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What is wrong in this amplifier

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awan

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Hi;

I am trying to simulate this in HSPICE. If i find my DC operating point, then the current ID is around 8mA and transistor is in saturation.

element 0:m1
model 0:cmosn
region Saturati
id 8.7958m

But when i give a very small AC, then rather than amplification, the simulation shows voltage and current dropping. I am sure there is something wrong as to the way i am entering the design. Can someone please help me out here.

Thanks in advance.

.OPTIONS LIST NODE POST
.OP
.opt post
VDD 1 0 DC 2.5
RL 1 2 140
M1 2 3 0 0 CMOSN w=40u l=.25u
CL 2 0 1p
CIN 4 3 .1
RS 5 4 1000
VIN 5 0 AC .01u
R1 1 3 1100
R2 3 0 1400
.AC DEC 10 1K 1000MEG

Added after 1 hours 54 minutes:

Hi;

I have a small signal AC source that has a series resistance and then the decoupling capacitor. If i remove the series resistance, then the gain is as per my calculation. But as soon as i include the series resistance, the gain drops below 1 for all frequency. As per my knowledge, the series resistance shouldnt have an effect on the gain. Any suggestions?

Added after 28 minutes:

Okay, so i realise that its due to the biasing resistors and the series resistance with the small signal AC source. So, now i am trying to bias it using a current mirror. But there is still no improvement.

What are the reasons if this doesnt work with the current resistance. What parameters should i be looking for? Should i decrease my Gain current.
 

AC magnitude should be 1 for ur input
as AC Gain is to be measured for unitty ac Mag. For lesser values it will always show less than 1. Dont know the reason though!
U should give input amplitude as 1u or whatever required but keep the ac mag '1' ALWAYS.
N yes by reducing Id gain willl increase but there is nothing wrong with ur circuit.
 

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