Q
Flexible analog input: 1 V p-p or 2 V p-p differential. How it could be
delivered when both operates from a single 1.8 V analog power supply?
A
In 2Vp-p “differential” span mode (also referred to as 1V Vref mode), each Ain
pin accepts a 1Vp-p swing centered around the ADC Common Mode of 0.9V. So each
input sees 0.9V +/-500mV, or a 1Vp-p swing of 0.4V to 1.4V.
The key word here is “differential”. Since the inputs are differential (180°
out of phase), the “differential” range of the ADC is +1.0V to -1.0V, or 2Vp-p
“differential”. Same pattern applies to the 1Vp-p differential (0.5V Vref)
mode. See attached coding table.
Good news is most all the high speed ADC’s operate like this, where the supply
voltage just sets the max allowable swing between the supply rails. The main
issue with the shrinking supply voltage is the loss of headroom, and the
ability to support larger voltage Ain differential swings.