I’m passing a dc signal through a voltage-follower buffer to drive my SAR input. Do I need to use a rail-to-rail input on my driver op amp?
This depends on the reference voltage of the ADC and the supply voltage of the op amp. Generally, the goal is to utilize the maximum input range (dynamic range) of the ADC. Assuming your ADC is a single-ended input with a 5V reference, you want to the output to range as close as possible between ground and 5V.
If the op amp has supplies that are above 5V and below ground (negative) you likely won’t need rail-to-rail input, as long as the input voltage range of the op amp is observed. If you have a 5V supply on the op amp, you will need to use a rail-to-rail input.
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