1What is the primary function of a sinusoidal oscillator?
Sinusoidal oscillators
Easy
A.To convert AC to DC
B.To generate a continuous sinusoidal waveform without an external AC input
C.To act as a low-pass filter
D.To amplify a DC signal
Correct Answer: To generate a continuous sinusoidal waveform without an external AC input
Explanation:
An oscillator is a circuit that produces a continuous, repeated, alternating waveform without any input signal, using a DC power supply.
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2Which of the following conditions is required for sustained oscillations (Barkhausen criterion)?
general form of oscillator circuit
Easy
A.Loop gain must be exactly 0
B.Loop gain must be negative
C.Loop gain must be less than 1
D.Loop gain must be greater than or equal to 1, and phase shift must be or
Correct Answer: Loop gain must be greater than or equal to 1, and phase shift must be or
Explanation:
The Barkhausen criterion states that for sustained oscillations, the loop gain must be at least 1, and the total phase shift around the loop must be or an integer multiple of .
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3In a basic RC phase shift oscillator, what is the typical phase shift introduced by each of the three RC networks?
RC phase shift oscillator
Easy
A.
B.
C.
D.
Correct Answer:
Explanation:
To achieve a total phase shift of in the feedback network, three RC sections are used, each contributing a phase shift of .
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4Which type of feedback is used in a Wien bridge oscillator to stabilize the amplitude?
wien bridge oscillator
Easy
A.Only positive feedback
B.No feedback
C.Only negative feedback
D.Both positive and negative feedback
Correct Answer: Both positive and negative feedback
Explanation:
A Wien bridge oscillator uses positive feedback for oscillation and negative feedback for amplitude stabilization and distortion reduction.
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5In a Hartley oscillator, the feedback network consists of:
hartley LC oscillators
Easy
A.Two inductors and one capacitor
B.Three inductors
C.Three capacitors
D.Two capacitors and one inductor
Correct Answer: Two inductors and one capacitor
Explanation:
A Hartley oscillator uses a tapped inductor (effectively two inductors) and a single capacitor in its tank circuit.
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6In a Colpitts oscillator, the feedback network consists of:
collpit oscillator
Easy
A.Two capacitors and one inductor
B.Resistors and inductors only
C.Resistors and capacitors only
D.Two inductors and one capacitor
Correct Answer: Two capacitors and one inductor
Explanation:
A Colpitts oscillator uses a capacitive voltage divider (two capacitors) and a single inductor in its tank circuit.
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7Why is a quartz crystal commonly used in oscillators?
Crystal oscillator
Easy
A.It dissipates high power
B.It is very cheap
C.It provides extremely high frequency stability
D.It can handle high voltages
Correct Answer: It provides extremely high frequency stability
Explanation:
Crystal oscillators are highly favored because quartz crystals have a very high Q-factor, which results in excellent frequency stability.
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8The piezoelectric effect in a crystal oscillator refers to the conversion of:
Crystal oscillator
Easy
A.Heat to electricity
B.Light to electricity
C.Mechanical stress to electrical voltage and vice versa
D.Magnetic field to electric field
Correct Answer: Mechanical stress to electrical voltage and vice versa
Explanation:
The piezoelectric effect is the property of certain materials (like quartz) to generate an electric charge in response to applied mechanical stress, and to change shape when an electric field is applied.
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9When reading the datasheet of a 1 MHz crystal, which parameter defines the maximum variation from the specified frequency at room temperature?
reading datasheet of 1 MHz crystal
Easy
A.Drive level
B.Frequency tolerance
C.Load capacitance
D.Equivalent Series Resistance (ESR)
Correct Answer: Frequency tolerance
Explanation:
Frequency tolerance indicates how much the actual frequency can deviate from the nominal frequency (e.g., 1 MHz) at a reference temperature.
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10An ideal operational amplifier has an input impedance of:
The operational amplifier
Easy
A.Infinity
B.1 k
C.Zero
D.100
Correct Answer: Infinity
Explanation:
An ideal op-amp is assumed to have infinite input impedance, meaning it draws no current from the input source.
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11What is the ideal output impedance of an operational amplifier?
The operational amplifier
Easy
A.100
B.10 k
C.Zero
D.Infinity
Correct Answer: Zero
Explanation:
An ideal op-amp has zero output impedance, allowing it to drive any load without a drop in output voltage.
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12The first stage of a typical operational amplifier block diagram is usually a:
block diagram of typical op-amp
Easy
A.Differential amplifier
B.Power amplifier
C.Class B push-pull amplifier
D.Level shifter
Correct Answer: Differential amplifier
Explanation:
The input stage of an op-amp is a differential amplifier, which provides high input impedance and high common-mode rejection.
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13In the schematic symbol for an op-amp, the '-' and '+' signs represent respectively:
schematic symbol
Easy
A.Non-inverting input and Inverting input
B.Negative supply and Positive supply
C.Inverting input and Non-inverting input
D.Ground and Power
Correct Answer: Inverting input and Non-inverting input
Explanation:
The '-' symbol indicates the inverting input terminal, and the '+' symbol indicates the non-inverting input terminal.
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14Which parameter describes an op-amp's ability to reject signals that are common to both input terminals?
characteristics of operational amplifier
Easy
A.Common-Mode Rejection Ratio (CMRR)
B.Gain-bandwidth product
C.Input offset voltage
D.Slew rate
Correct Answer: Common-Mode Rejection Ratio (CMRR)
Explanation:
CMRR is the ratio of the differential gain to the common-mode gain, representing the op-amp's ability to reject common-mode signals (noise).
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15The maximum rate at which an op-amp's output voltage can change is called:
characteristics of operational amplifier
Easy
A.Bandwidth
B.Input bias current
C.Open-loop gain
D.Slew rate
Correct Answer: Slew rate
Explanation:
Slew rate is defined as the maximum rate of change of the output voltage with respect to time, typically expressed in V/s.
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16What is the typical supply voltage range for a standard 741 operational amplifier?
reading datasheet of 741
Easy
A.$100$V to $200$V
B.$0$V to $5$V only
C.V to V
D.V to V (up to V)
Correct Answer: V to V (up to V)
Explanation:
A standard 741 op-amp typically operates on dual power supplies, commonly V, with an absolute maximum rating around V.
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17How many pins does a standard dual in-line package (DIP) 741 op-amp IC have?
reading datasheet of 741
Easy
A.4
B.14
C.8
D.6
Correct Answer: 8
Explanation:
The standard IC 741 is packaged in an 8-pin DIP (Dual In-line Package).
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18If an input signal is applied to the inverting terminal of an op-amp with the non-inverting terminal grounded, the output signal will be:
The operational amplifier
Easy
A. out of phase with the input
B. out of phase with the input
C.In phase with the input
D.A DC voltage of zero
Correct Answer: out of phase with the input
Explanation:
An inverting amplifier introduces a phase shift relative to the input signal.
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19Ideal open-loop voltage gain of an operational amplifier is:
characteristics of operational amplifier
Easy
A.1
B.Zero
C.Infinity
D.100
Correct Answer: Infinity
Explanation:
An ideal operational amplifier has an infinite open-loop voltage gain.
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20In an RC phase shift oscillator, what component provides the necessary additional phase shift to satisfy Barkhausen's criterion?
RC phase shift oscillator
Easy
A.A diode rectifier
B.A non-inverting amplifier
C.A step-up transformer
D.An inverting amplifier
Correct Answer: An inverting amplifier
Explanation:
The RC network provides of phase shift, and an inverting amplifier provides another , resulting in the (or ) total phase shift required for oscillation.
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21For a sinusoidal oscillator, what condition must the loop gain satisfy for sustained oscillations according to the Barkhausen criterion?
Sinusoidal oscillators
Medium
A. with phase shift or
B. with phase shift
C. with phase shift
D. with phase shift
Correct Answer: with phase shift or
Explanation:
The Barkhausen criterion states that for sustained oscillations, the magnitude of loop gain must be equal to or slightly greater than 1, and the total phase shift around the loop must be or .
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22In an RC phase shift oscillator using three identical RC sections, what is the frequency of oscillation?
RC phase shift oscillator
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
For an RC phase shift oscillator with three RC sections, each providing a phase shift, the frequency of oscillation is given by .
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23What is the minimum required voltage gain for the amplifier in an RC phase shift oscillator using three identical RC sections to sustain oscillations?
RC phase shift oscillator
Medium
A.
B.$29$
C.
D.$3$
Correct Answer: $29$
Explanation:
The attenuation of the three-stage RC feedback network is at the oscillating frequency. Therefore, the amplifier must have a minimum voltage gain of $29$ to satisfy the Barkhausen criterion ().
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24At the resonant frequency of a Wien bridge oscillator, what is the phase shift introduced by the lead-lag network?
wien bridge oscillator
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
At the resonant frequency, the Wien bridge (lead-lag) network introduces zero phase shift, requiring a non-inverting amplifier to maintain a total loop phase shift of .
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25For a standard Wien bridge oscillator with equal resistors () and equal capacitors () in the series and parallel branches, what is the required gain of the amplifier?
wien bridge oscillator
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The feedback fraction of the Wien bridge at resonance is . To maintain , the amplifier gain must be at least 3.
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26In a general LC oscillator circuit consisting of reactances , , and , what is the necessary condition for oscillation regarding the nature of the reactances?
general form of oscillator circuit
Medium
A. and must be of the same type, and must be of the opposite type
B. must all be of the same type
C. can be purely resistive
D. and must be of the same type, and must be of the opposite type
Correct Answer: and must be of the same type, and must be of the opposite type
Explanation:
For a general LC oscillator to work, the two reactances forming the voltage divider ( and ) must be of the same type (either both inductive or both capacitive), while the third reactance () must be of the opposite type.
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27The resonant frequency of a Hartley oscillator using an inductor divided into two parts and , with a mutual inductance , and a capacitor is given by:
hartley LC oscillators
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The total equivalent inductance in a Hartley oscillator tank circuit is (if aiding). The resonant frequency is .
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28In a Colpitts oscillator, the feedback network consists of:
collpit oscillator
Medium
A.Three capacitors
B.Three inductors
C.Two inductors and one capacitor
D.Two capacitors and one inductor
Correct Answer: Two capacitors and one inductor
Explanation:
A Colpitts oscillator uses a capacitive voltage divider (two capacitors) and a single inductor in its tank circuit.
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29Why are quartz crystals used in oscillators instead of standard LC tank circuits for high-frequency applications?
Crystal oscillator
Medium
A.They possess an exceptionally high Q-factor, ensuring high frequency stability.
B.They can operate without an amplifier.
C.They are strictly resistive and prevent phase shifts.
D.They provide higher output power.
Correct Answer: They possess an exceptionally high Q-factor, ensuring high frequency stability.
Explanation:
Quartz crystals have an extremely high quality factor (), often in the tens of thousands, which makes the oscillator highly stable against temperature and voltage variations.
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30A crystal oscillator operates between its series resonant frequency () and parallel resonant frequency (). What is the nature of the crystal's reactance in this frequency range?
Crystal oscillator
Medium
A.Resistive
B.Capacitive
C.Inductive
D.Zero
Correct Answer: Inductive
Explanation:
Between the series resonant frequency and the parallel resonant frequency , the net reactance of the crystal is inductive. This allows it to replace the inductor in circuits like the Colpitts oscillator.
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31When reading the datasheet of a 1 MHz crystal, the parameter 'load capacitance' () is specified. What happens if the actual circuit load capacitance is significantly different from the specified ?
reading datasheet of 1 MHz crystal
Medium
A.The oscillator frequency will shift away from exactly 1 MHz.
B.The Q-factor will become infinite.
C.The crystal will output a perfect sine wave.
D.The crystal will consume excessive power and burn out.
Correct Answer: The oscillator frequency will shift away from exactly 1 MHz.
Explanation:
The crystal is calibrated to oscillate at its nominal frequency with a specific load capacitance. A mismatch causes frequency pulling, resulting in a slight shift in the operating frequency.
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32Which of the following describes the ideal input impedance () and output impedance () of an operational amplifier?
The operational amplifier
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
An ideal operational amplifier has infinite input impedance (so it draws no current from the source) and zero output impedance (so it can drive any load).
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33Which stage in the block diagram of a typical operational amplifier provides the majority of the voltage gain?
block diagram of typical op-amp
Medium
A.Output push-pull stage
B.Intermediate high-gain stage
C.Input differential amplifier stage
D.Level shifter stage
Correct Answer: Intermediate high-gain stage
Explanation:
The intermediate stage (often a common-emitter or common-source amplifier) is responsible for providing the bulk of the op-amp's high open-loop voltage gain.
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34What is the primary function of the level shifter stage in a typical op-amp block diagram?
block diagram of typical op-amp
Medium
A.To increase the voltage gain
B.To provide impedance matching with the output load
C.To increase the Common-Mode Rejection Ratio (CMRR)
D.To shift the DC level of the signal down to zero volts with respect to ground
Correct Answer: To shift the DC level of the signal down to zero volts with respect to ground
Explanation:
Because the previous stages are direct-coupled, the DC voltage level rises. The level shifting stage brings the DC level back to zero volts so that a zero input signal gives a zero output voltage.
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35In the standard schematic symbol for an operational amplifier, what do the '-' and '+' terminals denote?
schematic symbol
Medium
A.'-' is the inverting input, '+' is the non-inverting input
B.'-' is the output, '+' is the input
C.'-' is the ground, '+' is the input signal
D.'-' is the negative power supply, '+' is the positive power supply
Correct Answer: '-' is the inverting input, '+' is the non-inverting input
Explanation:
The standard op-amp symbol uses '-' for the inverting input (where a signal is phase-shifted by ) and '+' for the non-inverting input (where a signal remains in phase).
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36For a practical op-amp, the Common-Mode Rejection Ratio (CMRR) is defined as:
characteristics of operational amplifier
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
CMRR is the ratio of differential gain () to common-mode gain (). In decibels, it is expressed as .
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37What does the Slew Rate of an operational amplifier define?
characteristics of operational amplifier
Medium
A.The rate at which the input bias current changes with temperature.
B.The maximum rate of change of the output voltage with respect to time.
C.The minimum input voltage required to saturate the output.
D.The maximum frequency at which the op-amp can operate without attenuation.
Correct Answer: The maximum rate of change of the output voltage with respect to time.
Explanation:
Slew rate is defined as the maximum rate of change of the output voltage (), typically expressed in . It limits how fast the op-amp output can respond to large input step changes.
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38According to the typical datasheet for a op-amp, what is the typical value of its slew rate?
reading datasheet of 741
Medium
A.
B.
C.
D.
Correct Answer:
Explanation:
The standard operational amplifier is an older, general-purpose device with a typical slew rate of about .
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39In the datasheet, offset null pins are provided (usually pins 1 and 5). What is their purpose?
reading datasheet of 741
Medium
A.To connect external frequency compensation capacitors.
B.To set the maximum output current limit.
C.To increase the slew rate of the op-amp.
D.To adjust the output to zero when both inputs are grounded.
Correct Answer: To adjust the output to zero when both inputs are grounded.
Explanation:
Due to internal component mismatches, a small DC voltage (input offset voltage) may cause a non-zero output even when inputs are zero. The offset null pins allow for external adjustment to cancel this out.
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40If an op-amp has an open-loop gain of and an input offset voltage of , what will be the output voltage if it is connected in an open-loop configuration and the inputs are tied to ground?
characteristics of operational amplifier
Medium
A.
B.
C.
D.It will saturate to the power supply rail.
Correct Answer: It will saturate to the power supply rail.
Explanation:
The output is . Since the op-amp cannot output a voltage higher than its power supply (usually ), the output will saturate at the supply rails.
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41In a BJT-based RC phase shift oscillator, the feedback network consists of three identical RC sections. If the transistor has a finite input impedance , how does this affect the minimum required current gain () for sustained oscillations compared to an ideal voltage-controlled amplifier?
RC phase shift oscillator
Hard
A.The feedback network becomes independent of if is chosen to be sufficiently large.
B.The minimum is reduced below 29 due to the loading effect of on the last RC stage.
C.The minimum remains 29 regardless of .
D.The minimum depends on the ratio , and is given by .
Correct Answer: The minimum depends on the ratio , and is given by .
Explanation:
In a BJT phase shift oscillator, the input impedance loads the feedback network. To account for this, the required for sustained oscillation is , where , which yields a minimum of 44.5 when .
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42A Wien bridge oscillator uses an operational amplifier with a finite unity-gain bandwidth (UGBW). If the desired oscillation frequency approaches the UGBW, what is the primary effect on the required nominal gain established by the resistive branch?
wien bridge oscillator
Hard
A.The op-amp will automatically adjust its open-loop gain to maintain the Barkhausen criterion without altering the resistor ratio.
B.The required nominal gain must be greater than 3 to compensate for the additional phase shift and gain roll-off of the op-amp.
C.The required nominal gain must be strictly less than 3 to compensate for the op-amp's internal phase lead.
D.The required nominal gain remains exactly 3, but the oscillation frequency shifts higher.
Correct Answer: The required nominal gain must be greater than 3 to compensate for the additional phase shift and gain roll-off of the op-amp.
Explanation:
At frequencies approaching the UGBW, the op-amp introduces its own phase lag and its open-loop gain decreases. To satisfy the Barkhausen criterion (loop gain = 1, total phase = 0), the feedback network or the closed-loop nominal gain must be adjusted (requiring ) to compensate for these non-ideal op-amp characteristics.
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43Consider the general generic LC oscillator model comprising three reactive elements , , and . For sustained oscillations, the sum of reactances must be zero (). If and are of the same reactance type, what defines the required amplifier voltage gain in terms of these reactances?
general form of oscillator circuit
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
In the general oscillator model, the feedback fraction is . To satisfy the Barkhausen criterion , the required minimum voltage gain is .
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44A Hartley oscillator utilizes a tapped inductor with sections and . If the mutual inductance between the two sections is , what is the exact expression for the oscillation frequency ?
hartley LC oscillators
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
Because the two inductors and are part of a single tapped coil, they are magnetically coupled. The total effective inductance in the tank circuit is , making the frequency .
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45In a high-frequency BJT Colpitts oscillator, the transistor's internal parasitic base-emitter capacitance is significant. How does affect the feedback network consisting of and (where is across the output and is across the input)?
collpit oscillator
Hard
A. appears in series with , decreasing the equivalent capacitance and increasing the frequency.
B. cancels out the effect of the Miller capacitance , maintaining a constant oscillation frequency.
C. appears in parallel with , increasing the equivalent capacitance across the input and altering the feedback fraction .
D. appears in parallel with the inductor , directly decreasing the oscillation frequency without affecting .
Correct Answer: appears in parallel with , increasing the equivalent capacitance across the input and altering the feedback fraction .
Explanation:
In the AC equivalent circuit of a Colpitts oscillator, is connected between the base and emitter. The internal parasitic capacitance is also between the base and emitter. Thus, adds in parallel to , changing both the effective tank capacitance and the feedback ratio .
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46A quartz crystal has a series resonance frequency and a parallel resonance frequency . The crystal equivalent circuit parameters are , , , and a mounting capacitance . Which of the following defines the relationship between and ?
Crystal oscillator
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The series resonance is . The parallel resonance occurs when the series arm resonates with the parallel mounting capacitance , giving . Therefore, .
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47When reading the datasheet of a 1 MHz quartz crystal, you observe the Equivalent Series Resistance (ESR) is specified as . What is the direct consequence of a higher ESR on the oscillator circuit design?
reading datasheet of 1 MHz crystal
Hard
A.It shifts the series resonant frequency significantly upwards, requiring inductive tuning.
B.It increases the pullability range of the crystal, requiring larger load capacitors.
C.It eliminates the parallel resonance mode, forcing the crystal to operate only in series mode.
D.It decreases the quality factor (Q) of the crystal, requiring an amplifier with a higher transconductance () to ensure startup.
Correct Answer: It decreases the quality factor (Q) of the crystal, requiring an amplifier with a higher transconductance () to ensure startup.
Explanation:
ESR represents the motional resistance in the crystal's equivalent circuit. A higher ESR lowers the Q-factor () and increases the losses in the tank, meaning the active device must provide more energy (higher or gain) to satisfy the Barkhausen criterion for startup.
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48The frequency stability of a sinusoidal oscillator is given by the normalized derivative evaluated at . To maximize frequency stability, how should the phase angle of the open-loop transfer function behave near resonance?
Sinusoidal oscillators
Hard
A.The phase angle should transition linearly with a very small slope to allow wide tuning.
B.The phase angle should undergo a very rapid change with respect to frequency at .
C.The phase angle should remain exactly constant at over a wide frequency band.
D.The phase angle should have a derivative of zero at .
Correct Answer: The phase angle should undergo a very rapid change with respect to frequency at .
Explanation:
Frequency stability depends on how strongly the feedback network resists deviations in frequency. A large value of means that a small shift in frequency causes a massive phase shift, immediately violating the Barkhausen criterion and pulling the frequency back. Hence, a rapid change in phase (high slope) maximizes stability.
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49An operational amplifier is configured as an inverting amplifier with and . To minimize the DC output offset voltage caused by the input bias currents and (assuming ), what value resistor should be connected between the non-inverting terminal and ground?
The operational amplifier
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
To compensate for the input bias current, the DC resistance seen by both input terminals must be equal. The inverting terminal sees in parallel with (assuming ideal voltage source at input). Therefore, .
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50In the block diagram of a typical operational amplifier, a level shifting stage is placed between the high-gain voltage amplifier and the output stage. What is the primary function of this level shifter?
block diagram of typical op-amp
Hard
A.To shift the AC signal phase by to prevent unstable positive feedback.
B.To match the low output impedance of the gain stage to the high input impedance of the output stage.
C.To shift the quiescent DC voltage level down to zero volts with respect to ground.
D.To provide dominant-pole frequency compensation for the amplifier.
Correct Answer: To shift the quiescent DC voltage level down to zero volts with respect to ground.
Explanation:
Because typical op-amps use direct coupling between stages without blocking capacitors, DC voltage levels build up (e.g., passing through multiple BJT collectors). The level shifting stage brings the quiescent (zero differential input) DC voltage back to before feeding it to the output stage, allowing maximum symmetrical voltage swing.
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51An op-amp has a specified slew rate of . It is used to amplify a sinusoidal signal to a peak output voltage of . What is the maximum frequency (full-power bandwidth) at which this signal can be output without slew-rate induced distortion?
characteristics of operational amplifier
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The maximum rate of change of a sine wave is . Setting this equal to the Slew Rate (SR), we get the full-power bandwidth . Substituting and , .
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52The datasheet of a op-amp lists a minimum Common-Mode Rejection Ratio (CMRR) of . If the op-amp is used in a non-inverting configuration with a closed-loop gain of $100$ and a common-mode input voltage of is applied, what is the maximum expected output error voltage due strictly to the finite CMRR?
reading datasheet of 741
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
corresponds to a linear ratio of . The common-mode error referred to the input is . This input error is amplified by the closed-loop gain , resulting in an output error of .
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53An ideal op-amp based RC phase-shift oscillator utilizes three identical High-Pass RC sections in the feedback loop. What is the required gain of the inverting amplifier, and what is the exact oscillation frequency ?
RC phase shift oscillator
Hard
A.Gain = ,
B.Gain = ,
C.Gain = ,
D.Gain = ,
Correct Answer: Gain = ,
Explanation:
For a phase-shift oscillator using three HPF RC sections (C first, R to ground), the transfer function yields an attenuation of at the phase shift of . Thus, an inverting amplifier (gain ) is required to achieve a loop gain of . The oscillation frequency for the HPF configuration is .
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54In a Wien bridge oscillator, the feedback network acts as a bandpass filter. If the frequency deviates slightly such that , what is the nature of the phase shift introduced by the Wien bridge network?
wien bridge oscillator
Hard
A.The phase shift remains zero, but the amplitude attenuates rapidly.
B.The network introduces a lagging phase shift (negative angle).
C.The network introduces a leading phase shift (positive angle).
D.The network introduces an exact phase shift.
Correct Answer: The network introduces a lagging phase shift (negative angle).
Explanation:
The Wien bridge feedback network has a phase response . When (e.g., ), the numerator becomes negative, making the arctangent negative. Thus, it introduces a lagging phase shift.
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55In the generic oscillator model utilizing three reactances , , and , which of the following combinations correctly describes a Hartley oscillator?
general form of oscillator circuit
Hard
A. is capacitive, is capacitive, is inductive
B. is inductive, is capacitive, is inductive
C. is capacitive, is inductive, is capacitive
D. is inductive, is inductive, is capacitive
Correct Answer: is inductive, is inductive, is capacitive
Explanation:
In a Hartley oscillator, the tank circuit consists of a tapped inductor (forming two inductive reactances and ) and one capacitor (). Therefore, and are inductive, and is capacitive.
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56To adjust (or 'pull') the frequency of a crystal oscillator slightly above its series resonance , a load capacitor is added in series with the crystal. If and are the motional and parallel capacitances of the crystal, what is the new resonant frequency ?
Crystal oscillator
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
When an external capacitor is placed in series with the crystal, it effectively appears in parallel with the crystal's shunt capacitance in the motional equivalent circuit analysis. The new effective parallel capacitance is . The resonant frequency formula is modified to .
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57When modeling non-ideal op-amp characteristics into a schematic equivalent, the Power Supply Rejection Ratio (PSRR) is typically modeled as:
schematic symbol
Hard
A.A dependent current source in parallel with the output stage.
B.A frequency-dependent capacitor between the supply pins and the non-inverting input.
C.A resistor network cross-coupling the positive and negative supply terminals to the output.
D.A DC voltage source in series with one of the input terminals, whose value fluctuates with supply voltage changes.
Correct Answer: A DC voltage source in series with one of the input terminals, whose value fluctuates with supply voltage changes.
Explanation:
PSRR measures how changes in the power supply voltage affect the op-amp's input offset voltage. In small-signal schematic modeling, this is represented as a dependent DC voltage source in series with the input, .
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58An operational amplifier is employed in a precision integrator circuit. If the op-amp has an input offset voltage , how does this non-ideality affect the output over time , assuming the input is grounded?
characteristics of operational amplifier
Hard
A. will settle at a constant DC error equal to .
B. will settle at a constant DC error of .
C. will oscillate at a high frequency due to triggering the dominant pole.
D. will drift linearly with time at a rate of , eventually saturating the op-amp.
Correct Answer: will drift linearly with time at a rate of , eventually saturating the op-amp.
Explanation:
In an integrator, the feedback loop is a capacitor and the input resistor is . An input offset voltage appears across , creating a constant offset current . This constant current is integrated by the capacitor, causing the output voltage to ramp linearly as , leading to saturation.
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59Dominant-pole compensation is internally implemented in an op-amp using a Miller capacitor across the high-gain stage. While this guarantees stability for unity-gain configurations, what is its primary detrimental side effect?
block diagram of typical op-amp
Hard
A.It causes severe crossover distortion in the push-pull output stage.
B.It increases the input bias current exponentially.
C.It drastically reduces the slew rate by limiting how fast the internal bias currents can charge the compensating capacitor.
D.It forces the op-amp to have a lower common-mode rejection ratio at DC.
Correct Answer: It drastically reduces the slew rate by limiting how fast the internal bias currents can charge the compensating capacitor.
Explanation:
The Miller compensation capacitor must be charged and discharged by the current from the preceding differential amplifier stage. Since this current is finite (limited by the tail current source), the maximum rate of change of voltage (Slew Rate) is severely limited, governed by the equation .
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60According to the typical parameters in a datasheet, the open-loop gain drops to (unity gain) at approximately . If this op-amp is wired as a non-inverting amplifier with resistors and , what is the closed-loop bandwidth?
reading datasheet of 741
Hard
A.
B.
C.
D.
Correct Answer:
Explanation:
The 741 op-amp is internally compensated, meaning it has a constant Gain-Bandwidth Product (GBWP). . The non-inverting closed-loop gain is . The closed-loop bandwidth is .