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Specifying a driver amp for high-resolution precision ADCs

How do I choose an op amp that will maintain the precision (effective number of bits) of the ADC that it will be driving?

  • The first thing to compare is the Signal-to-Noise and Distortion (known as SINAD) of the ADC to the distortion and noise (THD+Noise) of the op amp. You want the SNR+THD of the amplifier to be less  than (i.e., more dB)that of the ADC. For example, the AD7980 is a 16-bit precision ADC with a typical SINAD of 91dB at a signal frequency of 10 kHz. Analog devices has a number of precision op amps that have a THD+N of 91dB or better at 10kHz, such as the ADA4627, ADA4610, ADA4075, ADA8597, ADA8655, and AD8691. Selection of which amplifier to use will then depend on other criteria relative to the application (like power supply voltage, quiescent current, and input bias current).

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