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1
EE338K
HOMEWORK
ASSIGNMENT #8
Differential Amplifiers
1.
+
_
_
+
P
N
E
o2
Diff Amp
E
2
+
_
Measurement 2
_
+
E
1
P
N
E
o1
_
+
Diff Amp
Measurement 1
Two separate measurements are made on a Differential Amplifier to determine its Common Mode
Rejection Ratio. Measurement 1 consists of applying a source voltage
E
1
to the amplifier inputs as
shown above, and measuring the output voltage,
o1
.
For measurement 2 the voltage
2
is applied to the
inputs in the manner shown above and
o2
is measured at the output The result of Measurement 1 is that
o1
= 10
1
. For Measurement 2 it is found that
o2
= 10
2
2
. Use the results of these two measurements
to find the CMRR
dB
of the Op Amp.
2.
R
1
R
2
E
P
E
o
+
_
E
N
1
R
′
2
R
′
In the circuit above the resistors
1
R
and
1
R
′
are both nominally 3k
Ω
and both
2
R
and
2
R
′
are nominally
120k
Ω
. If the resistor values were exactly equal to the nominal values
G
c
= 0 and
d
= 40; however, the
resistors actually used in the circuit have a tolerance of 5% so assume that their actual values are
1
R
= 2.9k
Ω
,
1
R
′
= 3.1k
Ω
,
2
R
= 125k
Ω
,
and
2
R
′
= 114 k
Ω
.
Assuming that the Op Amp has infinite CMRR, use an asymptotic analysis with the actual resistor
values to find the CMRR
dB
of the differential amplifier circuit.
3.
+
_
+
_
R
1
R
2
E
P
E
o
+
_
E
N
1
R
′
2
R
′
R
3
4
R
′
R
4
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2
In the Instrumentation Amplifier circuit above the nominal values of the resistors are
1
R
=
1
R
′
= 3k
Ω
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This note was uploaded on 10/26/2009 for the course EE 338k taught by Professor Bostick during the Fall '09 term at University of Texas at Austin.
 Fall '09
 BOSTICK
 Amplifier

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