Deck 21: Oscillators Key

Question 1

RC oscillators can produce almost perfect sine waves at frequencies above 1 MHz.

Answer 1

False

Question 2

A frequency change of an oscillator over time caused by temperature,aging,and other causes is referred to as ________.

A) resonance
B) modulation
C) shift
D) drift

Answer 2

D

Question 3

A crystal oscillator that is designed to reduce the effect of stray capacitances is the ________.

A) Colpitts
B) Armstrong
C) FET Clapp
D) Pierce

Answer 3

C

Question 4

Which is not a mode of operation for the 555 timer?

A) astable
B) free running
C) bi-stable
D) monostable

Question 5

In a phase-shift oscillator,the lead circuits produce a 180° shift and the amplifier provides the additional 180° necessary for oscillation.

Question 6

A Hartley oscillator uses a tapped resistor to provide the feedback signal.

Question 7

The capacitive or link coupling loading effect is kept as high as possible to ensure an undistorted sinusoidal output.

Question 8

A twin-T filter acts like a lead-lag circuit with a changing phase angle.

Question 9

When accuracy and stability of oscillation frequency are important,a quartz-crystal oscillator is used.

Question 10

What is exhibited when an ac voltage placed across a crystal causes it to vibrate at the frequency of the applied voltage?

A) a modulating signal
B) a fundamental frequency
C) a harmonic frequency
D) the piezoelectric effect

Question 11

An Armstrong oscillator uses transformer coupling for the feedback signal and can be recognized by a small secondary winding sometimes called a tickler coil.

Question 12

The Colpitts oscillator is recognized by the capacitive voltage divider used to produce feedback necessary for oscillations.

Question 13

Higher resonant frequencies which are almost exact multiples of a fundamental frequency are called ________.

A) carriers
B) overtones
C) oscillations
D) cosine waves

Question 14

When using an FET oscillator,the loading effect on the tank circuit is much less than with a bipolar transistor.

Question 15

The twin-T oscillator is popular because it works well at many frequencies.

Question 16

Most designers use computers to model high-frequency oscillators.

Question 17

The Wien-bridge oscillator is the standard oscillator for frequencies in the range of 5 Hz to about 1 MHz.

Question 18

The frequency where the output of a lead-lag circuit is maximum is called the resonant frequency.

Question 19

Above 1 MHz,oscillators use transistors and the frequency of oscillation is determined by LC resonant circuits.

Question 20

A sinusoidal oscillator is basically an amplifier with negative feedback.

Question 21

Which of the following is not a waveform that can be generated by an IC function generator?

A) square
B) triangle
C) stereo
D) pulse

Question 22

A circuit that produces an output voltage proportional to the phase difference between two input signals is called the

A) VCO.
B) carrier.
C) multivibrator.
D) phase detector.

Question 23

When the 555 timer is used with only one stable state,it is referred to as

A) a monostable multivibrator.
B) an astable multivibrator.
C) a free running multivibrator.
D) a bi-stable multivibrator.

Question 24

A two-state circuit that has zero,one,or two stable output states is called

A) a multiplexer.
B) a multivibrator.
C) an oscillator.
D) bipolar transistor.

Question 25

An application of the 555 timer sometimes called a voltage-to-frequency converter because the input voltage changes the output frequency is the

A) quartz crystal oscillator.
B) twin-T oscillator.
C) astable multivibrator.
D) voltage-controlled oscillator.

Question 26

The span of input frequencies over which the VCO of a PLL can remain locked on to the input frequency is called the

A) VCO range.
B) lock range.
C) frequency range.
D) PLL range.

Question 27

When PWM is used in communications,what is the low-frequency signal such as voice or computer data called that is capacitively coupled to the 555 timer?

A) carrier
B) modulating signal
C) pulse-width signal
D) FM

Question 28

Some function generator ICs are well suited for electronic communications applications since they have an output impedance of ________.

A) 5000 Ω
B) 2.5 MΩ
C) 30 Ω
D) 600 Ω

Question 29

Charging a capacitor through a resistor produces

A) an exponential waveform.
B) a triangular waveform.
C) a sinusoidal waveform.
D) a truncated waveform.

Question 30

The oscillation frequency of an astable multivibrator is determined by

A) a diode and resistor.
B) a crystal.
C) two external resistors and one capacitor.
D) two external capacitors and one resistor.

Question 31

What type modulation exists when both the width and the period of the pulses vary with the modulating signal?

A) amplitude modulation
B) frequency modulation
C) pulse-position modulation
D) pulse-width modulation

Question 32

A phase-locked loop can be used as

A) an oscillator.
B) a voltage regulator.
C) an FM demodulator.
D) a multiplexer.

Question 33

Some phase-shift oscillator configurations use

A) one lead circuit to produce the required 180° of phase shift.
B) two lead circuits to produce the required 180° of phase shift.
C) four lead circuits to produce the required 180° of phase shift.
D) six lead circuits to produce the required 180° of phase shift.

Question 34

The output stage of a 555 timer can source ________.

A) 20 mA
B) 50 mA
C) 100 mA
D) 200 mA

Question 35

PWM allows a low-frequency modulating signal to change the pulse width of a high-frequency signal called the

A) carrier
B) modulating signal
C) pulse-width signal
D) FM

Question 36

When the 555 timer is operated with no stable states,it is called

A) a monostable multivibrator.
B) an astable multivibrator.
C) a bi-stable multivibrator.
D) a flip-flop.

Question 37

A flip-flop is another name for the

A) monostable multivibrator.
B) astable multivibrator.
C) free running multivibrator.
D) bi-stable multivibrator.

Question 38

A typical voltage-controlled oscillator can be varied over a

A) 10 to 1 range.
B) 100 to 1 range.
C) 1000 to 1 range.
D) 1 to 1 range.

Question 39

The monostable 555 timer circuit produces a single pulse whose width is determined by

A) the external resistor and capacitor used.
B) the trigger.
C) the value of the supply voltage.
D) the internal capacitance.

Question 40

An IC function generator cannot perform as which of the following?

A) voltage-to-frequency conversion
B) digital-to-analog conversion
C) voltage-controlled oscillator
D) frequency-shift keying

Question 41

RC oscillators can be used to produce almost perfect sine waves at frequencies

A) under 1 MHz.
B) of 5 MHz and 6 MHz.
C) above 2.5 MHz.
D) above 1 GHz.

Question 42

An Armstrong oscillator can be recognized by its

A) tickler coil secondary.
B) three lead circuits.
C) inductive voltage divider.
D) capacitive voltage divider.

Question 43

A phase-shift oscillator will oscillate if three lead circuits produce a total phase shift of ________.

A) 90°
B) 180°
C) 270°
D) 360°

Question 44

A Colpitts oscillator can be recognized by its

A) tickler coil secondary.
B) three lead circuits.
C) inductive voltage divider.
D) capacitive voltage divider.

Question 45

A standard oscillator circuit used for low to moderate frequencies in the range of 5 Hz to 1 MHz and the one almost always used in commercial audio generators is the ________.

A) Hartley
B) Armstrong
C) Wien-bridge
D) phase-shift

Question 46

The Wien-bridge oscillator uses a resonant feedback circuit called a

A) lead-lag circuit.
B) quartz crystal.
C) tuned tank.
D) notch circuit.

Question 47

A Hartley oscillator can be recognized by its

A) tickler coil secondary.
B) three lead circuits.
C) inductive voltage divider.
D) capacitive voltage divider.

Question 48

When accuracy and stability of the oscillation frequency are important,which oscillator is the best choice?

A) Armstrong
B) Colpitts
C) Hartley
D) quartz crystal

Question 49

An amplifier with positive feedback and no external input will

A) play music.
B) oscillate.
C) blow a fuse.
D) do nothing.

Question 50

LC oscillators can be used to produce almost perfect sine waves at frequencies

A) below 100 Hz.
B) below 1 KHz.
C) of 890 KHz and 990 KHz.
D) above 1 MHz.