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OP-AMP Schematic Help

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kiwi101

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Hey guys,

I'm trying to make a triangle wave generator circuit on cadence but in order to do that I have to make an OP-AMP first. This is the schematic I made for the OP-AMP and when I plot the Vout vs t or Vin vs t, it's clear to see that something is off.
Any suggestions are appreciated.
 

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erikl

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The Vsource V0 has a generator impedance of 0Ω, hence the output in your circuit is a superimposition of the (negative) open-loop amplified input signal and the (positive) input signal itself, fighting against each other via their generation impedances.

R1 should connect to Vin- for an (intended?) closed loop gain = -2 .
 

kiwi101

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So for the Vsource
I set the amplitute to 100 mV and the frequency to 1K so what do you mean by the generator impedence? Should I change it?

Thanks I changed the R1 can't believe I missed that. But my graph is still pretty much coming the same surprisingly

- - - Updated - - -

Here is what I got after changing the R1 to connect to Vin - and yes my intended closed loop gain is -2

- - - Updated - - -

Okay so I went back and changed some things in the Schematic of my opamp and now Im getting a gain. However the gain for Vout is not centered at the same place for the gain of Vin. Could someone tell me how I should current bias the Diff amp fo my op-amp to the gain part of my opamp.
 

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erikl

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If I interpret your wave outputs correctly, your amp doesn't show any gain. Probably your DC input voltage isn't within the correct ICMR. Check your node voltages and if the MOSFETs work in saturation region.

Strange: there is a 2V DC difference between output and input. Seems there's a 2nA leakage current over the 1GΩ feedback resistor.
 

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