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Simple differential amp design

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DamonKim

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Hi

I started to design a simple differential amplifier using cadence spectre.

I made an amplifier under low power condition.

So, input devices are in subthreshold.

I got the operating operating point shown below.

But, when I tried tran simulation, I got the gain lower than unity.
It's much smaller than I expected by hand calculation.

I want to know how to deal with this situation.

I expected gain by gm*(Ron || Rop) and it's bigger than 10 at least.

please help me.

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I think you connected the diff pair into diodes somehow. The vds and vgs voltages are almost the same for the devices. Then the expressions what you wrote aren't true.
 

The waveform voltage levels don't fit the parameters shown in schematic. May be a different DC offset?

Show the complete test setup including power supply and biasing, connection of all amplifier terminals.
 

Could you post the simulation setup and all nodes DC voltages?
 

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