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Questions and Answers
What does the slew rate (SR) measure?
What does the slew rate (SR) measure?
- The average response time of an op amp
- The maximum frequency of an op amp
- The change in output voltage over change in time (correct)
- The output voltage at peak signal
In the equation $SR = \frac{\Delta v_{out}}{\Delta t}$, what does the Greek letter delta (Δ) indicate?
In the equation $SR = \frac{\Delta v_{out}}{\Delta t}$, what does the Greek letter delta (Δ) indicate?
- A fixed time period
- A change in value (correct)
- A measurement of voltage
- A constant rate
What will happen if the output sine wave signal is very large and the frequency is high?
What will happen if the output sine wave signal is very large and the frequency is high?
- The output will become a square wave
- Slew rate will have no effect
- Slew rate will distort the output signal (correct)
- The output will remain unchanged
For a 741C op amp, what is the slew rate given?
For a 741C op amp, what is the slew rate given?
How can calculus be used regarding slew rate and sine waves?
How can calculus be used regarding slew rate and sine waves?
What does it mean when $SS \leq SR$ in terms of output distortion?
What does it mean when $SS \leq SR$ in terms of output distortion?
If the initial slope of an output waveform is represented by which variable?
If the initial slope of an output waveform is represented by which variable?
Why is the slew rate crucial in the data sheet of an op amp?
Why is the slew rate crucial in the data sheet of an op amp?
What does a voltage follower circuit produce at its output?
What does a voltage follower circuit produce at its output?
What is the closed-loop input impedance of a voltage follower circuit like?
What is the closed-loop input impedance of a voltage follower circuit like?
In a voltage follower, what happens to the closed-loop output impedance?
In a voltage follower, what happens to the closed-loop output impedance?
What is the power supply rejection ratio (PSRR) used to measure?
What is the power supply rejection ratio (PSRR) used to measure?
Why is a voltage follower ideal for interfacing a high-impedance source with a low-impedance load?
Why is a voltage follower ideal for interfacing a high-impedance source with a low-impedance load?
What does a closed-loop bandwidth equal to in a voltage follower?
What does a closed-loop bandwidth equal to in a voltage follower?
What is a key advantage of using a voltage follower regarding output offset error?
What is a key advantage of using a voltage follower regarding output offset error?
Which linear ICs are commonly used in conjunction with op amps?
Which linear ICs are commonly used in conjunction with op amps?
What is the output voltage equation for a differential amplifier?
What is the output voltage equation for a differential amplifier?
What is the phase relationship of the output voltage to the noninverting input voltage?
What is the phase relationship of the output voltage to the noninverting input voltage?
In applications where only one input is used, which input is typically active while the other is grounded?
In applications where only one input is used, which input is typically active while the other is grounded?
What happens to the output voltage when the two input voltages are equal?
What happens to the output voltage when the two input voltages are equal?
How does a single-ended output differ from a differential output in terms of voltage gain?
How does a single-ended output differ from a differential output in terms of voltage gain?
Which component is removed in the single-ended output configuration of a differential amplifier?
Which component is removed in the single-ended output configuration of a differential amplifier?
What is the total input referred to when both noninverting and inverting input voltages are present?
What is the total input referred to when both noninverting and inverting input voltages are present?
What characterizes the output polarity when $v_1$ is greater than $v_2$?
What characterizes the output polarity when $v_1$ is greater than $v_2$?
In a summing circuit, what is the significance of the virtual ground at the inverting input?
In a summing circuit, what is the significance of the virtual ground at the inverting input?
When the resistances in a summing circuit are equal, what is the resulting closed-loop voltage gain?
When the resistances in a summing circuit are equal, what is the resulting closed-loop voltage gain?
What defines the output voltage in a summing amplifier with multiple inputs?
What defines the output voltage in a summing amplifier with multiple inputs?
What happens to the voltage gain of a voltage follower circuit?
What happens to the voltage gain of a voltage follower circuit?
What is the role of Thevenin resistance in a summing circuit?
What is the role of Thevenin resistance in a summing circuit?
In the formula for output voltage of a summing circuit, which term shows the contribution from each input voltage?
In the formula for output voltage of a summing circuit, which term shows the contribution from each input voltage?
How is the effective resistance looking from the inverting input in a summing amplifier calculated?
How is the effective resistance looking from the inverting input in a summing amplifier calculated?
If you wanted to reduce the output voltage in a summing circuit, which modification would help?
If you wanted to reduce the output voltage in a summing circuit, which modification would help?
What is the output voltage equation when only the noninverting input is active?
What is the output voltage equation when only the noninverting input is active?
When both inputs are grounded in the dc analysis of a diff amp, what assumption is made regarding component characteristics?
When both inputs are grounded in the dc analysis of a diff amp, what assumption is made regarding component characteristics?
In the inverting input configuration, how does the phase relationship between the input and output change?
In the inverting input configuration, how does the phase relationship between the input and output change?
What distinguishes the differential single-ended output configuration from the differential differential output configuration?
What distinguishes the differential single-ended output configuration from the differential differential output configuration?
What is the overall behavior of the voltage gain $A_v$ in a single-ended output configuration compared to a differential output configuration?
What is the overall behavior of the voltage gain $A_v$ in a single-ended output configuration compared to a differential output configuration?
Which statement reflects a characteristic of the general case of a differential amplifier?
Which statement reflects a characteristic of the general case of a differential amplifier?
In the given configurations, which input does the equation $v_{out} = -A_v (v_2)$ specifically pertain to?
In the given configurations, which input does the equation $v_{out} = -A_v (v_2)$ specifically pertain to?
What is meant by the term 'tail current' in the context of a differential amplifier?
What is meant by the term 'tail current' in the context of a differential amplifier?
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Study Notes
Slew Rate
- The slew rate is the fastest rate of change of the output voltage of an operational amplifier (op amp).
- It is calculated as the change in output voltage divided by the change in time.
- The slew rate is specified in the datasheet for an op amp and represents the maximum speed at which the output voltage can change.
- A larger slew rate indicates a faster response time.
- Slew-rate distortion can occur when the input signal is large and the frequency is high, limiting the output signal's fidelity.
Inverting Summing Amplifier
- An inverting summing amplifier combines multiple input signals by multiplying each input by a corresponding gain factor and summing the results.
- If the feedback resistor (Rf) and all input resistors (R1, R2, etc.) have equal values, each input channel has a unity gain (1).
- This allows for combining multiple input signals while preserving their relative magnitudes.
Voltage Follower
- A voltage follower is an op-amp circuit that employs maximum negative feedback, producing a closed-loop voltage gain of unity.
- Since the output voltage directly feeds back to the inverting input, the output voltage is essentially equal to the input voltage.
- Voltage followers offer a low output impedance and high input impedance which makes it effective for interfacing between a high-impedance source and a low-impedance load.
- The closed-loop bandwidth of a voltage follower is maximized, as it is equal to the unity-gain frequency (fUNITY).
- Output offset errors are minimal because input errors are not amplified.
Differential Amplifier
- A differential amplifier (diff amp) amplifies the difference between two input signals.
- The noninverting input (v1) produces an output in phase with the input signal, while the inverting input (v2) produces an output that is 180° out of phase.
- The equation for the output voltage is: vout = Av (v1 - v2), where Av is the voltage gain.
- A diff amp can be configured with different input and output modes:
- Differential Input and Differential Output: The output is the difference of the two collector currents (vc2 - vc1)
- Differential Input and Single-Ended Output: The output is taken from one collector resulting in half the voltage gain.
- Single-Ended Input and Differential Output: One input is grounded and the other is the active input, providing a differential output and providing the same voltage gain as differential input.
- Single-Ended Input and Single-Ended Output: Similar to single-ended input and differential output with the same voltage gain but the output is taken from one collector only.
- Diff amps are used in circuits like operational amplifiers and in applications where the difference between two signals needs to be amplified.
DC Analysis of a Diff Amp
- The diff amp is sometimes called a long-tail pair, and the current flowing through the common emitter resistor (RE) is called the tail current.
- Ideal analysis assumes identical transistors with equal collector resistors and assumes both bases are grounded.
- The tail current provides a reference point for controlling the operating point of the transistors.
- Changes in input signals cause changes in the base currents of the transistors, which affects the collector currents and ultimately the output voltage.
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