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Unformatted text preview:   ⁄ ⁄ )
⁄ ⁄
. Thus, the CMMR is
( 11 ) 55:041 Electronic Circuits. The University of Iowa. Fall 2011.
Question 1 1 With inputs
With inputs
expressed in dB. (5 points) , and
, the output is , a difference amplifier has output
. Determine the CMRR, Solution
The differential input voltage is
⁄
is
With , and the differentialmode gain
⁄ the commonmode voltage gain is The commonmode rejection ratio is
   Expressed in dB 12  55:041 Electronic Circuits. The University of Iowa. Fall 2011.
Question 1 2 (J&B 6 th, P11.84) The multimeter in the figures below has a commonmode rejection
specification of 80 dB. What possible range of output voltages can the meter indicate? (6 points) Solution The difference voltage is
, and the commonmode voltage is
(
⁄
A commonmode rejection specification of 80 dB means that the multimeter
will suppress
by a 80 dB, which is equivalent to a factor
The contribution of the commonmode
⁄
error is thus
. However, the sign is unknown. Thus, the multimeter could display
anything in the range 13 55:041 Electronic Circuits. The University of Iowa. Fall 2011.
Question 1 3 (J&B 6 th, P11.85) We would like to measure the voltage
in the circuit below
with a voltmeter. What is the value of , and what is the commonmode voltage
associated with ?
What CMMR is required of the voltmeter if we are to measure to within 0.01%? Express you answer
in dB. (8 points) Solution
The current through the resistance is
therefore 3.75 V.
Further,
is then ( ⁄( . The voltage across the , and resistor is The commonmode voltage (
The error must be less than
or
or 3.75 V, which is 0.375 mV. Thus, the multimeter must
suppress the 7.5 V commonmode voltage to less than 0.375 mV. In other words, the CMMR must be at
least This is equivalent to 86 dB. 14 55:041 Electronic Circuits. The University of Iowa. Fall 2011.
Question 1 4 Suppose the amplifier below has a differentialmode gain of 2,500 and a CMMR of 80 dB.
What is the output voltage if
, and
? What is the error introduced by the finite
CMMR, expressed as a % of the differential input voltage? (5 points) Solution The differentialmode gain is 2,500 and the commonmode gain is 80 dB less, which corresponds to a
⁄
⁄(
factor
. Thus, the commonmode gain is
. The output
voltage is
( ( ( The error is 15 ( 55:041 Electronic Circuits. The University of Iowa. Fall 2011.
Question 1 5 A current source has an output impedance of
. Design a currenttovoltage
converter with an output voltage of
when the signal current is
. (6 points)
Solution
The following circuit is a current to voltage converter, with output voltage ( 16...
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This note was uploaded on 10/26/2013 for the course ECE 55:041 taught by Professor Kruger during the Fall '11 term at University of Iowa.
 Fall '11
 Kruger
 Amplifier

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