Reference current generator circuit for current mirror

Hi,

In the above schematic attached, I have calculated rin and Iref and both the parameters are the same for fig (a). and fig (b).
rin = R + I/gm and Iref = (Vdd - Vth)/ R.

Could you please clarify me, which way of connecting the circuit is correct and why?

Thank you.

Kind regards.

If the transistor symbol is meaned to show a NMOS transistor, only configuration a) makes sense. Sketch the complete current mirror and check yourself.

HI ams_ei

--First thing, the input resistance you have calculated should be= 1/((1/R)+gm) => R||(1/gm), for both the circuits. Anyway but this is not the question.

--In order to answer your question i would like to say that Drain current equation in saturation also include a multiple of (1+lambda*Vds) due to channel length modulation. Therefore while coping current from one branch (reference one) to required branch (out one), with (W/L), (1+lambda * Vds) will also come into picture i.e.

Iout = Iref (W/L)'(1+lamb * Vds')
................(W/L) (1+lamb * Vds)

Where ' is for required (out) branch.

in your fig(b) Vds will get differ if you use resistance at source . Fig(a) will be preferred to maintain equal Vds which will ensure accurate coping of current from reference branch.

ps- yes equal Vgs in mirror circuit is primarily requirement but for accuracy Vds should also be equal



-Rahul
"Take a step forward and things will start happening automatically"