LMH6321TSNOPB - NATIONAL SEMICONDUCTOR

January 24, 2008

LMH6514

600 MHz, Digital Controlled, Variable Gain Amplifier

General Description

The LMH6514 is a high performance, digitally controlled vari-

able gain amplifier (DVGA). It combines precision gain control

with a low noise, ultra-linear, differential amplifier. Typically,

the LMH6514 drives a high performance ADC in a broad

range of mixed signal and digital communication applications

such as mobile radio and cellular base stations where auto-

matic gain control (AGC) is required to increase system dy-

namic range. When used in conjunction with a high speed

ADC, system dynamic range can be extended by up to 42 dB.

The LMH6514 has a differential input and output allowing

large signal swings on a single 5V supply. It is designed to

accept signals from RF elements and maintain a terminated

impedance environment. The input impedance is 200Ω re-

sistive. The output impedance is either 200Ω or 400Ω and is

user selectable. A unique internal architecture allows use with

both single ended and differential input signals.

Input signals to the LMH6514 are scaled by a highly linear,

digitally controlled attenuator with seven accurate 6 dB steps.

The attenuator output provides the input signal for a high gain,

ultra linear differential transconductor. The transconductor

differential output current can be converted into a voltage by

using the on-chip 200Ω or 400Ω loads. The transconductance

gain is 0.1 Amp/Volt resulting in a maximum voltage gain of

+32 dB when driving a 200Ω load, or 38 dB when driving the

400Ω load. On chip digital latches are provided for local stor-

age of the gain setting. The gain step settling time is 5 ns and

care has been taken to reduce the sensitivity of bandwidth

and phase to gain setting.

The LMH6514 operates over the industrial temperature range

of −40°C to +85°C. The LMH6514 is available in a 16-Pin,

thermally enhanced, LLP package.

Features

■Adjustable gain with a 42 dB range

■Precise 6.02 dB gain steps

■Parallel 3 bit gain control

■On chip register gain setting

■Fully differential signal path

■Single ended to differential capable

■200Ω input impedance

■Small footprint (4 mm x 4 mm) LLP package

Key Specifications

■600 MHz bandwidth at 100Ω load

■39 dBm OIP3 at 75 MHz, 200Ω load

■26 dB to 38 dB maximum gain

■Selectable output impedance of 200Ω or 400Ω.

■8.3 dB noise figure

■5 ns gain step switching time

■100 mA supply current

Applications

■Cellular base stations

■IF sampling receivers

■Instrumentation

■Modems

■Imaging

■Differential line receiver

Typical Application

30042901

LMH™ is a trademark of National Semiconductor Corporation.

LMH6514 600 MHz, Digital Controlled, Variable Gain Amplifier

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

ESD Tolerance (Note 2)

Human Body Model 2 kV

Machine Model 150V

Positive Supply Voltage (Pin 3) −0.6V to 5.5V

Output Voltage (Pin 14,15) −0.6V to 6.8V

Differential Voltage between Any

Two Grounds <200 mV

Analog Input Voltage Range −0.6V to VCC

Digital Input Voltage Range −0.6V to 3.6V

Output Short Circuit Duration

(one pin to ground) Infinite

Junction Temperature +150°C

Storage Temperature Range −65°C to +150°C

Soldering Information

Infrared or Convection (20 sec) 235°C

Wave Soldering (10 sec) 260°C

Operating Ratings (Note 1)

Supply Voltage (Pin 3) 4V to 5.25V

Output Voltage Range (Pin 14, 15) 1.4V to 6.4V

Differential Voltage Between Any

Two Grounds <10 mV

Analog Input Voltage Range,

AC Coupled ±1.4V

Temperature Range (Note 3) −40°C to +85°C

Package Thermal Resistance (θJA)

16-Pin LLP 47°C/W

5V Electrical Characteristics (Note 4)

The following specifications apply for single supply with VCC = 5V, Maximum Gain , RL = 100Ω (200Ω external || 200Ω internal),

VOUT = 2 VPP, fin = 150 MHz. Boldface limits apply at temperature extremes.

Symbol Parameter Conditions Min

(Note 6)

Typ

(Note 5)

Max

(Note 6)

Units

Dynamic Performance

SSBW −3 dB Bandwidth Average of all Gain Settings 600 MHz

Noise and Distortion

Third Order Intermodulation

Products

f = 75 MHz, V OUT = 2 VPP −70

dBc

f = 150 MHz, V OUT = 2 VPP −66

f = 250 MHz, V OUT = 2 VPP −60

f = 450 MHz, V OUT = 2 VPP −52

OIP3 Output Third Order Intercept Point f = 75 MHz, V OUT = 2 VPP,

Tone Spacing = 0.5 MHz

dBm

f = 150 MHz, V OUT = 2 VPP,

Tone Spacing = 2 MHz

f = 250 MHz, V OUT = 2 VPP,

Tone Spacing = 2 MHz

f = 75 MHz, RL= 200Ω, V OUT = 2 VPP

Tone Spacing = 0.5 MHz

f = 150 MHz, RL = 200Ω, V OUT = 2 VPP,

Tone Spacing = 2 MHz

f = 250 MHz, RL = 200Ω, V OUT = 2 VPP,

Tone Spacing = 2 MHz

P1 dB Output Level for 1 dB Gain

Compression

f = 75 MHz, R L = 200Ω 16.7

dBm

f = 250 MHz, R L = 200Ω 14.7

f = 75 MHz 14.5

f = 450 MHz 13.2

VNI Input Noise Voltage Maximum Gain, f = 40 MHz 1.8 nV/

VNO Output Noise Voltage Maximum Gain, f = 40 MHz 36 nV/

NF Noise Figure Maximum Gain 8.3 dB

Analog I/O

Differential Input Resistance 165

158

188 220

230 Ω

Input Common Mode Resistance 825

785

955 1120

1160 Ω

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LMH6514

Symbol Parameter Conditions Min

(Note 6)

Typ

(Note 5)

Max

(Note 6)

Units

Differential Output Resistance Low Gain Option 186

Ω

High Gain Option 330

325

370 420

425

Internal Load Resistors Between Pins 13, 14 and Pins 15, 16 165

158

187 215

225 Ω

Input Signal Level (AC Coupled) Max Gain, VO = 2 VPP, RL = 1 kΩ 63 mVPP

Maximum Differential Input Signal AC Coupled 5.6 VPP

Input Common Mode Voltage Self Biased 1.3

1.1

1.4 1.5

1.7 V

Input Common Mode Voltage

Range

Driven Externally 0.9 to 2.0 V

Minimum Input Voltage DC 0 V

Maximum Input Voltage DC 3.3 V

Maximum Differential Output

Voltage Swing

VCC = 5V, Output Common Mode = 5V 5.5 VPP

VOS Output Offset Voltage All Gain Settings −21 mV

CMRR Common Mode Rejection Ratio Maximum Gain 81 dB

PSRR Power Supply Rejection Ratio Maximum Gain 63

81 dB

Gain Parameters

Maximum Gain DC, Internal RL = 186Ω,

External RL = 1280Ω

29.3

28.7

30 30.3

30.9 dB

Minimum Gain DC, Internal RL = 186Ω,

External RL = 1280Ω

−12.75

−13.15

−12 −11.85

−11.45 dB

Gain Step Size DC 6.02 dB

Gain Step Error DC 0.02 dB

f = 150 MHz 0.07

Cumulative Gain Step Error DC, Gain Step 7 to Gain Step 0 −0.35

−0.50

0.02 0.30

0.45 dB

Gain Step Switching Time 5 ns

Digital Inputs/Timing

Logic Compatibility CMOS Logic 3.3 V

VIL Logic Input Low Voltage 0.8 V

VIH Logic Input High Voltage 2.0 V

IIH Logic Input High Input Current Digital Input Voltage = 3.3V 33 40 μA

TSU Setup Time 3 ns

THOLD Hold Time 3 ns

TPW Minimum Latch Pulse Width 10 ns

Power Requirements

ICC Total Supply Current VOUT = 0V Differential, VOUT Common

Mode = 5V

107 124

134 mA

Amplifier Supply Current Pin 3 Only 56 66

74 mA

Output Stage Bias Currents Pins 13, 14 and Pins 15, 16;

VOUT Common Mode = 5 V

51 58

60 mA

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LMH6514

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

intended to be functional, but specific performance is not guaranteed. For guaranteed specifications, see the Electrical Characteristics tables.

Note 2: Human Body Model, applicable std. MIL-STD-883, Method 3015.7. Machine Model, applicable std. JESD22-A115-A (ESD MM std. of JEDEC)

Field-Induced Charge-Device Model, applicable std. JESD22-C101-C (ESD FICDM std. of JEDEC).

Note 3: The maximum power dissipation is a function of TJ(MAX), θJA. The maximum allowable power dissipation at any ambient temperature is

PD = (TJ(MAX) – TA)/ θJA. All numbers apply for packages soldered directly onto a PC Board.

Note 4: Electrical Table values apply only for factory testing conditions at the temperature indicated. No guarantee of parametric performance is indicated in the

electrical tables under conditions different than those tested

Note 5: Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary over time and will

also depend on the application and configuration. The typical values are not tested and are not guaranteed on shipped production material.

Note 6: Limits are 100% production tested at 25°C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality

Control (SQC) methods.

Note 7: Negative input current implies current flowing out of the device.

Note 8: Drift determined by dividing the change in parameter at temperature extremes by the total temperature change.

Connection Diagram

16-Pin LLP

30042904

Top View

Gain Control Pins

Pin Number Pin Name Gain Step Size

11 GAIN_0 6.02 dB

10 GAIN_1 12.04 dB

9 GAIN_2 24.08 dB

Ordering Information

Package Part Number Package Marking Transport Media NSC Drawing

16-Pin LLP LMH6514SQ L6514SQ 1k Units Tape and Reel SQA16A

LMH6514SQX 4.5k Units Tape and Reel

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LMH6514

Pin Descriptions

Pin Number Symbol Description

Analog I/O

6 IN+ Non-inverting analog input. Internally biased to 1.4V. Input voltage should not exceed

VCC or go below GND by more than 0.5V.

7 IN− Inverting analog input. Internally biased to 1.4V. Input voltage should not exceed VCC or

go below GND by more than 0.5V. If using amplifier single ended this input should be

capacitively coupled to ground.

15 OUT− Open collector inverting output. This pin is an output that also requires a power source.

This pin should be connected to 5V through either an RF choke or an appropriately sized

inductor that can form part of a filter. See application section for details.

14 OUT+ Open collector non-inverting output. This pin is an output that also requires a power

source. This pin should be connected to 5V through either an RF choke or an

appropriately sized inductor that can form part of a filter. See application section for

details.

16 LOAD− Internal 200Ω resistor connection to pin 15. This pin can be left floating for higher gain

or shorted to pin 13 for lower gain and lower effective output impedance. See application

section for details.

13 LOAD+ Internal 200Ω resistor connection to pin 14. This pin can be left floating for higher gain

or shorted to pin 16 for lower gain and lower effective output impedance. See application

section for details.

Power

3 VCC 5V power supply pin. Use ceramic, low ESR bypass capacitors. This pin powers

everything except the output stage.

5,8 GND Ground pins. Connect to low impedance ground plane. All pin voltages are specified with

respect to the voltage on these pins. The exposed thermal pad is also a ground

connection.

Digital Inputs

11,10,9 GAIN_0 to

GAIN_2

Gain setting pins. See above table for gain step sizes for each pin. These pins are 3.3V

CMOS logic compatible. 5V inputs may cause damage.

2 LATCH This pin controls the function of the gain setting pins mentioned above. With LATCH in

the logic HIGH state the gain is fixed and will not change. With the LATCH in the logic

LOW state the gain is set by the state of the gain control pins. Any changes in gain made

with the LATCH pin in the LOW state will take effect immediately. This pin is 3.3V CMOS

logic compatible. 5V inputs may cause damage.

1,4,12 NC These pins are not connected. They can be grounded or left floating.

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LMH6514

Typical Performance Characteristics VCC = 5V

Frequency Response All Gain Settings

30042922

Frequency Response over Temperature, Maximum Gain

30042949

Frequency Response over Temperature, Minimum Gain

30042950

OIP3 High Gain Mode

30042943

OIP3 Low Gain Mode

30042942

OIP3 Over Temperature

30042926

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LMH6514

IMD3 Low Gain Mode

30042940

IMD3 High Gain Mode

30042941

HD2 vs. Frequency

30042936

HD3 vs. Frequency

30042939

HD2 vs. Frequency

30042938

HD3 vs. Frequency

30042937

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LMH6514

Noise Figure for All Gain Settings

30042914

Noise Figure vs. Frequency

30042917

Differential Output Noise

30042918

Maximum Gain vs. Supply Voltage

30042927

Gain vs. External Load

30042912

Maximum Gain over Temperature

30042944

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LMH6514

Worst Case Gain Step Error vs Frequency

30042945

Gain Steps over Temperature

30042961

Worst Case Gain Step Error over Temperature

30042951

Input Impedance (S11) at Maximum Gain

30042964

Input Impedance (S11) at Minimum Gain

30042966

Output Impedance (S22) at Maximum Gain Low Gain Mode

30042965

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LMH6514

Output Impedance (S22) at Maximum Gain High Gain Mode

30042967

Digital Crosstalk

30042947

Digital Crosstalk

30042948

Digital Pin to Output Isolation

30042919

Minimum Gain to Maximum Gain Switching

Using Latch Pin

30042930

Maximum Gain to Minimum Gain Switching

Using Latch Pin

30042935

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LMH6514

24 dB Gain Step

30042932

24 dB Gain Step

30042929

12 dB Gain Step

30042928

12 dB Gain Step

30042931

6 dB Gain Step

30042934

6 dB Gain Step

30042933

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LMH6514

Power On Timing, Maximum Gain

30042953

Power On Timing, Minimum Gain

30042954

Power Off Timing, Maximum Gain

30042956

Power Off Timing, Minimum Gain

30042955

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LMH6514

Application Information

The LMH6514 is a fully differential amplifier optimized for sig-

nal path applications up to 400 MHz. The LMH6514 has a

200Ω input. The absolute gain is load dependent, however

the gain steps are always 6 dB. The LMH6514 output stage

is a class A amplifier. This class A operation results in excel-

lent distortion and linearity characteristics. This makes the

LMH6514 ideal for voltage amplification and an ideal ADC

driver where high linearity is necessary.

30042903

FIGURE 1. LMH6514 Typical Application

The LMH6514 output common mode should be set carefully.

Using inductors to set the output common mode is one pre-

ferred method and will give maximum output swing. AC cou-

pling of the output is recommended. The inductors mentioned

above will shift the idling output common mode to the positive

supply. Also, with the inductors, the output voltage can ex-

ceed the supply voltage. Other options for setting the output

common mode require supply voltages above 5V. If using a

supply higher than 5V care should be taken to make sure the

output common mode does not exceed the 5.25V supply rat-

ing.

It is also important to note the maximum voltage limits for the

OUT+ and OUT− pins, which is 6.4V. When using inductors

these pins will experience voltage swings beyond the supply

voltage. With a 5V output common mode operating point this

makes the effective maximum swing 5.6 VPP differential. Sys-

tem calibration and automatic gain control algorithms should

be tailored to avoid exceeding this limit. Figure 2 shows how

output voltage and output common mode add together and

approach the maximum output voltage.

30042962

FIGURE 2. Output Voltage with Respect to the Output

Common Mode

In order to help with system design National Semiconductor

offers the ADC14V155KDRB High IF Receiver reference de-

sign board. This board combines the LMH6514 DVGA with

the ADC14V155 ADC and provides a ready made solution for

many IF receiver applications. Using an IF frequency of 169

MHz it achieves a small signal SNR of 72 dBFS and an SFDR

of greater than 90 dBFS. Large signal measurements show

an SNR of 68 dBFS and an SFDR of 77 dBFS. The High IF

Receiver board also features the LMK03000 low-jitter preci-

sion clock conditioner.

30042911

FIGURE 3. LMH6514 Block Diagram

INPUT CHARACTERISTICS

The LMH6514 input impedance is set by internal resistors to

a nominal 200Ω. Process variations will result in a range of

values as shown in the 5V Electrical Characteristics table. At

higher frequencies parasitics will start to impact the

impedance. This characteristic will also depend on board lay-

out and should be verified on the customer’s system board.

At maximum gain the digital attenuator is set to 0 dB and the

input signal will be much smaller than the output. At minimum

gain the output is 4 dB or more smaller than the input. In this

configuration the input signal size may limit the amplifier out-

put amplitude, depending on the output configuration and the

desired output signal voltage. The input signal cannot swing

more than 0.5V below the negative supply voltage (normally

0V) nor should it exceed the positive supply voltage. The input

signal will clip and cause severe distortion if it is too large.

Because the input stage self biases to approximately 1.4V the

lower supply voltage will impose the limit for input voltage

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LMH6514

swing. To drive larger input signals the input common mode

can be forced higher than 1.4V to allow for more swing. An

input common mode of 2.0V will allow an 8 VPP maximum

input signal. The trade off for input signal swing is that as the

input common mode is shifted away from the 1.4V internal

bias point the distortion performance will suffer slightly.

30042907

FIGURE 4. Single Ended Input

(Note capacitor on grounded input)

At the frequencies where the LMH6514 is the most useful the

input impedance is not 200 Ω and it may not be purely resis-

tive. For many AC coupled applications the impedance can

be easily changed using LC circuits to transform the actual

impedance to the desired impedance.

30042968

FIGURE 5. Single Ended Input with LC Matching

As shown in Figure 5 a single ended 50Ω source is matched

to the LMH6514 input at 100 MHz. The loss in this circuit is

related to the parasitic resistance in the inductor and capacitor

and the bandwidth is related to the loaded Q of the circuit.

Since the Q, at 1.4 is quite low, the bandwidth is very wide.

(59 MHz 0.3 dB bandwidth). The input match of this circuit is

quite good. It converts the ZAMP of the amplifier, which is

(150 +j0)Ω to (50+j1)Ω. The benefit of LC matching circuits

over a transformer is the ability to match ratios that are not

commonly found on transformers and also the ability to neu-

tralize reactance to present a purely resistive load to the

voltage source.

30042969

FIGURE 6. Differential 200Ω LC Conversion Circuit

In Figure 6 the input source resistance is 200Ω differential.

Here the desired input impedance is higher than the amplifier

input impedance, and is differential as well. The amplifier

impedance of (150–j0)Ω is increased to (202–j0.5)Ω. For an

easy way to calculate the L and C circuit values there are

several options for online tools or down-loadable programs.

The following tool might be helpful.

http://www.circuitsage.com/matching/matcher2.html

Excel can also be used for simple circuits; however, the “Anal-

ysis ToolPak” add-in must be installed to calculate complex

numbers.

OUTPUT CHARACTERISTICS

The LMH6514 has the option of two different output configu-

rations. The LMH6514 is an open collector topology. As

shown in Figure 11 each output has an on chip 200Ω pull up

resistor. In addition there is an internal 400Ω resistor between

the two outputs. This results in a 200Ω or a 400Ω differential

load in parallel with the external load. The 400Ω option is the

high gain option and the 200Ω provides for less gain. The

200Ω configuration is recommended unless more gain is re-

quired.

The output common mode of the LMH6514 must be set by

external components. Most applications will benefit from the

use of inductors on the output stage. In particular, the 400Ω

option as shown in Figure 12 will require inductors in order to

be able to develop an output voltage. The 200Ω option as

shown in Figure 13 or Figure 14 will also require inductors

since the voltage drop due to the on chip 200Ω resistors will

saturate the output transistors. It is also possible to use re-

sistors and high voltage power supplies to set the output

common mode. This operation is not recommended, unless

it is necessary to DC couple the output. If DC coupling is re-

quired the input common mode and output common mode

voltages must be taken into account.

Maximum bandwidth with the LMH6514 is achieved by using

the low gain, low impedance output option and using a low

load resistance. With an effective load of 67Ω a bandwidth of

nearly a 1 GHz can be realized. As the effective resistance

on the output stage goes up the capacitance of the board

traces and amplifier output stage limit bandwidth in a roughly

linear fashion. At an output impedance of 100Ω the bandwidth

is down to 600 MHz, and at 200Ω the bandwidth is 260 MHz.

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LMH6514

For this reason driving very high impedance loads is not rec-

ommended.

Although bandwidth goes down with higher values of load re-

sistance, the distortion performance improves and gain in-

creases. The LMH6514 has a common emitter Class A output

stage and minimizing the amount of current swing in the out-

put devices improves distortion substantially.

The LMH6514 output stage is powered through the collectors

of the output transistors. Power for the output stage is fed

through inductors and the reactance of the inductors allows

the output voltage to develop. In Figure 1 the inductors are

shown with a value of 44.4 nH. The value of the inductors

used will be different for different applications. In Figure 1 the

inductors have been chosen to resonate with the ADC and

the load capacitor to provide a weak band pass filter effect.

For broad band applications higher value inductors will allow

for better low frequency operation. However, large valued in-

ductors will reduce high frequency performance, particularly

inductors of small physical sizes like 0603 or smaller. Larger

inductors will tend to perform better than smaller ones of the

same value even for narrow band applications. This is be-

cause the larger inductors will have a lower DC resistance

and less inter-winding capacitance and hence a higher Q and

a higher self resonance frequency. The self resonance fre-

quency should be higher than any desired signal content by

at least a factor of 2. Another consideration is that the power

inductors and the filter inductors need to be placed on the

circuit board such that their magnetic fields do not cause cou-

pling. Mutual coupling of inductors can compromise filter

characteristics and lead to unwanted distortion products.

30042915

FIGURE 7. Bandwidth Changes Due to Different Inductor

Values

30042906

FIGURE 8. Gain vs. External Load

DIGITAL CONTROL

The LMH6514 has eight gain settings covering a range of

42 dB. To avoid undesirable signal transients the LMH6514

should be powered on at the minimum gain state (all logic

input pins at 0V). The LMH6514 has a 3-bit gain control bus

as well as a Latch pin. When the Latch pin is low, data from

the gain control pins is immediately sent to the gain circuit (i.e.

gain is changed immediately). When the Latch pin transitions

high the current gain state is held and subsequent changes

to the gain set pins are ignored. To minimize gain change

glitches multiple gain control pins should not change while the

latch pin is low. In order to achieve the very fast gain step

switching time of 5 ns the internal gain change circuit is very

fast. Gain glitches could result from timing skew between the

gain set bits. This is especially the case when a small gain

change requires a change in state of three or more gain con-

trol pins. If continuous gain control is desired the Latch pin

can be tied to ground. This state is called transparent mode

and the gain pins are always active. In this state the timing of

the gain pin logic transitions should be planned carefully to

avoid undesirable transients.

The LMH6514 was designed to interface with 3.3V CMOS

logic circuits. If operation with 5V logic is required a simple

voltage divider at each logic pin will allow for this. To properly

terminate 100Ω transmission lines a divider with a 66.5Ω re-

sistor to ground and a 33.2Ω series resistor will properly

terminate the line as well as give the 3.3V logic levels. Care

should be taken not to exceed the 3.6V absolute maximum

voltage rating of the logic pins.

EXPOSED PAD LLP PACKAGE

The LMH6514 is packaged in a thermally enhanced package.

The exposed pad is connected to the GND pins. It is recom-

mended, but not necessary, that the exposed pad be con-

nected to the supply ground plane. In any case, the thermal

dissipation of the device is largely dependent on the attach-

ment of this pad. The exposed pad should be attached to as

much copper on the circuit board as possible, preferably ex-

ternal copper. However, it is also very important to maintain

good high speed layout practices when designing a system

board. Please refer to the LMH6514 evaluation board for sug-

gested layout techniques.

Package information is available on the National web site.

http://www.national.com/packaging/folders/sqa16a.html

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LMH6514

INTERFACING TO ADC

The LMH6514 was designed to be used with high speed

ADCs such as the ADC14155. As shown in the Typical Ap-

plication on page 1, AC coupling provides the best flexibility

especially for IF sub-sampling applications. Any resistive net-

works on the output will also cause a gain loss because the

output signal is developed across the output resistors. The

chart Maximum Gain vs. External Load shows the change in

gain when an external load is added.

The inputs of the LMH6514 will self bias to the optimum volt-

age for normal operation. The internal bias voltage for the

inputs is approximately 1.4V. In most applications the

LMH6514 input will need to be AC coupled.

The output common mode voltage is not self biasing, it needs

to be pulled up to the positive supply rail with external induc-

tors as shown in Figure 1. This gives the LMH6514 the

capability for large signal swings with very low distortion on a

single 5V supply. The internal load resistors provide the

LMH6514 with very consistent gain.

A unique internal architecture allows the LMH6514 to be driv-

en by either a differential or single ended source. If driving the

LMH6514 single ended the unused input should be terminat-

ed to ground with a 0.01 µF capacitor. Directly shorting the

unused input to ground will disrupt the internal bias circuitry

and will result in poor performance.

30042906

FIGURE 9. Bandpass Filter

Center Frequency is 140 MHz with a 20 MHz Bandwidth

Designed for 200Ω Impedance

ADC Noise Filter

Below is a filter schematic and a table of values for some

common IF frequencies. The filter shown below offers a good

compromise between bandwidth, noise rejection and cost.

This filter topology is the same as is used on the AD-

C14V155KDRB High IF Receiver reference design board.

This filter topology works best with the 12 and 14 bit sub-

sampling analog to digital converters shown in the Compati-

ble High Speed Analog to Digital Converters table.

Filter Component Values

Fc 75 MHz 140

MHz

170

MHz

250 MHz

BW 40 MHz 20 MHz 25 MHz Narrow

Band

Components L1, L2 10 µH 10 µH 10 µH 10 µH

L3, L4 390 nH 39 0nH 560 nH —

C1,

10 pF 3 pF 1.4 pF 47 pF

C3 22 pF 41 pF 32 pF 11 pF

L5 220 nH 27 nH 30 nH 22 nH

R1,

100 200 100 499

30042913

FIGURE 10. Sample Filter

POWER SUPPLIES

As shown in Figure 11, the LMH6514 has a number of options

for power supply connections on the output pins. Pin 3 (VCC)

is always connected. The output stage can be connected as

shown in Figure 12, Figure 13, and Figure 14. The supply

voltage range for VCC is 4V to 5.25V. A 5V supply provides

the best performance while lower supplies will result in less

power consumption. Power supply regulation of 2.5% or bet-

ter is advised.

Of special note is that the digital circuits are powered from an

internal supply voltage of 3.3V. The logic pins should not be

driven above the absolute maximum value of 3.6V. See the

Digital Control section for details.

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LMH6514

30042902

FIGURE 11. Internal Load Resistors

30042908

FIGURE 12. Using High Gain Mode (400Ω Load)

30042909

FIGURE 13. Using Low Gain Mode (200Ω Load)

30042910

FIGURE 14. Alternate Connection for Low Gain Mode

(200Ω Load)

17 www.national.com

LMH6514

Compatible High Speed Analog to Digital Converters

Product Number Max Sampling Rate (MSPS) Resolution Channels

ADC12L063 62 12 SINGLE

ADC12DL065 65 12 DUAL

ADC12L066 66 12 SINGLE

ADC12DL066 66 12 DUAL

CLC5957 70 12 SINGLE

ADC12L080 80 12 SINGLE

ADC12DL080 80 12 DUAL

ADC12C080 80 12 SINGLE

ADC12C105 105 12 SINGLE

ADC12C170 170 12 SINGLE

ADC12V170 170 12 SINGLE

ADC14C080 80 14 SINGLE

ADC14C105 105 14 SINGLE

ADC14DS105 105 14 DUAL

ADC14155 155 14 SINGLE

ADC14V155 155 14 SINGLE

ADC08D500 500 8 DUAL

ADC08500 500 8 SINGLE

ADC08D1000 1000 8 DUAL

ADC081000 1000 8 SINGLE

ADC08D1500 1500 8 DUAL

ADC081500 1500 8 SINGLE

ADC08(B)3000 3000 8 SINGLE

ADC08L060 60 8 SINGLE

ADC08060 60 8 SINGLE

ADC10DL065 65 10 DUAL

ADC10065 65 10 SINGLE

ADC10080 80 10 SINGLE

ADC08100 100 8 SINGLE

ADCS9888 170 8 SINGLE

ADC08(B)200 200 8 SINGLE

ADC11C125 125 11 SINGLE

ADC11C170 170 11 SINGLE

www.national.com 18

LMH6514

Physical Dimensions inches (millimeters) unless otherwise noted

16-Pin Package

NS Package Number SQA16A

19 www.national.com

LMH6514

Notes

LMH6514 600 MHz, Digital Controlled, Variable Gain Amplifier

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