Question about gain booster circuit in folded cascode opamp

[ljy4468]

gain booster circuit

hey everybody

i've question about gain booster circuit in folded cascode opamp

there are 2 booster (N input pair, P input pair)
N booster is upper, and P booster is lower part.

I applied these two booster and there are about 50db improvement,
but i applied only one N input pair booster, and there's no change in Av in comparison with main opamp without booster.

I surmise there are at least 20dB up with only one booster.
Am i wrong?
somebody gives me advise.

thank you
have a good day

 

[ocarnu]

Re: gain booster circuit

Obviously, if you put two resistors in parallel, one large, one small, the large one will not influence the value of the equivalent resistor. In your case, one pair is boosted, having a large impedance, but too bad.... is shorted by the other one (non-boosted) with a much smaller impedance (50db > 100 times).