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to make op amp gain more bigger with fixed bandwidth

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Member level 1
Aug 21, 2015
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As you know, If i make output resistance more bigger, my op amp has big gain but it has narrow bandwidth.

So I want to make transconductance gm of op amp more bigger

And then I think I can get more bigger gain with fixed output resistance and output capacitance(fixed bandwidth)

But I heard that if i make gm more bigger, bias current is larger and so output resistance is smaller

Is it true?

And If it is right,

why output resistance is smaller?

I want to know relation output resistance and bias current.

You do not make the output resistance "more bigger" (higher). Instead for more gain you make the negative feedback resistance higher.
An opamp has a frequency compensation capacitor to reduce the gain at high frequencies so that its phase shift does not cause oscillation when negative feedback is applied then at high gain the bandwidth is narrow and at low gain the bandwidth is wide.

If you want high gain with wide bandwidth then use a wide bandwidth opamp or use two opamps in series, each having fairly low gain.

The output impedance of an opamp is extremely low at DC and low frequencies due to its very high open-loop gain and negative feedback.
The bias current of most opamps is extremely low.
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