Ultralow Distortion, Differential ADC Driver ADA4937-1
FEATURES
Extremely low harmonic distortion −112 dBc HD2 @ 10 MHz −79 dBc HD2 @ 70 MHz −70 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% 0.1 dB gain flatness to 200 MHz Fast overdrive recovery of 1 ns 1 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 Pb-free, 3 mm × 3 mm 16-lead LFCSP
FUNCTIONAL BLOCK DIAGRAM
16 –VS 15 –VS 14 –VS 13 –VS
12 PD 11 –OUT 10 +OUT 9 VOCM
–FB 1 +IN 2 –IN 3 +FB 4
ADA4937-1
+VS 7
+VS 8
+VS 5
Figure 1.
–55 –60 –65 –70 HD2, HD3, HD2, HD3, VS = 5.0V VS = 5.0V VS = 3.3V VS = 3.3V
DISTORTION (dBc)
–75 –80 –85 –90 –95 –100
APPLICATIONS
ADC drivers Single-ended-to-differential converters IF and baseband gain blocks Differential buffers Line drivers
–105 –110 1 10 FREQUENCY (MHz) 100
06591-002
–115
Figure 2. Harmonic Distortion vs. Frequency
GENERAL DESCRIPTION
The ADA4937-1 is 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 ADA4937-1 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 ADA4937-1, differential gain configurations are easily realized with a simple external feedback network of four resistors determining the closed-loop gain of the amplifier. The ADA4937-1 is fabricated using Analog Devices, Inc. proprietary 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 ADA4937-1 make it well suited for a wide variety of data acquisition and signal processing applications. The ADA4937-1 is available in a Pb-free, 3 mm × 3 mm 16-lead LFCSP. The pinout has been optimized to facilitate PCB layout and minimize distortion. The part is specified to operate over the −40°C to +105°C temperature range for 3.3 V supplies and the −40°C to +85°C temperature range for 5 V supplies.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no 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 license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
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+VS 6
06591-001
ADA4937-1 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications....................................................................................... 1 Functional Block Diagram .............................................................. 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 5 V Operation ............................................................................... 3 3.3 V Operation ............................................................................ 5 Absolute Maximum Ratings............................................................ 7 Thermal Resistance ...................................................................... 7 ESD Caution.................................................................................. 7 Pin Configuration and Function Descriptions............................. 8 Typical Performance Characteristics ............................................. 9 Test Circuits..................................................................................... 16 Operational Description................................................................ 17 Definition of Terms.................................................................... 17 Theory of Operation ...................................................................... 18 Analyzing an Application Circuit ............................................ 18 Setting the Closed-Loop Gain .................................................. 18 Estimating the Output Noise Voltage ...................................... 18 The Impact of Mismatches in the Feedback Networks ......... 19 Calculating the Input Impedance of an Application Circuit 19 Input Common-Mode Voltage Range in Single-Supply Applications ................................................................................ 19 Setting the Output Common-Mode Voltage .......................... 19 Layout, Grounding, and Bypassing.............................................. 21 High Performance ADC Driving ................................................. 22 3.3 V Operation .......................................................................... 24 Outline Dimensions ....................................................................... 25 Ordering Guide .......................................................................... 25
REVISION HISTORY
5/07—Revision 0: Initial Version
Rev. 0 | Page 2 of 28
ADA4937-1 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. Table 1. ±DIN to ±OUT Performance
Parameter DYNAMIC PERFORMANCE −3 dB Small Signal Bandwidth Bandwidth for 0.1 dB Flatness Large Signal Bandwidth Slew Rate Overdrive Recovery Time NOISE/HARMONIC PERFORMANCE Second Harmonic Conditions VOUT, dm = 0.1 V p-p VOUT, dm = 0.1 V p-p VOUT, dm = 2 V p-p VOUT, dm = 2 V p-p; 25% to 75% VIN = 0 V to 1.5 V step; G = 3.16 See Figure 45 for distortion test circuit VOUT, dm = 2 V p-p; 10 MHz VOUT, dm = 2 V p-p;, 70 MHz VOUT, dm = 2 V p-p; 100 MHz VOUT, dm = 2 V p-p; 10 MHz VOUT, dm = 2 V p-p; 70 MHz VOUT, dm = 2 V p-p; 100 MHz f1 = 70 MHz; f2 = 70.1 MHz; VOUT, dm = 2 V p-p f = 100 kHz f = 100 kHz G = 4; RT = 136 Ω; RF = 200 Ω; RG = 37 Ω; f = 100 MHz VOS, dm = VOUT, dm/2; VDIN+ = VDIN− = 2.5 V TMIN to TMAX variation TMIN to TMAX variation Input Offset Current Input Resistance Input Capacitance Input Common-Mode Voltage CMRR OUTPUT CHARACTERISTICS Output Voltage Swing Linear Output Current Output Balance Error −2 Differential Common mode −2.5 −30 Min Typ 1900 200 1700 6000 100 −61
Rev. 0 | Page 3 of 28
ADA4937-1
Table 2. VOCM to ±OUT Performance
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 Conditions Min Typ 440 1150 7.5 1.2 8 VOS, cm = VOUT, cm; VDIN+ = VDIN– = +VS/2 ΔVOUT, dm/ΔVOCM; ΔVOCM = ±1 V ΔVOUT, cm/ΔVOCM; ΔVOCM = ±1 V 3.8 12 6.1 Max Unit MHz V/μs nV/√Hz V kΩ mV μA dB V/V V mA μA/°C mA dB V V μs ns 50 −150 +85 μA μA °C
VIN = 1.5 V to 3.5 V; 25% to 75% f = 100 kHz
0.97 3.0 38.5
10 2 0.5 −75 0.98
1.00 5.25 41.0 0.4
Power Supply Rejection Ratio POWER DOWN (PD) PD Input Voltage Turn-Off Time Turn-On Time PD Bias Current Enabled Disabled OPERATING TEMPERATURE RANGE
TMIN to TMAX variation Powered down ΔVOUT, dm/ΔVS; ΔVS = 1 V Powered down Enabled
0.02 −70
39.5 17 0.3 −90 ≤1 ≥2 1 200
PD = 5 V PD = 0 V
10 −300 −40
40 −200
Rev. 0 | Page 4 of 28
ADA4937-1
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. Table 3. ±DIN to ±OUT Performance
Parameter DYNAMIC PERFORMANCE −3 dB Small Signal Bandwidth Bandwidth for 0.1 dB Flatness Large Signal Bandwidth Slew Rate Overdrive Recovery Time NOISE/HARMONIC PERFORMANCE Second Harmonic Conditions VOUT, dm = 0.1 V p-p VOUT, dm = 0.1 V p-p VOUT, dm= 2 V p-p VOUT, dm = 2 V p-p; 25% to 75% VIN = 0 V to 1.0 V step; G = 3.16 See Figure 45 for distortion test circuit VOUT, dm = 2 V p-p; 10 MHz VOUT, dm = 2 V p-p; 70 MHz VOUT, dm = 2 V p-p; 100 MHz VOUT, dm = 2 V p-p; 10 MHz VOUT, dm = 2 V p-p; 70 MHz VOUT, dm = 2 V p-p; 100 MHz f1 = 70 MHz; f2 = 70.1 MHz; VOUT, dm = 2 V p-p f = 100 kHz f = 100 kHz G = 4; RT = 136 Ω; RF = 200 Ω; RG = 37 Ω; f = 100 MHz VOS, dm = VOUT, dm/2; VDIN+ = VDIN− = +VS/2 TMIN to TMAX variation TMIN to TMAX variation Differential Common mode −2.5 −50 Min Typ 1900 200 1300 4000
