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help~~(about the gain boost)

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janice

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I browsed almost all the papers of the IEEE of the gain boosted OTA, all mostly said about the same thing, just add a Op Amp to increase Rout, like the picture attached.... The problem is how to decide the bias and the Width/Length of the the added Op Amp. I used the Op Amp as same as the original one(the one needed gain boost), the gain decreased..:cry:
 

OpAmp

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Please take a look at:
 

wdd

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janice said:
I browsed almost all the papers of the IEEE of the gain boosted OTA, all mostly said about the same thing, just add a Op Amp to increase Rout, like the picture attached.... The problem is how to decide the bias and the Width/Length of the the added Op Amp. I used the Op Amp as same as the original one(the one needed gain boost), the gain decreased..:cry:

do u use the architecture as you proposed?
the added ota need antoher input to bias the input voltage,
i.e. the added ota need three inputs, one used bias DC input voltage.
also, you can use four added otas each has two inputs.

u gain is low, so check every transistors' working condition.
 

    janice

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janice

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wdd said:
do u use the architecture as you proposed?
the added ota need antoher input to bias the input voltage,
i.e. the added ota need three inputs, one used bias DC input voltage.
also, you can use four added otas each has two inputs.

u gain is low, so check every transistors' working condition.

I only added one fully differential OTA on the cascode transistors(the common gate ones). I copied the original OTA as the gain boosted OTA, the same bias, and the same CMFB. But the gain decrease to about half.....

Yes...I checked the working conditions and found the common gate transistors (on which I added the gain boosted OTA) work in the linear region.......but when I change the Widths of them, the condition changes little, and output waves looks terrible.....anything else I can do?

Thanks~~~~
 

wdd

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janice said:
wdd said:
I only added one fully differential OTA on the cascode transistors(the common gate ones). I copied the original OTA as the gain boosted OTA, the same bias, and the same CMFB. But the gain decrease to about half.....

Yes...I checked the working conditions and found the common gate transistors (on which I added the gain boosted OTA) work in the linear region.......but when I change the Widths of them, the condition changes little, and output waves looks terrible.....anything else I can do?

Thanks~~~~

then you need some tricky define the input dc value of the new added ota(such as three inputs ota you can see in some papers, ie the link proposed by OpAmp)
the new added ota does not need cmfb in my opinion.

you need carefully check the bias, transistor working conditions, because there are internal feedbacks in gain-boosted ota, so stability must be considered.

Regards,
wdd
 

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