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Questions and Answers
What is a feedback amplifier?
What is a feedback amplifier?
Define negative feedback.
Define negative feedback.
The feedback signal is out of phase with the input signal and is commonly used in amplifier circuits.
What are the advantages of negative feedback in amplifiers?
What are the advantages of negative feedback in amplifiers?
Reduces frequency distortion, noise, and nonlinear distortion; Increases bandwidth and stability.
The open-loop gain of a feedback system can be estimated as $\frac{x_0}{x_s} = 1 + A \beta$. Here, $A \beta$ is called the ____ of feedback.
The open-loop gain of a feedback system can be estimated as $\frac{x_0}{x_s} = 1 + A \beta$. Here, $A \beta$ is called the ____ of feedback.
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What are the four basic types of feedback connections?
What are the four basic types of feedback connections?
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In Example 2, what is the percentage fall in gain with feedback if the gain without feedback falls by 20%?
In Example 2, what is the percentage fall in gain with feedback if the gain without feedback falls by 20%?
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Study Notes
Feedback Circuits
- A feedback amplifier consists of two parts: an amplifier and a feedback circuit.
- The feedback signal can be either negative (out of phase with the input signal) or positive (in phase with the input signal).
Feedback Types
- Negative feedback: used in amplifier circuits, the feedback signal is out of phase with the input signal.
- Positive feedback: used in oscillator circuits, the feedback signal is in phase with the input signal.
Feedback Amplifier Concepts
- A simple block diagram of a feedback amplifier consists of a mixer circuit, an amplifier block, and a feedback network block.
- The gain of the feedback system can be estimated as:
A_f = A / (1 + AB). - When
ABis very large, the gain of the feedback amplifier is almost determined by the feedback network.
Advantages of Negative Feedback
- Reduces frequency distortion: the gain with feedback is approximately
B, which is purely resistive and not dependent on frequency. - Reduces noise and nonlinear distortion: the noise signal gain is reduced by
(1+AB). - Increases bandwidth (BW): the bandwidth
BWincreases for an amplifier with negative feedback. - Gain is stable with feedback: the change in the closed-loop gain
A_fis less than the corresponding percent change in the open-loop gainAby the factor(1+AB).
Feedback Connection Types
- There are four basic ways of connecting the feedback signal:
- Voltage-series feedback
- Voltage-shunt feedback
- Current-series feedback
- Current-shunt feedback
Example Problems
- Example 1: Calculate the voltage gain of an amplifier with negative feedback.
- Example 2: Calculate the fraction of the output feedback and the percentage fall in gain with feedback due to ageing of components.
- Example 3: Calculate the change in gain of the feedback amplifier due to temperature.
- Example 4: Calculate the feedback fraction, overall voltage gain, and output voltage for a negative voltage feedback amplifier.
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Description
This quiz covers feedback circuits, including types of feedback and their applications in amplifier circuits.
