Page 149 - Op Amps Design, Applications, and Troubleshooting

132 AMPLIFIERS

negative), then the op amp is probably bad. If no basic theory principles are
violated, check the following:
a. Correct input (especially the DC level)
b. Feedback path
c. Input path
Your most powerful troubleshooting tool when diagnosing op amp circuits
is a solid grasp of the basic theory of operation. Although the performance of op
amps can deteriorate in some ways, it is far more common for the device to exhibit
catastrophic failure.

REVIEW QUESTIONS

1, A certain amplifier has a voltage gain of 100. Express this gain in decibels.
2. Suppose the amplifier circuit shown in Figure 2.3 is altered to have the following values:

What is the voltage gain of the circuit with the new values? What happens to the
voltage gain if R L is decreased to 27 kilohms?
3. Refer to the amplifier circuit described in question 2. Compute the input impedance of
the circuit. Does the input impedance change if R L is reduced to 27 kilohms?
4. If a 741 op amp is powered by a ±15-volt supply, what is the largest voltage swing that
can be guaranteed on the output if the load is 18 kilohms? Repeat this question for a
2.0-kilohm load.
5. A certain op amp application requires a 5-volt RMS output voltage swing and operates
at a maximum sinewave frequency of 21.5 kilohertz. What is the minimum slew rate
for the op amp that will allow the signal to pass without substantial slew rate
distortion?
6. A simple noninverting amplifier (similar to Figure 2.12) has the following component
values:

Op amp 741
RI 4.7m
R F 68 fcQ
RL 18 kQ,
RB 4.3 kQ,

Compute the small signal bandwidth of the amplifier (ignore slew rate considera-
tions).