Jim Thompson wrote:
See attachment.

WhatZit?

That is, what does it do?

VDD=2V

All current directions from top to bottom:

Source current of MN1:
Is_MN1 = Id_MN1 = I1 = IDC

Current through R1:
I_R1 = Id_MP1 + Is_MN1 - I3
= Id_MP1 + IDC - IDC
= Id_MP1

Voltage across R1:
V_R1 = V_IN1 - VGS_MN1 = I_R1 * R1 = Id_MP1 * R1

Drain current of MP1:
Id_MP1 = (V_IN1 - VGS_MN1) / R1

Drain current of MP2 is the same, as MP1 is equal to MP2:
Id_MP2 = Id_MP1 = (V_IN1 - VGS_MN1) / R1

Source current of MN2:
Is_MN2 = Id_MN2 = I2 = IDC

Current through R3:
I_R3 = Id_MP3 + Id_MP2 + Is_MN2 - I4
= Id_MP3 + Id_MP2 + IDC - IDC
= Id_MP3 + Id_MP2

Voltage across R3:
V_R3 = V_IN2 - VGS_MN2 = I_R3 * R3 = (Id_MP3 + Id_MP2) * R3

Drain current of MP3:
(Id_MP3 + Id_MP2) * R3 = V_IN2 - VGS_MN2
Id_MP3 + Id_MP2 = (V_IN2 - VGS_MN2) / R3
Id_MP3 = (V_IN2 - VGS_MN2) / R3 - Id_MP2
= (V_IN2 - VGS_MN2) / R3 - (V_IN1 - VGS_MN1) / R1

Drain current of MP4 is the same, as MP4 is equal to MP3:
Id_MP4 = Id_MP3

Output voltage:
V_OUT = V_R2 = Id_MP4 * R2
= R2 * ((V_IN2 - VGS_MN2) / R3 - (V_IN1 - VGS_MN1) / R1)

As MN1 and MN2 are identical, and R1 = R2 = R3:
V_OUT = V_IN2 - V_IN1

So itZ a differential amplifier with a gain of 1.

Laurent


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