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Hi, I'm trying to find the resistance Rx in the picture.

Now, usually I would assume that (if channel length modulation is non-zero), that this would be 1/gm2 in parallel with ro2. However, I remember that was when our drain of M2 was connected straight to Vdd (AC ground in small-signal). But in this case, the drain is no longer just AC ground, Rd is there.

I'm assuming the Rx in this case won't just be 1/gm2 in parallel with ro2 will it?

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    \$\begingroup\$ This would be a good time to draw some equivalent circuits and find the resistances by seeing what's in parallel and in series. \$\endgroup\$ – KingDuken Dec 17 '18 at 0:11
  • \$\begingroup\$ I'm assuming the Rx in this case won't just be 1/gm2 in parallel with ro2 will it? Imagine that Rd has a very high value, like 1 Mohm (let's ignore that would influence the DC biasingof the circuit). Then it is easy to see that Rd does have an influence on the value of Rx. My point: don't assume but use reasoning. \$\endgroup\$ – Bimpelrekkie Dec 17 '18 at 11:31

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