Does gain booast increase of decrease the unity GBW?

[Usman Hai]

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

 

[jinnose]

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.

 

[evence]

Gain boosting won't change bandwidth.
If the additional pole of gain boosting loop is outside the bandwidth, phase margin won't be affected.

 

[Humungus]

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.

 

[yschuang]

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"