hi dear all:

i have been questioned about the biasing current:

(1) Why do we use those biasing current which vary with temp?
i find the biasing current of many many circuits come from the BGP circuit, so its amplitude must change with temperature. i think if we use the constant current the performance of circuit may be better than those using varying circuit.(just guess)

(2) Can i use the un-changing current to bias every circuit?

many thanks!!
hope you can help me!

You may use PTAT current in amplifiers partially compensate for the band width reduction.

And, yes, you may use constant current to bias particulary any circuit...

mikki33 wrote on Jun 27^th, 2006, 7:32am:


thanks! Mikki, like the above reply, i know PTAT current is used in bipolar circuit to hold the gm constant. but in cmos circuit(i.e., cmos amplifier), what advantage is using PTAT current? and could you explain the reason for band width reduction in detail. why do many CMOS circuits (i.e., amp, comp, OTA,...) still use PTAT current? i plan to use constant current in my circuit. but i am afraid there may be some reason for using PTAT i have not known. so i want to ask for your help.