considerations
For application circuits to operate correctly, the amplifier
must be in its linear operating range. To be in the linear
operating range, the input signal’s common mode voltage
must be within the part’s specified limits and the rail-to-rail
outputs must stay within the supply voltage rails. Addition-
ally, the fixed gain LTC1992-X parts have input protection
diodes that limit the input signal to be within the supply
voltage rails. The unconstrained LTC1992 uses external
resistors allowing the source signals to go beyond the
supply voltage rails.
When taken outside of the linear operating range, the
circuit does not perform as expected, however nothing
extreme occurs. Outputs driven into the supply voltage
rails are simply clipped. There is no phase reversal or
oscillation. Once the outputs return to the linear operating
range, there is a small recovery time, then normal opera-
tion proceeds. When the input common mode voltage is
below the specified lower limit, on-chip protection diodes
conduct and clamp the signal. Once the signal returns to
the specified operating range, normal operation proceeds.
If the input common mode voltage goes slightly above the
specified upper limit (by no more than about 500mV),
the amplifier’s open-loop gain reduces and DC offset and
closed-loop gain errors increase. Return the input back to
the specified range and normal performance commences.
If taken well above the upper limit, the amplifier’s input
stage is cut off. The gain servo is now open loop; however,
the common mode servo is still functional. Output bal-
ance is maintained and the outputs go to opposite supply
rails. However, which output goes to which supply rail is
random. Once the input returns to the specified input
common mode range, there is a small recovery time then
normal operation proceeds.
The LTC1992’s input signal common mode range (VINCMR)
is from (–VS – 0.1V) to (+VS – 1.3V). This specification
applies to the voltage at the amplifier’s input, the INP and
INM nodes of Figure 2. The specifications for the fixed gain
LTC1992-X parts reflect a higher maximum limit as this
specification is for the entire gain block and references
the signal at the input resistors. Differential input signals
and single-ended signals require a slightly different set
of formulae. Differential signals separate very nicely into
common mode and differential components while single
ended signals do not. Refer to Figure 5 for the formulae
for calculating the available signal range. Additionally,
Table 1 lists some common configurations and their ap-
propriate signal levels.
The LTC1992’s outputs allow rail-to-rail signal swings. The
output voltage on either output is a function of the input
signal’s amplitude, the gain configured and the output
signal’s common mode level set by the VOCM pin. For
maximum signal swing, the VOCM pin is set at the midpoint
of the supply voltages. For other applications, such as an
ADC driver, the required level must fall within the VOCM
range of (–VS + 0.5V) to (+VS – 1.3V). For single-ended
input signals, it is not always obvious which output will
clip first thus both outputs are calculated and the minimum
value determines the signal limit. Refer to Figure 5 for the
formula and Table 1 for examples.
To ensure proper linear operation both the input common
mode level and the output signal level must be within
the specified limits. These same criteria are also present
with standard op amps. However, with a fully differential
amplifier, it is a bit more complex and old familiar op amp
intuition often leads to the wrong result. This is especially
true for single-ended to differential conversion with level
shifting. The required calculations are a bit tedious, but
are necessary to guarantee proper linear operation.
LTC1992 Family
32
1992fb
APPLICATIONS INFORMATION
Figure 5. Input Signal Limitations
–
–
+
+
RIN
INM
NODE
INP
NODE
RIN
RFB
VOCM
VOCM
A. CALCULATE VINCM MINIMUM AND MAXIMUM GIVEN RIN, RFB AND VOCM
VINCM(MAX) = (+VS – 1.3V) + (+VS – 1.3V – VOCM)
V
INCM(MIN) = (–VS – 0.1V) + (–VS – 0.1V – VOCM)
B. WITH A KNOWN VINCM, RIN, RFB AND VOCM, CALCULATE COMMON MODE
VOLTAGE AT INP AND INM NODES (VINCM(AMP)) AND CHECK THAT IT IS
WITHIN THE SPECIFIED LIMITS.
V
INCM(AMP) = = VINCM + VOCM
RFB
B
B
–B
–B
–VIN
–A
–A
VINCM VOUTCM
VINDIFF
4AVP-PDIFF A
A
+VIN
2AVP-P
2AVP-P
2BVP-P
2BVP-P
–VOUT
+VOUT
LTC1992 VOUTDIFF
4BVP-PDIFF
1
G
1
G
4
G
4
G
VINP + VINM
2
G
G + 1
1
G + 1
Differential Input Signals
–
–
+
+
1992 F05
RIN
INM
NODE
INP
NODE
RIN
RFB
VOCM
VOCM
RFB
B
B
–B
–B
VINREF
–A
VOUTCM
VREF
AVINSIG
2AVP-P
2BVP-P
2BVP-P
–VOUT
+VOUT
LTC1992 VOUTDIFF
4BVP-PDIFF
Single-Ended Input Signals
INPUT COMMON MODE LIMITS
OUTPUT SIGNAL CLIPPING LIMIT
INPUT COMMON MODE LIMITS (NOTE: FOR THE FIXED GAIN LTC1992-X PARTS, VINREF AND VINSIG CANNOT EXCEED THE SUPPLIES)
OUTPUT SIGNAL CLIPPING LIMIT
OR
OR
VINDIFF(MAX)(VP-PDIFF) = THE LESSER VALUE OF (+VS – VOCM) OR (VOCM – –VS)
VINREF
2
1
G
VINSIG(MAX) = 2
VINSIG(MAX) = THE LESSER VALUE OF VINREF + (+VS – VOCM) OR VINREF + (VOCM – –VS)
+VS – 1.3V – +VS – 1.3V – VOCM
+
(())
VINREF
2
1
G
VINSIG(MIN) = 2 –VS – 0.1V – –VS – 0.1V – VOCM
+
(())
1
G
2
G
2
G
VINSIG(MIN) = THE GREATER VALUE OF VINREF + (–VS – VOCM) OR VINREF + (VOCM – +VS)
2
G
2
G
VINSIGP-P = 2 (+VS – –VS) – 1.2V (+VS – –VS) – 1.2V+
(())
RFB
RIN
G =
RFB
RIN
G =
LTC1992 Family
33
1992fb
APPLICATIONS INFORMATION
Table 1. Input Signal Limitations for Some Common Applications
Differential Input Signal, VOCM at Typical ADC Levels. (VINCM must be within the Min and Max table values and
VINDIFF must be less than the table value)
+VS
(V)
–VS
(V)
GAIN
(V/V)
VOCM
(V)
VINCM(MAX)
(V)
VINCM(MIN)
(V)
VINDIFF(MAX)
(VP-PDIFF)
VOUTDIFF(MAX)
(VP-PDIFF)
2.7 0 1 1 1.800 –1.200 4.00 4.00
2.7 0 2 1 1.600 –0.650 2.00 4.00
2.7 0 5 1 1.480 –0.320 0.80 4.00
2.7 0 10 1 1.440 –0.210 0.40 4.00
5 0 1 2 5.400 –2.200 8.00 8.00
5 0 2 2 4.550 –1.150 4.00 8.00
5 0 5 2 4.040 –0.520 1.60 8.00
5 0 10 2 3.870 –0.310 0.80 8.00
5 –5 1 2 5.400 –12.200 12.00 12.00
5 –5 2 2 4.550 –8.650 6.00 12.00
5 –5 5 2 4.040 –6.520 2.40 12.00
5 –5 10 2 3.870 –5.810 1.20 12.00
Differential Input Signal, VOCM at Mid-Supply. (VINCM must be within the Min and Max table values and
VINDIFF must be less than the table value)
+VS
(V)
–VS
(V)
GAIN
(V/V)
VOCM
(V)
VINCM(MAX)
(V)
VINCM(MIN)
(V)
VINDIFF(MAX)
(VP-PDIFF)
VOUTDIFF(MAX)
(VP-PDIFF)
2.7 0 1 1.35 1.450 –1.550 5.40 5.40
2.7 0 2 1.35 1.425 –0.825 2.70 5.40
2.7 0 5 1.35 1.410 –0.390 1.08 5.40
2.7 0 10 1.35 1.405 –0.245 0.54 5.40
5 0 1 2.5 4.900 –2.700 10.00 10.00
5 0 2 2.5 4.300 –1.400 5.00 10.00
5 0 5 2.5 3.940 –0.620 2.00 10.00
5 0 10 2.5 3.820 –0.360 1.00 10.00
5 –5 1 0 7.400 –10.200 20.00 20.00
5 –5 2 0 5.550 –7.650 10.00 20.00
5 –5 5 0 4.440 –6.120 4.00 20.00
5 –5 10 0 4.070 –5.610 2.00 20.00
LTC1992 Family
34
1992fb
APPLICATIONS INFORMATION
Table 1. Input Signal Limitations for Some Common Applications
+VS
(V)
–VS
(V)
GAIN
(V/V)
VOCM
(V)
VINREF
(V)
VINSIG(MAX)
(V)
VINSIG(MIN)
(V)
VINSIGP-P(MAX)
(VP-P AROUND VINREF)
VOUTDIFF(MAX)
(VP-PDIFF)
2.7 0 1 1.35 1.35 1.550 –1.350 0.40 0.40
2.7 0 2 1.35 1.35 1.500 0.000 0.30 0.60
2.7 0 5 1.35 1.35 1.470 0.810 0.24 1.20
2.7 0 10 1.35 1.35 1.460 1.080 0.22 2.20
5 0 1 2.5 2.5 7.300 –2.500 9.60 9.60
5 0 2 2.5 2.5 5.000 0.000 5.00 10.00
5 0 5 2.5 2.5 3.500 1.500 2.00 10.00
5 0 10 2.5 2.5 3.000 2.000 1.00 10.00
5 –5 1 0 0 10.000 –10.000 20.00 20.00
5 –5 2 0 0 5.000 –5.000 10.00 20.00
5 –5 5 0 0 2.000 –2.000 4.00 20.00
5 –5 10 0 0 1.000 –1.000 2.00 20.00
Mid-Supply Referenced Single-Ended Input Signal, VOCM at Mid-Supply. (The VINSIG Min and Max values listed account for both the input
common mode limits and the output clipping)
+VS
(V)
–VS
(V)
GAIN
(V/V)
VOCM
(V)
VINREF
(V)
VINSIG(MAX)
(V)
VINSIG(MIN)
(V)
VINSIGP-P(MAX)
(VP-P AROUND VINREF)
VOUTDIFF(MAX)
(VP-PDIFF)
2.7 0 1 1 1.35 2.250 –0.650 1.80 1.80
2.7 0 2 1 1.35 1.850 0.350 1.00 2.00
2.7 0 5 1 1.35 1.610 0.950 0.52 2.60
2.7 0 10 1 1.35 1.530 1.150 0.36 3.60
5 0 1 2 2.5 6.500 –1.500 8.00 8.00
5 0 2 2 2.5 4.500 0.500 4.00 8.00
5 0 5 2 2.5 3.300 1.700 1.60 8.00
5 0 10 2 2.5 2.900 2.100 0.80 8.00
5 –5 1 2 0 6.000 –6.000 12.00 12.00
5 –5 2 2 0 3.000 –3.000 6.00 12.00
5 –5 5 2 0 1.200 –1.200 2.40 12.00
5 –5 10 2 0 0.600 –0.600 1.20 12.00
Mid-Supply Referenced Single-Ended Input Signal, VOCM at Typical ADC Levels. (The VINSIG Min and Max values listed account for both
the input common mode limits and the output clipping)
LTC1992 Family
35
1992fb
APPLICATIONS INFORMATION
Fully Differential Amplifier Applications
Circuit Analysis
All of the previous applications circuit discussions have as-
sumed perfectly matched symmetrical feedback networks.
To consider the effects of mismatched or asymmetrical
feedback networks, the equations get a bit messier.
Figure 6 lists the basic gain equation for the differential
output voltage in terms of +VIN, –VIN, VOSDIFF, VOUTCM
and the feedback factors β1 and β2. The feedback factors
are simply the portion of the output that is fed back to the
input summing junction by the RFB-RIN resistive voltage
divider. β1 and β2 have the range of zero to one. The
VOUTCM term also includes its offset voltage, VOSCM, and
its gain mismatch term, KCM. The KCM term is determined
by the matching of the on-chip RCMP and RCMM resistors
in the common mode level servo (see Figure 2).
While mathematically correct, the basic signal equation
does not immediately yield any intuitive feel for fully
differential amplifier application operation. However, by
nulling out specific terms, some basic observations and
sensitivities come forth. Setting β1 equal to β2, VOSDIFF
to zero and VOUTCM to VOCM gives the old gain equation
from Figure 3. The ground referenced, single-ended input
signal equation yields the interesting result that the driven
side feedback factor (β1) has a very different sensitivity
than the grounded side (β2). The CMRR is twice the
feedback factor difference divided by the feedback fac-
tor sum. The differential output offset voltage has two
terms. The first term is determined by the input offset
term, VOSDIFF, and the application’s gain. Note that this
term equates to the formula in Figure 3 when β1 equals
β2. The amount of signal level shifting and the feedback
factor mismatch determines the second term. This term
Table 1. Input Signal Limitations for Some Common Applications
Single Supply Ground Referenced Single-Ended Input Signal, VOCM at Mid-Supply. (The VINSIG Min and Max values listed account for
both the input common mode limits and the output clipping)
Single Supply Ground Referenced Single-Ended Input Signal, VOCM at Typical ADC Reference Levels. (The VINSIG Min and Max values
listed account for both the input common mode limits and the output clipping)
+VS
(V)
–VS
(V)
GAIN
(V/V)
VOCM
(V)
VINREF
(V)
VINSIG(MAX)
(V)
VINSIG(MIN)
(V)
VINSIGP-P(MAX)
(VP-P AROUND VINREF)
VOUTDIFF(MAX)
(VP-PDIFF)
2.7 0 1 1.35 0 2.700 –2.700 5.40 5.40
2.7 0 2 1.35 0 1.350 –1.350 2.70 5.40
2.7 0 5 1.35 0 0.540 –0.540 1.08 5.40
2.7 0 10 1.35 0 0.270 –0.270 0.54 5.40
5 0 1 2.5 0 5.000 –5.000 10.00 10.00
5 0 2 2.5 0 2.500 –2.500 5.00 10.00
5 0 5 2.5 0 1.000 –1.000 2.00 10.00
5 0 10 2.5 0 0.500 –0.500 1.00 10.00
+VS
(V)
–VS
(V)
GAIN
(V/V)
VOCM
(V)
VINREF
(V)
VINSIG(MAX)
(V)
VINSIG(MIN)
(V)
VINSIGP-P(MAX)
(VP-P AROUND VINREF)
VOUTDIFF(MAX)
(VP-PDIFF)
2.7 0 1 1 0 2.000 –2.000 4.00 4.00
2.7 0 2 1 0 1.000 –1.000 2.00 4.00
2.7 0 5 1 0 0.400 –0.400 0.80 4.00
2.7 0 10 1 0 0.200 –0.200 0.40 4.00
5 0 1 2 0 4.000 –4.000 8.00 8.00
5 0 2 2 0 2.000 –2.000 4.00 8.00
5 0 5 2 0 0.800 –0.800 1.60 8.00
5 0 10 2 0 0.400 –0.400 0.80 8.00
LTC1992 Family
36
1992fb
APPLICATIONS INFORMATION
quantifies the undesired effect of signal level shifting
discussed earlier in the Signal Level Shifting section.
Asymmetrical Feedback Application Circuits
The basic signal equation in Figure 6 also gives insight
to another piece of intuition. The feedback factors may
be deliberately set to different values. One interesting
class of these application circuits sets one or both of the
feedback factors to the extreme values of either zero or
one. Figure 7 shows three such circuits.
At first these application circuits may look to be unstable
or open loop. It is the common mode feedback loop that
enables these circuits to function. While they are useful
circuits, they have some shortcomings that must be con-
sidered. First, due to the severe feedback factor asymmetry,
the VOCM level influences the differential output voltage
with about the same strength as the input signal. With
this much gain in the VOCM path, differential output offset
and noise increase. The large VOCM to VOUTDIFF gain also
necessitates that these circuits are largely limited to dual,
split supply voltage applications with a ground referenced
input signal and a grounded VOCM pin.
The top application circuit in Figure 7 yields a high input
impedance, precision gain of 2 block without any external
resistors. The on-chip common mode feedback servo
resistors determine the gain precision (better than 0.1
percent). By using the –VOUT output alone, this circuit is
also useful to get a precision, single-ended output, high
input impedance inverter. To intuitively understand this
circuit, consider it as a standard op amp voltage follower
(delivered through the signal gain servo) with a comple-
mentary output (delivered through the common mode level
servo). As usual, the amplifier’s input common mode range
must not be exceeded. As with a standard op amp voltage
follower, the common mode signal seen at the amplifier’s
input is the input signal itself. This condition limits the
input signal swing, as well as the output signal swing, to
be the input signal common mode range specification.
The middle circuit is largely the same as the first except
that the noninverting amplifier path has gain. Note that
Figure 6. Basic Equations for Mismatched or Asymmetrical Feedback Applications Circuits
–
–
+
+
RIN2
RIN1
2[+VIN • (1 – B1) – (–VIN) • (1 – B2)] + 2VOSDIFF + 2VOUTCM (B1 – B2)
B1 + B2
RFB1
VOCM
VOCM
VOUTDIFF =
WHERE:
• FOR GROUND REFERENCED, SINGLE-ENDED INPUT SIGNAL, LET +VIN = VINSIG AND –VIN = 0V
RFB2
–VIN
VINDIFF
+VIN – –VIN
+VIN –VOUT
+VOUT
1992 F06
LTC1992 VOUTDIFF
+VOUT – –VOUT
2 • VINSIG • (1 – B1) + 2VOSDIFF + 2VOUTCM (B1 – B2)
B1 + B2
VOUTDIFF =
• COMMON MODE REJECTION: SET +VIN = –VIN = VINCM, VOSDIFF = 0V, VOUTCM = 0V
ΔVINCM
ΔVOUTDIFF
CMRR = = 2 ; OUTPUT REFERRED
B1 + B2
B2 – B1
B2 – B1
B1 + B2
• OUTPUT DC OFFSET VOLTAGE: SET +VIN = –VIN = VINCM
VOSDIFFOUT = VOSDIFF + (VOUTCM – VINCM) 2
2
B1 + B2
RIN1
RIN1 + RFB1
B1 = ;B2 = ; VOSDIFF = AMPLIFIER INPUT REFERRED OFFSET VOLTAGE
VOUTCM = KCM • VOCM + VOSCM
0.999 < KCM < 1.001
RIN2
RIN2 + RFB2
LTC1992 Family
37
1992fb
Figure 7. Asymmetrical Feedback Application Circuits (Most Suitable in Applications with Dual,
Split Supplies (e.g., ±5V), Ground Referenced Single-Ended Input Signals and VOCM Connected to Ground)
once the VOCM voltage is set to zero, the gain formula is the
same as a standard noninverting op amp circuit multiplied
by two to account for the complementary output. Taking
RFB to zero (i.e., taking β to one) gives the same formula
as the top circuit. As in the top circuit, this circuit is also
useful as a single-ended output, high input impedance
inverting gain block (this time with gain). The input com-
mon mode considerations are similar to the top circuit’s,
but are not nearly as constrained since there is now gain
in the noninverting amplifier path. This circuit, with VOCM
at ground, also permits a rail-to-rail output swing in most
applications.
The bottom circuit is another circuit that utilizes a standard
op amp configuration with a complementary output. In this
case, the standard op amp circuit has an inverting con-
figuration. With VOCM at zero volts, the gain formula is the
same as a standard inverting op amp circuit multiplied by
two to account for the complementary output. This circuit
does not have any common mode level constraints as the
inverting input voltage sets the input common mode level.
This circuit also delivers rail-to-rail output voltage swing
without any concerns.
APPLICATIONS INFORMATION
–
–
+
++VOUT VOUTDIFF = 2(+VIN – VOCM)
SETTING VOCM = 0V
VOUTDIFF = 2VIN
–VOUT
VIN
VOCM VOCM LTC1992
–
–
+
++VOUT
RFB
RIN
VOUTDIFF = 2
SETTING VOCM = 0V
VOUTDIFF = 2VIN
–VOUT
VIN
VOCM
RIN
RFB
()
+VIN ; B =
= 2VIN 1 +
– VOCM
1
B
()
1
B
()
RIN
RIN + RFB
RFB
RIN
–
–
+
++VOUT VOUTDIFF = 2
SETTING VOCM = 0V
VOUTDIFF = 2VIN
–VOUT
1992 F07
VIN
VOCM
()
+VIN ; B =
= 2VIN
+ VOCM
1 – B
B
()
1 – B
B
()
RIN
RIN + RFB
RFB
RIN
VOCM LTC1992
VOCM LTC1992
LTC1992 Family
38
1992fb
TYPICAL APPLICATIONS
Interfacing a Bipolar, Ground Referenced, Single-Ended Signal to a Unipolar Single Supply,
Differential Input ADC (VIN = 0V Gives a Digital Mid-Scale Code)
Compact, Unipolar Serial Data Conversion
Zero Components, Single-Ended Adder/Subtracter
–
–
+
+
LTC1992
3
6
VOCM
VMID
0.1μF
100pF
7
6
5
13.3k
40k
4
5
2
7
8
1
10k
10k
5V
13.3k
40k
5V
10k
10k
100Ω
100Ω
0.1μF
+IN VREF VCC
2
18
3
4
1992 TA02a
–IN
1μF
SCK
SDO
CONV
LTC1864
SERIAL
DATA
LINK
GND
0VVIN
2.5V
–2.5V
–
–
+
+
LTC1992-2
3
6
VOCM
VMID
0.1μF
100pF
7
6
5
4
5
2
7
8
1100Ω
5V
100Ω
0.1μF
+IN VREF VCC
2
18
3
4
1992 TA03a
–IN
1μF
SCK
SDO
CONV
LTC1864
SERIAL
DATA
LINK
GND
VIN
2.5V
0V
–
–
+
+V1 = VB + VC – VA
V2 = VB + VA – VC
VA
14
0.1μF
3
+VS
–VS
65
2
8
VC
VBVOCM LTC1992-2
0.1μF
1992 TA04
LTC1992 Family
39
1992fb
TYPICAL APPLICATIONS
Single-Ended to Differential Conversion Driving an ADC
2.2μF 10μF 10μF
10Ω
47μF
4
6
REFCOMP
4.375V
CONTROL
LOGIC
AND
TIMING
B15 TO B0
16-BIT
SAMPLING
ADC
–
+
10μF
5V OR
3V
μP
CONTROL
LINES
D15 TO D0
OUTPUT
BUFFERS 16-BIT
PARALLEL
BUS
11 TO 26
1992 TA06a
OGND
OVDD
28
29
1
2
AIN+
AIN–
SHDN
CS
CONVST
RD
BUSY
33
32
31
30
27
LTC1603
336 35 10
9
5V 5V
AVDD AVDD
7.5k
DVDD DGND
VREF
8
AGND
AGND
7
AGND
5
AGND
34
–5V
VSS
10μF
2.5V
REF
10μF
1.75X
+
+
+ +
+
+
–
–
+
+
5V
–5V
LTC1992-1
3
6
VOCM
VMID
VIN
100pF
4
5
2
7
8
1100Ω
100Ω
0.1μF
0.1μF
FFT of the Output Data
SNR =85.3dB
THD = –72.1dB
SINAD = –72dB
fIN = 10.0099kHz
fSAMPLE = 333kHz
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
–130
–140
FREQUENCY (kHz)
0
AMPLITUDE (dB)
8070
1992 TA06b
2010 4030 6050 10090
LTC1992 Family
40
1992fb
PACKAGE DESCRIPTION
MS8 Package
8-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1660 Rev F)
MSOP (MS8) 0307 REV F
0.53 p 0.152
(.021 p .006)
SEATING
PLANE
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.18
(.007)
0.254
(.010)
1.10
(.043)
MAX
0.22 – 0.38
(.009 – .015)
TYP
0.1016 p 0.0508
(.004 p .002)
0.86
(.034)
REF
0.65
(.0256)
BSC
0o – 6o TYP
DETAIL “A”
DETAIL “A”
GAUGE PLANE
12
34
4.90 p 0.152
(.193 p .006)
8765
3.00 p 0.102
(.118 p .004)
(NOTE 3)
3.00 p 0.102
(.118 p .004)
(NOTE 4)
0.52
(.0205)
REF
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
0.889 p 0.127
(.035 p .005)
RECOMMENDED SOLDER PAD LAYOUT
0.42 p 0.038
(.0165 p .0015)
TYP
0.65
(.0256)
BSC
LTC1992 Family
41
1992fb
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
A 7/10 Updated Part Markings 2
B 6/11 Revised Features
Updated to Specified Temperature Range in Absolute Maximum Ratings and Order Information
Revised Block Diagram
Revised subtitle in Figure 5 of Applications Information section
1
2
24
32
LTC1992 Family
42
1992fb
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2005
LT 0611 REV A • PRINTED IN USA
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BNC
VINP
–
–
+
+
147
8
11
4
12
17
13
14
16
0.1μF
V+
1/2 LTC1043
3
5V
–5V
65
2
8VOCM
7
BNC
VINP
VOCM
VMID LTC1992
0.1μF
0.1μF
CLK V–
0.1μF
1992 TA05a
0.1μF
CLK
0.1μF
–
–
+
+
14
3
65
2
8VOCM
7VMID LTC1992 BNC
VOUTM
BNC
VOUTP
60kHz LOW PASS FILTER SAMPLER 2kHz LOWPASS FILTER
9.53k
9.53k
9.53k
37.4k 60.4k
37.4k 60.4k
9.53k 8.87k
8.87k
75k
75k
120pF
120pF
390pF
390pF
330pF
180pF
0.1μF
10k
Balanced Frequency Converter (Suitable for Frequencies up to 50kHz)
0V
0V
0V
0V
200μs/DIV
VINP = 24kHz
(1V/DIV)
VOUTP = 1kHz
(0.5V/DIV)
VOUTM = 1kHz
(0.5V/DIV)
CLK = 25kHz
(LOGIC SQUARE WAVE)
(5V/DIV)
1992 TA05b
