# Constant-gm bias circuit

1. ## Constant-gm bias circuit

For https://designers-guide.org/forum/At...amp.pdf#page=3 , how to derive expression (14) ?

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2. ## Re: Constant-gm bias circuit

Do you guys know how to come up with the equation for RDS4C ?

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3. ## Re: Constant-gm bias circuit

I got a different answer, maybe I made a mistake in the derivation but you can check to see if it's right though.

edit:
Oh I see my mistake now, when I absorbed (W/L)4c into the square root I forgot to square it. and (W/L)4c=P/M * (W/L)2E which would make
Rds=[2uCox(P/M)^2(W/L)2E*ID]^-1/2 which would equate to gm2E^-1/2 * M/P

1 members found this post helpful.

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4. ## Re: Constant-gm bias circuit

Thanks. Could you rewrite the correct solution ?

I am having problem following your derivation (with mistake).

5. ## Re: Constant-gm bias circuit

1 members found this post helpful.

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6. ## Re: Constant-gm bias circuit

Besides P, the M should have been squared inside the square root. I think you forgot it.

I do not understand why gm4e is always independent of process, temperature and load variations ?

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