Cascode Op-amp Topologies :

In order to achieve high gain, the differential cascode topology can be used. Figure below shows the single ended output configuration of cascode opamp.

Fig1-Cascode-Op-amp.png

Further, Figure below shows the differential output configurations of cascode opamp topology respectively.

Fig2-Cascode-Op-amp.png

These configurations are also called as the telescopic cascode op-amps. The voltage gain of these circuits can be given as,

An = â€" gm1, 2 [(gm3, 4 × ro1, 2 × ro3, 4) || (gm5, 6 × ro5, 6 × ro7, 8)]

· The drawback to telescopic topology is that the output swings are relatively limited.

The output swing is given by,

Swing = 2 [VDD - (VOD1 + VOD3 + V CSS + | VOD5 | + | VOD7 |)]

other drawback of telescopic cascode is the difficulty in shorting their inputs and outputs

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