tackling the problem of offset voltage and CMRR

[AZALBE1975]

could someone tell me how to tackle both the problem of offset voltage and CMRR in the design of my amplifier. this mostly at the level of circuit.

 

[dhasmana]

For getting a good CMRR, design the current source of the amplifier to have large/high impedance.This can be done by using large lengths and operation in deep saturation.

In order to reduce the offset at the input of the amplifier , increase the gain of the amplifier by having higher GM of the input and gain stage.

Regards.

 

[dreamteam]

You could also increase size of input transistor to reduce mismatch and then reduce offset. But them in WI could also be usefull.

 

[elbadry]

Improving CMRR can be done by improving the tail current source impedance. Increasing length wil help at low frequencies but will cause a deterioration of high frequency CMRR as the shunt capacitance to the current source will also increase...

Offset voltage needs high degree of matching which translates into larger area and smaller veff (for input pair ) or large veff ( for current sources )

If this is not enough, you may need offset cancellation