Q.1 What is the primary function of an oscillator in an electronic circuit?
Generate a steady DC voltage
Create a periodic AC signal
Amplify an input signal
Filter out noise
Explanation - An oscillator produces a continuous, periodic waveform (AC) without requiring a continuous input, used as clock, carrier, or reference.
Correct answer is: Create a periodic AC signal
Q.2 Which of the following is a key component of a simple RC phase‑shift oscillator?
Inductor
Capacitor
Transformer
Diode
Explanation - The RC phase‑shift oscillator uses capacitors and resistors to create the necessary phase shift; inductors are not used in this topology.
Correct answer is: Capacitor
Q.3 In an LC oscillator, the oscillation frequency is primarily determined by:
Resistor value
Capacitor value
Inductor value
Load impedance
Explanation - The resonant frequency of an LC tank is f = 1/(2π√(LC)), so both L and C matter, but changing L has a direct effect on f.
Correct answer is: Inductor value
Q.4 What type of oscillator uses a quartz crystal to provide frequency stability?
RC oscillator
LC oscillator
Crystal oscillator
VCO
Explanation - A crystal oscillator employs the piezoelectric effect of quartz to maintain a very stable resonant frequency.
Correct answer is: Crystal oscillator
Q.5 A voltage‑controlled oscillator (VCO) changes its output frequency in response to:
Input voltage
Temperature
Load current
Ambient noise
Explanation - A VCO’s tuning element (usually a varactor or MEMS capacitor) varies with the control voltage, altering the oscillation frequency.
Correct answer is: Input voltage
Q.6 Which of the following is NOT a typical application of oscillators?
Clock generation in digital systems
Signal carrier in radio transmitters
Analog-to-digital conversion reference
Power supply regulation
Explanation - Oscillators generate signals; power supply regulation uses voltage regulators, not oscillators.
Correct answer is: Power supply regulation
Q.7 The phase shift required for sustained oscillation in an RC phase‑shift oscillator is:
90°
180°
270°
360°
Explanation - For positive feedback, a 180° shift from the inverting amplifier plus an additional 90° from the RC network equals 270°, satisfying Barkhausen criterion.
Correct answer is: 270°
Q.8 Which parameter describes the rate at which oscillators lose amplitude in a closed loop?
Gain margin
Phase margin
Damping factor
Q factor
Explanation - Damping factor indicates how quickly oscillations die out; low damping means sustained oscillation.
Correct answer is: Damping factor
Q.9 A Wien‑bridge oscillator is most suitable for which frequency range?
DC to 10 kHz
10 kHz to 1 MHz
1 MHz to 10 MHz
Above 10 MHz
Explanation - Wien‑bridge oscillators are common for audio to low‑frequency RF but are limited above a few MHz by component tolerances.
Correct answer is: 10 kHz to 1 MHz
Q.10 Phase noise in an oscillator is best quantified in which of the following units?
Decibels relative to the carrier (dBc/Hz)
Hertz per second (Hz/s)
Volts per hertz (V/Hz)
Degrees per second (°/s)
Explanation - Phase noise is expressed as the power spectral density of phase fluctuations relative to the carrier, in dBc/Hz.
Correct answer is: Decibels relative to the carrier (dBc/Hz)
Q.11 In a crystal oscillator, the dominant factor determining the resonant frequency is:
Crystal mass
Crystal temperature
Crystal cut orientation
Crystal geometry
Explanation - The cut determines the piezoelectric stiffness and thus the resonant frequency, more so than mass or geometry within the same cut.
Correct answer is: Crystal cut orientation
Q.12 Which of the following is a major source of temperature drift in LC oscillators?
Resistor tolerance
Inductor core permeability
Capacitor dielectric loss
Supply voltage ripple
Explanation - Inductor permeability varies with temperature, altering L and thus the resonant frequency of LC oscillators.
Correct answer is: Inductor core permeability
Q.13 In a PLL, the VCO is typically:
Frequency locked to the reference
Independent of the phase detector output
A linear amplifier
A high‑Q crystal oscillator
Explanation - The PLL locks the VCO’s frequency to the reference by adjusting its control voltage to match the phase error.
Correct answer is: Frequency locked to the reference
Q.14 What is the role of the phase detector in a PLL?
Generate the reference clock
Compare phases and output error signal
Filter the error signal
Provide power to the VCO
Explanation - The phase detector measures the phase difference between reference and feedback signals and produces an error voltage.
Correct answer is: Compare phases and output error signal
Q.15 The loop bandwidth of a PLL determines:
Maximum oscillation amplitude
Response speed and noise performance
Frequency stability only
Only the phase margin
Explanation - A wider bandwidth allows faster lock but passes more phase noise; a narrower bandwidth improves noise rejection.
Correct answer is: Response speed and noise performance
Q.16 Which component is commonly used to provide negative feedback in a Wien‑bridge oscillator?
Op‑amp
Transformer
Capacitor
Resistor network
Explanation - The Wien‑bridge network provides the 90° shift and an op‑amp supplies the necessary gain and feedback.
Correct answer is: Op‑amp
Q.17 The frequency of an LC tank is given by f = 1/(2π√(LC)). If L is doubled, the frequency will:
Remain the same
Double
Halve
Increase by √2
Explanation - f is inversely proportional to √L; doubling L reduces f by a factor of √2 ≈ 1.414, i.e., about halving.
Correct answer is: Halve
Q.18 A crystal oscillator’s temperature coefficient is:
Zero
Positive
Negative
Variable
Explanation - High‑quality crystals are designed to have very low (ideally zero) temperature coefficient of frequency.
Correct answer is: Zero
Q.19 Which statement best describes a VCO’s tuning curve?
It is linear over its entire range
It is linear near the center frequency
It is logarithmic
It is exponential
Explanation - A VCO is designed to have a nearly linear tuning characteristic around its nominal frequency for simplicity.
Correct answer is: It is linear near the center frequency
Q.20 In an oscillator, the Barkhausen criterion requires:
Loop gain > 1 and phase shift of 0°
Loop gain = 1 and phase shift of 360°
Loop gain < 1 and phase shift of 180°
Loop gain = 1 and phase shift of 0°
Explanation - For sustained oscillation, the net loop gain must be unity and the phase shift must be an integer multiple of 360°.
Correct answer is: Loop gain = 1 and phase shift of 360°
Q.21 Which oscillator topology is best suited for very low‑frequency audio applications?
Colpitts
Hartley
RC phase‑shift
Wien‑bridge
Explanation - RC phase‑shift oscillators can be easily tuned into low audio frequencies with simple RC networks.
Correct answer is: RC phase‑shift
Q.22 An oscillator’s output amplitude is typically stabilized by:
Adding a resistor in series
Using a negative feedback loop
Increasing supply voltage
Shorting the output to ground
Explanation - Negative feedback keeps the output at a set amplitude by reducing gain once the desired amplitude is reached.
Correct answer is: Using a negative feedback loop
Q.23 Which device is used to create a stable reference frequency for a PLL?
Crystal oscillator
RC oscillator
LC oscillator
VCO
Explanation - A crystal oscillator provides the low‑phase‑noise reference frequency that the PLL locks onto.
Correct answer is: Crystal oscillator
Q.24 Which of the following is a common issue when an oscillator is overloaded by the load?
Increased output power
Reduced phase noise
Amplitude distortion
Higher Q factor
Explanation - Heavy loading can pull the amplitude down and introduce distortion and frequency shift.
Correct answer is: Amplitude distortion
Q.25 A MEMS oscillator typically replaces which conventional component?
Resistor
Inductor
Capacitor
Transformer
Explanation - MEMS resonators replace traditional inductors to achieve higher Q and smaller size in RF applications.
Correct answer is: Inductor
Q.26 The term 'Q factor' in oscillators refers to:
Quality of the output waveform
Resonant frequency
Energy loss per cycle relative to stored energy
Amplitude of oscillation
Explanation - Q = (energy stored)/(energy lost per cycle); a higher Q means lower losses and a narrower bandwidth.
Correct answer is: Energy loss per cycle relative to stored energy
Q.27 Which type of oscillator uses a feedback network that provides a 90° phase shift?
RC phase‑shift
Wien‑bridge
LC Colpitts
Crystal
Explanation - The Wien‑bridge network consists of two RC stages that supply the required 90° phase shift for oscillation.
Correct answer is: Wien‑bridge
Q.28 A frequency‑synthesizer commonly uses which building block to multiply a reference frequency?
Phase‑locked loop (PLL)
Amplifier
Filter
Rectifier
Explanation - A PLL can multiply the input frequency by using a frequency divider in the feedback path.
Correct answer is: Phase‑locked loop (PLL)
Q.29 In an oscillator, the term 'amplitude stability' refers to:
Constant output amplitude over time
Consistent output waveform shape
Fixed frequency over temperature
No harmonic distortion
Explanation - Amplitude stability ensures the signal stays within a narrow range without drifting due to component changes.
Correct answer is: Constant output amplitude over time
Q.30 The main difference between a crystal oscillator and a quartz resonator is:
Crystal oscillators are larger
Quartz resonators are used for low‑frequency applications
Crystal oscillators provide active feedback
Quartz resonators are passive devices
Explanation - A quartz resonator is just a resonant element, whereas a crystal oscillator includes an active stage to sustain oscillation.
Correct answer is: Quartz resonators are passive devices
Q.31 Which of the following best describes phase noise in a VCO?
It is constant across all offset frequencies
It increases with VCO tuning voltage
It is negligible at high frequencies
It is independent of the control voltage
Explanation - Higher control voltages typically increase the VCO’s sensitivity to voltage fluctuations, raising phase noise.
Correct answer is: It increases with VCO tuning voltage
Q.32 The 'load pull' of an oscillator refers to:
Change in frequency with load impedance
Maximum load the oscillator can drive
Input impedance of the oscillator
Power consumption when loaded
Explanation - 'Load pull' describes how the oscillator’s resonant frequency shifts when the load impedance changes.
Correct answer is: Change in frequency with load impedance
Q.33 Which circuit element is commonly used in a Colpitts oscillator to provide the feedback network?
Capacitor divider
Inductor divider
Resistor divider
Transformer
Explanation - The Colpitts oscillator uses a capacitive voltage divider for feedback, with the inductor forming the tank.
Correct answer is: Capacitor divider
Q.34 Phase noise at 1 kHz offset from the carrier is:
Typically lower than at 10 kHz offset
Independent of oscillator design
Always the same for all oscillators
Higher than at 100 Hz offset
Explanation - Phase noise generally increases with offset frequency; 1 kHz is lower offset than 10 kHz, so noise is usually less.
Correct answer is: Typically lower than at 10 kHz offset
Q.35 Which of these is NOT a characteristic of a crystal oscillator?
High Q factor
Temperature stability
Large frequency drift
Narrow bandwidth
Explanation - Crystal oscillators are prized for low drift; a large drift would defeat their purpose.
Correct answer is: Large frequency drift
Q.36 In a PLL, the 'loop filter' primarily performs which function?
Generate a reference clock
Filter the phase detector output to control VCO
Amplify the VCO signal
Detect the phase error
Explanation - The loop filter smooths the error signal from the phase detector before it is used to drive the VCO.
Correct answer is: Filter the phase detector output to control VCO
Q.37 An oscillator that uses a 4‑pole LC tank is known as a:
Hartley
Colpitts
Clapp
Stern‑Gerlach
Explanation - The Hartley oscillator typically uses a 4‑pole LC network with an inductor split by a tapped coil.
Correct answer is: Hartley
Q.38 The term 'loop gain' in oscillators refers to:
Gain of the amplifier alone
Total product of amplifier gain and feedback factor
Voltage gain at the output
Frequency response slope
Explanation - Loop gain is the combined effect of the active and passive components that determines oscillation.
Correct answer is: Total product of amplifier gain and feedback factor
Q.39 Which of the following is a common technique to reduce oscillator phase noise?
Add more resistors in the tank
Use a higher‑Q resonator
Increase the supply voltage
Short the output to ground
Explanation - Higher Q reduces energy loss per cycle, thus lowering phase noise.
Correct answer is: Use a higher‑Q resonator
Q.40 What is the main disadvantage of an RC phase‑shift oscillator compared to an LC oscillator?
Higher Q
Higher power consumption
Lower frequency range
More complex design
Explanation - RC oscillators are limited by RC time constants and cannot achieve the same high frequencies as LC oscillators.
Correct answer is: Lower frequency range
Q.41 A 'temperature compensated crystal oscillator' (TCXO) is designed to:
Maintain a constant temperature
Adjust frequency with temperature changes
Operate only at a fixed temperature
Compensate for voltage variations
Explanation - TCXOs include circuitry that counters the temperature drift of the crystal’s frequency.
Correct answer is: Adjust frequency with temperature changes
Q.42 Which oscillator type is typically used in a watch face?
RC phase‑shift
LC Colpitts
Quartz crystal
MEMS resonator
Explanation - Quartz crystals provide the necessary precision and stability for time‑keeping devices.
Correct answer is: Quartz crystal
Q.43 A 'frequency‑modulated oscillator' (FMO) is:
An oscillator with fixed frequency
An oscillator whose frequency varies with input voltage
An oscillator used only for AM
An oscillator that does not oscillate
Explanation - FMOs change their output frequency in response to a control voltage, enabling frequency modulation.
Correct answer is: An oscillator whose frequency varies with input voltage
Q.44 Which factor most directly affects the bandwidth of an oscillator’s output?
Supply voltage
Component Q factor
Load impedance
Temperature stability
Explanation - Higher Q results in a narrower bandwidth; low Q yields a broader frequency response.
Correct answer is: Component Q factor
Q.45 In a VCO, the 'varactor' is used to:
Increase the output power
Control the frequency by varying capacitance
Reduce the phase noise
Provide bias voltage
Explanation - A varactor’s capacitance changes with applied voltage, tuning the LC tank and thus the oscillation frequency.
Correct answer is: Control the frequency by varying capacitance
Q.46 The 'phase margin' in a PLL determines:
Maximum frequency deviation
Stability of the closed‑loop system
Amplitude of the VCO output
Bandwidth of the loop filter
Explanation - A higher phase margin ensures the PLL does not oscillate or overshoot when locking.
Correct answer is: Stability of the closed‑loop system
Q.47 Which component is typically used to limit the amplitude of an LC oscillator?
Resistor in series with the tank
Capacitive divider
Non‑linear device such as a diode
Inductor with high Q
Explanation - A non‑linear element introduces gain compression that stabilizes amplitude.
Correct answer is: Non‑linear device such as a diode
Q.48 What is the primary advantage of using a MEMS resonator in a VCO?
Higher power consumption
Lower frequency stability
Reduced size and improved temperature stability
More complex packaging
Explanation - MEMS resonators offer small form factor and low drift across temperature ranges.
Correct answer is: Reduced size and improved temperature stability
Q.49 In a crystal oscillator, the 'frequency pulling' effect is caused by:
Load impedance changes
Temperature variations
Supply voltage fluctuations
All of the above
Explanation - Pulling refers to small changes in resonant frequency caused by various external influences.
Correct answer is: All of the above
Q.50 Which of the following is NOT a typical feature of a digital PLL?
Zero‑phase error at lock
Discrete frequency tuning
Use of an analog VCO
Frequency division in the feedback path
Explanation - Digital PLLs normally employ a digital VCO or digitally controlled oscillator, not an analog one.
Correct answer is: Use of an analog VCO
Q.51 In a crystal oscillator, the 'guard band' refers to:
Frequency range above the target frequency
Margin of stability against load changes
Safety margin for the oscillator’s power supply
The frequency of the crystal’s overtone
Explanation - The guard band ensures the oscillator remains stable even with load impedance variations.
Correct answer is: Margin of stability against load changes
Q.52 A 'harmonic‑free oscillator' is designed to produce:
Multiple harmonics of the fundamental frequency
Only the fundamental frequency
A wideband signal
A low‑frequency square wave
Explanation - Harmonic‑free oscillators suppress higher frequency components to maintain a clean sine wave.
Correct answer is: Only the fundamental frequency
Q.53 Which component in a Colpitts oscillator primarily determines the resonant frequency?
Capacitor divider
Inductor
Resistor network
Op‑amp gain
Explanation - The LC tank’s inductor and capacitors together set the oscillation frequency in a Colpitts design.
Correct answer is: Inductor
Q.54 A 'phase‑locked loop' (PLL) is used to:
Generate random noise
Synchronize an oscillator to a reference frequency
Amplify low‑level signals
Convert analog to digital
Explanation - A PLL forces an oscillator to track a reference clock in frequency and phase.
Correct answer is: Synchronize an oscillator to a reference frequency
Q.55 Which type of oscillator is most likely to have the lowest phase noise?
RC phase‑shift
LC Colpitts
Quartz crystal
MEMS resonator
Explanation - Quartz crystals offer the highest Q and thus the lowest phase noise among common oscillators.
Correct answer is: Quartz crystal
Q.56 In an oscillator, the 'frequency pull' caused by a change in supply voltage is also known as:
Voltage‑frequency conversion
Power supply rejection ratio
Power‑frequency coupling
Supply‑pull effect
Explanation - Supply‑pull describes frequency variation with supply voltage, a key spec for oscillator performance.
Correct answer is: Supply‑pull effect
Q.57 Which of the following is a typical load impedance for an LC oscillator?
1 Ω
50 Ω
1 kΩ
100 kΩ
Explanation - LC oscillators are often designed to drive standard 50 Ω systems, such as RF front‑ends.
Correct answer is: 50 Ω
Q.58 The 'phase noise floor' of an oscillator is primarily determined by:
Supply voltage ripple
Temperature coefficient
Resonator Q factor
Output power
Explanation - Higher Q reduces intrinsic noise, lowering the phase noise floor.
Correct answer is: Resonator Q factor
Q.59 What is the function of a 'loop filter' in a PLL?
Generate a reference clock
Set the division ratio in the feedback path
Filter the phase detector output to smooth VCO control
Detect the phase error
Explanation - The loop filter shapes the error signal to control the VCO, balancing bandwidth and noise.
Correct answer is: Filter the phase detector output to smooth VCO control
Q.60 A 'Hartley oscillator' uses:
A tapped inductor for feedback
Two capacitors for phase shift
A varactor diode for tuning
A crystal for stability
Explanation - The Hartley oscillator’s inductor is split, providing the required feedback and resonant network.
Correct answer is: A tapped inductor for feedback
Q.61 Which of the following is a key benefit of using a crystal oscillator over an LC oscillator?
Higher power output
Lower cost
Better frequency stability
Larger size
Explanation - Crystals provide superior frequency stability due to the high Q of the quartz resonator.
Correct answer is: Better frequency stability
Q.62 In an oscillator circuit, the term 'gain margin' refers to:
The maximum allowable gain before oscillation starts
The difference between actual gain and required gain for oscillation
The amount of gain left for the amplifier
The ratio of output to input voltage
Explanation - Gain margin indicates how much the loop gain can change before oscillations cease.
Correct answer is: The difference between actual gain and required gain for oscillation
Q.63 Which of these is NOT a type of frequency synthesizer?
Direct digital synthesizer (DDS)
Phase‑locked loop (PLL)
Voltage‑controlled oscillator (VCO)
Frequency multiplier chain
Explanation - A VCO is a component used by synthesizers, not a synthesizer itself.
Correct answer is: Voltage‑controlled oscillator (VCO)
Q.64 The 'quality factor' (Q) of an LC tank is defined as:
Resistance over inductance
Inductance over resistance
Resonant frequency times the inductance
Resonant frequency divided by bandwidth
Explanation - Q = f₀ / BW, measuring how narrow the resonance is.
Correct answer is: Resonant frequency divided by bandwidth
Q.65 Which component is most responsible for the stability of a crystal oscillator?
Capacitor network
Resistor divider
Crystal resonator itself
Op‑amp biasing
Explanation - The quartz resonator’s properties dominate the oscillator’s frequency stability.
Correct answer is: Crystal resonator itself
Q.66 A 'Wien‑bridge oscillator' typically uses:
An LC tank
An RC phase‑shift network
A crystal
A varactor diode
Explanation - The Wien‑bridge network supplies the required 90° phase shift for oscillation in the circuit.
Correct answer is: An RC phase‑shift network
Q.67 Which of the following best describes the 'loop bandwidth' in a PLL?
The range of frequencies the VCO can generate
The range of frequencies over which the PLL can lock
The bandwidth of the phase detector
The bandwidth of the loop filter
Explanation - Loop bandwidth sets how fast the PLL can respond and how much frequency deviation it can correct.
Correct answer is: The range of frequencies over which the PLL can lock
Q.68 In a crystal oscillator, what does the 'pulling' effect refer to?
Change in resonant frequency with load
Frequency drift due to temperature
Power consumption changes
Variation in output amplitude
Explanation - Pulling is the shift in oscillation frequency caused by changes in load or other environmental factors.
Correct answer is: Change in resonant frequency with load
Q.69 Which of the following is a characteristic of a VCO in a PLL?
Fixed frequency output
Frequency changes with control voltage
No output amplitude control
Used only in analog circuits
Explanation - The VCO is tuned by an external voltage, enabling dynamic frequency adjustment.
Correct answer is: Frequency changes with control voltage
Q.70 The 'phase noise figure' is expressed as a function of:
Amplitude
Frequency offset
Temperature
Supply voltage
Explanation - Phase noise is plotted versus offset from the carrier frequency to illustrate the noise spectral density.
Correct answer is: Frequency offset
Q.71 Which type of oscillator uses a crystal to provide frequency stability?
RC phase‑shift
LC colpitts
Crystal oscillator
VCO
Explanation - A crystal oscillator uses the quartz crystal's piezoelectric effect for stable frequency.
Correct answer is: Crystal oscillator
Q.72 The 'temperature coefficient' of a quartz crystal is:
Zero
Positive
Negative
Depends on frequency
Explanation - High‑quality quartz crystals are designed to have a very low, almost zero, temperature coefficient.
Correct answer is: Zero
Q.73 What does a 'phase‑shift network' in an oscillator do?
Provide the necessary gain
Generate the feedback signal
Introduce a phase shift to satisfy Barkhausen
Stabilize the amplitude
Explanation - The network adds phase shift to meet the 360° condition for sustained oscillation.
Correct answer is: Introduce a phase shift to satisfy Barkhausen
Q.74 A 'frequency synthesizer' typically uses:
A single crystal oscillator
A PLL with a VCO and frequency dividers
A fixed‑frequency LC tank
A resistor divider chain
Explanation - Synthesizers generate a wide range of frequencies using a PLL architecture.
Correct answer is: A PLL with a VCO and frequency dividers
Q.75 Which of these is NOT a typical application of oscillators?
Clock generation in microcontrollers
Radio transmitter carrier generation
Power supply regulation
Signal reference for PLLs
Explanation - Oscillators generate signals, not regulate DC power.
Correct answer is: Power supply regulation
Q.76 The 'load pull' of an oscillator refers to:
Change in frequency with load impedance
Maximum load the oscillator can drive
Input impedance of the oscillator
Power consumption when loaded
Explanation - Load pull measures frequency shift due to changes in the connected load.
Correct answer is: Change in frequency with load impedance
Q.77 Which component in an LC oscillator is typically selected for its high Q?
Resistor
Inductor
Capacitor
Op‑amp
Explanation - High‑Q inductors provide low loss, essential for a stable LC oscillator.
Correct answer is: Inductor
Q.78 In a phase‑locked loop, the 'phase detector' performs what function?
Generate the reference clock
Amplify the signal
Detect phase difference and produce an error voltage
Filter the VCO output
Explanation - It compares reference and feedback signals, generating an error signal for the VCO.
Correct answer is: Detect phase difference and produce an error voltage
Q.79 Which type of oscillator is known for having the lowest phase noise at high frequencies?
RC phase‑shift
LC colpitts
Quartz crystal
MEMS resonator
Explanation - Quarz crystals have extremely high Q, leading to very low phase noise.
Correct answer is: Quartz crystal
Q.80 The 'loop filter' in a PLL is usually:
A low‑pass filter
A high‑pass filter
A band‑stop filter
An all‑pass filter
Explanation - A low‑pass filter smooths the error signal, controlling the VCO speed and noise.
Correct answer is: A low‑pass filter
Q.81 The 'phase noise floor' of an oscillator is set primarily by:
Supply voltage ripple
Temperature coefficient
Resonator Q factor
Load impedance
Explanation - Higher Q reduces intrinsic noise, lowering the phase noise floor.
Correct answer is: Resonator Q factor
Q.82 Which of the following best describes a crystal oscillator’s temperature stability?
Highly unstable across temperature changes
Stable within ±10 ppm per °C
Stable within ±100 ppm per °C
Unpredictable drift
Explanation - High‑grade quartz crystals offer temperature stability on the order of 10 ppm/°C or better.
Correct answer is: Stable within ±10 ppm per °C
Q.83 In a VCO, what is the role of the 'varactor diode'?
Provide DC bias to the oscillator
Act as a variable capacitor for frequency tuning
Amplify the output signal
Control the oscillator’s amplitude
Explanation - The varactor’s capacitance changes with voltage, tuning the LC tank frequency.
Correct answer is: Act as a variable capacitor for frequency tuning
Q.84 Which of the following is a typical frequency range for a MEMS oscillator used in mobile phones?
50 kHz–100 kHz
1 MHz–10 MHz
100 MHz–500 MHz
1 GHz–5 GHz
Explanation - MEMS oscillators in mobile devices generally operate in the 1–10 MHz band for clock generation.
Correct answer is: 1 MHz–10 MHz
Q.85 Which type of oscillator is commonly used in digital clocks?
RC phase‑shift
LC colpitts
Quartz crystal
VCO
Explanation - Quartz crystals provide the high stability required for accurate time‑keeping.
Correct answer is: Quartz crystal
Q.86 What does the 'phase margin' of a PLL indicate?
The amount of phase error tolerated before loss of lock
The maximum output power
The frequency deviation of the VCO
The bandwidth of the loop filter
Explanation - A higher phase margin means the PLL can handle larger phase errors without destabilizing.
Correct answer is: The amount of phase error tolerated before loss of lock
Q.87 Which of these is a typical advantage of using a crystal oscillator in RF transmitters?
High power output
Low cost
Low phase noise
Large size
Explanation - Crystals have very low phase noise, which is essential for clear RF transmission.
Correct answer is: Low phase noise
Q.88 Which component is NOT typically used in a Wien‑bridge oscillator?
RC network
Operational amplifier
Resistor divider
Inductor
Explanation - Wien‑bridge oscillators are based on RC phase shift, not inductors.
Correct answer is: Inductor
Q.89 What does the 'pull' of a crystal oscillator refer to?
Change in frequency with temperature
Change in frequency with supply voltage
Change in frequency with load impedance
All of the above
Explanation - Pulling refers to any external factor (temperature, voltage, load) that shifts the resonant frequency.
Correct answer is: All of the above
Q.90 Which of the following is a key parameter for determining oscillator stability?
Input impedance
Resonator Q factor
Output power
Capacitor value
Explanation - A higher Q means the oscillator’s frequency is less affected by component variations.
Correct answer is: Resonator Q factor
Q.91 In a crystal oscillator, the resonant frequency is set by:
The crystal’s cut and geometry
The amplifier’s gain
The load capacitor
The supply voltage
Explanation - The cut orientation and physical dimensions determine the fundamental resonance of the quartz.
Correct answer is: The crystal’s cut and geometry
Q.92 A 'phase‑locked loop' (PLL) is used to:
Generate random numbers
Synchronize an oscillator to a reference frequency
Amplify signals
Detect temperature
Explanation - PLLs adjust the output oscillator to match the phase and frequency of a reference clock.
Correct answer is: Synchronize an oscillator to a reference frequency
Q.93 Which of the following is a major benefit of a MEMS oscillator over a quartz crystal?
Higher temperature drift
Larger form factor
Lower power consumption
Lower frequency range
Explanation - MEMS devices are typically smaller and consume less power, beneficial for battery‑powered devices.
Correct answer is: Lower power consumption
Q.94 Which component is most commonly used to provide the active stage in a crystal oscillator?
Operational amplifier
Transistor
Diode
Resistor
Explanation - A transistor or op‑amp provides the necessary gain to sustain the crystal’s oscillation.
Correct answer is: Transistor
Q.95 The 'frequency tolerance' of an oscillator is:
The difference between the output and the input
The allowable deviation from the nominal frequency
The amount of power the oscillator can handle
The number of harmonics present
Explanation - Tolerance specifies how closely the oscillator frequency stays to its designed value.
Correct answer is: The allowable deviation from the nominal frequency
Q.96 Which of the following is a typical application of a VCO?
Analog clock generation
Frequency synthesis in RF
Power regulation
Temperature sensing
Explanation - VCOs are core components in RF synthesizers for tunable frequency generation.
Correct answer is: Frequency synthesis in RF
Q.97 The 'bandwidth' of an oscillator refers to:
The range of frequencies over which the oscillator can operate
The width of the output waveform
The range of output amplitudes
The supply voltage range
Explanation - Bandwidth indicates how much the frequency can be tuned or how wide the spectrum is.
Correct answer is: The range of frequencies over which the oscillator can operate
Q.98 Which of the following is NOT a typical design consideration for an LC oscillator?
Component Q factors
Inductor tolerances
Resistor values
Capacitor dielectric losses
Explanation - While resistors set bias and damping, they are not the primary determinant of resonant frequency in LC oscillators.
Correct answer is: Resistor values
Q.99 Which of the following best describes 'frequency pull' in an oscillator?
Change in output amplitude with temperature
Change in frequency due to load or supply variations
Increase in phase noise with offset
Decrease in Q factor with frequency
Explanation - Frequency pull occurs when external parameters shift the resonant frequency of the oscillator.
Correct answer is: Change in frequency due to load or supply variations
Q.100 The 'phase noise' of an oscillator is usually expressed in:
Volts
Ohms
Decibels relative to carrier per Hz (dBc/Hz)
Hertz per second
Explanation - Phase noise is measured as the power spectral density relative to the carrier frequency.
Correct answer is: Decibels relative to carrier per Hz (dBc/Hz)
Q.101 Which oscillator topology uses an inductor and two capacitors for feedback?
RC phase‑shift
LC Colpitts
Wien‑bridge
Crystal
Explanation - The Colpitts oscillator employs a capacitor divider for feedback and an inductor as the resonant tank.
Correct answer is: LC Colpitts
Q.102 What is the typical temperature coefficient of a high‑quality quartz crystal?
±10 ppm/°C
±100 ppm/°C
±1 ppm/°C
±1000 ppm/°C
Explanation - High‑grade quartz crystals exhibit very low temperature drift, typically around ±10 ppm/°C.
Correct answer is: ±10 ppm/°C
Q.103 In an oscillator circuit, the 'loop gain' must be:
Greater than 1
Exactly equal to 0
Less than 1
Independent of frequency
Explanation - To sustain oscillation, the loop gain must be at least 1 (Barkhausen criterion).
Correct answer is: Greater than 1
Q.104 Which of these is a typical application of a crystal oscillator?
Generating a carrier for AM radio
Power supply filtering
Digital clock generation
Signal amplification
Explanation - Crystals are widely used for precise time‑keeping in digital systems.
Correct answer is: Digital clock generation
Q.105 The 'phase‑shift network' in a Wien‑bridge oscillator provides:
Amplitude control
Phase shift of 90°
Frequency tuning
Voltage amplification
Explanation - The network supplies the necessary 90° shift to meet the 360° Barkhausen condition.
Correct answer is: Phase shift of 90°
Q.106 Which parameter is directly proportional to the quality factor Q of an oscillator?
Resonant frequency
Bandwidth
Output power
Gain
Explanation - Q = f₀ / bandwidth; a higher Q means a narrower bandwidth.
Correct answer is: Bandwidth
Q.107 A 'phase‑locked loop' (PLL) typically uses which of the following components to convert the reference frequency to a desired output frequency?
Frequency divider
Variable resistor
Capacitor
Resistor network
Explanation - The PLL uses a frequency divider in the feedback path to synthesize multiples of the reference frequency.
Correct answer is: Frequency divider
Q.108 In an LC oscillator, increasing the inductance will:
Increase the resonant frequency
Decrease the resonant frequency
Leave the frequency unchanged
Double the frequency
Explanation - The resonant frequency f = 1/(2π√(LC)), so increasing L lowers f.
Correct answer is: Decrease the resonant frequency
Q.109 Which of the following is a typical application of an RC phase‑shift oscillator?
Audio tone generation
High‑frequency RF transmission
Precise time‑keeping
Power conversion
Explanation - RC phase‑shift oscillators are commonly used in audio circuits for tone generation.
Correct answer is: Audio tone generation
Q.110 The 'loop filter' in a PLL is often designed with which of the following characteristics?
High Q to increase bandwidth
Low Q to reduce bandwidth
Zero phase shift
High gain at high frequencies
Explanation - A low‑Q filter provides a wider bandwidth but may increase noise; designers choose based on requirements.
Correct answer is: Low Q to reduce bandwidth
Q.111 Which of the following statements is true regarding a crystal oscillator’s frequency stability?
It degrades with temperature only
It is independent of load impedance
It is affected by temperature, load, and supply voltage
It improves with higher supply voltage
Explanation - All these factors can cause frequency drift in a crystal oscillator.
Correct answer is: It is affected by temperature, load, and supply voltage
Q.112 The 'phase noise floor' is mainly determined by:
Resonator Q factor
Supply voltage ripple
Load impedance
Capacitor ESR
Explanation - Higher Q reduces the intrinsic noise, lowering the phase noise floor.
Correct answer is: Resonator Q factor
Q.113 Which of the following is a major benefit of a MEMS resonator for oscillators?
Very low cost
Large size
High temperature drift
Small form factor
Explanation - MEMS resonators are compact, making them ideal for integrated RF circuits.
Correct answer is: Small form factor
Q.114 An oscillator that uses a crystal and an amplifier is called a:
RC oscillator
LC oscillator
Crystal oscillator
VCO
Explanation - The crystal provides the resonant element; the amplifier sustains the oscillation.
Correct answer is: Crystal oscillator
Q.115 In a PLL, the 'reference frequency' is:
The oscillator’s output frequency
The frequency of the feedback path
The frequency that the PLL locks to
The supply voltage
Explanation - The PLL adjusts its output so it matches the reference frequency in both frequency and phase.
Correct answer is: The frequency that the PLL locks to
Q.116 Which oscillator type is most suitable for low‑frequency timing applications?
RC phase‑shift
LC colpitts
Wien‑bridge
Crystal
Explanation - RC phase‑shift oscillators can easily generate frequencies in the kHz range for timing circuits.
Correct answer is: RC phase‑shift
Q.117 The 'load pull' effect causes the oscillator frequency to:
Increase with higher load impedance
Decrease with higher load impedance
Remain constant regardless of load
Oscillate unpredictably
Explanation - Higher load impedance often lowers the effective load on the tank, shifting the resonant frequency lower.
Correct answer is: Decrease with higher load impedance
Q.118 The 'Barkhausen criterion' for oscillation requires:
Loop gain > 2
Phase shift = 180°
Loop gain = 1 and phase shift = 360°
Loop gain < 1
Explanation - This ensures the signal reproduces itself each cycle without growing or decaying.
Correct answer is: Loop gain = 1 and phase shift = 360°
Q.119 Which of the following is a typical use of a VCO in a communication system?
Clock generation for digital logic
Frequency synthesis for RF transmission
Voltage regulation
Temperature sensing
Explanation - VCOs are core components of frequency synthesizers for tunable RF signals.
Correct answer is: Frequency synthesis for RF transmission
Q.120 What is the primary function of the 'loop filter' in a PLL?
Amplify the error signal
Set the division ratio
Smooth the control voltage to the VCO
Detect the reference frequency
Explanation - It shapes and filters the error signal before it reaches the VCO, controlling lock behavior.
Correct answer is: Smooth the control voltage to the VCO
Q.121 Which of the following is a major source of phase noise in an oscillator?
Supply noise
Component Q factor
Temperature drift
All of the above
Explanation - Phase noise arises from a combination of supply instability, Q loss, and temperature changes.
Correct answer is: All of the above
Q.122 Which of the following best describes a 'Wien‑bridge oscillator'?
An RC oscillator with a bridge network
An LC oscillator with a crystal
A VCO used in PLLs
A DC power supply
Explanation - The Wien‑bridge topology uses an RC bridge to provide the necessary phase shift and gain.
Correct answer is: An RC oscillator with a bridge network
Q.123 In a crystal oscillator, the 'guard band' refers to:
The frequency margin above the carrier
The minimum frequency deviation allowed
The difference between nominal and actual frequency
The load capacitance range
Explanation - Guard band ensures the oscillator can tolerate load changes without losing lock.
Correct answer is: The difference between nominal and actual frequency
Q.124 Which component is commonly used to control the frequency of a VCO?
Varactor diode
Resistor
Capacitor
Inductor
Explanation - The varactor’s capacitance varies with voltage, tuning the LC tank’s resonant frequency.
Correct answer is: Varactor diode
Q.125 The 'phase noise floor' of a crystal oscillator is typically:
-50 dBc/Hz
-80 dBc/Hz
-100 dBc/Hz
-120 dBc/Hz
Explanation - High‑quality quartz crystals often achieve phase noise floors around -100 dBc/Hz at 1 kHz offset.
Correct answer is: -100 dBc/Hz
Q.126 A 'phase‑shift network' in an oscillator provides a phase shift of:
30°
90°
180°
270°
Explanation - The network supplies the 90° shift needed to satisfy the 360° Barkhausen condition with a 180° amplifier.
Correct answer is: 90°
Q.127 Which of the following is a typical load impedance for a crystal oscillator?
1 Ω
10 Ω
50 Ω
200 Ω
Explanation - Standard crystal load capacitors are designed for 50 Ω systems in RF applications.
Correct answer is: 50 Ω
Q.128 Which type of oscillator is commonly used in digital clock generators?
RC phase‑shift
LC colpitts
Wien‑bridge
Crystal
Explanation - The crystal’s high stability is essential for accurate clock generation.
Correct answer is: Crystal
Q.129 The 'frequency multiplier' in a PLL is implemented using:
A frequency divider in the feedback path
A varactor diode
A resistor ladder
An op‑amp
Explanation - Dividing the feedback frequency allows the PLL to synthesize higher multiples of the reference.
Correct answer is: A frequency divider in the feedback path
Q.130 Which component is NOT typically part of a crystal oscillator’s resonant tank?
Inductor
Crystal
Capacitor
Resistor
Explanation - The tank is formed by the crystal and any external capacitance; resistors are not part of the tank.
Correct answer is: Resistor
Q.131 What is a common method to reduce the load pull effect in an LC oscillator?
Use a larger inductor
Add a high‑Q resistor
Use a matched load
Increase supply voltage
Explanation - Matching the load impedance minimizes frequency shift due to changes in the load.
Correct answer is: Use a matched load
Q.132 The 'loop filter' in a PLL can be implemented with:
Passive RC low‑pass
Active high‑pass
All‑pass network
Band‑stop filter
Explanation - A simple RC low‑pass filter is commonly used to smooth the error signal before VCO control.
Correct answer is: Passive RC low‑pass
Q.133 Which of the following is a typical feature of a high‑Q crystal oscillator?
High phase noise
Large temperature drift
Low frequency stability
Excellent frequency stability
Explanation - High‑Q crystals provide very stable frequencies over temperature and load variations.
Correct answer is: Excellent frequency stability
Q.134 What is the purpose of the 'varactor' in a VCO?
Provide bias voltage
Set the resonant frequency via variable capacitance
Amplify the output
Control the amplitude
Explanation - The varactor’s voltage‑dependent capacitance tunes the LC tank’s resonant frequency.
Correct answer is: Set the resonant frequency via variable capacitance
Q.135 Which of the following best describes a 'phase‑locked loop' (PLL)?
A circuit that generates random noise
A feedback system that locks an oscillator to a reference frequency
A device that amplifies signals
An oscillator that operates only at DC
Explanation - PLLs synchronize a VCO to the reference, maintaining phase and frequency alignment.
Correct answer is: A feedback system that locks an oscillator to a reference frequency
Q.136 Which of the following is an advantage of an RC phase‑shift oscillator?
High frequency operation
Simple implementation
Excellent frequency stability
Low power consumption
Explanation - RC phase‑shift oscillators use only resistors and capacitors, making them easy to build.
Correct answer is: Simple implementation
Q.137 The 'phase noise floor' of an oscillator is determined by:
Supply voltage stability
Resonator Q factor
Output power
Load impedance
Explanation - A higher Q reduces the phase noise floor, improving overall signal quality.
Correct answer is: Resonator Q factor
Q.138 In a PLL, the 'phase detector' typically produces an error signal that is:
High frequency
Low frequency
DC
Noise
Explanation - The phase detector output is a low‑frequency error voltage that controls the VCO.
Correct answer is: Low frequency