1What is the input impedance of an ideal operational amplifier?
A.Zero
B.1 k
C.1 M
D.Infinity
Correct Answer: Infinity
Explanation:An ideal op-amp has infinite input impedance (), meaning no current flows into the input terminals.
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2What is the output impedance of an ideal operational amplifier?
A.Zero
B.Infinity
C.100
D.50
Correct Answer: Zero
Explanation:An ideal op-amp has zero output impedance (), allowing it to drive any load without a voltage drop.
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3Which of the following parameters is infinite for an ideal op-amp?
A.Input offset voltage
B.Output resistance
C.Open-loop voltage gain
D.Noise figure
Correct Answer: Open-loop voltage gain
Explanation:The open-loop voltage gain () of an ideal op-amp is considered to be infinite.
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4What is the bandwidth of an ideal operational amplifier?
A.0 Hz
B.20 kHz
C.1 MHz
D.Infinity
Correct Answer: Infinity
Explanation:An ideal op-amp has infinite bandwidth, meaning it can amplify signals of any frequency with constant gain.
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5In the equivalent circuit of an op-amp, the output voltage is modeled as:
A.A current source controlled by input current
B.A voltage source dependent on the differential input voltage
C.A fixed DC voltage source
D.A variable resistor
Correct Answer: A voltage source dependent on the differential input voltage
Explanation:The output stage in the equivalent circuit is modeled as a dependent voltage source with value , where is the difference between input voltages.
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6Ideally, the Common Mode Rejection Ratio (CMRR) of an op-amp should be:
A.Zero
B.Unity (1)
C.Finite but high
D.Infinity
Correct Answer: Infinity
Explanation:Ideally, an op-amp should completely reject common-mode signals (noise), resulting in an infinite CMRR.
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7The ideal voltage transfer curve of an op-amp represents a plot between:
A.Output voltage and time
B.Output voltage and differential input voltage
C.Input current and output current
D.Supply voltage and gain
Correct Answer: Output voltage and differential input voltage
Explanation:The transfer curve plots versus . For an ideal op-amp, this is a vertical line at the origin transitioning immediately to saturation.
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8In the ideal voltage transfer curve, what happens when the differential input voltage is non-zero?
A.The output remains at 0V
B.The output increases linearly indefinitely
C.The output immediately saturates to or
D.The output oscillates
Correct Answer: The output immediately saturates to or
Explanation:Because the open-loop gain is infinite, any non-zero differential input drives the ideal op-amp immediately into positive or negative saturation.
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9Which of the following is NOT a characteristic of an ideal op-amp?
A.Infinite Slew Rate
B.Zero Input Offset Voltage
C.Infinite Output Resistance
D.Zero Common Mode Gain
Correct Answer: Infinite Output Resistance
Explanation:An ideal op-amp has zero output resistance, not infinite.
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10In an open-loop configuration, the op-amp functions primarily as a:
A.Linear amplifier
B.Voltage follower
C.Comparator
D.Filter
Correct Answer: Comparator
Explanation:Due to infinite (or very high) gain, the open-loop op-amp acts as a comparator, switching between saturation levels based on which input is higher.
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11Why are open-loop op-amp configurations rarely used for linear amplification?
A.The gain is too low
B.The bandwidth is too high
C.The gain is extremely high and unstable due to temperature and process variations
D.The input impedance is too low
Correct Answer: The gain is extremely high and unstable due to temperature and process variations
Explanation:The open-loop gain is massive and varies significantly with temperature and manufacturing, making it impossible to control the output linearly without feedback.
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12What is the effect of negative feedback on the stability of an op-amp circuit?
A.It decreases stability
B.It increases stability
C.It has no effect on stability
D.It causes oscillations
Correct Answer: It increases stability
Explanation:Negative feedback stabilizes the gain and reduces the sensitivity of the circuit to parameter variations.
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13Applying negative feedback to an op-amp generally:
A.Increases gain and decreases bandwidth
B.Decreases gain and increases bandwidth
C.Increases both gain and bandwidth
D.Decreases both gain and bandwidth
Correct Answer: Decreases gain and increases bandwidth
Explanation:Negative feedback reduces the overall gain but extends the frequency range (bandwidth) over which the amplifier operates effectively. The Gain-Bandwidth Product remains constant.
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14In a block diagram representation of a feedback amplifier, the feedback network connects:
A.The input to the power supply
B.The output back to the input
C.The non-inverting terminal to ground
D.The output to the power supply
Correct Answer: The output back to the input
Explanation:A feedback network samples the output signal and returns a portion of it to the input.
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15A Voltage Series Feedback amplifier corresponds to which standard op-amp configuration?
A.Inverting Amplifier
B.Non-Inverting Amplifier
C.Differentiator
D.Integrator
Correct Answer: Non-Inverting Amplifier
Explanation:In a Non-Inverting amplifier, the output voltage is sampled (Voltage) and fed back in series with the input signal to the differential input (Series).
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16A Voltage Shunt Feedback amplifier corresponds to which standard op-amp configuration?
A.Inverting Amplifier
B.Non-Inverting Amplifier
C.Voltage Follower
D.Differential Amplifier
Correct Answer: Inverting Amplifier
Explanation:In an Inverting amplifier, the output voltage is sampled (Voltage) and the feedback current mixes with the input current at the node (Shunt).
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17In a Non-Inverting amplifier with feedback resistor and input resistor , the closed-loop voltage gain is:
A.
B.
C.
D.
Correct Answer:
Explanation:The standard gain formula for a Non-Inverting amplifier (Voltage Series Feedback) is .
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18In an Inverting amplifier with feedback resistor and input resistor , the closed-loop voltage gain is:
A.
B.
C.
D.
Correct Answer:
Explanation:The standard gain formula for an Inverting amplifier (Voltage Shunt Feedback) is .
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19What is the input resistance of a standard Inverting Amplifier (Voltage Shunt Feedback)?
A.Infinity
B.Zero
C.Equal to the input resistor
D.Equal to the feedback resistor
Correct Answer: Equal to the input resistor
Explanation:Because of the virtual ground at the inverting terminal, the input impedance seen by the source is simply .
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20What is the input resistance of an ideal Non-Inverting Amplifier (Voltage Series Feedback)?
A.
B.
C.Zero
D.Infinity
Correct Answer: Infinity
Explanation:Since the input signal is applied directly to the non-inverting terminal of the ideal op-amp (which draws no current), the input impedance is infinite.
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21The concept of 'Virtual Ground' applies primarily to which configuration?
A.Non-Inverting Amplifier
B.Voltage Follower
C.Inverting Amplifier
D.Open loop comparator
Correct Answer: Inverting Amplifier
Explanation:In the Inverting configuration, the non-inverting terminal is grounded. Due to the virtual short concept, the inverting terminal is maintained at approximately 0V (Virtual Ground).
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22For a Voltage Follower (Buffer) circuit:
A.,
B.,
C.
D.,
Correct Answer: ,
Explanation:A voltage follower connects the output directly to the inverting input () with no resistor to ground ().
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23What is the voltage gain of a Voltage Follower?
A.
B.1
C.-1
D.Infinity
Correct Answer: 1
Explanation:A voltage follower has a unity gain (), meaning .
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24In a Voltage Series Feedback amplifier (Non-Inverting), the output resistance relates to the open-loop output resistance as:
A.
B.
C.
D.
Correct Answer:
Explanation:Voltage sampling (taking voltage from output) in negative feedback reduces the output resistance by the factor .
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25Calculate the gain of a Non-Inverting amplifier with and .
A.9
B.10
C.-9
D.-10
Correct Answer: 10
Explanation:.
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26Calculate the gain of an Inverting amplifier with and .
A.5
B.-5
C.6
D.-6
Correct Answer: -5
Explanation:.
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27In a Voltage Shunt Feedback (Inverting) amplifier, the feedback factor (current ratio) is often approximated in terms of resistance as:
A.
B.
C. (Transresistance)
D.
Correct Answer: (Transresistance)
Explanation:In strict feedback analysis for voltage-shunt, the feedback network senses voltage and returns current. The feedback parameter is often measured in Siemens (). However, loosely in voltage gain derivations, the feedback ratio for the voltage divider is often discussed. In the context of the transresistance block model, .
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28What is the phase shift between input and output in a Non-Inverting amplifier?
A.
B.
C.
D.
Correct Answer:
Explanation:The output signal is in phase with the input signal in a non-inverting configuration.
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29What is the phase shift between input and output in an Inverting amplifier?
A.
B.
C.
D.
Correct Answer:
Explanation:The negative sign in the gain formula indicates a phase shift.
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30A differential amplifier amplifies:
A.The sum of the two input voltages
B.The difference between the two input voltages
C.Only the input connected to the positive terminal
D.The average of the two input voltages
Correct Answer: The difference between the two input voltages
Explanation:Differential amplifiers are designed to amplify the difference () and reject common signals.
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31In a standard difference amplifier utilizing one op-amp and four resistors (two input resistors, two resistors), the output voltage is given by:
A.
B.
C.
D.
Correct Answer:
Explanation:If the resistor ratios are balanced (i.e., matched and matched pairs), the output is the difference multiplied by the gain factor .
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32What happens to the CMRR of a difference amplifier if the resistors are not perfectly matched?
A.CMRR increases significantly
B.CMRR remains infinite
C.CMRR degrades (decreases)
D.CMRR becomes negative
Correct Answer: CMRR degrades (decreases)
Explanation:Mismatch in resistors leads to unequal gains for the two inputs, causing common-mode signals to appear at the output, thus lowering the Common Mode Rejection Ratio.
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33In the concept of 'Virtual Short', if the non-inverting terminal is at 2V, what is the potential at the inverting terminal (assuming negative feedback)?
A.0V
B.-2V
C.2V
D.Saturation Voltage
Correct Answer: 2V
Explanation:Due to the virtual short characteristic created by high open-loop gain and negative feedback, the voltage at the inverting terminal tracks the non-inverting terminal.
Explanation:Shunt mixing at the input (connecting feedback to the input node) lowers the input impedance due to the Miller effect / feedback current.
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35The feedback fraction for a non-inverting amplifier circuit (voltage divider network) is:
A.
B.
C.
D.
Correct Answer:
Explanation:The voltage fed back to the inverting terminal is determined by the voltage divider and across the output. .
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36If an op-amp has an open-loop gain of and a feedback factor , the desensitivity factor is approximately:
A.100
B.1000
C.
D.
Correct Answer: 1000
Explanation:The desensitivity factor is .
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37What is the primary advantage of using a Voltage Follower between a source and a load?
A.To increase the voltage amplitude
B.To invert the signal polarity
C.To prevent loading effects (Impedance Matching)
D.To filter high frequency noise
Correct Answer: To prevent loading effects (Impedance Matching)
Explanation:Because it has high input impedance and low output impedance, it isolates the source from the load, preventing the load from drawing current from the source.
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38In a practical differential amplifier circuit, the Common Mode Gain () should ideally be:
A.Infinite
B.Equal to Differential Gain ()
C.Zero
D.1
Correct Answer: Zero
Explanation:Ideally, a differential amplifier should not amplify signals common to both inputs ().
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39Which equation represents the output of a summing amplifier (inverting summer) with three inputs and equal resistors ?
A.
B.
C.
D.
Correct Answer:
Explanation:An inverting summer with equal resistors sums the inputs and inverts the sign.
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40What defines the 'Saturation Region' of an op-amp?
A.The region where output voltage is proportional to input voltage
B.The region where output voltage is constant at or regardless of input changes
C.The region where input impedance becomes zero
D.The region where frequency response drops
Correct Answer: The region where output voltage is constant at or regardless of input changes
Explanation:Saturation occurs when the output reaches the supply rail limits and cannot increase further.
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41For a Voltage Series Feedback amplifier, if and , the circuit acts as:
A.Inverting Amplifier
B.Differential Amplifier
C.Unity Gain Buffer
D.Current Amplifier
Correct Answer: Unity Gain Buffer
Explanation:This configuration creates a direct connection from output to inverting input with no ground path, creating a voltage follower (Unity Gain Buffer).
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42If the input to an ideal inverting amplifier is 2V, , and , the current flowing through the feedback resistor is:
A.0 mA
B.1 mA
C.2 mA
D.4 mA
Correct Answer: 2 mA
Explanation:Virtual ground is at 0V. Current through is . Ideally, all this current flows through .
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43In a feedback amplifier block diagram, the mixing of signals at the input for Voltage Series feedback is:
A.Current mixing (Parallel)
B.Voltage mixing (Series)
C.Power mixing
D.Resistive mixing
Correct Answer: Voltage mixing (Series)
Explanation:In Voltage Series feedback (Non-Inverting), the feedback voltage is placed in series with the input voltage (subtracted from it) at the differential input.
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44The slew rate of an ideal op-amp is:
A.0 V/s
B.0.5 V/s
C.100 V/s
D.Infinity
Correct Answer: Infinity
Explanation:Ideally, the op-amp output can change instantaneously, implying an infinite slew rate.
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45What is the CMRR in decibels (dB) if and ?
A.40 dB
B.60 dB
C.80 dB
D.100 dB
Correct Answer: 80 dB
Explanation:. In dB: .
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46In the equivalent circuit, the input terminals of an ideal op-amp are shown as:
A.Short circuit
B.Open circuit
C.Connected via a resistor
D.Connected to ground
Correct Answer: Open circuit
Explanation:Because input impedance is infinite, there is no electrical connection (open circuit) between the inverting and non-inverting terminals in the ideal model.
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47Voltage Shunt Feedback stabilizes:
A.Voltage gain ()
B.Transresistance ()
C.Current gain ()
D.Transconductance ()
Correct Answer: Transresistance ()
Explanation:Voltage Shunt feedback (Inverting configuration) takes an input current and produces an output voltage. The feedback stabilizes the ratio (Transresistance).
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48If the open-loop gain decreases due to aging, the closed-loop gain of a negative feedback amplifier:
A.Decreases proportionally
B.Remains almost constant
C.Increases drastically
D.Becomes zero
Correct Answer: Remains almost constant
Explanation:Because provided , the closed-loop gain is desensitized to changes in the open-loop gain.
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49The difference mode input voltage is defined as :
A.
B.
C.
D.
Correct Answer:
Explanation:The differential input is simply the difference between the voltage at the non-inverting terminal () and the inverting terminal ().
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50An op-amp connected with positive feedback usually results in:
A.A stable amplifier
B.An oscillator or Schmitt Trigger
C.An attenuator
D.A rectifier
Correct Answer: An oscillator or Schmitt Trigger
Explanation:Positive feedback drives the op-amp into saturation (hysteresis), creating bistable states used in Schmitt triggers or oscillations.
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