EE114 Autumn 09/10
R. Dutton, B. Murmann
Page 1 of 3
Last modified 10/9/2009 5:07:00 PM
HOMEWORK #3
(Due: Friday, October 16, 2009, noon PT)
1.
Assume that you have just joined a new company and that their technology and
technology files for SPICE are quite different from what you have worked with at
your previous company.
Hence, you need to do some hand calculations and related
SPICE simulations (using your own “my_nmos”) to confirm what you can expect
with the technology at hand.
Here is how you will go about the task:
a)
Assume a W=25
μ
m and L=1.4
μ
m NMOS device, with KP=50
μ
A/V
2
,
VTO=0.5V and COX=2.3mF/m
2
(use the Lambda scaling rule given in Lect.
5, p. 1819); for a bias current of 0.35mA and assumed Vds=2.5V, compute
(by hand) the required Vgs and resulting Cgs as well as smallsignal gm and
gds (ignoring all extrinsic capacitances).
b)
Construct an HSPICE deck, similar to that shown in Lect. 6, p. 21 but only to
be used for the dc operating point and “.op” output.
This time use R=10K
Ω
and R
i
=20K
Ω
.
Run the simulations and confirm your hand calculations in
part a)—these should be virtually identical to your hand calculations.
Your
HW must include both your input and output files as shown on p. 21 of Lect.
6.
(Remember:
it is your job to correctly specify V
I
to get Vds=2.5V).
c)
Now you will add in the relevant extrinsic capacitance effects, both in hand
calculations and then in simulations.
Assume that CGSO=0.5nF/meter and
CGDO=0.5nF/meter, additionally the junction capacitances are specified by
the formulae Lect. 7, p. 5 and the associated HSPICE parameters (i.e. CJ,
CJSW etc.) shown on p. 6 (same lecture—note the units milliF/meter
2
,
nF/meter).
Compute the resulting Cgd and Cdb values, using L
diff
=3
μ
m.
d)
Modify your HSPICE deck appropriately and rerun the simulations to
confirm the above hand calculations in part c).
How do you actually confirm
the handcalculated Cdb value based on the HSPICE results? You should
include a .model statement in your netlist to define the device model
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 Fall '08
 MURMANN
 Grid bias, B. Murmann, hand calculations, R. Dutton

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