Explain about Current mirror advantages and disadvantages

[vinodhsaminathan]

Hi,

I know what is current mirror and what are the advantages but can somebody tell me the disadvantages of current mirror in a ckt if is there.
Thx

 

[godfreyl]

Hi

It depends on the circuit obviously, but I can think of two possible problems:

1) The mirror adds noise. This is worst if there are no emmitter resistors. With big enough emmitter resistors, the noise can be reduced to an insignificant level.

2) The mirror may add distortion.This is worst if the Vbe of the transistors are very different and emmiter resisters are used. There's two ways to minimize this:
A) Use closely matched transistors for the mirror.
B) Make sure the resistance of the emmitter resistors is much greater than the dynamic emitter impedance of the transistors.

 

[vinodhsaminathan]

hi thx for the post. can u tell me how it add noise and distortion to ckt. am working with CMOS technology.