Analog Integrated Circuits
Question 1
Don’t just sit there! Build something!! |
You will learn much more by actually building and analyzing real circuits, letting your test equipment provide the “answers” instead of a book or another person. For successful circuit-building exercises, follow these steps:
- Carefully measure and record all component values prior to circuit construction.
- Draw the schematic diagram for the circuit to be analyzed.
- Carefully build this circuit on a breadboard or other convenient medium.
- Check the accuracy of the circuit’s construction, following each wire to each connection point, and verifying these elements one-by-one on the diagram.
- Mathematically analyze the circuit, solving for all voltage and current values.
- Carefully measure all voltages and currents, to verify the accuracy of your analysis.
- If there are any substantial errors (greater than a few percent), carefully check your circuit’s construction against the diagram, then carefully re-calculate the values and re-measure.
As usual, avoid very high and very low resistor values, to avoid measurement errors caused by meter “loading”. I recommend resistor values between 1 kΩ and 100 kΩ.
One way you can save time and reduce the possibility of error is to begin with a very simple circuit and incrementally add components to increase its complexity after each analysis, rather than building a whole new circuit for each practice problem. Another time-saving technique is to re-use the same components in a variety of different circuit configurations. This way, you won’t have to measure any component’s value more than once.
Question 2
In very simple, qualitative terms, rate the
impedance of capacitors and inductors as “seen” by low-frequency and
high-frequency signals alike:
- Capacitor as it “appears” to a low frequency signal: (high or low) impedance?
- Capacitor as it “appears” to a high frequency signal: (high or low) impedance?
- Inductor as it “appears” to a low frequency signal: (high or low) impedance?
- Inductor as it “appears” to a high frequency signal: (high or low) impedance?
Question 3
Question 4
Question 5
Question 6
Real filters never exhibit perfect
“square-edge” Bode plot responses. A typical low-pass filter circuit,
for example, might have a frequency response that looks like this:
What does the term rolloff refer to, in the context of filter circuits and Bode plots? Why would this parameter be important to a technician or engineer?
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Question 7
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Question 9
Question 10
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Question 14
Describe what will happen to the impedance of both the capacitor and the resistor as the input signal frequency increases:
Also, describe what result the change in impedances will have on the
op-amp circuit’s voltage gain. If the input signal amplitude remains
constant as frequency increases, what will happen to the amplitude of
the output voltage? What type of filtering function does this behavior
represent?
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Question 15
Describe what will happen to the impedance of both the capacitor and the resistor as the input signal frequency increases:
Also, describe what result the change in impedances will have on the
op-amp circuit’s voltage gain. If the input signal amplitude remains
constant as frequency increases, what will happen to the amplitude of
the output voltage? What type of filtering function does this behavior
represent?
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Question 16
Approximate the voltage gains of this active filter circuit at f = 0 and f = ∞ (assume ideal op-amp behavior):
Approximate the voltage gains of this other “active filter” circuit at f = 0 and f = ∞ (assume ideal op-amp behavior):
What type of filtering function (low pass, high pass, band pass,
band stop) is provided by both these filter circuits? Comparing these
two circuit designs, which one do you think is more practical? Explain
your answer.
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Question 17
Approximate the voltage gains of this active filter circuit at f = 0 and f = ∞ (assume ideal op-amp behavior):
Approximate the voltage gains of this other “active filter” circuit at f = 0 and f = ∞ (assume ideal op-amp behavior):
What type of filtering function (low pass, high pass, band pass,
band stop) is provided by both these filter circuits? Comparing these
two circuit designs, which one do you think is more practical? Explain
your answer.
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Question 18
Question 19
Question 20
Question 21
Question 22
Choose appropriate values for this Sallen-Key
high-pass filter circuit to give it a cutoff frequency of 7 kHz with a
“Butterworth” response:
A good guideline to follow is to make sure no component impedance (ZR or ZC) at the cutoff frequency is less than 1 kΩ or greater than 100 kΩ.
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Question 23
Choose appropriate values for this Sallen-Key
low-pass filter circuit to give it a cutoff frequency of 4.2 kHz with a
“Butterworth” response:
A good guideline to follow is to make sure no component impedance (ZR or ZC) at the cutoff frequency is less than 1 kΩ or greater than 100 kΩ.
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Question 24
A popular passive filtering network called the twin-tee is often coupled with an operational amplifier to produce an active filter circuit. Two examples are shown here:
Identify which of these circuits is band-pass, and which is
band-stop. Also, identify the type of response typically provided by the
twin-tee network alone, and how that response is exploited to make two different types of active filter responses.
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Question 25
Singers who wish to practice singing to popular music find that the following vocal eliminator circuit is useful:
The circuit works on the principle that vocal tracks are usually
recorded through a single microphone at the recording studio, and thus
are represented equally on each channel of a stereo sound system. This
circuit effectively eliminates the vocal track from the song, leaving
only the music to be heard through the headphone or speaker.
Operational amplifiers U1 and U2 provide input buffering so that the other opamp circuits do not excessively load the left and right channel input signals. Opamp U3 performs the subtraction function necessary to eliminate the vocal track.
You might think that these three opamps would be sufficient to make a vocal eliminator circuit, but there is one more necessary feature. Not only is the vocal track common to both left and right channels, but so is most of the bass (low-frequency) tones. Thus, the first three opamps (U1, U2, and U3) eliminate both vocal and bass signals from getting to the output, which is not what we want.
Explain how the other three opamps (U4, U5, and U6) work to restore bass tones to the output so they are not lost along with the vocal track.
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Operational amplifiers U1 and U2 provide input buffering so that the other opamp circuits do not excessively load the left and right channel input signals. Opamp U3 performs the subtraction function necessary to eliminate the vocal track.
You might think that these three opamps would be sufficient to make a vocal eliminator circuit, but there is one more necessary feature. Not only is the vocal track common to both left and right channels, but so is most of the bass (low-frequency) tones. Thus, the first three opamps (U1, U2, and U3) eliminate both vocal and bass signals from getting to the output, which is not what we want.
Explain how the other three opamps (U4, U5, and U6) work to restore bass tones to the output so they are not lost along with the vocal track.
Question 26
Predict how the operation of this active filter
circuit will be affected as a result of the following faults. Consider
each fault independently (i.e. one at a time, no multiple faults):
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- Resistor R1 fails open:
- Capacitor C1 fails open:
- Solder bridge (short) across resistor R1:
- Solder bridge (short) across capacitor C1:
- Resistor R2 fails open:
- Resistor R3 fails open:
Question 27
Predict how the operation of this active filter
circuit will be affected as a result of the following faults. Consider
each fault independently (i.e. one at a time, no multiple faults):
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- Resistor R1 fails open:
- Capacitor C1 fails open:
- Solder bridge (short) across resistor R1:
- Solder bridge (short) across capacitor C1:
- Resistor R2 fails open:
- Resistor R3 fails open:
Question 28
Predict how the operation of this active
differentiator circuit will be affected as a result of the following
faults. Consider each fault independently (i.e. one at a time, no
multiple faults):
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- Resistor R1 fails open:
- Capacitor C1 fails open:
- Solder bridge (short) across resistor R1:
- Solder bridge (short) across capacitor C1:
Question 29
Predict how the operation of this active filter
circuit will be affected as a result of the following faults. Consider
each fault independently (i.e. one at a time, no multiple faults):
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- Resistor R1 fails open:
- Resistor R2 fails open:
- Capacitor C1 fails open:
- Solder bridge (short) across resistor R1:
- Solder bridge (short) across resistor R2:
- Solder bridge (short) across capacitor C1:
Question 30
Predict how the operation of this active filter
circuit will be affected as a result of the following faults. Consider
each fault independently (i.e. one at a time, no multiple faults):
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- Resistor R1 fails open:
- Resistor R2 fails open:
- Capacitor C1 fails open:
- Solder bridge (short) across resistor R1:
- Solder bridge (short) across resistor R2:
- Solder bridge (short) across capacitor C1:
Question 31
This vocal eliminator circuit used to work just
fine, but then one day it seemed to lose a lot of its bass. It still
did its job of eliminating the vocal track, but instead of hearing the
full range of musical tones it only reproduced the high frequencies,
while the low frequency tones were lost:
Identify the following fault possibilities:
One resistor failure (either open or shorted) that could cause this to happen:
One capacitor failure (either open or shorted) that could cause this to happen:
One opamp failure that could cause this to happen:
For each of these proposed faults, explain why the bass tones would be lost.
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One resistor failure (either open or shorted) that could cause this to happen:
One capacitor failure (either open or shorted) that could cause this to happen:
One opamp failure that could cause this to happen:
For each of these proposed faults, explain why the bass tones would be lost.
Question 32
This vocal eliminator circuit used to work just
fine, but then one day it stopped eliminating the vocal track. The tone
of the music sounded a bit heavy on the bass, and the vocal track was
there when it shouldn’t have been there:
Identify the following fault possibilities:
One resistor failure (either open or shorted) that could cause this to happen:
One opamp failure that could cause this to happen:
For each of these proposed faults, explain why the bass tones would be lost.
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One resistor failure (either open or shorted) that could cause this to happen:
One opamp failure that could cause this to happen:
For each of these proposed faults, explain why the bass tones would be lost.
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