Re: CM swing !!
I don’t know exactly what is the application that you are interested in. I will assume that you want to know what the common-mode input swing will has to do with an opamp input stage.
If you are asking about a common-mode issue, is certainly because the signals that you want to process are differential. This means that you have two signals (negative and positive) vp=VCM+DeltaV/2 and vn= VCM-DeltaV/2. In this case the differential voltage, which is you are processing is DeltaV. VCM is the common-mode voltage.
Your fully differential opamp amplifies the differential input voltage: for example if the gain is set to 3, the DIFFERENTIAL output voltage will be 3x larger than the differential input voltage. Ideally this amplification operation should be independent of the input common mode voltage…. but it is not.
Imagine that your amplifier as a NMOS input differential pair. If the common-mode voltage of your input signal is near the negative supply, the differential pair will not work properly (the transistors will cutoff). In this case you must increase the input common-mode voltage, to have the differential pair biased correctly. If you ensure this, the output voltage will be (almost) independent of the input common-mode voltage variations.
Hope this helps !