Cascode op-amp(Telescopic)

i) In order to achieve a high gain-differential cascade topologies used.

ii) Above circuit display a gain of
$A_v=gm_n[(gm_n*r_{on}^2)||(gm_p*r_{op}^2)]$

iii) Configuration shown above are called "Telescopic cascade op-amp".

Fig:(a): Single ended output-suffers from a minor pole at 'X' -creates stability issues.

Drawbacks:

• Less output voltage swing.
• Difficulty in shorting inputs and outputs. This is required in implementing unity gain buffer.