a question on the dc offset loop

chang830 said:

I have a question on the dc offset loop for high gain amplifiers(such as limiting amplifiers). we know, to reduce the mismatch effect of very high gain amolifier, a dc offset loop is always included in the design. Except the low pass RC filter, I found some of them have a buffer(such as source follower)in the loop path, while some of them have a amplifier(transconductor)stage in the loop opath.

Would anyone tell me why a buffer, amp stage included in the lop path? In what conditions, a buffer, amp stage or none of them selected in the loop path?

Thanks

Click to expand...

sixth said:

chang830 said:

I have a question on the dc offset loop for high gain amplifiers(such as limiting amplifiers). we know, to reduce the mismatch effect of very high gain amolifier, a dc offset loop is always included in the design. Except the low pass RC filter, I found some of them have a buffer(such as source follower)in the loop path, while some of them have a amplifier(transconductor)stage in the loop opath.

Would anyone tell me why a buffer, amp stage included in the lop path? In what conditions, a buffer, amp stage or none of them selected in the loop path?

Thanks

Click to expand...

I can only guess because I can't see the schemtic of the buffer method and the transconductor method. Maybe the source follower is used as a level shifter for some particular consideration. Sometimes the Gm-Cell is used in the feedback path in order to reduce the chip area by replacing the RC integrator with Gm-C integrator.
Any way, the RC filter is the most popular method in DC offset cancellation loop and most effective.

sixth

Click to expand...