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a question on the dc offset loop

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chang830

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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
 

sixth

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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

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
 

chang830

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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

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

Thanks for the reply!

Sorry, it caused some confuse. I mean the low pass filter is still consists of RC filter, but some also have a buffer or Gm stage in their loop path.

Can anyone explain it?

Thanks
 

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