On Tue, 27 Mar 2007 12:25:12 +0200, Laurent Lamesch wrote:
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
(Replace 'nospam' with 'email')
Laurent, You are correct!
It is refreshing to see that there are lurkers here who can actually
analyse!
(Circuit is from an RFID tag.)
...Jim Thompson
--
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