Download Solutions #3

Electronics Homework Set #3
Chapter 2: #2, 10,18
Problem 2.2
The input signals to a differential amplifier are:
v1 HtL = 0.1 cosH20 p tL + 20 sinH120 p tL
and
v2 HtL = -0.1 cosH20 p tL + 20 sinH120 p tL
Find expressions for the common-mode signal and the differential signal.
ü Solution: The common-mode signal is given by
1
Hv1 HtL + v2 HtLL = 20 sin(120 p t)
2
The differential signal is
v1 HtL - v2 HtL = 0.2 cosH20 p tL
Problem 2.10
Each of the circuits shown below employs negative feedback. Assume that op amps are ideal, and
use the summing-point constraint. Analyze the circuits to find the value of vo for each circuit.
2
HW_02a.08.nb
ü a) - (2 mA) (1kW) = -2 Volts
b) Similar to a), this one has 5 V - (2 mA)(3 kW) = -1 Volt
c) 4V - 1V = 3 V. Note that since no current flows into the - input, the 3 kW resistor does nothing.
d) Again, no current flows into the - input, which must be at 0 Volts, so there is no voltage drop between the output and the input. The output must be at 0 Volts, and the 3 mA at the output must be absorbed by the op amp output circuit.
e) 5V - 2V = 3V at the output.
Problem 2.18
The circuit below employs negative feedback. Use the summing-point constraintfor both op-amps)
to derive expressions for the voltage gains A1 =vo1 ê vin and A2 =vo2 ê vin .
ü Solution
HW_02a.08.nb
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