# on-resistance of a mosfet

1. ## on-resistance of a mosfet

Hello everyone

I am trying to plot the on-resistance of a mosfet (switch) operating at 100GHz using cadence .

Best regards.

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2. ## Re: on-resistance of a mosfet

On-resistance is a DC parameter. At 100GHz you are looking
for an on -impedance- which is a complex number, and it is also
shunted at both ends (and the middle, if you care to get really
fine grained) by complex capacitances (losses).

Now the DC on resistance doesn't care about small signal high
frequency riding on it, it "is what it is". But "it is" shunted by
Cds across, Cdb and Cds aside and all it's worth is a rough idea
of how low Zds might be (but Ld, Ls, Cds all meddle).

The phase relation between V and I is unlikely to be 0 degrees
at 100GHz. That makes mag(V)/mag(I) not the same thing as
DC OP calculation of VDC/IDC. Different cast of characters.

I think you're probably after something related to Ron, but
different, and how it ought to be expressed / presented might

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3. ## Re: on-resistance of a mosfet

Originally Posted by dick_freebird
On-resistance is a DC parameter. At 100GHz you are looking
for an on -impedance- which is a complex number, and it is also
shunted at both ends (and the middle, if you care to get really
fine grained) by complex capacitances (losses).

Now the DC on resistance doesn't care about small signal high
frequency riding on it, it "is what it is". But "it is" shunted by
Cds across, Cdb and Cds aside and all it's worth is a rough idea
of how low Zds might be (but Ld, Ls, Cds all meddle).

The phase relation between V and I is unlikely to be 0 degrees
at 100GHz. That makes mag(V)/mag(I) not the same thing as
DC OP calculation of VDC/IDC. Different cast of characters.

I think you're probably after something related to Ron, but
different, and how it ought to be expressed / presented might

Actually I could estimate it using simple ac analysis (with transistor biased in triode region)
I measured the small signal ac current at the drain(ac voltage source applied at the drain) then take the Y admittance expression which is Y=I/V ≈(1/Ron)+jwCout

Then Ron=1/Re(Y) ,

the result is confirmed by the Input impedance simulation of a passive mixer first receiver.

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