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how to do constant current biasing in analog circuits

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ashish_soni

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Hi,


I have a doubt regarding constant current biasing in the analog circuits.

if I bias a circuit using the current mirror, it's current is going to be fixed. now if I want to change the gain, I have two choices a) change the gm b) increase the ro

say I want to increase the gm, I can play with W and L of the transistors. now my doubt is, will it change the current? if not then why?
 

I think your question would be much more clear if you had included a picture or so.

But, if you have a current mirror and want to change its gm or ro, you could change the W/L ratio in both branches. The current will not change (to first-order) since the current through the mirror is dictated by the reference current that is provided to the primary side. That's the whole idea with the current mirror...
 
Current mirrors only (when proper) scale current that was
provided from a reference. So look to the reference source
if you want to change the tempco / voltco. Seems like you
want CTAT (constant) rather than the usual PTAT (proportional
to temp) type.
 
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