Test your understanding of operational amplifiers, including gain, bandwidth, and stability concepts. This quiz covers key principles of op-amp circuits, feedback types, and important performance parameters for electronics learners.
Which characteristic describes an ideal operational amplifier when used in linear applications?
Explanation: An ideal operational amplifier is characterized by infinite input impedance, ensuring that it draws no current from the signal source. High output resistance is incorrect; the ideal op-amp should have zero output resistance. A low common mode rejection ratio is undesirable, as a high CMRR ensures only the difference between inputs is amplified. Finite gain is also wrong; the ideal op-amp has infinite gain.
What is the primary reason for applying negative feedback to an operational amplifier circuit?
Explanation: Negative feedback is mainly used to stabilize the gain of an op-amp circuit, making amplification more predictable and less sensitive to component variations. While it can also increase input resistance, this is not its primary purpose. Decreasing bandwidth is usually an unintended side effect, not a goal. Introducing distortion is not a function of negative feedback—on the contrary, negative feedback reduces distortion.
What does the gain-bandwidth product of an operational amplifier specify?
Explanation: The gain-bandwidth product refers to the frequency at which an amplifier's gain drops to one, multiplied by its open-loop gain at low frequencies, which remains quite constant for op-amps. Summing gain and bandwidth is nonsensical and not used. The difference between input and output voltages is just the amplified signal, unrelated to this parameter. The ratio of output to input resistance is known as impedance, not gain-bandwidth.
In an inverting op-amp amplifier, what is the phase relationship between the input and output signals?
Explanation: An inverting amplifier produces an output that is 180 degrees out of phase with the input, meaning the output reverses the input signal's polarity. 90 or 45 degrees would indicate a phase shift but not a true inversion. The in-phase option describes a non-inverting configuration, not the inverting setup.
What primarily sets the closed-loop gain of an op-amp configured as an inverting amplifier?
Explanation: For an inverting amplifier, the closed-loop gain equals the negative ratio of the feedback resistor to the input resistor, allowing precise control with external components. Open-loop gain does not directly set this value as negative feedback dominates. Supply voltage affects the output swing, not the gain. Bandwidth limitation constrains frequency response but doesn't set static gain.
Where is the input signal applied in a non-inverting op-amp amplifier configuration?
Explanation: In a non-inverting amplifier, the signal is applied to the non-inverting input for unity or greater gain while retaining the input signal's phase. The inverting input is used for feedback, not the direct signal. Power supply and ground pins are necessary for operation but not for input signal application.
As the closed-loop gain of an op-amp circuit increases, what typically happens to its bandwidth?
Explanation: The bandwidth of an op-amp is inversely related to its closed-loop gain due to the constant gain-bandwidth product; increasing gain results in reduced bandwidth. Bandwidth does not increase as gain rises. It rarely remains constant except in idealistic cases, and it certainly does not become infinite in real circuits.
Which function commonly uses positive feedback in op-amp circuits?
Explanation: Positive feedback is essential in oscillator circuits to sustain oscillations by reinforcing the input. It is generally avoided in linear amplifiers, which rely on negative feedback for stability. Voltage regulation and low-pass filtering do not typically use positive feedback—these prefer negative feedback for accuracy and stability.
What is the input offset voltage in an operational amplifier?
Explanation: Input offset voltage is the small differential voltage that must be applied between the inputs for the output to be exactly zero, compensating for internal imbalances. It is not the difference in supply voltages, which is unrelated. Output currents being different do not define input offset voltage, nor does the maximum rated input voltage.
What is the main use of an op-amp configured as a unity-gain buffer (voltage follower)?
Explanation: A unity-gain buffer is used to connect circuits while offering high input impedance and low output impedance, minimizing signal loss and loading effects. Amplifying by 10 times is untrue—gain is exactly one. It does not invert the signal, and phase shift introduced is negligible under normal circumstances.
If an op-amp has a low slew rate, what problem can occur when amplifying a fast, large signal?
Explanation: A low slew rate limits how quickly an op-amp can change its output voltage, causing distortion for rapid signal transitions. Increased gain is unrelated to slew rate, and zero offset voltage refers to another specification. Infinite bandwidth is impossible, especially with a low slew rate.
What is the role of frequency compensation in an operational amplifier?
Explanation: Frequency compensation shapes the open-loop response to ensure stability and avoid unwanted oscillations when feedback is applied. It does not increase DC gain or reduce input impedance. Amplifying only high frequencies is incorrect; compensation usually rolls off high-frequency gain to help stability.
Which statement best defines a common-mode signal in an operational amplifier?
Explanation: A common-mode signal appears equally at both op-amp inputs, and should be rejected for optimal performance. If applied only to one input, it is not common. The output is not a common-mode signal, and a differential signal is the difference between the two inputs, not common-mode.
Why is low input bias current desirable in sensitive op-amp circuits?
Explanation: Low input bias current prevents unwanted voltage drops across the resistors connected to op-amp inputs, which could affect measurement accuracy. Output swing capability depends on supply voltage and output stage design, not bias current. Power supply rejection and negative feedback are not directly governed by input bias current.
Why is phase margin important for op-amp stability when using feedback?
Explanation: Phase margin reflects the safety buffer before feedback turns from negative to positive (loss of stability), so it tells you how near oscillation the circuit is. It does not measure voltage gain, which is a separate specification. Input offset voltage and common-mode rejection are unrelated to phase margin.
Compared with open-loop operation, what is a primary benefit of using an op-amp in closed-loop configuration?
Explanation: Closed-loop operation with feedback provides a set and reliable gain determined by external resistors, which is ideal for most practical op-amp applications. Infinite output voltage is not achievable. Op-amps always have some input bias current, and closed-loop operation does not necessarily mean higher power consumption.