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I was asked to calculate the voltage gain of a circuit containing 2 P-MOS and one N-MOS transistors: enter image description here

I calculated the operating point and got: gm1 = gm2 = gm3 = 2 [ms] The circuit that I built for small signal analysis was: enter image description here

but now I am not sure how to find the relationship between Vin and Vout.

EDIT: Ignore the Rds resistor, it is for another question.

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  • \$\begingroup\$ Raed Jayyousi - Hi, Where did that image come from? To comply with the site rule on referencing, details of the original source of copied / adapted material must be provided by you, next to each copied / adapted item. If the original source is online & public, please edit the question & add the webpage/PDF name & its link (URL) (e.g. website name + webpage title + its URL). If the source is offline (e.g. book or private intranet) then edit the question & add full source details e.g. title, author, page, publisher, edition. TY (More site rules in the tour & help center.) \$\endgroup\$
    – SamGibson ♦
    Commented Sep 14 at 16:14

2 Answers 2

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See M2 & M3 form a current mirror -- M3's current is equal to M2. M2's current is equal to M1.

For your (homework ?) answer, be sure to include the polarity (+ or -) of the gain.

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There are two inverting stages. Ignoring rds, the gain of each stage is determined by gm times drain load. The load in the 1st stage is a diode connected PMOS. First stage gain is Av1 = - gm1 * 1/gm2 and 2nd stage gain is Av2 = - gm3 * (RD || RL). Total gain would then be Av = Av1 * Av2. With gm1 = gm2 = gm3 = gm the overall gain is Av = gm * (RD || RL).

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