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the images of the buffer amplifier ckt and its freq response(gain and phase plots) are below....it is unstable right? wat modifications do i have to do for the circuit if i hav to make it stable? the load cap. can be >=3.5pF.
There seems to be some problem with the simulation setup. If you look at the mag and the phase plots, they don't go hand-in-hand. Near to 0Hz, the mag plot shows a +x dB roll-off, whereas the phase rolls off by -x deg. At 1K the phase plot flattens out, but the mag plot rolls off.
Please check the setup and the measurements.
I think in Gray meyer book there is a mention of the a 3-amp structure for AC analysis, instead of opening the loop using the elements.
It is clear from your sim results that something is wrong. Your DC gain is negative, which is indicitive of something is not biased right or something. You should be seeing a gain of at least 40-50db with that amp. You shouldn't be seeing -50dB. Something is wrong with your setup.