Unformatted text preview: we remove it from the circuit. The circuit to
current . Then
the right indicates the setup to determine
. The output voltage is
yields , no current flows into the inverting input and applying Ohm’s law
( Since ⁄ , it follows that ⁄( . 6 55:041 Electronic Circuits. The University of Iowa. Fall 2011.
Question 6 Show that the output resistance seen by the load in the voltagetocurrent converter circuit
below is (1 5 points)
Solution
Determining the output resistance is equivalent to determining the Thevenin equivalent resistance, which
we do as follows: turn off independent sources ( in this instance), add a test voltage
and determine
⁄
the resulting current . Then
The circuit to the right indicates the setup. Note that
turning off a voltage source means shorting it.
Furth, and KCL at the inverting input node gives
( ) ( If one recognizes that the opamp and
form a noninverting
amplifier, one could also write this expression down by inspection.
KCL at the noninverting input gives
(
Combining equations (1) and (2) yields
(
(
Finally, ) ) ( ⁄ , so that 7 ) 55:041 Electronic Circuits. The University of Iowa. Fall 2011.
Question 7 The circuit shown is a representation of the
commonmode and differentialinput signals to a difference
amplifier. One can write the output voltage as
, where
is the differentialmode gain and
is
the commonmode gain. Assuming an ideal opamp, and
setting
show that the commonmode gain is
( ) ( ⁄ Hint: Consider replacing the
source with two identical sources
a nd
as
a nd
respectively. Then use superposition to solve for the output voltage. connected (1 5 points)
Solution Using the supplied hint, we add two sources and then turn on on one at a time and add the
results (superposition). (a) (b) (c) With input , the circuit is a inverting amplifier and the output voltage is
(⁄
( With input , the circuit is a noninverting amplifier and the output voltage is
( ⁄ ( ⁄ Using superposition the, the output voltage is
( ⁄
(
( ⁄ ) ( : ( ( ( ⁄ ⁄ ( (
( ) ⁄
⁄ (
⁄ 8 ⁄ ( ⁄ ( )
⁄ 55:041 Electronic Circuits. The University of Iowa. Fall 20...
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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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