PMOS Diode connected

[AMSA84]

Hello guys,

I was calculating the Rout of a diode connected PMOS transistor when I came across with the following resistance:

Rx = 1 / (1/ro + gm)

But the result seems to be 1/gm // ro. I that it is like that, because that the result of a parallel combination of resistances. However, how can I go from that result to an explicit one that give use a clear look that they are in parallel? (don't know if I made myself clear :-D)

For example, transform that result into this one: 1 / (1/gm + ro).

Thanks in advance.

 

[chris.mourad]

Hi

The formula for combining two resistors in Parallel R1 and R2 is: Req = 1/(1/R1 + 1/R2)

Indeed the output impedance of a diode-connected PMOS Rout is its output resistance in parallel with the inverse of its transconductance.

So your result is correct: consider ro as R1 in my formula, and R2 is 1/gm.


Cheers