The AD7400A specifies an analog input range of +/- 200mV and a specified full
range of +/- 320mV, which I interpret as a bipolar input. When looking at the
abs max ratings, it can only be on the negative side GND -
1. The part can accept the differential signal with +/- 250 mV applied to both
Vin + and Vin – (but input signals are out of phase).
The specifications are guaranteed for SE mode as you have highlighted. This is
mainly because the end application is mainly SE and not differential. Fig 21
applies to SE and diff
2. The Common mode Voltage Range while not specified, is -0.1v to 0.4V.
However, for the AD7400 In terms of the common mode range, there are two
inherent limits as far as the inputs go.
i) The analogue input is not permitted to go to less than -250mV or greater
than +0.5V with respect to GND1
ii) Additionally, neither input can be further than 250mV away from the other
input for specified performance.
In terms of the common-mode voltage, the user can choose whatever value he or
she pleases so long as it doesn't break the rules outlined previously. In
production test we ground Vin- and drive Vin+ with a 200mV/250mV peak sinewave
to derive the specs in the datasheet, thus meeting both criteria.