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OTA followed by buffer

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Member level 2
Aug 30, 2010
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Dear all,

We know OTA followed by a load driving buffer stage is what constitutes an operational amplifier. Can anyone show me how to design a buffer stage stage such that it doe not insert the dominant pole and the frequency response of the OTA remains undisturbed and the load is also driven!!

The question doesn't sound well considered. What do you expect for the "undisturbed frequency response" of an OTA followed by a buffer? Infinite bandwidth, infinite gain, or even both? An unloaded real OTA will always have a pole related to it's ouput impedance. If you don't manage to make it the dominant one and aplly pole-splitting to the others in return, the OP will be most likely useless as an amplifier, because it doesn't allow stable feedback operation.

If OTA output would be exposed as a terminal, it's reasonable to omit a compensation capacitor.

Thanks for reply
Ok let me be a little more clear. It is a fact that OTA has practically very less output load driving capability and we need an output buffer stage to drive our load. I am confused with this output load stage which must drive a load of atleast 5pF. I want my unity gain frequency to be at 2GHz with my OTA driving the required load at 1GHz where I shall have a gain of about 25dB. You can construct the image in your mind.
My OTA is ready but it can not drive the capacitive load, as soon as i append some load at its output the unity gain frequency falls back to paltry 100-500 MHz from 2GHz. So I need a load driver between my OTA and load which must drive the load but not alter the unity gain frequency. How can I do that???

It should be hard to add a buffer without introducing a pole. However, a zero might be generated to compensation one of high frequency pole.

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