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Chapter 5, Problem 1.
The equivalent model of a certain op amp is shown in Fig. 5.43. Determine:
(a) the input resistance. (b) the output resistance. (c) the voltage gain in dB.
Figure 5.43 for Prob. 5.
8x10^4 vd
Chapter 5, Solution 1.
(a) Rin = 1.5 M Ω (b) Rout = 60 Ω (c) A = 8x
4
Therefore AdB = 20 log 8x
4 = 98.0 dB
Chapter 5, Problem 2
The open-loop gain of an op amp is 100,000. Calculate the output voltage when there are
inputs of +10 μ V on the inverting terminal and + 20 μ V on the noninverting terminal.
Chapter 5, Solution 2.
v 0 = Avd = A(v 2 - v 1 )
5 (20-10) x 10
Chapter 5, Problem 3
Determine the output voltage when .20 μ V is applied to the inverting terminal of an op
amp and +30 μ V to its noninverting terminal. Assume that the op amp has an open-loop
gain of 200,000.
Chapter 5, Solution 3.
v 0 = Avd = A(v 2 - v 1 ) = 2 x 10
5 (30 + 20) x 10
Chapter 5, Problem 4
The output voltage of an op amp is .4 V when the noninverting input is 1 mV. If the
open-loop gain of the op amp is 2 × 10 6 , what is the inverting input?
Chapter 5, Solution 4.
v 0 = Avd = A(v 2 - v 1 )
v 2 - v 1 = 2 V 2 x 10
A
v 6
0 =−μ
v 2 - v 1 = -2 μV = –0.002 mV 1 mV - v 1 = -0.002 mV v 1 = 1.002 mV
Chapter 5, Solution 5.
Av (^) d
v (^) i +
I
Rin
R 0
v (^) d
v (^0)
-
-vi + Avd + (Ri + R 0 ) I = 0 (1)
But vd = RiI,
-vi + (Ri + R 0 + RiA) I = 0
I =
0 i
i R ( 1 A)R
v
-Avd - R 0 I + v 0 = 0
v 0 = Avd + R 0 I = (R 0 + RiA)I = 0 i
0 i i R ( 1 A)R
(R RA)v
4 5
4 5
0 i
0 i
i
0 10 100 ( 1 10 )
100 10 x 10
R ( 1 A)R
R RA
v
v ⋅
4 5
9 10 1 10
Chapter 5, Problem 6
Using the same parameters for the 741 op amp in Example 5.1, find vo in the op amp
circuit of Fig. 5.45.
Figure 5.45 for Prob. 5.
Example 5.
A 741 op amp has an open-loop voltage gain of 2× 10
5 , input resistance of 2 MΩ, and
output resistance of 50Ω. The op amp is used in the circuit of Fig. 5.6(a). Find the closed-
loop gain vo/vs. Determine current i when vs = 2 V.
Chapter 5, Problem 7
The op amp in Fig. 5.46 has Ri = 100 kΩ, Ro = 100 Ω , A = 100 , 000. Find the differential
voltage vd and the output voltage vo.
+
-
Figure 5.46 for Prob. 5.
