Discrepancy in the extracted frequency response from cadence and plotted frequency response using Transfer function

Dear all,

I am designing a buffer scheme for which I did AC analysis in virtuoso and plotted Vout/Vin  bode magnitude plot. For the same buffer I extracted all the DC operating point values and substituted in the Transfer function derived for this buffer scheme and plotted bode magnitude plot. I observed that there is a discrepancy in this two plots. The 3dB frequency and gain peaking is significantly different in these two plots. I guessed that it may be due to wrong method of extracting parasitic capacitances. Is there any other method for extracting these parasitic capacitances correctly?

Referring to the figure that I have attached,

C1=cgdbi1 + cgdbi2

C2=cdd1 + cdd2 + cgg3 + cgg4

C3=cgdbi3 + cgdbi4

C4=cdd2 + cdd3

Your suggestion would be really helpful to gain insights !!!

Thanks & Regards,

Tejal

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