# A zero at folded cascode apmlifier

1. ## A zero at folded cascode apmlifier

Why there is a zero by counting the gain from the input to node2. Why the gain at high frequency is gm1/gm2? Thanks.

page 10.

http://ece.tamu.edu/~spalermo/ecen47...ascode_ota.pdf

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2. ## Re: A zero at folded cascode apmlifier

Because looking into the source of at low enough frequencies you see big resistance and gain is defined by ro1||ro5. When CL reduces the impedance at the output, then looking into n2 you start seeing 1/gm2 and you get the behavior shown on the plots.

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3. ## Re: A zero at folded cascode apmlifier

Originally Posted by sutapanaki
Because looking into the source of at low enough frequencies you see big resistance and gain is defined by ro1||ro5. When CL reduces the impedance at the output, then looking into n2 you start seeing 1/gm2 and you get the behavior shown on the plots.
The above should read " Because looking into the source of M2 at low enough frequencies...."

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4. ## Re: A zero at folded cascode apmlifier

That's really helpful. Could you please explanate the zero? Why there is a zero and why the zero location is that? Thank you.

5. ## Re: A zero at folded cascode apmlifier

Here is a short explanation

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6. ## Re: A zero at folded cascode apmlifier

Wz is a zero location.

I didn't know what the zero location calculation can also use the gain-bandwidth constant relationship to obtain. Thanks.

7. ## Re: A zero at folded cascode apmlifier

The gain bandwidth relation just relates two frequencies on a + or - 20db/dec response. It doesn't care if you call one frequency a zero or a pole or just pick two frequencies on the slope.

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