VCLP can be used as a reference in S/H mode. It isn't necessary in CDS mode. Remember how CDS works. It takes two samples, during a pixel period, compares them and the output is the difference between the two samples. If you are just putting in a low frequency sine wave, you might not be seeing a big enough difference between the samples to get a high output. Unless you are synchronizing that wave with the capture windows, you will just see random outputs. In S/H mode, taking OS- higher than OS+ with result in a 0 output. It is not imediately destructive but long term it could impact the life of the part. Note that we have an evaulation board available: LM98640CVAL
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