Remember to turn in clearly written
and easy to follow homework
Problem 1: Derive an expression for the input resistance
of a common-gate amplifier connected to a load with resistance RL.
Your final answer should be in terms of gm, ro,
and RL, and in the final step of this derivation you should
assume that gm >> gmb and gds
(where gds = 1/ro).
Problem 2: Problem 3.11 from the textbook.
Problem 3: Problem 3.12 form the textbook. Assume m COX = 90m
A/V2.
Problem 4: Common-Source Amplifier
If we attach a pMOS transistor to the current mirror of Homework 6
Problem 5, we can create the common-source amplifier shown below with a
pMOS amplifier transistor.
a) Using SPICE, determine the small signal gain if this amplifier if the
pMOS device is W=18m m and L=2m m. Attach a 1pF capacitor to the output to create
a defined high frequency roll-off. Be sure to use the Homework 6 Problem
5 circuit with a reference current close to 100m
A. See circuit below.
*Set Vin to 3.0V DC and click on Use AC.
*You may want to use the .OP and .SHOW analysis to check if your circuit
is biased correctly.
*Perform a .AC analysis (start=10, stop=10Meg) and plot the gain (use
mag(V(out)/V(in)) where mag = magnitude and ‘out’ and ‘in’ are
the output and input node numbers).
*Set the x-axis to log scale.
b) How could we increase the gain of this circuit? (Look back at HW6
Problem 1).
c) Describe what you would expect to happen to the gain if we set the
pMOS input transistor to W=40m m and L=2m m. Try this in SPICE and comment on the results.
SPICE MOS Model Statements for L=2m m
transistors.
.model cmosn nmos level = 1 vto = 0.77 kp = 7.7e-5 gamma = 0.71 phi =
0.73
lambda = 0.0625 tox = 3e-8 ld = 2e-7 u0 = 670 nsub = 2e16
.model cmosp pmos level = 1 vto = -1.1 kp = 2.1e-5 gamma = 0.355 phi =
0.66
lambda = 0.053 tox = 3e-8 ld = 5e-8 u0 = 180 nsub = 5e15 |
