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If this is a differential folded cascode CMOS amplifier

schematic

simulate this circuit – Schematic created using CircuitLab

(where the "first" stage is nMOS and the "second" one is pMOS), can the following be considered as its dual?

schematic

simulate this circuit

It doesn't matter the different DC sources disposition and their values. My question is: is the second circuit built following the same cascode principle of the first one?

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  • \$\begingroup\$ My problem with this question is that the top circuit doesn't look like a cascode circuit. Please justify that the 1st circuit is a cascode amplifier. \$\endgroup\$
    – Andy aka
    Commented Mar 3, 2015 at 12:46
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    \$\begingroup\$ Can we assume that this is an IC design, and that the substrate connection on each transistor is NOT connected to its source? Otherwise, you have a lot of parasitic "body" diodes that prevent the circuit from working as intended. \$\endgroup\$
    – Dave Tweed
    Commented Mar 3, 2015 at 12:51
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    \$\begingroup\$ It's a folded cascode amplifier. \$\endgroup\$
    – HKOB
    Commented Mar 3, 2015 at 18:37
  • \$\begingroup\$ Yes, sorry, the circuit was wrong; now I corrected the schematic. \$\endgroup\$
    – BowPark
    Commented Mar 4, 2015 at 10:49
  • \$\begingroup\$ @Andyaka It is a folded cascode CMOS amplifier, as stated by HKOB. \$\endgroup\$
    – BowPark
    Commented Mar 4, 2015 at 10:50

2 Answers 2

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Yes, except for the location of the output connection (the first circuit looks wrong), the two circuits are topologically equivalent.

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This is what I consider to be a differential cascode amplifer: -

enter image description here

Note the important difference - the output is taken from the drains of the upper transistors. What you appear to have is Vout taken from the drain of the 1st pair of transistors but this voltage will tend to be clamped by the sources of the 2nd pair.

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  • \$\begingroup\$ Thats a cascode circuit; the OP's circuit is a folded cascode cirucit (when working properly !) \$\endgroup\$
    – jp314
    Commented Nov 27, 2015 at 5:10
  • \$\begingroup\$ @jp314 you are absolutely correct but, if you go and look at the edits performed on the question you will see that he originally called it a "plain" cascode circuit and had the output in the wrong place. This of course makes my answer look stupid so here I am justifying that it's not a stupid answer and that the guy raising the question altered it after I made my answer. \$\endgroup\$
    – Andy aka
    Commented Nov 27, 2015 at 9:40

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