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Ultralow Distortion

Differential ADC Driver

Data Sheet

ADA4937-1/ADA4937-2

Rev. D Document Feedback

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FEATURES

Extremely low harmonic distortion (HD)

−112 dBc HD2 @ 10 MHz

−84 dBc HD2 @ 70 MHz

−77 dBc HD2 @ 100 MHz

−102 dBc HD3 @ 10 MHz

−91 dBc HD3 @ 70 MHz

−84 dBc HD3 @ 100 MHz

Low input voltage noise: 2.2 nV/√Hz

High speed

−3 dB bandwidth of 1.9 GHz, G = 1

Slew rate: 6000 V/µs, 25% to 75%

Fast overdrive recovery of 1 ns

0.5 mV typical offset voltage

Externally adjustable gain

Differential-to-differential or single-ended-to-differential

operation

Adjustable output common-mode voltage

Single-supply operation: 3.3 V to 5 V

APPLICATIONS

ADC drivers

Single-ended-to-differential converters

IF and baseband gain blocks

Differential buffers

Line drivers

GENERAL DESCRIPTION

The ADA4937-xis a low noise, ultralow distortion, high speed

differential amplifier. It is an ideal choice for driving high

performance ADCs with resolutions up to 16 bits from dc to

100 MHz. The adjustable level of the output common mode

allows the ADA4937-x to match the input of the ADC. The

internal common-mode feedback loop also provides exceptional

output balance as well as suppression of even-order harmonic

distortion products.

With the ADA4937-x, differential gain configurations are easily

realized with a simple external feedback network of four resis-

tors that determine the closed-loop gain of the amplifier.

The ADA4937-x is fabricated using Analog Devices, Inc., proprie-

tary silicon-germanium (SiGe), complementary bipolar process,

enabling it to achieve very low levels of distortion with an input

voltage noise of only 2.2 nV/√Hz. The low dc offset and excellent

dynamic performance of the ADA4937-x make it well-suited

for a wide variety of data acquisition and signal processing appli-

cations.

FUNCTIONAL BLOCK DIAGRAMS

1–FB

2+IN

3–IN

4+FB

11 –OUT

12 PD

10 +OUT

9 V

OCM

5+V

6+V

7+V

8+V

–V

ADA4937-1

06591-001

Figure 1. ADA4937-1

ADA4937-2

1–IN1

2+FB1

3+V

4+V

5–FB2

6+IN2

–V

16 –V

17 V

OCM1

18 +OUT1

PD2

13 –OUT2

7–IN2

8+FB2

9+V

11V

OCM2

12+OUT2

10+V

–V

–FB1

+IN1

PD1

–OUT1

06591-002

Figure 2. ADA4937-2

–55

–60

–65

–70

–75

–80

–85

–90

–95

–100

–105

–110

–115

1 10 100

DISTORTION (dBc)

FREQUENCY (MHz)

HD2, V

= 5.0V

HD3, V

= 5.0V

HD2, V

= 3.3V

HD3, V

= 3.3V

06591-003

Figure 3. Harmonic Distortion vs. Frequency

The ADA4937-x is available in a Pb-free, 3 mm × 3 mm, 16-lead

LFCSP (ADA4937-1, single) or a Pb-free, 4 mm × 4 mm, 24-lead

LFCSP (ADA4937-2, dual). The pinout has been optimized to

facilitate PCB layout and minimize distortion. The ADA4937-x

is specified to operate over the automotive (−40°C to +105°C)

temperature range and between 3.3 V and 5 V supplies.

Summary of content (29 pages)

PAGE 1
Ultralow Distortion Differential ADC Driver ADA4937-1/ADA4937-2 Data Sheet ADA4937-1 12 PD 9 VOCM 06591-001 +VS 8 10 +OUT +FB 4 +VS 7 11 –OUT –IN 3 +VS 5 +IN 2 24 23 22 21 20 19 +IN1 –FB1 –VS1 –VS1 PD1 –OUT1 Figure 1.
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ADA4937-1/ADA4937-2 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Analyzing an Application Circuit ............................................ 18 Applications ....................................................................................... 1 Setting the Closed-Loop Gain .................................................. 18 General Description ................................................................
PAGE 4
Data Sheet ADA4937-1/ADA4937-2 SPECIFICATIONS 5 V OPERATION TA = 25°C, +VS = 5 V, −VS = 0 V, VOCM = +VS/2, RT = 61.9 Ω, RG = RF = 200 Ω, G = +1, RL, dm = 1 kΩ, unless otherwise noted. All specifications refer to single-ended input and differential outputs, unless otherwise noted. ±DIN to ±OUT Performance Table 1. Parameter DYNAMIC PERFORMANCE −3 dB Small Signal Bandwidth Bandwidth for 0.
PAGE 5
ADA4937-1/ADA4937-2 Data Sheet VOCM to ±OUT Performance Table 2. Parameter VOCM DYNAMIC PERFORMANCE −3 dB Bandwidth Slew Rate Input Voltage Noise (RTI) VOCM INPUT CHARACTERISTICS Input Voltage Range Input Resistance Input Offset Voltage Input Bias Current VOCM CMRR Gain POWER SUPPLY Operating Range Quiescent Current per Amplifier Power Supply Rejection Ratio POWER-DOWN (PD) PD Input Voltage Turn-Off Time Turn-On Time PD Bias Current per Amplifier Enabled Powered Down Test Conditions/Comments Min 1.
PAGE 6
Data Sheet ADA4937-1/ADA4937-2 3.3 V OPERATION TA = 25°C, +VS = 3.3 V, −VS = 0 V, VOCM = +VS/2, RT = 61.9 Ω, RG = RF = 200 Ω, G = 1, RL, dm = 1 kΩ, unless otherwise noted. All specifications refer to single-ended input and differential outputs, unless otherwise noted. ±DIN to ±OUT Performance Table 3. Parameter DYNAMIC PERFORMANCE −3 dB Small Signal Bandwidth Bandwidth for 0.
PAGE 7
ADA4937-1/ADA4937-2 Data Sheet VOCM to ±OUT Performance Table 4.
PAGE 8
Data Sheet ADA4937-1/ADA4937-2 ABSOLUTE MAXIMUM RATINGS Rating 5.5 V See Figure 4 −65°C to +125°C −40°C to +105°C 300°C 150°C Stresses above those listed under 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.
PAGE 9
ADA4937-1/ADA4937-2 Data Sheet +IN1 –FB1 –VS1 –VS1 PD1 –OUT1 24 23 22 21 20 19 –IN 3 TOP VIEW (Not to Scale) 10 +OUT NOTES 1. EXPOSED PADDLE. THE EXPOSED PAD IS NOT ELECTRICALLY CONNECTED TO THE DEVICE. IT IS TYPICALLY SOLDERED TO GROUND OR A POWER PLANE ON THE PCB THAT IS THERMALLY CONDUCTIVE. PIN 1 INDICATOR ADA4937-2 TOP VIEW (Not to Scale) 18 17 16 15 14 13 +OUT1 VOCM1 –VS2 –VS2 PD2 –OUT2 7 8 9 10 11 12 +VS 8 +VS 5 9 VOCM 1 2 3 4 5 6 NOTES 1. EXPOSED PADDLE.
PAGE 10
Data Sheet ADA4937-1/ADA4937-2 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, +VS = 5 V, −VS = 0 V, VOUT, dm = 2 V p-p, VOCM = +VS/2, RT = 61.9 Ω, RG = RF = 200 Ω, G = 1, RL, dm = 1 kΩ, unless otherwise noted. Refer to Figure 49 for the test setup circuit. 6 0 –3 –6 –9 –12 G = +1, RF = 200Ω G = +2, RF = 402Ω G = +5, RF = 402Ω –15 1 10 100 1000 FREQUENCY (MHz) 0 –3 –6 –9 –12 G = +1, RF = 200Ω G = +2, RF = 402Ω G = +5, RF = 402Ω –15 1 6 VS = 3.3V 1000 VS = 3.3V VS = 5.
PAGE 11
ADA4937-1/ADA4937-2 6 Data Sheet 6 RL = 1kΩ RL = 100Ω RL = 200Ω 3 CLOSED-LOOP GAIN (dB) 0 –3 –3 1 10 100 1000 FREQUENCY (MHz) –9 06591-013 –9 1 10 100 1000 FREQUENCY (MHz) Figure 13. Small Signal Frequency Response for Various Loads, VOUT, dm = 100 mV p-p 06591-016 –6 –6 Figure 16. Large Signal Frequency Response for Various Loads 6 3 0 –3 –6 –9 VS = 3.3V, G = +1, VS = 3.3V, G = +2, VS = 3.
PAGE 12
Data Sheet VOCM CLOSED-LOOP GAIN (dB) 3 ADA4937-1/ADA4937-2 –50 VOCM = 1.0V VOCM = 2.5V VOCM = 3.9V HD2, HD3, HD2, HD3, –60 0 G G G G = +1, = +1, = +2, = +2, RF = RF = RF = RF = 200Ω 200Ω 402Ω 402Ω DISTORTION (dBc) –70 –3 –6 –80 –90 –100 –9 –110 10 100 1000 –120 FREQUENCY (MHz) 1 Figure 22. Harmonic Distortion vs.
PAGE 13
ADA4937-1/ADA4937-2 –30 HD2, HD3, HD2, HD3, –40 0 f = 10MHz f = 10MHz f = 75MHz f = 75MHz –20 DISTORTION (dBc) DISTORTION (dBc) –50 Data Sheet –60 –70 –80 –90 –40 –60 –80 –100 –100 1.5 2.0 2.5 3.0 3.5 –120 69.4 06591-025 –120 1.0 4.0 VOCM (V) HD2, HD3, HD2, HD3, –50 69.8 70.0 70.2 70.4 70.6 FREQUENCY (MHz) Figure 25. Harmonic Distortion vs. VOCM and Frequency –40 69.6 06591-028 –110 Figure 28.
PAGE 14
Data Sheet –30 ADA4937-1/ADA4937-2 28 VOUT, dm PSRR, VS = 3.3V VOUT, dm PSRR, VS = 5.0V –40 26 G = +1 G = +2 G = +4 24 NOISE FIGURE (dB) PSRR (dB) –50 –60 –70 22 20 18 16 –80 14 –90 1 10 100 10 10 06591-031 –100 1000 FREQUENCY (MHz) 0 100 FREQUENCY (MHz) Figure 31. PSRR vs. Frequency, RL = 200 Ω Figure 34. Noise Figure vs. Frequency 5 S11 S22 –5 VIN × 3.
PAGE 15
Data Sheet 60 60 55 55 50 50 45 45 SUPPLY CURRENT (mA) 40 35 +105°C 30 +25°C +55°C 25 0°C 15 –40°C +25°C 30 0°C 15 –40°C 5 5 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 POWER-DOWN VOLTAGE (V) 0 1.0 06591-037 1.2 +55°C 20 10 1.1 +105°C 25 10 0 1.0 Figure 37. Supply Current vs. PD for Various Temperatures 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 POWER-DOWN VOLTAGE (V) Figure 40. Supply Current vs. PD for Various Temperatures, VS = 3.3 V 0.20 3.5 +VS = +2.5V –VS = –2.
PAGE 16
Data Sheet ADA4937-1/ADA4937-2 10 10 G=1 9 8 POWER-DOWN PULSE IMPEDANCE (Ω) AMPLITUDE (V) 7 6 5 4 1 3 OUTPUT 2 0 0.5 1.0 1.5 2.0 2.5 0.1 0.01 0.1 1 TIME (ms) 10 100 1k FREQUENCY (MHz) Figure 43. PD Response vs. Time Figure 46. Closed-Loop Output Impedance 2 –40 1.0 –50 VIN INPUT2, OUTPUT1 –60 0.5 1 –70 SETTLING ERROR –80 0 0.1 0 –0.1 –1 –0.5 VIN (V) CROSSTALK (dB) 06591-146 –0.5 –90 –100 INPUT1, OUTPUT2 –110 SETTLING ERROR (%) 0 –1.
PAGE 17
ADA4937-1/ADA4937-2 Data Sheet TEST CIRCUITS 200Ω 5V 50Ω 200Ω VIN VOCM 61.9Ω ADA4937 1kΩ 200Ω 06591-046 27.5Ω 200Ω Figure 49. Equivalent Basic Test Circuit 200Ω 5V 50Ω 200Ω VIN 50Ω VOCM 61.9Ω ADA4937 200Ω 50Ω 06591-047 27.5Ω 200Ω Figure 50. Test Circuit for Output Balance 200Ω 5V VIN FILTER 61.9Ω 0.1µF 200Ω VOCM 412Ω FILTER ADA4937 0.1µF 200Ω 412Ω 27.5Ω 200Ω Figure 51. Test Circuit for Distortion Measurements Rev.
PAGE 18
Data Sheet ADA4937-1/ADA4937-2 TERMINOLOGY Common-Mode Voltage Common-mode voltage refers to the average of two node voltages. The output common-mode voltage is defined as –FB RF +IN VOCM –OUT ADA4937 –DIN RG R F –IN RL, dm VOUT, dm +OUT +FB VOUT, cm = (V+OUT + V−OUT)/2 06591-049 +DIN RG Figure 52. Circuit Definitions Differential Voltage Differential voltage refers to the difference between two node voltages.
PAGE 19
ADA4937-1/ADA4937-2 Data Sheet THEORY OF OPERATION Two feedback loops control the differential and common-mode output voltages. The differential feedback loop, set with external resistors, controls only the differential output voltage. The common-mode feedback loop controls only the common-mode output voltage. This architecture makes it easy to set the output common-mode level to any arbitrary value.
PAGE 20
Data Sheet ADA4937-1/ADA4937-2 RF Similar to the case of a conventional op amp, the output noise voltage densities can be estimated by multiplying the inputreferred terms at +IN and −IN by the appropriate output factor, ADA4937 +VS where: 2 GN  is the circuit noise gain. β1  β2  RG1 RG2 β1  and β2  are the feedback factors.
PAGE 21
ADA4937-1/ADA4937-2 RF For the source termination to be 50 Ω, the termination resistor (RT) is calculated using RT||RIN = 50 Ω, which makes RT equal to 61.9 Ω. +VS RS RF 200Ω +VS 50Ω RS VS 2V VS 2V RTS 27.4Ω 200Ω RT 61.9Ω RG RT 61.9Ω 200Ω VOCM VOCM ADA4937 RL RF Figure 60. Complete Single-Ended-to-Differential System 06591-082 –VS RF 200Ω Figure 57. Adding Termination Resistor RT RS RTH VTH 1.1V 27.4Ω 06591-083 RT 61.9Ω SETTING THE OUTPUT COMMON-MODE VOLTAGE Figure 58.
PAGE 22
Data Sheet ADA4937-1/ADA4937-2 Table 10. Differential Ground-Referenced Input, DC-Coupled, 1 kΩ Load; See Figure 54 Nominal Gain (dB) 0 6 10 14 RF (Ω) 200 402 402 402 RG (Ω) 200 200 127 80.6 RIN, dm (Ω) 400 400 254 161 Differential Output Noise Density (nV/√Hz) 5.8 9.6 12.1 16.2 Table 11. Single-Ended Ground-Referenced Input, DC-Coupled, RS = 50 Ω, RL = 1 kΩ; See Figure 55 Nominal Gain (dB) 0 6 10 14 1 RF (Ω) 200 402 402 402 RG1 (Ω) 200 200 127 80.6 RT (Ω) 61.9 60.4 66.5 76.
PAGE 23
ADA4937-1/ADA4937-2 Data Sheet LAYOUT, GROUNDING, AND BYPASSING As a high speed device, the ADA4937-x is sensitive to the PCB environment in which it operates. Realizing its superior performance requires attention to the details of high speed PCB design. This section shows a detailed example of how the design issues of the ADA4937-1 were addressed. Bypass the power supply pins as close to the device as possible and directly to a nearby ground plane. Use high frequency ceramic chip capacitors.
PAGE 24
Data Sheet ADA4937-1/ADA4937-2 HIGH PERFORMANCE ADC DRIVING The ADA4937-x is ideally suited for broadband IF applications. The circuit in Figure 64 shows a front-end connection for an ADA4937-1 driving an AD9445, 14-bit, 105 MSPS ADC. The AD9445 achieves its optimum performance when driven differentially. The ADA4937-x eliminates the need for a transformer to drive the ADC and performs a single-ended-to-differential conversion and buffering of the driving signal.
PAGE 25
ADA4937-1/ADA4937-2 Data Sheet The AD9246 is set for a 2 V p-p full-scale input by connecting the SENSE pin to AGND. The inputs of the AD9246 are biased at 1 V by connecting the CML output, as shown in Figure 66. The circuit in Figure 66 shows a simplified front-end connection for an ADA4937-1 driving an AD9246, 14-bit, 125 MSPS ADC. The AD9246 achieves its optimum performance when driven differentially.
PAGE 26
Data Sheet ADA4937-1/ADA4937-2 59 Ω termination resistor, in parallel with the single-ended input impedance of 306 Ω, provides a 50 Ω termination for the source. The additional 26 Ω (226 Ω total) at the inverting input balances the parallel impedance of the 50 Ω source and the termination resistor that drives the noninverting input. The signal generator has a symmetric, ground-referenced bipolar output.
PAGE 27
ADA4937-1/ADA4937-2 Data Sheet OUTLINE DIMENSIONS 3.00 BSC SQ 0.60 MAX 0.45 13 12 2.75 BSC SQ TOP VIEW 0.80 MAX 0.65 TYP 12° MAX 9 0.30 0.23 0.18 1.30 SQ 1.15 5 8 4 0.25 MIN 1.50 REF FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. 0.05 MAX 0.02 NOM SEATING PLANE *1.45 1 EXPOSED PAD 0.50 BSC 1.00 0.85 0.80 16 PIN 1 INDICATOR 0.20 REF 072208-A PIN 1 INDICATOR 0.50 0.40 0.
PAGE 28
Data Sheet ADA4937-1/ADA4937-2 NOTES Rev.
PAGE 29
ADA4937-1/ADA4937-2 Data Sheet NOTES ©2007–2013 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D06591-0-8/13(D) Rev.