1Which of the following conditions represents the Barkhausen criterion for sustained oscillations?
A. and loop phase shift =
B. and loop phase shift = or
C. and loop phase shift =
D. and loop phase shift =
Correct Answer: and loop phase shift = or
Explanation:The Barkhausen criterion states that for sustained oscillations, the magnitude of the loop gain must be equal to unity (1), and the total phase shift around the loop must be or (integral multiple of ).
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2In a general oscillator circuit, what type of feedback is primarily used to generate oscillations?
A.Negative Feedback
B.Positive Feedback
C.Degenerative Feedback
D.Unity Gain Feedback
Correct Answer: Positive Feedback
Explanation:Oscillators employ positive feedback (regenerative feedback), where a portion of the output signal is fed back to the input in phase with the original signal to sustain oscillations.
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3For an RC Phase Shift Oscillator using a standard non-inverting amplifier or BJT, what is the minimum gain () required for oscillations to start?
A.29
B.3
C.1
D.10
Correct Answer: 29
Explanation:In an RC Phase Shift oscillator, the feedback network attenuates the signal by a factor of . Therefore, the amplifier must provide a voltage gain of at least 29 () to satisfy .
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4What is the formula for the frequency of oscillation in a standard RC Phase Shift Oscillator?
A.
B.
C.
D.
Correct Answer:
Explanation:For a standard RC phase shift oscillator with three identical RC sections, the frequency of oscillation is given by .
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5Which component determines the frequency stability of a Crystal Oscillator?
A.The external resistors
B.The external capacitors
C.The piezoelectric quartz crystal
D.The supply voltage
Correct Answer: The piezoelectric quartz crystal
Explanation:The frequency stability is determined by the quartz crystal, which has a very high Quality Factor () and precise resonant frequency due to the piezoelectric effect.
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6In a Wien Bridge Oscillator, what is the phase shift introduced by the feedback network at the resonant frequency?
A.
B.
C.
D.
Correct Answer:
Explanation:At the resonant frequency (), the Wien Bridge feedback network introduces a phase shift. Consequently, the amplifier used must also be non-inverting ( phase shift) to satisfy the Barkhausen criterion.
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7What is the condition for the voltage gain () in a Wien Bridge Oscillator to sustain oscillations?
A.
B.
C.
D.
Correct Answer:
Explanation:The Wien Bridge network attenuates the signal by a factor of 3 at resonance (output is 1/3 of input). Therefore, the non-inverting amplifier gain must be at least 3 ().
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8Which of the following oscillators is generally used for high-frequency (RF) applications?
A.RC Phase Shift Oscillator
B.Wien Bridge Oscillator
C.Hartley Oscillator
D.Relaxation Oscillator
Correct Answer: Hartley Oscillator
Explanation:LC oscillators like the Hartley Oscillator are used for Radio Frequencies (RF), whereas RC oscillators (Wien Bridge, Phase Shift) are typically used for Audio Frequencies (AF).
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9Identify the distinct feature of the feedback network in a Hartley Oscillator.
A.Two capacitors and one inductor
B.Two inductors (or a tapped inductor) and one capacitor
C.Three RC stages
D.A bridge rectifier circuit
Correct Answer: Two inductors (or a tapped inductor) and one capacitor
Explanation:A Hartley oscillator is identified by a tank circuit consisting of two inductors in series (often a tapped inductor) and a capacitor in parallel with them.
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10What is the frequency of oscillation for a Colpitts Oscillator?
A. where
B.
C.
D.
Correct Answer: where
Explanation:The Colpitts oscillator uses two capacitors in series within the tank circuit. The equivalent capacitance is the series combination , making the frequency .
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11In the equivalent electrical circuit of a quartz crystal, the series branch consists of:
A.A resistor, an inductor, and a capacitor
B.A single capacitor only
C.A resistor and a diode
D.Two inductors
Correct Answer: A resistor, an inductor, and a capacitor
Explanation:The electrical equivalent of a crystal has a series R-L-C branch (representing mechanical mass, compliance, and friction) in parallel with a mounting capacitance .
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12A crystal oscillator operates between which two frequencies?
A.DC and 10 Hz
B.Series resonant frequency () and Parallel resonant frequency ()
C. and
D.0 Hz and
Correct Answer: Series resonant frequency () and Parallel resonant frequency ()
Explanation:The crystal behaves inductively between its series resonant frequency () and parallel resonant frequency (). This inductive reactance is required for the oscillation condition in circuits like the Pierce oscillator.
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13When reading a 1 MHz crystal datasheet, what does 'Load Capacitance ()' refer to?
A.The maximum capacitance the crystal can withstand
B.The capacitance required across the crystal terminals for it to oscillate at the specified frequency
C.The internal series capacitance of the crystal
D.The power supply decoupling capacitor
Correct Answer: The capacitance required across the crystal terminals for it to oscillate at the specified frequency
Explanation:Load Capacitance () is the specified external circuit capacitance as seen by the crystal. If the circuit's actual load capacitance differs from , the oscillation frequency will shift slightly from the nominal value.
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14What is the primary advantage of a Colpitts oscillator over a Hartley oscillator?
A.It uses fewer components
B.Better frequency stability due to lack of mutual inductance issues
C.It can generate square waves directly
D.It works only at low frequencies
Correct Answer: Better frequency stability due to lack of mutual inductance issues
Explanation:Colpitts oscillators generally offer better frequency stability because they use capacitors for the feedback divider, avoiding the mutual inductance coupling issues found in the tapped inductor of the Hartley design.
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15In an operational amplifier block diagram, which stage provides the majority of the voltage gain?
A.Input Stage
B.Intermediate Stage
C.Level Shifting Stage
D.Output Stage
Correct Answer: Intermediate Stage
Explanation:The Intermediate Stage (usually a common-emitter or equivalent amplifier) is typically designed to provide the majority of the high open-loop voltage gain of the op-amp.
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16What is the main function of the Level Shifting Stage in an op-amp?
A.To increase the bandwidth
B.To shift the DC level of the signal to zero volts with respect to ground
C.To provide high input impedance
D.To drive low impedance loads
Correct Answer: To shift the DC level of the signal to zero volts with respect to ground
Explanation:Because the previous stages are direct-coupled, the DC level rises. The level shifting stage brings the DC quiescent voltage back down to zero so that the output can swing symmetrically around 0V.
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17Which of the following is the standard schematic symbol for an Operational Amplifier?
A.A circle with a plus sign
B.A triangle with two inputs (inverting -, non-inverting +) and one output
C.A square with 8 pins
D.Two parallel lines
Correct Answer: A triangle with two inputs (inverting -, non-inverting +) and one output
Explanation:The standard symbol is a triangle pointing towards the output, with two input terminals on the left (marked - and +) and one output terminal on the right.
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18What is the value of the Input Impedance () for an Ideal Op-Amp?
A.Zero ()
B.50
C.Infinite ()
D.1 M
Correct Answer: Infinite ()
Explanation:An ideal op-amp draws no current at its input terminals, which implies an infinite input impedance.
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19What is the value of the Output Impedance () for an Ideal Op-Amp?
A.Zero ()
B.Infinite ()
C.100
D.Equal to load resistance
Correct Answer: Zero ()
Explanation:An ideal op-amp acts as a perfect voltage source, meaning it has zero output impedance and can drive any load without voltage drop.
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20Which characteristic defines how fast the output of an op-amp can change in response to a step input?
A.Common Mode Rejection Ratio (CMRR)
B.Slew Rate (SR)
C.Input Offset Voltage
D.Gain Bandwidth Product
Correct Answer: Slew Rate (SR)
Explanation:The Slew Rate is defined as the maximum rate of change of the output voltage per unit of time (typically ).
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21Calculate the frequency of a Wien Bridge oscillator if and .
A.1 kHz
B.10 kHz
C.100 Hz
D.159 Hz
Correct Answer: 1 kHz
Explanation:.
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22The Common Mode Rejection Ratio (CMRR) is defined as:
A.
B.
C.
D.
Correct Answer:
Explanation:CMRR is the ratio of the differential voltage gain () to the common-mode voltage gain (). It indicates the op-amp's ability to reject noise present on both inputs.
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23What is the Input Offset Voltage ()?
A.The voltage required at the input to make the output voltage zero
B.The breakdown voltage of the input transistors
C.The voltage difference between power supply rails
D.The noise voltage at the input
Correct Answer: The voltage required at the input to make the output voltage zero
Explanation:Due to transistor mismatches in the internal differential amplifier, a small DC voltage () must be applied to the inputs to force the output DC voltage to zero.
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24In the context of an Op-Amp, what is Input Bias Current ()?
A.Current flowing from the output to ground
B.The average of the currents flowing into the two input terminals
C.The difference between the currents flowing into the input terminals
D.The current drawn from the power supply
Correct Answer: The average of the currents flowing into the two input terminals
Explanation:Input Bias Current is defined as the average value of the two input currents: .
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25According to the datasheet of the IC 741 Op-Amp, what is the typical Open Loop Voltage Gain?
A.10
B.100
C.200,000 (106 dB)
D.Infinite
Correct Answer: 200,000 (106 dB)
Explanation:While an ideal op-amp has infinite gain, the practical IC 741 typically has a large signal voltage gain of approximately 200,000 (or roughly 106 dB).
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26Identify Pin 2 and Pin 3 of the 741 Op-Amp (8-pin DIP).
Explanation:Pins 1 and 5 are the Offset Null terminals. A potentiometer is connected between them (wiper to -Vee) to nullify the input offset voltage.
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29Which oscillator circuit relies on the Piezoelectric Effect?
A.Hartley
B.Colpitts
C.Crystal Oscillator
D.Phase Shift Oscillator
Correct Answer: Crystal Oscillator
Explanation:Crystal oscillators use a quartz crystal that exhibits the Piezoelectric effect, where mechanical stress produces voltage and vice versa, creating a very stable resonator.
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30In a Hartley Oscillator, if , (uncoupled), and , what is the total inductance and approximate frequency?
Explanation:The input stage is a Differential Amplifier (often dual-input, balanced-output) to provide high input impedance and CMRR.
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32What is the Output Stage of a typical Op-Amp (like the 741) designed to be?
A.Differential Amplifier
B.Class B or Class AB Push-Pull Emitter Follower
C.Common Base Amplifier
D.Common Emitter Amplifier
Correct Answer: Class B or Class AB Push-Pull Emitter Follower
Explanation:The output stage is typically a Push-Pull (Class AB) complementary symmetry amplifier to provide low output impedance and drive current to the load.
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33What is the ideal Bandwidth of an Operational Amplifier?
A.0 Hz
B.20 kHz
C.Infinite
D.1 MHz
Correct Answer: Infinite
Explanation:An ideal op-amp has infinite bandwidth, meaning it can amplify signals of any frequency with constant gain.
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34Why is the Wien Bridge Oscillator preferred for Audio Frequency applications over LC oscillators?
A.It requires large bulky inductors for low frequencies
B.LC oscillators cannot generate sine waves
C.Wien bridge is a variable frequency oscillator that can be easily tuned
D.Both A and C
Correct Answer: Both A and C
Explanation:LC oscillators require very large inductors for low (audio) frequencies, which is impractical. Wien bridge uses RC components which are smaller and can be easily tuned using a variable capacitor or potentiometer (ganged).
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35In a 741 datasheet, the Supply Voltage Rejection Ratio (SVRR) or PSRR indicates:
A.How much the output voltage changes with temperature
B.How much the input offset voltage changes with variation in power supply voltage
C.The maximum supply voltage allowed
D.The noise rejection from the input
Correct Answer: How much the input offset voltage changes with variation in power supply voltage
Explanation:SVRR/PSRR measures the change in Input Offset Voltage resulting from a change in power supply voltage (typically expressed in or or dB).
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36Which pin is the Output pin on an 8-pin DIP 741 Op-Amp?
A.Pin 1
B.Pin 4
C.Pin 6
D.Pin 8
Correct Answer: Pin 6
Explanation:Standard 741 Pinout: Pin 6 is the Output terminal.
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37In a Crystal Oscillator datasheet, Frequency Tolerance (e.g., ) refers to:
A.The maximum deviation from nominal frequency at room temperature ()
B.The deviation over the entire temperature range
C.The aging rate per year
D.The tolerance of the package dimensions
Correct Answer: The maximum deviation from nominal frequency at room temperature ()
Explanation:Frequency Tolerance specifies the maximum allowable deviation from the nominal frequency at a specific reference temperature (usually ).
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38The concept of Virtual Ground in an op-amp circuit exists because:
A.The non-inverting terminal is physically connected to ground
B.The infinite gain () implies the differential input voltage () is effectively zero ()
C.The output is grounded
D.The input impedance is zero
Correct Answer: The infinite gain () implies the differential input voltage () is effectively zero ()
Explanation:Since and is extremely large, the difference must be extremely small to keep finite. Thus, if is ground, is at Virtual Ground.
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39What is the minimum number of RC sections required in an RC Phase Shift Oscillator?
A.1
B.2
C.3
D.4
Correct Answer: 3
Explanation:Each RC section can provide a maximum phase shift approaching . To achieve the required phase shift for the feedback network, at least 3 sections (usually providing each) are required.
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40In a Colpitts oscillator, if the feedback fraction is defined by the capacitor divider and , the feedback factor is approximately:
A.
B.
C.
D.
Correct Answer:
Explanation:The voltage is divided across the capacitors. The feedback fraction is usually determined by the ratio of reactances, resulting in (depending on which capacitor is across the input).
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41Which of the following is NOT a characteristic of an Ideal Op-Amp?
A.Infinite Input Impedance
B.Zero Output Impedance
C.Infinite Bandwidth
D.Infinite Offset Voltage
Correct Answer: Infinite Offset Voltage
Explanation:An ideal op-amp should have Zero input offset voltage. Infinite offset voltage would be a defect.
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42In the general form of an oscillator consisting of an amplifier and a feedback network with reactances , , and , the condition for oscillation is:
A.
B.
C.
D.
Correct Answer:
Explanation:In the general analysis (covering Hartley and Colpitts), the sum of the reactances in the feedback loop must be zero () to satisfy the phase criterion.
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43What is the typical Common Mode Rejection Ratio (CMRR) value for a 741 Op-Amp in decibels?
A.10 dB
B.30 dB
C.90 dB
D.200 dB
Correct Answer: 90 dB
Explanation:A typical 741 op-amp has a CMRR of approximately 90 dB, meaning it attenuates common-mode signals significantly compared to differential signals.
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44If a crystal has a series resonant frequency and a parallel resonant frequency , which is higher?
A. is higher
B. is higher
C.They are equal
D.Depends on temperature
Correct Answer: is higher
Explanation:The parallel resonant frequency is always slightly higher than the series resonant frequency . The crystal is inductive between these two frequencies.
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45Pin 4 and Pin 7 of the 741 Op-Amp are used for:
A.Inputs
B.Offset Nulling
C.Power Supply ( and )
D.Output and Ground
Correct Answer: Power Supply ( and )
Explanation:Pin 7 is connected to the Positive Supply () and Pin 4 is connected to the Negative Supply ().
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46Which oscillator uses a bridge circuit containing a series RC arm and a parallel RC arm?
A.Hartley
B.Colpitts
C.Wien Bridge
D.Crystal
Correct Answer: Wien Bridge
Explanation:The Wien Bridge oscillator feedback network consists of a series RC combination in one arm and a parallel RC combination in the adjoining arm.
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47What limits the high-frequency response of a standard Op-Amp like the 741?
A.The coupling capacitors
B.The internal compensation capacitor
C.The input resistors
D.The power supply voltage
Correct Answer: The internal compensation capacitor
Explanation:Most general-purpose op-amps (like the 741) are 'internally compensated' with a small capacitor to ensure stability (prevent oscillations). This capacitor dominates the frequency response, reducing the gain at high frequencies.
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48The Quality Factor (Q) of a Quartz Crystal is typically in the range of:
A.1 to 10
B.50 to 100
C.10,000 to 100,000
D.Less than 1
Correct Answer: 10,000 to 100,000
Explanation:Quartz crystals have extremely high Q factors (typically to ) compared to LC tanks (Q ~ 100), which results in superior frequency stability.
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49Which parameter in an Op-Amp datasheet describes the maximum differential input voltage that can be applied without damaging the device?
A.Input Offset Voltage
B.Differential Input Voltage Range
C.Common Mode Voltage Range
D.Large Signal Voltage Gain
Correct Answer: Differential Input Voltage Range
Explanation:The datasheet specifies a Differential Input Voltage limit (often equal to the supply voltage range for some op-amps, or less for others like the 741 usually absolute max) to prevent breakdown.
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50To change the frequency of a Hartley Oscillator, one typically varies:
A.The capacitor C in the tank circuit
B.The supply voltage
C.The transistor beta
D.The load resistor
Correct Answer: The capacitor C in the tank circuit
Explanation:The frequency is . Variable capacitors are more common and practical than variable inductors for tuning frequency.
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