General-Purpose, −55°C to +125°C,
Wide Bandwidth, DC-Coupled VGA
AD8336
Rev. C
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responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
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Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©2006–2011 Analog Devices, Inc. All rights reserved.
FEATURES
Low noise
Voltage noise: 3 nV/√Hz
Current noise: 3 pA/√Hz
Small-signal BW: 115 MHz
Large-signal BW: 2 V p-p = 80 MHz
Slew rate: 550 V/μs, 2 V p-p
Gain ranges (specified)
−14 dB to +46 dB
0 dB to 60 dB
Gain scaling: 50 dB/V
DC-coupled
Single-ended input and output
Supplies: ±3 V to ±12 V
Temperature range: −55°C to +125°C
Power
150 mW @ ±3 V, −55°C < T < +125°C
84 mW @ ±3 V, PWRA = 3 V
APPLICATIONS
Industrial process controls
High performance AGC systems
I/Q signal processing
Video
Industrial and medical ultrasound
Radar receivers
FUNCTIONAL BLOCK DIAGRAM
V
G
A
I
VOUT
PRAO
GNEG
AD8336
VCOMVPOS GPOS
34dBPrA
PWRA
ATTENUATOR
–60dB TO 0dB
GAIN CONTROL
INTERFACE
INPP
8 9
INPN
+
4
1
5
BIAS
2
06228-001
10 13 311 12
VNEG
Figure 1.
GENERAL DESCRIPTION
The AD8336 is a low noise, single-ended, linear-in-dB, general-
purpose variable gain amplifier, usable over a large range of supply
voltages. It features an uncommitted preamplifier (preamp) with
a usable gain range of 6 dB to 26 dB established by external
resistors in the classical manner. The VGA gain range is 0 dB to
60 dB, and its absolute gain limits are −26 dB to +34 dB. When
the preamplifier gain is adjusted for 12 dB, the combined 3 dB
bandwidth of the preamp and VGA is 100 MHz, and the amplifier
is fully usable to 80 MHz. With ±5 V supplies, the maximum
output swing is 7 V p-p.
Thanks to its X-Amp® architecture, excellent bandwidth uni-
formity is maintained across the entire gain range of the VGA.
Intended for a broad spectrum of applications, the differential
gain control interface provides precise linear-in-dB gain scaling
of 50 dB/V over the temperature span of −55°C to +125°C. The
differential gain control is easy to interface with a variety of
external circuits within the common-mode voltage limits of the
AD8336.
The large supply voltage range makes the AD8336 particularly
suited for industrial medical applications and for video circuits.
Dual-supply operation enables bipolar input signals, such as
those generated by photodiodes or photomultiplier tubes.
The fully independent voltage feedback preamp allows both
inverting and noninverting gain topologies, making it a fully
bipolar VGA. The AD8336 can be used within the specified
gain range of −14 dB to +60 dB by selecting a preamp gain
between 6 dB and 26 dB and choosing appropriate feedback
resistors. For the nominal preamp gain of 4×, the overall gain
range is −14 dB to +46 dB.
In critical applications, the quiescent power can be reduced by
about half by using the power adjust pin, PWRA. This is especially
useful when operating with high supply voltages of up to ±12 V,
or at high temperatures.
The operating temperature range is −55°C to +125°C. The
AD8336 is available in a 16-lead LFCSP (4 mm × 4 mm).
AD8336
Rev. C | Page 2 of 28
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
Functional Block Diagram .............................................................. 1
General Description ......................................................................... 1
Revision History ............................................................................... 2
Specifications ..................................................................................... 3
Absolute Maximum Ratings ............................................................ 5
ESD Caution .................................................................................. 5
Pin Configuration and Function Descriptions ............................. 6
Typical Performance Characteristics ............................................. 7
Test Circuits ..................................................................................... 16
Theory of Operation ...................................................................... 20
Overvie w ...................................................................................... 20
Preamplifier ................................................................................. 20
VGA ............................................................................................. 20
Setting the Gain .......................................................................... 21
Noise ............................................................................................ 21
Offset Voltage .............................................................................. 21
Applications Information .............................................................. 22
Amplifier Configuration ........................................................... 22
Preamplifier ................................................................................. 22
Using the Power Adjust Feature ............................................... 23
Driving Capacitive Loads .......................................................... 23
Evaluation Board ............................................................................ 24
Optional Circuitry ...................................................................... 24
Board Layout Considerations ................................................... 24
Outline Dimensions ....................................................................... 26
Ordering Guide .......................................................................... 26
REVISION HISTORY
5/11—Rev. B to Rev. C
Change to Figure 2 and Table 3 ...................................................... 6
4/11—Rev. A to Rev. B
Change to Table 2 ............................................................................. 5
Changes to Figure 77 and Preamplifier Section ......................... 20
Changes to Evaluation Board Section, Optional Circuitry
Section, and Board Layout Considerations Section ................... 24
Added Table 6 .................................................................................. 24
Deleted Figure 83; Renumbered Figures Sequentially ............... 24
Changes to Figure 82, Figure 83, and Figure 84 ......................... 24
Changes to Figure 85, Figure 86, Figure 87, and Figure 88 ....... 25
Deleted Table 6 ................................................................................ 26
9/08—Rev. 0 to Rev. A
Change to General Description Section ......................................... 1
Deleted Input Capacitance Parameter, Table 1 .............................. 3
Added Exposed Pad Notation to Figure 2 ...................................... 6
Changes to Figure 11 ......................................................................... 8
Changes to Figure 55 ...................................................................... 15
Change to Preamplifier Section .................................................... 20
Changes to Noise Section .............................................................. 21
Change to Circuit Configuration for Noninverting
Gain Section .................................................................................... 22
Changes to Table 5 .......................................................................... 22
Changes to Figure 89 and Table 6................................................. 26
Updated Outline Dimensions ....................................................... 27
Changes to Ordering Guide .......................................................... 27
10/06—Revision 0: Initial Version
AD8336
Rev. C | Page 3 of 28
SPECIFICATIONS
VS = ±5 V, T = 25°C, gain range = −14 dB to +46 dB, preamp gain = 4×, f = 1 MHz, CL = 5 pF, RL = 500 Ω, PWRA = GND, unless
otherwise specified.
Table 1.
Parameter Test Conditions/Comments Min Typ Max Unit1
PREAMPLIFIER
−3 dB Small-Signal Bandwidth VOUT = 10 mV p-p 150 MHz
−3 dB Large-Signal Bandwidth VOUT = 2 V p-p 85 MHz
Bias Current, Either Input 725 nA
Differential Offset Voltage ±600 V
Input Resistance 900 kΩ
Input Capacitance 3 pF
PREAMPLIFIER + VGA
−3 dB Small-Signal Bandwidth VOUT = 10 mV p-p 115 MHz
V
OUT = 10 mV p-p, PWRA = 5 V 40 MHz
V
OUT = 10 mV p-p, PrA gain = 20× 20 MHz
V
OUT = 10 mV p-p, PrA gain = −3× 125 MHz
−3 dB Large-Signal Bandwidth VOUT = 2 V p-p 80 MHz
V
OUT = 2 V p-p, PWRA = 5 V 30 MHz
V
OUT = 2 V p-p, PrA gain = 20× 20 MHz
V
OUT = 2 V p-p, PrA gain = −3× 100 MHz
Slew Rate VOUT = 2 V p-p 550 V/µs
Short-Circuit Preamp Input Voltage
Noise Spectral Density
±3 V ≤ VS ≤ ±12 V 3.0 nV/√Hz
Input Current Noise Spectral Density 3.0 pA/√Hz
Output-Referred Noise VGAIN = 0.7 V, PrA gain = 4× 600 nV/√Hz
V
GAIN = −0.7 V, PrA gain = 4× 190 nV/√Hz
V
GAIN = 0.7 V, PrA gain = 20× 2500 nV/√Hz
V
GAIN = −0.7 V, PrA gain = 20× 200 nV/√Hz
V
GAIN = 0.7 V, −55°C ≤ T ≤ +125°C 700 nV/√Hz
V
GAIN = −0.7 V, −55°C ≤ T ≤ +125°C 250 nV/√Hz
DYNAMIC PERFORMANCE
Harmonic Distortion VGAIN = 0 V, VOUT = 1 V p-p
HD2 f = 1 MHz −58 dBc
HD3 f = 1 MHz −68 dBc
HD2 f = 10 MHz −60 dBc
HD3 f = 10 MHz −60 dBc
Input 1 dB Compression Point VGAIN = −0.7 V 11 dBm
V
GAIN = +0.7 V −23 dBm
Two-Tone Intermodulation VGAIN = 0 V, VOUT = 1 V p-p, f1 = 0.95 MHz, f2 = 1.05 MHz −71 dBc
Distortion (IMD3) VGAIN = 0 V, VOUT = 1 V p-p, f1 = 9.95 MHz, f2 = 10.05 MHz −69 dBc
V
GAIN = 0 V, VOUT = 2 V p-p, f1 = 0.95 MHz, f2 = 1.05 MHz −60 dBc
V
GAIN = 0 V, VOUT = 2 V p-p, f1 = 9.95 MHz, f2 = 10.05 MHz −58 dBc
Output Third-Order Intercept VGAIN = 0 V, VOUT = 1 V p-p, f = 1 MHz 34 dBm
V
GAIN = 0 V, VOUT = 1 V p-p, f = 10 MHz 32 dBm
V
GAIN = 0 V, VOUT = 2 V p-p, f = 1 MHz 34 dBm
V
GAIN = 0 V, VOUT = 2 V p-p, f = 10 MHz 33 dBm
Overdrive Recovery VGAIN = 0.7 V, VIN = 100 mV p-p to 5 mV p-p 50 ns
Group Delay Variation 1 MHz < f < 10 MHz, full gain range ±1 ns
PrA Gain = 20× 1 MHz < f < 10 MHz, full gain range ±3 ns
AD8336
Rev. C | Page 4 of 28
Parameter Test Conditions/Comments Min Typ Max Unit1
ABSOLUTE GAIN ERROR2
−0.7 V < VGAIN < −0.6 V 0 1 to 5 6 dB
−0.6 V < VGAIN < −0.5 V 0 0.5 to 1.5 3 dB
−0.5 V < VGAIN < +0.5 V −1.25 ±0.2 +1.25 dB
−0.5 V < VGAIN < +0.5 V, ±3 V ≤ VS ≤ ±12 V ±0.5 +1.25 dB
−0.5 V < VGAIN < +0.5 V, −55°C ≤ T ≤ +125°C ±0.5 dB
−0.5 V < VGAIN < +0.5 V, PrA gain = −3× ±0.5 dB
0.5 V < VGAIN < +0.6 V −4.0 −1.5 to −3.0 0 dB
0.6 V < VGAIN < +0.7 V −9.0 −1 to −5 0 dB
GAIN CONTROL INTERFACE
Gain Scaling Factor 48 49.9 52 dB/V
Intercept Preamp + VGA 16.4 dB
VGA only 4.5 dB
Gain Range 58 60 62 dB
Input Voltage (VGAIN) Range No foldover −VS +VS V
Input Current 1 A
Response Time 60 dB gain change 300 ns
OUTPUT PERFORMANCE
Output Impedance, DC to 10 MHz ±3 V ≤ VS ≤ ±12 V 2.5
Output Signal Swing RL ≥ 500 Ω (for |VS| ≤ ±5 V); RL ≥ 1 kΩ above that |VS| − 1.5 V
R
L ≥ 1 kΩ (for |VS| = ±12 V) |VS| − 2.25 V
Output Current Linear operation − minimum discernable distortion 20 mA
Short-Circuit Current VS = ±3 V +123/−72 mA
V
S = ±5 V +123/−72 mA
V
S = ±12 V +72/−73 mA
Output Offset Voltage VGAIN = 0.7 V, gain = 200× −250 −125 +150 mV
±3 V ≤ VS ≤ ±12 V −200 mV
−55°C ≤ T ≤ +125°C −200 mV
PWRA PIN
Normal Power (Logic Low) VS = ±3 V 0.7 V
Low Power (Logic High) VS = ±3 V 1.5 V
Normal Power (Logic Low) VS = ±5 V 1.2 V
Low Power (Logic High) VS = ±5 V 2.0 V
Normal Power (Logic Low) VS = ±12 V 3.2 V
Low Power (Logic High) VS = ±12 V 4.0 V
POWER SUPPLY
Supply Voltage Operating Range ±3 ±12 V
Quiescent Current
VS = ±3 V 22 25 30
−55°C ≤ T ≤ +125°C 23 to 31 mA
PWRA = 3 V 10 14 18
VS = ±5 V 22 26 30
−55°C ≤ T ≤ +125°C 23 to 31 mA
PWRA = 5 V 10 14 18
VS = ±12 V 23 28 31
−55°C ≤ T ≤ +125°C 24 to 33 mA
PWRA = 5 V 16
Power Dissipation VS = ±3 V 150 mW
V
S = ±5 V 260 mW
V
S = ±12 V 672 mW
PSRR VGAIN = 0.7 V, f = 1 MHz −40 dB
1 All dBm values are calculated with 50 Ω reference, unless otherwise noted.
2 Conformance to theoretical gain expression (see the S section). etting the Gain
AD8336
Rev. C | Page 5 of 28
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Rating
Supply Voltage (VPOS, VNEG) ±15 V
Input Voltage (INPP, INPN) VPOS, VNEG
Gain Voltage (GPOS, GNEG) VPOS, VNEG
PWRA 5 V, GND
VGAI VPOS + 0.6 V,
VNEG − 0.6 V
Power Dissipation
VS ≤ ±5 V 0.43 W
±5 V < VS ≤ ±12 V 1.12 W
Operating Temperature Range
±3 V < VS ≤ ±10 V −55°C to +125°C
±10 V < VS ≤ ±12 V −55°C to +85°C
Storage Temperature Range −65°C to +150°C
Lead Temperature (Soldering 60 sec) 300°C
Thermal Data1
θJA 58.2°C/W
θJB 35.9°C/W
θJC 9.2°C/W
ΨJT 1.1°C/W
ΨJB 34.5°C/W
1 4-layer JEDEC board, no airflow, exposed pad soldered to printed circuit board.
Stresses above those listed under the Absolute Maximum
Ratings may cause permanent damage to the device. This is a
stress rating only; functional operation of the device at these or
any other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD CAUTION
AD8336
Rev. C | Page 6 of 28
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
1
4
3
2
14 131516
9
12
11
10
8765
VPOS
NC
NC
NC
VOUT
PWRA
VCOM
INPP
INPN
NC
PRAO
NC
VGAI
VNEG
GNEG
GPOS
PIN 1
INDICATOR
AD8336
TOP VIEW
(Not to Scale)
06228-002
NOTES
1. NC = NO CONNECT.
2. THE EXPOSED PAD IS NOT CONNECTED INTERNALLY.
FOR INCREASED RELIABILITY OF THE SOLDE
R
JOINTS AND MAXIMUM THERMAL CAPABILITY, IT IS
RECOMMENDED THAT THE PADDLE BE SOLDERED
TO THE GROUND PLANE.
Figure 2. Pin Configuration
Table 3. Pin Function Descriptions
Pin No. Mnemonic Description
1 VOUT Output Voltage.
2 PWRA Power Control. Normal power when grounded; power reduced by half if PWRA is pulled high.
3 VCOM Common-Mode Voltage. Normally GND when using a dual supply.
4 INPP Positive Input to Preamp.
5 INPN Negative Input to Preamp.
6 NC No Connect.
7 NC No Connect.
8 PRAO Preamp Output.
9 VGAI VGA Input.
10 VNEG Negative Supply.
11 GPOS Positive Gain Control Input.
12 GNEG Negative Gain Control Input.
13 VPOS Positive Supply.
14 NC No Connect.
15 NC No Connect.
16 NC No Connect.
AD8336
Rev. C | Page 7 of 28
TYPICAL PERFORMANCE CHARACTERISTICS
VS = ±5 V, T = 25°C, gain range = −14 dB to +46 dB, preamp gain = 4×, f = 1 MHz, CL = 5 pF, RL = 500 Ω, PWRA = GND, unless
otherwise specified.
–20
0–800
V
GAIN
(mV)
–600 –400 –200 200 400 600 800
40
10
30
50
–10
0
20
T = +125°C
T = +25°C
T = –55°C
GAIN (dB)
06228-003
Figure 3. Gain vs. VGAIN for Three Values of Temperature (T)
(See Figure 56)
–20
40
10
30
50
–10
0
20
GAIN (dB)
V
S
= ±12V
V
S
= ±5V
V
S
= ±3V
0–800
V
GAIN
(mV)
–600 –400 –200 200 400 600 800
0
6228-004
Figure 4. Gain vs. VGAIN for Three Values of Supply Voltage (VS)
(See Figure 56)
GAIN (dB)
40
10
30
50
–10
0
20
60
70
–20
PREAMP GAIN = PREAMP GAIN = 20×
0–800
V
GAIN
(mV)
–600 –400 –200 200 400 600 800
0
6228-005
Figure 5. Gain vs. VGAIN for Preamp Gains of 4× and 20×
(See Figure 56)
GAIN ERRO
R
(dB)
–1.0
1.5
–1.5
1.0
2.0
0.5
0
–2.0
T = +125°C
T = +25°C
T = –55°C
–0.5
0–800
V
GAIN
(mV)
–600 –400 –200 200 400 600 800
06228-006
GAIN ERROR (dB)
–1.0
1.5
–1.5
1.0
2.0
0.5
0
–2.0
Figure 6. Gain Error vs. VGAIN for Three Values of Temperature (T)
(See Figure 56)
–0.5
V
S
= ±12V
V
S
= ±5V
V
S
= ±3V
0–800
V
GAIN
(mV)
–600 –400 –200 200 400 600 800
06228-007
GAIN ERROR (dB)
1.5
1.0
2.0
0.5
0
–2.0
Figure 7. Gain Error vs. VGAIN for Three Values of Supply Voltage (VS)
(See Figure 56)
PREAMP GAIN = 20×
PREAMP GAIN = 4×
–0.5
–1.0
–1.5
0–800
VGAIN (mV)
–600 –400 –200 200 400 600 800
06228-008
Figure 8. Gain Error vs. VGAIN for Preamp Gains of 4× and 20×
(See Figure 56)
AD8336
Rev. C | Page 8 of 28
GAIN ERROR (dB)
0
PREAMP GAIN = , f = 1MHz
PREAMP GAIN = 20×, f = 1MHz
PREAMP GAIN = , f = 10MHz
PREAMP GAIN = 20×, f = 10MHz
0–800
VGAIN (mV)
–600 –400 –200 200 400 600 800
–2.0
–1.5
2.0
–1.0
–0.5
0.5
1.0
1.5
06228-009
–2.0
Figure 9. Gain Error vs. VGAIN at 1 MHz and 10 MHz and
for Preamp Gains of 4× and 20×
(See Figure 56)
GAIN ERROR (dB)
1.5
1.0
2.0
0.5
0
–0.5
–1.0
% OF UNITS
GAIN ERROR (dB)
0
30
50
20
40
10
0.16
0.12
0.08
0.04
0
–0.12
–0.08
–0.04
60 UNITS
V
GAIN
= –0.3V
V
GAIN
= +0.3V
06228-012
–1.5
0–800
V
GAIN
(mV)
–600 –400 –200 200 400 600 800
PREAMP GAIN = –3×, f = 1MHz
PREAMP GAIN = –3×, f = 10MHz
PREAMP GAIN = –19×, f = 1MHz
PREAMP GAIN = –19×, f = 10MHz
0
6228-010
Figure 10. Gain Error vs. VGAIN at 1 MHz and 10 MHz and
for Inverting Preamp Gains of −3× and −19×
(See Figure 56)
GAIN (dB)
0
–5
–10
35
50
45
40
Figure 12. Gain Error Histogram
% OF UNITS
GAIN SCALING (dB/V)
0
30
50
20
40
10
49.6 49.7 49.8 49.9 50.0 50.1 50.2
60 UNITS
–0.3V V
GAIN
0.3V
06228-013
Figure 13. Gain Scaling Factor Histogram
OUTPUT OFFSET VOLTAGE (mV)
–60
–40
0
20
–20
–80
–15
–15 –10 –5 0 5 10 15
COMMON-MODE VOLTAGE V
GAIN
(V)
V
S
= ±12V
V
S
= ±5V
V
S
= ±3V
–140
–120
–100
–160
–200
–180
–220
T = +125°C
T = +85°C
T = +25°C
T = –40°C
T = –55°C
V
GAIN
(V)
0.2000.60.4–0.8 –0.6 –0.2–0.4
06228-014
06228-011
Figure 11. Gain vs. Common-Mode Voltage at VGAIN
.8
Figure 14. Output Offset Voltage vs. VGAIN for
Various Values of Temperature (T)
AD8336
Rev. C | Page 9 of 28
OUTPUT OFFSET VOLTAGE (mV)
–60
–40
0
20
–20
V
GAIN
(V)
0.200.80.60.4
–80
–0.8
–140
–120
–100
–160
–200
–180
–0.6 –0.2–0.4
V
S
12V
V
S
5V
V
S
3V
06228-015
OUTPUT OFFSET (mV)
0
Figure 15. Output Offset Voltage vs. VGAIN for
Three Values of Supply Voltage (VS)
30
20
10
SAMPLE SIZE = 60 UNITS
V
GAIN
= 0.7V
–200–240 –160 –120 –80 –40 0 40 80
–20–24 –16 –12 –8 –4 0 4 8
0
30
20
10
OUTPUT OFFSET (mV)
% OF UNITS
SAMPLE SIZE = 60 UNITS
V
GAIN
= 0V
06228-016
Figure 16. Output Offset Histogram
%
OF UNITS
30
20
10
60 UNITS
INTERCEPT (dB)
0
16.45 16.5516.5016.4016.25 16.30 16.35
40
50
06228-017
GAIN (dB)
Figure 17. Intercept Histogram
–10
0
10
20
40
30
50
100k
–20
FREQUENCY (Hz)
200M1M 100M10M
V
GAIN
= +0.7V
+0.5V
+0.2V
0V
–0.2V
–0.5V
–30
–0.7V
06228-018
GAIN (dB)
Figure 18. Frequency Response for Various Values of VGAIN
(See Figure 57)
–10
0
10
20
40
30
50
100k
–20
FREQUENCY (Hz)
200M1M 100M10M
V
GAIN
= +0.7V
+0.5V
+0.2V
0V
–0.2V
–0.5V
–30
–0.7V
LOW POWER MODE
06228-019
Figure 19. Frequency Response for Various Values of VGAIN, Low Power Mode
(See Figure 57)
GAIN (dB)
–10
0
10
20
40
30
50
70
V
GAIN
= +0.7V
60
+0.5V
+0.2V
0V
PREAMP GAIN = 20×
–0.2V
–0.7V
–0.5V
100k
FREQUENCY (Hz)
1M 200M100M10M
0
6228-020
Figure 20. Frequency Response for Various Values of VGAIN
When the Preamp Gain is 20×
(See Fi
g
ure 57
)
AD8336
Rev. C | Page 10 of 28
GAIN (dB)
–10
0
10
20
40
30
50
GAIN (dB)
–10
0
10
20
15
5
25
100k
FREQUENCY (Hz)
1M 500M100M10M
–5
30
100k
–20
FREQUENCY (Hz)
1M 200M100M10M
–30
PREAMP GAIN = –
VGAIN = +0.7V
+0.5V
+0.2V
0V
–0.2V
–0.7V
–0.5V
06228-021
Figure 21. Frequency Response for Various Values of VGAIN
When the Preamp Gain is −3×
(See Figure 69 and Figure 57)
GAIN (dB)
0
10
20
15
5
25
–10
100k
FREQUENCY (Hz)
1M 200M100M10M
–5
V
GAIN
= 0V
C
L
=47pF
C
L
=22pF
C
L
=10pF
C
L
= 0pF
0
6228-022
Figure 22. Frequency Response for Various Values of Load Capacitance (CL)
(See Figure 57)
GAIN (dB)
0
10
20
15
5
25
30
–10
100k
FREQUENCY (Hz)
1M 500M100M10M
–5
V
S
= ±12V
V
S
= ±5V
V
S
= ±3V
GAIN = 20×
GAIN =
06228-023
Figure 23. Preamp Frequency Response for Three Values of Supply Voltage (VS)
When the Preamp Gain is 4× or 20×
(See Figure 58)
GAIN = –3×
GAIN = –19×
V
S
= ±12V
V
S
= ±5V
V
S
= ±3V
0
6228-024
Figure 24. Preamp Frequency Response for Three Values of Supply Voltage (VS)
When the Inverting Gain Value is −3× or −19×
(See Figure 69)
GROUP DELAY (ns)
0
10
20
15
5
FREQUENCY (Hz)
1M 100M10M
PREAMP GAIN = 20×
PREAMP GAIN = 4×
0
6228-025
OUTPUT RESISTANCE ()
0.1
1
100
1k
10
FREQUENCY (Hz)
0.01
Figure 25. Group Delay vs. Frequency for Preamp Gains of 4× and 20×
(See Figure 59)
1M 500M100M10M
100k
06228-026
Figure 26. Output Resistance vs. Frequency of the Preamp
(See Figure 61)
AD8336
Rev. C | Page 11 of 28
OUTPUT RESISTANCE ()
0.1
1
100
1k
10
FREQUENCY (Hz)
1M 500M100M10M
0.01
100k
V
S
= ±12V
V
S
= ±5V
V
S
= ±3V
06228-027
Figure 27. Output Resistance vs. Frequency of the VGA
for Three Values of Supply Voltage (VS)
(See Figure 61)
OUTPUT-REFERRED NOISE (nV/
Hz
)
1000
900
800
700
600
500
400
300
200
0
100
–800
V
GAIN
(mV)
–600 –200–400 400 600200 800
0
T = +125°C
T = +85°C
T = +25°C
T = –40°C
T = –55°C
f= 5MHz
06228-028
Figure 28. Output-Referred Noise vs. VGAIN at Various Temperatures (T)
(See Figure 62)
0–800
VGAIN (mV)
–600 –200–400 400 600200 800
OUTPUT-REFERRED NOISE (nV/
Hz
)
3000
2700
2400
2100
1800
1500
1200
900
600
300
0
f = 5MHz
PREAMP GAIN = 20×
T = +125°C
T = +85°C
T = +25°C
T = –40°C
T = –55°C
06228-029
0–800
VGAIN (mV)
–600 –200–400 400 600200 800
INPUT-REFERRED NOISE (nV/Hz)
1k
100
10
1
f = 5MHz
PREAMP GAIN = 4×
PREAMP GAIN = 20×
0
6228-030
INPUT-REFERRED NOISE (nV/
Hz
)
Figure 29. Output-Referred Noise vs. VGAIN at Various Temperatures (T)
When the Preamp Gain is 20×
(See Figure 62)
Figure 30. Input-Referred Noise vs. VGAIN for Preamp Gains of 4× and 20×
(See Figure 62)
2
3
5
6
100k
4
FREQUENCY (Hz)
1M 100M10M
0
1
VGAIN =
0.7V
VS = ±12V
VS = ±5V
VS = ±3V
06228-031
Figure 31. Short-Circuit Input-Referred Noise vs. Frequency at Maximum Gain
for Three Values of Supply Voltage (VS)
(See Figure 62)
2
3
5
6
100k
4
1M 100M10M
INPUT-REFERRED NOISE (nV/
Hz)
0
1
V
GAIN
= 0.7V
PREAMP GAIN = –3×
FREQUENCY (Hz)
06228-032
Figure 32. Short-Circuit Input-Referred Noise vs. Frequency
at Maximum Inverting Gain
(See Figure 73)
AD8336
Rev. C | Page 12 of
28
10k10
0.1 100 1k
SOURCE RESISTANCE ()
1
10
INPUT-REFERRED NOISE (nV/
Hz)
INPUT-REFERRED NOISE
100
V
GAIN
= 0.7V
R
S
THERMAL NOISE ALONE
40
25
–50
0
LOAD CAPACITANCE (pF)
54010 3515 3020
–60
06228-033
Figure 33. Input-Referred Noise vs. Source Resistance
(See Figure 72)
NOISE FIGURE (dB)
40
20
50
30
0–800 –600 –200–400 400 600200 800
0
10
60
SIMULATED
DATA
UNTERMINATED
70
V
GAIN
(mV)
f = 10MHz
50 SOURCE
0
6228-034
Figure 34. Noise Figure vs. VGAIN
(See Figure 63)
HARMONIC DISTORTION (dBc)
40
–50
–60
–65
–45
–55
1.0k0
LOAD RESISTANCE ()
200 1.6k400 1.4k600 1.2k800
–70 1.8k 2.0k 2.2k
HD3
HD2
V
OUT
= 2V p-p
V
GAIN
= 0V
f = 5MHz
0
6228-035
Figure 35. Harmonic Distortion vs. Load Resistance
(See Figure 64)
HARMONIC DISTORTION (dBc)
HD3
–65
–70
45 50
HD2
V
OUT
= 2V p-p
V
GAIN
= 0V
f = 5MHz
06228-036
–45
–55
Figure 36. Harmonic Distortion vs. Load Capacitance
(See Figure 64)
20
HARMONIC DISTORTION (dBc)
–30
400
–50
V
GAIN
(mV)
–600 800–400 600–200 2000
–60
–80
–70
–40
OUTPUT SWING OF PREAMP
LIMITS V
GAIN
TO 400mV
HD2 @ 1MHz
HD2 @ 10MHz
HD3 @ 1MHz
HD3 @ 10MHz
V
OUT
= 1V p-p
06228-037
Figure 37. Second and Third Harmonic Distortion vs. VGAIN at 1 MHz and 10 MHz
(See Figure 64)
HARMONIC DISTORTION (dBc)
–30
–50
–60
–80
–70
–40
20
400
V
GAIN
(mV)
–600 800–400 600–200 2000
06228-038
OUTPUT SWING OF PREAMP LIMITS
V
GAIN
LEVELS
V
OUT
= 0.5V p-p
V
OUT
= 1V p-p
V
OUT
= 2V p-p
V
OUT
= 4V p-p
HD2
f = 5MHz
Figure 38. Second Harmonic Distortion vs. VGAIN
for Four Values of Output Voltage (VOUT)
(See Figure 64)
AD8336
Rev. C | Page 13 of
20
28
OUTPUT IP3 (dBm)
25
200
30
–800
V
GAIN
(mV)
–600 800–400 600–200 4000
20
0
10
40
HARMONIC DISTORTION (dBc)
–30
–50
–60
–80
–70
–40
VOUT = 0.5V p-p
VOUT = 1V p-p
VOUT = 2V p-p
VOUT = 4V p-p
OUTPUT SWING OF PREAMP LIMITS
MINIMUM USABLE VGAIN LEVELS
HD3
f = 5MHz
400
VGAIN (mV)
–600 800–400 600–200 2000
06228-039
Figure 39. Third Harmonic Distortion vs. VGAIN
for Four Values of Output Voltage (VOUT)
(See Figure 64)
HARMONIC DISTORTION (dBc)
–60
–50
20
–30
–40
1M
–70
FREQUENCY (Hz)
10M 50M
HD2
HD3
V
OUT
= 2V p-p
V
GAIN
= 0V
06228-040
Figure 40. Harmonic Distortion vs. Frequency
(See Figure 64)
IMD3 (dBc)
–60
–50
–20
–30
–70
–40
–80
1M
FREQUENCY (Hz)
10M 100M
0
–10
V
OUT
= 1V p-p
V
GAIN
= 0V
TONES SEPARATED BY 100kHz
–90
06228-041
Figure 41. IMD3 vs. Frequency
(see Figure 76)
5
15
35
1MHz 500mV
1MHz 1V
10MHz 500mV
10MHz 1V
V
OUT
= 1V p-p
V
GAIN
= 0V
COMPOSITE INPUTS SEPARATED BY 100kHz
06228-042
200–800
V
GAIN
(mV)
–600 800–400 600–200 4000
Figure 42. Output-Referred IP3 (OIP3) vs. VGAIN
at Two Frequencies and Two Input Levels
(see Figure 76)
IP1dB (dBm)
0
–30
–10
10
30
20
–20
V
S
= ±5V
V
S
= ±3V
V
S
= ±12V
INPUT LEVEL LIMITED
BY GAIN OF PREAMP
06228-043
Figure 43. Input P1dB (IP1dB) vs. VGAIN at Three Power Supply Values (VS)
(see Figure 74 and Figure 75)
VOLTAGE (V)
–1
2
0
1
3
–2
300–100
TIME (ns)
100 2000
–3
V
IN
(V)
V
OUT
(V)
0
6228-044
Figure 44. Large-Signal Pulse Response of the Preamp
(See Figure 65)
AD8336
Rev. C | Page 14 of 28
V
OUT
(mV)
–20
20
40
–40
V
IN
(mV)
0
–0.2
0.2
0.4
–0.4
0
0.6
60
V
IN
(mV)
–15
0
–20
20
10
15
–10
–25
25
–60
0–100 –50 150100 25050 300200 350
–0.6
INPUT
OUTPUT WHEN PWRA = 0
OUTPUT WHEN PWRA = 1
V
GAIN
= 0.7V
TIME (ns)
06228-045
Figure 45. Noninverting Small-Signal Pulse Response for Both Power Levels
(See Figure 65)
V
GAIN
= 0.7V
PREAMP GAIN = –3×
INPUT
OUTPUT
V
OUT
(mV)
–20
20
40
–40
V
IN
(mV)
0
–0.2
0.2
0.4
–0.4
0
0.6
60
–60
0–100
TIME (ns)
–50 150100 25050 300200 350
–0.6
06228-046
Figure 46. Inverting Gain Small-Signal Pulse Response
(See Figure 70)
–2.0–20
–2.5–25
–1.0
0
2.0
1.5
–1.5
V
IN
(mV)
–15
0
20
10
15
–10
1.0
2.525
5
–5 –0.5
0.5
INPUT
OUTPUT WHEN PWRA = 0
OUTPUT WHEN PWRA = 1
VOUT (mV)
VGAIN = 0.7V
0–100
TIME (ns)
–50 150100 25050 300200 350
06228-047
Figure 47. Large-Signal Pulse Response for Both Power Levels
(See Figure 65)
5
–5
–1.5
0
–2.0
2.0
1.0
1.5
–1.0
–2.5
2.5
0.5
–0.5
INPUT
OUTPUT
0–100
TIME (ns)
–50 150100 25050 300200 350
V
OUT
(mV)
V
GAIN
= 0.7V
PREAMP GAIN = –
06228-048
Figure 48. Inverting Gain Large-Signal Pulse Response
(See Figure 70)
V
OUT
(V)
–2.0
–1.0
0
0
2.0
1.5
–100
–1.5
TIME (ns)
–50 20015010050 300250
V
IN
(mV)
–15
0
–20
20
10
15
–10
1.0
350
5
–5 –0.5
0.5
400
V
GAIN
= 0.7V
V
S
= ±3V
06228-049
INPUT
C
L
= 0pF
C
L
= 10pF
C
L
= 22pF
C
L
= 47pF
Figure 49. Large-Signal Pulse Response for Various Values of Load
Capacitance Using ±3 V Power Supplies
(See Figure 65)
V
GAIN
= 0.7V
V
S
= ±5V
V
IN
(mV)
*WITH 20 RESISTOR IN SERIES WITH OUTPUT.
V
OUT
(mV)
–1
1
2
–2
0
3
–10
10
20
–20
0
30
INPUT
C
L
= 0pF
C
L
= 10pF
C
L
= 22pF
C
L
= 47pF*
0–100
TIME (ns)
–50 150100 25050 300200 350
–3
–30
0
6228-050
Figure 50. Large-Signal Pulse Response for Various Values of Load
Capacitance Using ±5 V Power Supplies
(See Figure 65)
AD8336
Rev. C | Page 15 of 28
V
GAIN
= 0.7V
V
S
= ±12V
V
IN
(mV)
0–100
TIME (ns)
–50 150100 25050 300200 350
V
OUT
(mV)
–3
–1
1
2
–2
0
3
–30
–10
10
20
–20
0
30
–60
–50
–30
–20
100k
–40
FREQUENCY (Hz)
1M 5M
PSRR (dB)
–10
0
10
V
POS
PSRR
V
NEG
V
GAIN
= 0.7V
V
GAIN
= 0V
V
GAIN
= –0.7V
*WITH 20 RESISTOR IN SERIES WITH OUTPUT
INPUT
C
L
= 0pF
C
L
= 10pF*
C
L
= 22pF*
C
L
= 47pF*
06228-051
06228-052
6228-054
0
Figure 51. Large-Signal Pulse Response for Various Values of Load
Capacitance Using ±12 V Power Supplies
(See Figure 65)
VOLTAGE (V)
2.5
1.5
0.5
Figure 54. PSRR vs. Frequency for Three Values of VGAIN
(See Figure 71)
QUIESCENT SUPPLY CURRENT (mA)
0–25
40
30
–65
10
TEMPERATURE (°C)
–45 15–5 35 55
20
75
2.0
TIME (µs)
01.51.0
–2.5
V
GAIN
V
OUT
–0.5
–1.5
–0.5 0.5
Figure 52. Gain Response
(See Figure 66)
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
–1
2
0
5
4
1
3
–2
–3
–0.1
0.2
0.5
0.4
0.1
0.3
–0.2
–0.3
HIGH POWER
LOW POWER
V
S
= ±12V
V
S
= ±5V
V
S
= ±3V
6228-055
95 115 135
0
Figure 55. IQ vs. Temperature for Three Values of Supply Voltage
and High and Low Power
(See Figure 68)
–6–9
TIME (µs)
–3 306
–5
–4
–0.5
–0.4 V
IN
(V)
V
OUT
(V)
V
GAIN
= 0.7V
0
0
6228-053
Figure 53. VGA Overdrive Recovery
(See Figure 67)
AD8336
Rev. C | Page 16 of 28
TEST CIRCUITS
NETWORK ANALYZER
50
INOUT
453
NETWORK ANALYZER
50
INOUT
100
301
49.9
50
V
GAIN
AD8336
4
5
118
1
12
PrA
+
9
06228-056
Figure 56. Gain vs. VGAIN and Gain Error vs. VGAIN
NETWORK ANALYZER
100
301
49.9
50
INOUT
453
OPTIONAL
C
L
50
4
5
115
1
12
PrA
+
8
AD8336
V
GAIN
06228-057
Figure 57. Frequency Response
NETWORK ANALYZER
100
301
49.9
50
INOUT
50
453NC
NC 453
4
5
118
1
12
PrA
+
9
AD8336
06228-058
NC = NO CONNECT
Figure 58. Frequency Response of the Preamp
100
301
49.9
50
453
4
5
11
8
1
12
PrA
+
9
AD8336
06228-059
Figure 59. Group Delay
100
301
45350
AD8336
DMM
4
5
11
8
1
12
PrA
+
9
+
¯
06228-060
Figure 60. Offset Voltage
NETWORK ANALYZER
0
0
100
301
49.9
IN
50
NC
NC
4
5
11
8
1
12
PrA
+
9
AD8336
228-061
CONFIGURE TO
MEASURE
Z-CONVERTED S22
06
NC = NO CONNECT
Figure 61. Output Resistance vs. Frequency
AD8336
Rev. C | Page 17 of 28
100
OSCILLOSCOPE
SPECTRUM ANALYZE
R
301
IN
50
5
118
1
12
PrA
+
9
4
AD8336
V
GAIN
06228-062
Figure 62. Input-Referred Noise and Output-Referred Noise
NOISE FIGURE METE
R
100
1
301
49.9
(OR )
INPUT
0
0
NOISE
SOURCE
DRIVE
NOISE
SOURCE
4
5
118
1
12
PrA
+
9
AD8336
V
GAIN
06228-063
Figure 63. Noise Figure vs. VGAIN
SPECTRUM ANALYZE
R
100
301
49.9
INPUT
LOW-PASS
FILTER
CL
50
RL
4
5
118
1
12
PrA
+
9
SIGNAL
GENERATOR
AD8336
VGAIN
06228-064
Figure 64. Harmonic Distortion
301
CH2
50
OUT
50
CH1
PULSE
GENERATOR POWER
SPLITTER
4
9.9
20453
0.7V
AD8336 OPTIONAL
100
4
5
11
8
1
12
PrA
+
9
06228-065
Figure 65. Pulse Response
OSCILLOSCOPE
SQUARE
WAVE
100
301
CH2
5050
CH1
FUNCTION
GENERATOR
49.9NC
NC = NO CONNECT
POWER
SPLITTER
DIFFERENTIAL
FET PROBE
11
4
5
8
1
12
453
PrA
+
9
SINE
WAVE
PULSE
GENERATOR
AD8336
06228-066
Figure 66. Gain Response
OSCILLOSCOPE
–20dB
100
301
CH2
50
CH1
49.9
POWER
SPLITTER 50
453
NC
4
5
118
1
12
PrA
+
9
ARBITRARY
WAVEFORM
GENERATOR
0.7V
AD8336
06228-067
NC = NO CONNECT
Figure 67. VGA Overdrive Recovery
AD8336
Rev. C | Page 18 of 28
NETWORK ANALYZER
100
301
DMM
(+I)
DMM
(–I)
AD8336
4
5
118
1
12
PrA
+
10
13
9
06228-068
Figure 68. Supply Current
NETWORK ANALYZER
100
301
100
50
INOUT
453
50
V
GAIN
AD8336
4
118
1
12
PrA
+
9
5
49.9
06228-069
Figure 69. Frequency Response, Inverting Gain
OSCILLOSCOPE
100
301
CH2
50
OUT
50
CH1
PULSE
GENERATOR
100
453
0.7V
POWER
SPLITTER
AD8336
4
5
118
1
12
PrA
+
9
49.9
06228-070
Figure 70. Pulse Response, Inverting Gain
V
GAIN
100
301
49.9
50
INOUT
BY
PASS
CAPACITORS
REMOVED FOR
MEASUREMENT
50
DIFFERENTIAL
FET PROBE
BENCH
POWER SUPPLY
VPOS OR VNEG
POWER SUPPLIES
CONNECTED TO
NETWORK ANALYZER
BIAS PORT
AD8336
4
5
11
8
1
12
PrA
+
9
06228-071
Figure 71. Power Supply Rejection Ratio
SPECTRUM ANALYZER
IN
50
AD8336
100
301
0.7V
4
5
118
1
12
PrA
+
9
06228-072
Figure 72. Input-Referred Noise vs. Source Resistance
SPECTRUM ANALYZE
R
IN
50
AD8336
100
301
0.7V
4
5
11
8
1
12
PrA
+
9
06228-073
Figure 73. Short-Circuit Input-Referred Noise vs. Frequency
AD8336
Rev. C | Page 19 of 28
SIGNAL
GENERATOR
100
301
49.9
50
OUT
453
22dB
AD8336
4
5
118
1
12
PrA
+
9
IN
50
SPECTRUM
ANALYZER
OPTIONAL 20dB
ATTENUATOR
V
GAIN
06228-074
Figure 74. IP1dB vs. VGAIN
SIGNAL
GENERATOR
100
301
49.9
50
OUT
453
AD8336 DUT
4
118
1
12
PrA
+
9
5
IN
50
SPECTRUM
ANALYZER
–20dB
AD8336 AMPLIFIER
4
5
118
1
12
PrA
+
9
100
0
3010.7V V
GAIN
06228-075
Figure 75. IP1dB vs. VGAIN, High Signal Level Inputs
SPECTRUM ANALYZER
INPUT
100
49.9
50
453
SIGNAL
GENERATOR
SIGNAL
GENERATOR
+22dB –6dB
+22dB –6dB
COMBINER
–6dB AD8336 DUT
4
118
1
12
PrA
+
9
5
301
VGAIN
6228-076
0
Figure 76. IMD and OIP3
AD8336
Rev. C | Page 20 of 28
THEORY OF OPERATION
OVERVIEW
The AD8336 is the first VGA designed for operation over
exceptionally broad ranges of temperature and supply voltage.
Its performance has been characterized from temperatures
extending from −55°C to +125°C, and supply voltages from ±3 V
to ±12 V. It is ideal for applications requiring dc coupling, large
output voltage swings, very large gain ranges, extreme temperature
variations, or a combination thereof.
The simplified block diagram is shown in Figure 77. The
AD8336 includes a voltage feedback preamplifier, an amplifier
with a fixed gain of 34 dB, a 60 dB attenuator, and various bias
and interface circuitry. The independent voltage feedback op amp
can be used in noninverting and inverting configurations and
functions as a preamplifier to the variable gain amplifier (VGA).
If desired, the op amp output (PRAO) and VGA input (VGAI)
pins provide for connection of an interstage filter to eliminate
noise and offset. The bandwidth of the AD8336 is dc to 100 MHz
with a gain range of 60 dB (−14 dB to +46 dB).
For applications that require large supply voltages, a reduction
in power is advantageous. The power reduction pin (PWRA)
permits the power and bandwidth to be reduced by about half
in such applications.
VOUT
V
GAIPRAO
GNEG VCOMVPOS GPOS
PWRA
–60dB TO 0dB
ATTENUATOR
AND GAIN
CONTROL
INTERFACE
BIAS
INPP
INPN
R
FB2
301
4.48k
+
_
*
34dB12dB
+
PrA
91.43
VNEG
*OPTIONAL DEPEAKING CAPACITOR. SEE TEXT.
06228-077
R
FB1
100
1.28k
Figure 77. Simplified Block Diagram
To maintain low noise, the output stages of both the preamplifier
and the VGA are capable of driving relatively small load resistances.
However, at the largest supply voltages, the signal current may
exceed safe operating limits for the amplifiers and, therefore,
the load current must not exceed 50 mA. With a ±12 V supply
and ±10 V output voltage at the preamplifier or VGA output,
load resistances as low as 200  are acceptable.
For power supply voltages ≥ ±10 V, the maximum operating
temperature range is derated to +85°C because the power may
exceed safe limits (see the Absolute Maximum Ratings section).
Because harmonic distortion products may increase for various
combinations of low impedance loads and high output voltage
swings, it is recommended that the user determine load and
drive conditions empirically.
PREAMPLIFIER
The gain of the uncommitted voltage feedback preamplifier is set
with external resistors. The combined preamplifier and VGA gain
is specified in two ranges: −14 dB to +46 dB and 0 dB to 60 dB.
Since the VGA gain is fixed at 34 dB (50×), the preamp gain is
adjusted for gains of 12 dB (4×) and 26 dB (200×).
With low preamplifier gains between 2× and 4×, it may be desirable
to reduce the high frequency gain with a shunt capacitor across
RFB2 to ameliorate peaking in the frequency domain (see Figure 77).
To maintain stability, the gain of the preamplifier must be 6 dB
(2×) or greater.
Typical of voltage feedback amplifier configurations, the gain-
bandwidth product of the AD8336 is fixed (at 600); therefore,
the bandwidth decreases as the gain is increased beyond the
nominal gain value of 4×. For example, if the preamp gain is
increased to 20×, the bandwidth reduces by a factor of 5 to about
20 MHz. The −3 dB bandwidth of the preamplifier with a gain
of 4× is about 150 MHz, and for the 20× gain is about 30 MHz.
The preamp gain diminishes for an amplifier configured for
inverting gain, using the same value of feedback resistors as for a
noninverting amplifier, but the bandwidth remains unchanged. For
example, if the noninverting gain is 4×, the inverting gain is −3×,
but the bandwidth stays the same as in the noninverting gain of 4×.
However, because the output-referred noise of the preamplifier
is the same in both cases, the input-referred noise increases as
the ratio of the two gain values increases. For the previous example,
the input-referred noise increases by a factor of 4/3.
The output swing of the preamplifier is the same as for the VGA.
VGA
The architecture of the variable gain amplifier (VGA) section
of the AD8336 is based on the Analog Devices, Inc., X-AMP
(exponential amplifier), found in a wide variety of Analog Devices
variable gain amplifiers. This type of VGA combines a ladder
attenuator and interpolator, followed by a fixed-gain amplifier.
The gain control interface is fully differential, permitting positive
or negative gain slopes. Note that the common-mode voltage of
the gain control inputs increases with increasing supply.
The gain slope is 50 dB/V and the intercept is 16.4 dB when the
nominal preamp gain is 4× (12 dB). The intercept changes with
the preamp gain; for example, when the preamp gain is set to
20× (26 dB), the intercept becomes 30.4 dB.
Pin VGAI is connected to the input of the ladder attenuator.
The ladder ratio is R/2R and the nominal resistance is 320 . To
reduce preamp loading and large-signal dissipation, the input
resistance at Pin VGAI is 1.28 k. Safe current density and
power dissipation levels are maintained even when large dc
signals are applied to the ladder.
The tap resistance of the resistors within the R/2R ladder is 640 /3,
or 213.3 , and is the Johnson noise source of the attenuator.
AD8336
Rev. C | Page 21 of 28
SETTING THE GAIN
The overall gain of the AD8336 is the sum (in decibels) or the
product (magnitude) of the preamp gain and the VGA gain.
The preamp gain is calculated as with any op amp, as seen in
the Applications Information section. It is most convenient to
think of the device gain in exponential terms (that is, in decibels)
since the VGA responds linearly in decibels with changes in
control voltage VGAIN at the gain pins.
The gain equation for the VGA is
dB4.4
V
dB50
(V)(dB) +
×= GAIN
VGainVGA
where VGAIN = VGPOSVGNEG.
The gain and gain range of the VGA are both fixed at 34 dB and
60 dB, respectively; thus, the composite device gain is changed
by adjusting the preamp gain. For a preamp gain of 12 dB (4×),
the composite gain is −14 dB to +46 dB. Therefore, the calculation
for the composite gain (in decibels) is
Composite Gain = GPRA + [VGAIN (V) × 49.9 dB/V] + 4.4 dB
For example, the midpoint gain when the preamp gain is 12 dB is
12 dB + [0 V × 49.9 dB/V] + 4.4 dB = 16.4 dB
Figure 3 is a plot of gain in decibels vs. VGAIN in millivolts, when
the preamp gain is 12 dB (4×). Note that the computed result
closely matches the plot of actual gain.
In Figure 3, the gain slope flattens at the limits of the VGAIN
input. The gain response is linear-in-dB over the center 80% of
the control range of the device. Figure 78 shows the ideal gain
characteristics for the VGA stage gain, the composite gain, and
the preamp gain.
GAIN (dB)
40
50
30
10
0
20
–10
60
70
V
GAIN
(V)
FOR PREAMP GAIN = 26dB
–20
–30
FOR PREAMP GAIN = 6dB
GAIN CHARACTERISTICS
COMPOSITE GAIN
VGA STAGE GAIN
USABLE GAIN RANGE OF
AD8336
FOR PREAMP GAIN = 12dB
0.5 0.70.30.1–0.1–0.3–0.5–0.7
06228-078
Figure 78. Ideal Gain Characteristics of the AD8336
NOISE
The noise of the AD8336 is dependent on the value of the VGA
gain. At maximum VGAIN, the dominant noise source is the
preamp, but it shifts to the VGA as VGAIN diminishes.
The input-referred noise at the highest VGA gain and a preamp
gain of 4×, with RFB1 = 100  and RFB2 = 301 , is 3 nV/Hz and
is determined by the preamp and its gain setting resistors. See
Tabl e 4 for the noise components for the preamp.
Table 4. AD8336 Noise Components for Preamp Gain = 4×
Noise Component Noise Voltage (nV/√Hz)
Op Amp (Gain = 4×) 2.6
RFB1 = 100 Ω 0.96
RFB2 = 301 Ω 0.55
VGA 0.77
Using the values listed in Table 4, the total noise of the AD8336
is slightly less than 3 nV/Hz, referred to the input. Although
the input noise referred to the VGA is 3.1 nV/Hz, the input-
referred noise at the preamp is 0.77 nV/Hz when divided by
the preamplifier gain of 4×.
At other than maximum gain, the noise of the VGA is determined
from the output noise. The noise in the center of the gain range
is about 150 nV/Hz. Because the gain of the fixed-gain amplifier
that is part of the VGA is 50×, the VGA input-referred noise is
approximately 3 nV/Hz, the same value as the preamp and VGA
combined. This is expected since the input-referred noise is the
same at the input of the attenuator at maximum gain. However,
the noise referred to the VGAI pin (the preamp output) increases
by the amount of attenuation through the ladder network. The
noise at any point along the ladder network is primarily composed
of the ladder resistance noise, the noise of the input devices, and
the feedback resistor network noise. The ladder network and
the input devices are the largest noise sources.
At minimum gain, the output noise increases slightly to about
180 nV/Hz because of the finite structure of the X-AMP.
OFFSET VOLTAGE
Extensive cancellation circuitry included in the variable gain
amplifier section minimizes locally generated offset voltages.
However, when operated at very large values of gain, dc voltage
errors at the output can still result from small dc input voltages.
When configured for the nominal gain range of −14 dB to +46 dB,
the maximum gain is 200× and an offset of only 100 V at the
input generates 20 mV at the output.
The primary source for dc offset errors is the preamplifier;
ac coupling between the PRAO and VGAI pins is the simplest
solution. In applications where dc coupling is essential, a
compensating current can be injected at the INPN input (Pin 5)
to cancel preamp offset. The direction of the compensating
current depends on the polarity of the offset voltage.
AD8336
Rev. C | Page 22 of 28
APPLICATIONS INFORMATION
AMPLIFIER CONFIGURATION
The AD8336 amplifiers can be configured in various options. In
addition to the 60 dB gain range variable gain stage, an uncommit-
ted voltage gain amplifier is available to the user as a preamplifier.
The preamplifier connections are separate to enable noninverting
or inverting gain configurations or the use of interstage filtering.
The AD8336 can be used as a cascade connected VGA with pre-
amp input, as a standalone VGA, or as a standalone preamplifier.
This section describes some of the possible applications.
VOUT
V
GAI
2
13
PRA
O
1
GNEG
3
AD8336
VCOMVPOS GPOS
98
34dB
PrA
PWRA
ATTENUATOR
–60dB TO 0dB
12
GAIN CONTROL
INTERFACE
11
INPP
4
5
INPN
+
BIAS
10
VNEG
06228-079
Figure 79. Application Block Diagram
PREAMPLIFIER
While observing just a few constraints, the uncommitted voltage
feedback preamplifier of the AD8336 can be connected in a
variety of standard high frequency op amp configurations. The
amplifier is optimized for a gain of 4× (12 dB) and has a gain
bandwidth product of 600 MHz. At a gain of 4×, the bandwidth
is 150 MHz. The preamplifier gain can be adjusted to a minimum
gain of 2×; however, there will be a small peak in the response at
high frequencies. At higher preamplifier gains, the bandwidth
diminishes proportionally in conformance to the classical voltage
gain amplifier GBW relationship.
While setting the overall gain of the AD8336, the user needs
to consider the input-referred offset voltage of the preamplifier.
Although the offset of the attenuator and postamplifier are almost
negligible, the preamplifier offset voltage, if uncorrected, is
increased by the combined gain of the preamplifier and post-
amplifier. Therefore, for a maximum gain of 60 dB, an input
offset voltage of only 200 V results in an error of 200 mV at
the output.
Circuit Configuration for Noninverting Gain
The noninverting configuration is shown in Figure 80. The
preamp gain is described by the classical op amp gain equation:
1
1
2+=
FB
FB
R
R
Gain
The practical gain limits for this amplifier are 6 dB to 26 dB.
The gain bandwidth product is about 600 MHz, so at 150 MHz,
the maximum achievable gain is 12 dB (4×). The minimum gain
is established internally by fixed loop compensation and is 6 dB
(2×). This amplifier is not designed for unity-gain operation.
Tabl e 5 shows the gain and bandwidth for the noninverting gain
configuration.
PRAO
34dB
AD8336
PREAMPLIFIER
INPP
–60dB TO 0dB
4
5
INPN
9
GAIN = 12dB
R
FB1
100
VGAI
13
VPOSVNEG
10
VOUT
1
06228-080
R
FB2
301
+5V
–5V
PWRA
2 3
VCOM
8
Figure 80. Circuit Configuration for Noninverting Gain
The preamplifier output reliably sources and sinks currents up
to 50 mA. When using ±5 V power supplies, the suggested sum
of the output resistor values is 400  total for the optimal trade-
off between distortion and noise. Much of the low gain value
device characterization was performed with resistor values of
301  and 100 , resulting in a preamplifier gain of 12 dB (4×).
With supply voltages between ±5 V and ±12 V, the sum of the
output resistance should be increased accordingly; a total
resistance of 1 k is recommended. Larger resistance values,
subject to a trade-off in higher noise performance, can be used
if circuit power and load driving is an issue. When considering
the total power dissipation, remember that the input ladder
resistance of the VGA is part of the preamp load.
Table 5. Gain and Bandwidth for Noninverting Preamplifier
Configuration
Preamp Gain Preamp BW
(MHz)
Composite
Gain (dB)
Numerical dB
12 150 −14 to +46
18 60 −8 to +52
16× 24 30 −2 to +58
20× 26 25 0 to +60
AD8336
Rev. C | Page 23 of 28
Circuit Configuration for Inverting Gain
The preamplifier can also be used in an inverting configuration,
as shown in Figure 81.
PRAO
34dB
AD8336
PREAMPLIFIER
INPP
4
5
+
8
VOUT
1
9
GAIN = 9.6dB INPN
R
FB1
100
R
FB2
301
–60dB TO 0dB
13
VPOSVNEG
10
+5V
–5V
PWRAVGAI
2 3
VCOM
06228-081
Figure 81. Circuit Configuration for Inverting Gain
The considerations regarding total resistance vs. distortion, noise,
and power that were noted in the noninverting case also apply
in the inverting case, except that the amplifier can be operated
at unity inverting gain. The signal gain is reduced while the
noise gain is the same as for the noninverting configuration:
FB1
FB2
R
R
GainSignal =
and
1+=
FB1
FB2
R
R
GainNoise
USING THE POWER ADJUST FEATURE
The AD8336 has the provision to operate at lower power with a
trade-off in bandwidth. The power reduction applies to the preamp
and the VGA sections, and the bandwidth is reduced equally
between them. Reducing the power is particularly useful when
operating with higher supply voltages and lower values of output
loading that would otherwise stress the output amplifiers. When
Pin PWRA is grounded, the amplifiers operate in their default
mode, and the combined 3 dB bandwidth is 80 MHz with the
preamp gain adjusted to 4×. When the voltage on Pin PWRA is
between 1.2 V and 5 V, the power is reduced by approximately
half and the 3 dB bandwidth reduces to approximately 35 MHz.
The voltage at Pin PWRA must not exceed 5 V.
DRIVING CAPACITIVE LOADS
The output stages of the AD8336 are stable with capacitive loads
up to 47 pF for a supply voltage of ±3 V and with capacitive loads
up to 10 pF for supply voltages up to ±8 V. For larger combined
values of load capacitance and/or supply voltage, a 20  series
resistor is recommended for stability.
The influence of capacitance and supply voltage are shown in
Figure 50 and Figure 51, where representative combinations of
load capacitance and supply voltage requiring a 20  resistor
are marked with an asterisk. No resistor is required for the ±3 V
plots in Figure 49, but a resistor is required for most of the ±12 V
plots in Figure 51.
AD8336
Rev. C | Page 24 of 28
EVALUATION BOARD
An evaluation board, AD8336-EVALZ, is available online for
the AD8336. Figure 82 is a photo of the board.
The board is shipped from the factory configured for a non-
inverting preamp gain of 4×. To change the value of the gain
of the preamp or to change the gain polarity to inverting, alter
the component values or install components in the alternate
locations provided. All components are standard 0603 size, and
the board is compliant with RoHS requirements. Table 6 shows
the components to be removed and added to change the amplifier
configuration to inverting gain.
Table 6. Component Changes for Inverting Configuration
Remove Install
R4, R7 R5, R6
OPTIONAL CIRCUITRY
The AD8336 features differential inputs for the gain control,
permitting nonzero or floating gain control inputs. To avoid any
delay in making the board operational, the gain input circuit is
shipped with Pin GNEG connected to ground via a 0 Ω resistor
in the R17 location. The user can adjust the gain of the device
by driving the GPOS test loop with a power supply or voltage
reference. Optional resistor networks R15/R17 and R13/R14
provide fixed-gain bias voltages at Pin GNEG and Pin GPOS for
non-zero common-mode voltages. The gain control can also be
driven with an active input such as a ramp. Provision is made for
an optional SMA connector at PRVG for monitoring the preamp
output or for driving the VGA from an external source. Remove
the 0 Ω resistor at R9 to isolate the preamp from an external
generator. The capacitor at Location C1 limits the bandwidth
of the preamplifier.
BOARD LAYOUT CONSIDERATIONS
The evaluation board uses four layers, with power and ground
planes located between two conductor layers. This arrangement
is highly recommended for customers, and several views of the
board are provided as reference for board layout details. When
laying out a printed circuit board for the AD8336, remember to
provide a pad beneath the device to solder the exposed pad of
the matching device. The pad in the board should have at least
five vias to provide a thermal path for the chip scale package.
Unlike leaded devices, the thermal pad is the primary means
to remove heat dissipated within the device.
0
6228-083
Figure 82. AD8336 Evaluation Board
06228-084
Figure 83. Component Side Copper
0
6228-085
Figure 84. Secondary Side Copper
AD8336
06228-088
Figure 87. Internal Power Plane Copper
Rev. C | Page 25 of 28
06228-086
Figure 85. Component Side Silkscreen
06228-087
Figure 86. Internal Ground Plane Copper
VIN
–V
S
112
11
10
94
3
2
VOUT
PWRA
VCOM
VPOS
GPOS
VNEG
PRAO
INPP
AD8336
VPOS
VOUTL
R2
49.9
GND GND3GND2GND1
R8
301
R7
100
R4
0
R9
0PRVG
L2
120nH
R10
49.9
R14
L1
120nH
R5
C4
10µF
35V
C2
10µF
C5
0.1µF
C3
0.1µF
25V
U1
16 131415
5876
INPN NC NC
VGAI
R12
0
R11
GNEG
0
R13
R15
R17
0
R6
R3
0
C1
NC NC NC
GNEG
GPOS
+
+
VIN1
POWER
LOW
NORM
VOUT
VOUTD
VP
R16
4.99k
CR1
5.1V C8
0.1µF
VP
C7
1nF
C6
1nF
R1
0
06228-082
NC = NO CONNECT. DO NOT CONNECT TO THIS PIN.
Figure 88. AD8336-EVALZ Schematic Shown as Shipped, Configured for a Noninverting Gain of 4×
AD8336
Rev. C | Page 26 of 28
COMPLIANT TO JEDEC STANDARDS MO-220-VGGC
OUTLINE DIMENSIONS
2.25
2.10 SQ
1.95
16
5
13
8
9
12 1
4
1.95 BSC
PIN 1
INDICATOR TOP
VIEW
4.00
BSC SQ
3.75
BSC SQ
COPLANARITY
0.08
(BOTTOM VIEW)
12° MAX
1.00
0.85
0.80 SEATING
PLANE
0.35
0.30
0.25
0.80 MAX
0.65 TYP
0.05 MAX
0.02 NOM
0.20 REF
0.65 BSC
0.60 MAX
0.60 MAX
PIN 1
INDICATOR
0.25 MIN
072808-A
0.75
0.60
0.50
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.
Figure 89. 16-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
4 mm × 4 mm Body, Very Thin Quad
(CP-16-4)
Dimensions shown in millimeters
ORDERING GUIDE
Model1Temperature Range Package Description Package Option
AD8336ACPZ-R7 −40°C to +85°C 16-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-16-4
AD8336ACPZ-RL −40°C to +85°C 16-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-16-4
AD8336ACPZ-WP −40°C to +85°C 16-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-16-4
AD8336-EVALZ Evaluation Board
1 Z = RoHS Compliant Part.
AD8336
Rev. C | Page 27 of 28
NOTES
AD8336
Rev. C | Page 28 of 28
NOTES
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registered trademarks are the property of their respective owners.
D06228-0-5/11(C)
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