hi,
I am designing a telescopic opamp. I achieved all the specs but not gain, so my question is whether gain boosting increase or decrease the unity Gain bandwidth? how it affects the phase margin.
Thanks
The unity gain bandwidth is Gm.effective/C. Thus, if you increase the gain by increasing Gm, then the BW will increase as well (assuming C remains the same). The phase margin is only depending on the second pole location and the unity gain bw assuming second pole is outside the unity gain bw.
Gain boosting does not changes (at least to a first order) the "gain bandwiwth product". This is because normally Gm is not changes while the output gd is reduced.
To a second order analysis, gain boosting introduces some extra poles and zeros that could reduce a little the unity gain frequency.
Be careful about the effect of doublets which will have an impact on the settling time. For more details, please refer to "A Fast-Settling CMOS Op Amp for SC. Circuits with 90-dB DC Gain by Bult"