Voltage Amplifier with OpAmp & 2 NMOS - GAIN?

[vidak]

Please find the circuit enclosed in the attachment. The main problem I have here is calculating the Bias Point currents of the two transistors (\[I_{1}\] and \[I_{2}\] so I can get the voltage gain for small-signal model.

I have calculated that \[a = -10\cdot\frac{g_{m1}}{g_{m2}}\] , where \[g_{m1}=\sqrt{2BI_{1}}\] and \[g_{m2}=\sqrt{2BI_{2}}\]. Is this correct? Please help!

 

[godfreyl]

The main problem I have here is calculating the Bias Point currents of the two transistors (\[I_{1}\] and \[I_{2}\]....

Io is shared almost equally between M1 and M2 so:
I1 = I2 = Io/2 =50uA.

Consider:

• Maximum output voltage from the opamp is +-1.65V.
• Voltage gain of the opamp is 1000.
• Therefore the maximum voltage difference between the opamp's input pins is 16.5mV (unless it is over-driven).
• Therefore the maximum difference between I1 and I2 is 16.5mV/10K = 1.65uA.