after taking CoNVST low? I imagine it is a short time.
The AD7654 incorporates a sample and hold circuit at the input.
There is no requirement for the input to be stable when convst goes low. Convst
will "freeze" the analog input voltage approximately 2ns after CONVST goes low.
This is specified as the aperture delay. If convst is a perfectly periodic
signal (i.e. no jitter), the the sampling instant will have a jitter of
typically 5ps rms.