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WorksheetsElectronics#4: Feedback & Oscillator Circuit
Total questions: 53
Worksheet time: 31mins
Which of the following improvements is (are) a result of the negative feedback in a circuit?
Higher input impedance
Better stabilized voltage gain
Improved frequency response
All of the above
Which of the following improvements is (are) a result of the negative feedback in a circuit?
Lower output impedance
Reduced noise
More linear operation
All of the above
Which of the following is (are) feedback?
Voltage-series
Voltage-shunt
Current-series
All of the above
What is the ratio of the input impedance with series feedback to that without feedback?
1 + βA
βA
β
1
What is the ratio of the output impedance with series feedback to that without feedback?
1
1 + βA
βA
A
The frequency distortion arising because of varying amplifier gain with frequency is considerably reduced in a negative-voltage feedback amplifier circuit.
True
False
Which of the following is (are) the determining factor(s) of the stability of a feedback amplifier?
A
Phase shift between input and output signals
Both A and the phase shift between input and output signals
None of the above
At what phase shift is the magnitude of βA at its maximum in the Nyquist plot?
90°
180°
270°
0°
At what phase shift is the magnitude of βA at its minimum in the Nyquist plot?
90°
180°
270°
0°
The Nyquist plot combines the two Bode plots of gain versus frequency and phase shift versus frequency on a single plot.
True
False
The amplifier is unstable if the Nyquist curve plotted encloses (encircles) the –1 point, and it is stable otherwise.
True
False
Which of the following is required for oscillation?
βA > 1
The phase shift around the feedback network must be 180º.
Both βA > 1 and the phase shift around the feedback network must be 180°.
None of the above
An input signal is needed for an oscillator to start.
True
False
Only the condition βA = _____ must be satisfied for self-sustained oscillations to result.
0
–1
1
None of the above
In the IC phase-shift oscillator, what should the ratio of feedback resistor Rf to R1 be?
Zero
Greater than –29
Less than 29
Any value
For a phase-shift oscillator, the gain of the amplifier stage must be greater than ________.
19
29
30
1
Which of the following oscillators is (are) tuned oscillators?
Colpitts
Hartley
Crystal
All of the above
What is the typical value of quality factor for crystal oscillators?
20,000
1000
100
10
Negative feedback results in ________.
decreased voltage gain
increased voltage gain
oscillation in the circuit
None of the above
Positive feedback results in _________.
decreased voltage gain
increased voltage gain
oscillation in the circuit
None of the above
Series-feedback connections tend to _______ the input resistance. Shunt feedback connections tend to ________ the input resistance.
decrease, increase
increase, decrease
increase, increase
decrease, decrease
Voltage feedback connections tend to ________ the output impedance. Current feedback connections tend to ________ the output impedance.
decrease, increase
increase, decrease
increase, increase
decrease, decrease
With feedback, β, the overall gain of the circuit is reduced by a factor _______ where A is the gain without the feedback.
β
Aβ
A
1 + βA
An amplifier with negative feedback has _______ bandwidth than (as) the amplifier without feedback.
the same
less
more
None of the above
A feedback amplifier has a _______ upper 3-dB frequency and a _______ lower 3-dB frequency compared to an amplifier without feedback.
smaller, higher
higher, smaller
smaller, smaller
higher, higher
What is the gain at the origin of the Nyquist plot?
Zero
A negative value
A positive value
Undefined
In a Nyquist plot, as the frequency increases, the phase shift between input and output signals _______.
remains the same
decreases
increases
None of the above
An amplifier is stable if the absolute magnitude of βA is _______.
∞
less than 1
greater than 1
None of the above
In the Barkhausen criterion, the loop gain A is equal to _______.
∞
200,000
0
1
In practice, A is made _______ and the system is started oscillating by amplifying noise voltage, which is always present.
greater than 1
smaller than 1
equal to 1
None of the above
In the phase-shift oscillator, the gain of the amplifier stage must be _______.
0
less than 29
greater than 29
∞
In the phase-shift oscillator, the operating frequency is determined by _______.
resistance only
capacitance only
LC combinations
RC combinations
In the Colpitts oscillator, the frequency is determined by _______ .
resistance only
inductance only
capacitance only
both inductance and a capacitance
Crystal oscillators are used whenever a(n) _______ level of stability is required.
lower
average
greater
None of the above
Since the crystal losses represented by R are small, the equivalent crystal Q (quality factor) is _______.
very low
low
medium
high
The series-resonant impedance of a crystal oscillator is _______.
very low
low
medium
very high
The parallel-resonant impedance of a crystal oscillator is _______.
very low
low
medium
very high
At the series-resonant frequency, the amount of positive feedback is _______.
very large
large
small
very small
_______ is a frequency-determining component in a unijunction oscillator.
Total resistance
Total capacitance
Intrinsic stand-off ratio
All of the above
Typically, a unijunction transistor has a stand-off ratio from _____ to _____.
0.0, 0.2
0.2, 0.4
0.4, 0.6
0.6, 0.8
What is the level of the output voltage of a ladder-network conversion?
The analog output voltage proportional to the digital input voltage
The digital output voltage proportional to the linear input voltage
A fixed analog value Vref
A fixed digital value Vref
Which of the following is not a linear/digital IC?
Phase-locked loop
Voltage-controlled oscillator
Comparator
Passive filter
A 339 IC is an example of a fourteen-pin DIP that can be made to function as a ________.
comparator
555 timer
ladder network
D to A converter
Which of the following is (are) the results of improvements built into a comparator IC?
Faster switching between the two output levels
Noise immunity
Outputs capable of directly driving a variety of loads
All of the above
The Op-amp can amplify
a.c. signals only
both a.c. and d.c. signals
neither d.c. nor a.c. signals
d.c. signals only
The node voltage at the top of the til resistor is closes to ……….
collector supply voltage
zero
tail current times base resistance
emitter supply voltage
By how much does the output signal vary for a class AB power amplifier?
360°
Between 180° and 360°
Less than 180°
180°
Which type of power amplifier is biased for operation at less than 180º of the cycle?
Class C
Class A
Class D
Class B or AB
Which type of amplifier uses pulse (digital) signals in its operation?
Class A
Class C
Class B or AB
Class D
At which of the following period(s) is the counter advanced (incremented) in dual-slope conversion?
During the charging of the capacitor of the integrator
During the discharging of the capacitor of the integrator
During both the charging and discharging of the capacitor of the integrator
None of the above
At a party, everyone shook hands with everybody else. There were 66 handshakes. How many people were at the party?
(a)
It's dark. You have ten grey socks and ten blue socks you want to put into pairs. All socks are exactly the same except for their colour. How many socks would you need to take with you to ensure you had at least a pair?
(a)
My grandson is about as many days as my daughter in weeks, and my grandson is as many months as I am in years. My grandson, my daughter and I together are 120 years. Can you tell me my age in years ?
(a)
