ADI ADA4939高性能ADC驱动方案

ADI 公司的ADA4939是低噪音超低失真高速差分放大器,它在100MHz的二次谐波系数为-77dBc, 三次谐波系数为-91dBc,3dB增益带宽为1.4GHz,转换速率高达6800V/us,非常适度用来驱动频率DC-100MHz和高达16位分辨率的ADC.本文介绍了ADA4939的主要性能, 失真测量电路图, 单端到差分转换电路图以及驱动AD9445 ADC电路图.

The ADA4939 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 output common-mode voltage is user adjustable by means of an internal common-mode feedback loop, allowing the ADA4939 output to match the input of the ADC. The internal feedback loop also provides exceptional output balance as well as suppression of even-order harmonic distortion products.
With the ADA4939, differential gain configurations are easily realized with a simple external feedback network of four resistors that determine the closed-loop gain of the amplifier.
The ADA4939 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 2.3 nV/√Hz. The low dc offset and excellent dynamic performance of the ADA4939 make it well suited for a wide variety of data acquisition and signal processing applications.

ADA4939主要特性:
Extremely low harmonic distortion
−102 dBc HD2  10 MHz
−83 dBc HD2  70 MHz
−77 dBc HD2  100 MHz
−101 dBc HD3  10 MHz
−97 dBc HD3  70 MHz
−91 dBc HD3  100 MHz
Low input voltage noise: 2.3 nV/√Hz
High speed
−3 dB bandwidth of 1.4 GHz, G = 2
Slew rate: 6800 V/μs, 25% to 75%
Fast overdrive recovery of <1 ns
±0.5 mV typical offset voltage
Externally adjustable gain
Stable for differential gains ≥2
Differential-to-differential or single-ended-to-differential operation
Adjustable output common-mode voltage
Single-supply operation: 3.3 V to 5 V
ADA4939应用:
ADC drivers
Single-ended-to-differential converters
IF and baseband gain blocks
Differential buffers
Line drivers



图1.ADA4939功能方框图



图2.ADA4939失真测量电路图



图3. G=2时ADA4939单端到差分系统电路图



图4.输入和输出采用AC耦合的驱动AD9445 ADC电路图