I suspect the PSpice model is not quite right. Do you have a complete
listing you can compare against a similar type of MOSFET?

Richard P



                                                                                                                                  
                    Alan Bermudez                                                                                                 
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                    Sent by:               Subject:     [EE] Hand analysis not matching PSpice of MOS Differential Amp            
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I'm having so much trouble with this.

I need to do the hand analysis of an MOS Differential Amplifier and my
results are way off the Pspice simulation. The parameters of the
technology are:

W/L = 2
Vt0 = 0.6 (Threshold with source-bulk voltage equal to 0)
k' = 110e-6 (uA/V^2)
Gamma (Threshold voltage parameter) = 0.4
Lambda (Channel length modulation parameter ) = 0.04
2*PHIf (Twice Fermi Level) = 0.7
Ibias (Bias current) = 200 uA
Rd (Drain bias resistor) = 10k Ohm
Vdd (+ supply) = 5V
Vgate = 2V = Vg
Vbody = 0V = Vb
The body of each transistor is connected to GND.  Body effects have to
be included in the Vt calculation.

Here's my simulation:
www.geocities.com/castaways3373/schem.html

Here's my hand calculation:
1) Vd = Vdd-(Id*Rd) = 5-(100e-6*10e3) = 4V
2). Since the bias current is 200 uA, each side of the differential
amplifier gets 100 uA, so Id = 100uA
3). Using an iterative process, guess Vsb = 0.284V and check.
Vt = Vt0 + Gamma*(sqrt((2*PHIf)+Vsb)-sqrt(2*PHIf)) =
0.7+0.4*(sqrt(.984)-sqrt(.7))=0.762
Vgs = vt+sqrt((2*Id)/(k'*(W/L))) = 0.762+sqrt(100/110) = 1.84
Vs (source voltage)  = Vgate - Vgs = 2-1.84=0.2844
Vsb = Vs-Vb = 0.2844-0=0.2844
Therefore, Vs

Here's where I'm stuck, by my hand calculation I get Vs = 0.284, but
my simulations gives me Vs= -0.236 (negative).
Any help is appreciated, TIA
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