Folded Cascode opamps:

i) In order to reduce the drawbacks of Telescopic cascode opamp namely, limited output swing and difficulty in shorting the input and output, a folded cascade opamp can be used.

ii) In folded cascode, unlike telescope cascode, we use NMOS and PMOS to form a cascode.

iii) The folding idea explained above, can easily be applied to opamps as shown below:

$|A_v| \approx gm_1{[(gm_3+gmb_3)r_{o3}(r_{o1}||r_o5)] \,||\,[(gm_7+gm_7)r_{o2}*r_{09}]}$

Advantages:

• Slightly higher swing, input and output can be shorted.

Disadvantages:

• Gain trades off with $V_{in}$ swing.