Problem Set #3
EE3115
Spring 2019
Assigned: Feb. 6, 2019
Due: Feb. 13, 2019
1. A MOSFET=based differential amplifier is shown below. The resistor RSS is
the Thevenin equivalent resistance of the current source. It is needed for
small signal calculations.
10 V
MOSFET Parameters
100 kΩ
100 kΩ
+
_Vi1 Q1
Vo1 Vo2
0.1 mA
Q2
K = 6.6x10-3 A/V2
Vt = 1 V ; VA = 50 V
+
Vi2 _
RSS
-10 V
a. What is the differential gain Ad = Vod/Vid. Vod = Vo1-Vo2.
b. What should be the value of Rss if the CMRR = 104? The CMRR is for
when the output is taken single-ended i.e. referenced with respect to
ground as are Vo1 and Vo2.
2. A p-channel MOSFET-based differential amplifier is shown below.
15 V
+
Vcs
_
I
+
Vi1
_
RD
Rss
MOSFET Parameters
+
Q2
Q1
+ +
V
Vo1
_ _ o2
Vi2
K = 6.55x10-3 A/V2
Vt = 1 V
VA = 50 V
RD
-15 V
a. The dc power drawn from he bias supplies under quiescent conditions is 6 milliwatts.
The quiescent dc values of Vo1 = Vo2 = -8 V. Determine the value of RD.
b. Determine the allowab le ranage of Vicm. The voltage across the current source must
not drop below 2 V. Assume RSS is infinite for this step.
c. Determine the allowable range of Vid assuming a linearity of 99% or better (as
discussed in lecture).
d. What is the single-ended differential gain Ad = Vo2/Vid?
e. The CMRR of the circuit for single-ended outputs is to be 60 db. Determine the
minimum required value of RSS. Assume VA = infinite for this step.
3. 9.16
4. 9.55