The SNR that I had received while calculating in Matlab for a specific NTF is around 80 dB. I realised the same using ideal op amps and the SNR was the same. But the SNR after using nonideal op amps went down to 40 dB. What can be the reasons for the degradation?
Added after 17 minutes:
and also suggest what can be done to rectify them?
also noise (but i don't think you put it into your simulation), ron of switches, clock feedthrough or charge injection, lousy cm-feedback of the opamp. Also saturation of the opamp, limited gbw, sr, finite gain, ...