Connect OTA output to an voltage source whose value equal to OTA o/p common mode. And through Ac simulation find the current through voltage source. That's all.

Thanks,
Raj.

hi,

As Raja answered, connect OTA in unity-gain mode. once you have done that you will be able to measure all the parameters that you want.

common-mode is the range of voltages that we need to have (either at input or output) such that the performance of the OTA will not deviate form the assumptions that we make during the analysis (such as "all devices are in sat." for example). common-mode will be the important specification if the circuit is driven by or driving any stage.

by the way..all the material that is needed to design an OTA or to understand how to simulate analog circuits (atleast to the basic level) is given in various text books. As it seems you are new to the design domain, my suggestion is that you first read any good book and try to get some understanding. (read the book by razavi,  if you like)

Thannks
Anil