Reference current generator Circuit for current mirror

Thread Starter

Babun Pal

Joined Jul 13, 2016
17
IMG_20160722_161858.jpg
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.
 

ci139

Joined Jul 11, 2016
1,898
with fets - i guess - the both work while fig.a has a U.g setting voltage drop on R , it's mirrors´ current (I.d.Q.mir) would be similar to I.d.Q.ref
then on the other hand the fig.b acts as a voltage ref (setting it´s U.g - though it requires some additinal R.d to work in practice as voltage ref) - so in the latter modified case you have U.g const that deafines for its mirror a similar I.d.Q.mir
!!! but both (fig. a & b ) work only where U.g to GND (U.g.Q.ref to U.s.Q.mir) falls the non saturated linear region of Q.mir (has small or no resistance between it's source and GND !!!)

the type of voltage mirrors work fine only for near fixed supply voltage and I. or U. ref being const

if you need a true mirror you have to buold a complex amplifier
- where each replicated node has it's own control/feedback/adjustment
-- basically an input(eighter I or U)-controlled set of current sources

if you dont need so true mirror - you can use your figures a,b @ the mirrors linear region.
 

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