What's In Your Sar-adc Application?

摘要

"Finding an amplifier that doesn't tarnish an ADC's performance is hard enough. But now you also have to deal with single-supply voltages and the quirky switched-capacitor input structure" (Reference 1). Engineers have been struggling with the task of driving the SAR (successive-approximation-register)-ADC, charge-redistribution, or C-DAC (capacitive-data-acquisition-converter) input architectures for more than a decade.rnDriving a SAR ADC with an amplifier seems like a simple task. You choose an amplifier with a bandwidth that is appropriate for the input-signal requirements, then connect the amplifier directly to the ADC as a buffer. Not so fast. You are not finished until you accommodate the effects of the ADC-input charge injection on your amplifier (Figure 1). The transient currents at the input of the SAR ADC can disrupt the output of the amplifier so that the conversion process produces inaccurate digital results.