unity gain buffer design problem

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greenjuice

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I want to make unity gain buffer.

So I have some question.

I think to make in(+) and in(-) equal(virtual short)

amplifier has negative feedback and large open loop gain.

Is it right? Or only negative feedback make amplifier virtual short?

and I made unity gain buffer using one stage differential amp and I did it

But after that, I made unity gain buffer using two stage differential amp.

however it didn't work. only one side transistor is saturated. and another side transistor is in

triode region. I don't know why this happened.

please advise consideration to design unity gain buffer amplifier to me.
 

Hi,

it seems you are talking about ASIC design. If so, then please post in the ASIC design section.

***

Generally a unity gain buffer is an amplifier with gain of +1.

With an OPAMP you can IN+ use as input
and connect IN- to the output. Maybe with a resistor.

Then you have high impedance input and low impedance output.

***
There are unity gain buffer ICs available.
***
A schemaitc could help to better understand your problem.
Additional informations like technology, bandwith, supply voltage and so on will lead to more appropriate answers.
***

Klaus
 

at 1.3v supply like this, i design 40u current source in differential amp. so current of each input TR should flow 20u.

and at second stage i design 3 times ratio. so current of second stage should flow 60u.

But current source has only 33u current and in(-) is almost off.
 

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