My desired signal has a frequency of 100Hz. So, I'm guessing that would classify as a very low frequency signal and the AD637 wouldn't be an appropriate choice.
Can there be another alternative chip which would not have this problem for low frequency signals?
Otherwise, the best solution for me is to add a summer to the existing circuit and turn it completely positive?
Or, as Richard suggested, is there any converter that I could use to take bipolar signals and digitize them?

Thanks