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Describe Folded Cascode Operational Amplifier

Subject: CMOS VLSI Design

Topic: MOS Operational Amplifiers

Difficulty: Medium

cvd • 993  views
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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.

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

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

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Advantages:

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

Disadvantages:

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