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99.5.1. Changes in Voltage Gain and Current Gain
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Today, we're discussing current gain in amplifier circuits. Can anyone tell me what current gain refers to?
Isn't it the ratio of output current to input current?
Exactly! It's commonly denoted as A. When feedback is applied, do you think this current gain changes?
I wonder if it stays the same because feedback is supposed to stabilize things.
You're right! The current gain remains unchanged due to the balancing effects of feedback. Remember this: 'Feedback boosts stability, holding gains in equilibrium.'
Why is it important that the current gain doesn't change?
Great question! It allows designers to predict performance without unexpected alterations when feedback is introduced. Let's summarize: Current gain remains constant due to feedback's stabilizing effect.
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Now, let's shift our focus to voltage gain. Can anyone recall how feedback influences voltage gain?
From what we learned, the gain decreases with feedback, right?
Correct! However, as the voltage gain decreases, the output resistance increases simultaneously. Can anyone explain why this happens?
Because feedback essentially redistributes the signal effects throughout the circuit?
That's a great observation! The increased output resistance counteracts the decreased gain, keeping voltage gain stable overall. Let's cement this concept with a mnemonic: 'Vicious Velcro – Voltage remains, though resistance gains.'
That helps a lot! So, we won't see any change in voltage gain even with feedback?
Exactly! Due to the balancing nature of these characteristics, voltage gain retains its value. Let's recap: Voltage gain is stable due to simultaneous decreases and increases.
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Create a free accountFinally, let’s investigate trans-impedance. What does trans-impedance represent in our circuits?
Is it the output voltage per input current?
Yes, that’s right! Trans-impedance is defined as Z = V/I. Now, how does feedback affect this parameter?
I think it increases because feedback enhances overall stability and performance?
Indeed! The output voltage rises more than the input current response diminishes, resulting in increased trans-impedance. As a mnemonic: 'Zig-Zagging in circuits, trans-impedance escalates.'
That makes sense! So, trans-impedance benefits from feedback, unlike voltage and current gains.
Exactly! It's crucial to distinguish these differences. In summary: Trans-impedance increases due to effective feedback in the circuit.
Overview
Short Summary
This section discusses how feedback affects voltage gain, current gain, and trans-impedance in amplifier circuits.
Medium Summary
The impact of feedback on amplifier circuits is examined, focusing on how both voltage and current gains decrease while input and output resistances increase. The section also explains the significance of trans-impedance and provides guidelines for selecting feedback values.
Detailed Summary
Changes in Voltage Gain and Current Gain
In this section, we explore the effects of feedback on voltage gain, current gain, and trans-impedance in analog circuits. Feedback is an essential technique employed in amplifiers to enhance stability and performance. Feedback affects the gains and resistances as follows:
- Current Gain: The current gain, denoted as A, is found to remain unchanged despite the introduction of feedback. This is attributed to the relationship between the current gain (G) and the load resistance (R), where both parameters are influenced similarly by feedback.
- Voltage Gain: The voltage gain also remains constant due to the opposite effects on the gain (G) decreasing and resistance (R) increasing by the same factor. Therefore, any change in one is countered by a change in the other, illustrating the principle of feedback stability.
- **Trans-Impedance (
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Create a free accountIn fact, we are making this G getting reduced by a factor of that desensitization. So, this is getting decreased D = (1 + G′ β ) and it is (1 + g R).
Detailed Explanation
The desensitization factor is a key metric in feedback circuits. When feedback is applied to an amplifier, it can reduce the gain, denoted by G and G′. The desensitization factor D reflects this reduction and is calculated as D = (1 + G′ β) or D = (1 + g R), indicating how much the gain has decreased due to the feedback mechanism.
Examples & Analogies
Think of a speaker with a loud sound system. When you adjust the volume down to avoid distortion, you are effectively desensitizing the output sound level. Similarly, feedback in circuits lowers the overall gain to prevent distortion in signals.
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Create a free accountAlso, we know that input resistance getting increased by this factor, output resistance it is also getting increased by the same factor D.
Detailed Explanation
When feedback is applied, both the input and output resistances of the amplifier circuit increase by the same desensitization factor. This change is significant because a higher input resistance can improve the circuit's ability to not load the source signal too much, while a higher output resistance may be advantageous in certain applications.
Examples & Analogies
Imagine you have a sponge (input resistance) and you are trying to absorb water (input signal). If the sponge increases in size (input resistance increases), it can hold more water without becoming too saturated, thereby preventing interference with your work.
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Create a free accountIf I want to see what kind of changes do you expect or do you see for a current gain, then, we have to look into the expression of the current gain in terms of G. A = G R.
Detailed Explanation
Current gain in an amplifier circuit is defined by the relationship A = G R, where G is the trans-conductance and R is the resistance in the circuit. It can be observed that although G decreases due to feedback, R increases correspondingly, resulting in no change in the overall current gain.
Examples & Analogies
Consider a water pump that can push water (current) through a pipe. If the capacity of the pump decreases (lower G) but the pipe diameter increases (higher R), the overall flow rate remains the same. This mirrors how feedback affects current gain in amplifiers.
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Create a free accountIf I consider the expression of the voltage gain from here which is G m times R. A = G R and here again G it is decreased but R it got increased by the same factor D.
Detailed Explanation
Voltage gain is described by the expression A = G R. Even if G decreases due to feedback, the resistance R increases by a correspondingly matching factor. As such, the changes in G and R counteract each other, leading to no observable change in voltage gain.
Examples & Analogies
Picture a seesaw at the playground: if one side is lowered (reduced gain), the other side can be lifted (increased resistance), thereby keeping the seesaw level (no change in voltage gain). This image helps visualize how opposing changes in circuit parameters balance out.
Key Concepts
Core takeaways and short definitions to help you quickly recall the key ideas from this section.
Feedback: A technique that applies part of the output back to the input for improved control.
Current Gain: Remains constant despite feedback application due to balancing factors.
Voltage Gain: Stays constant because of reciprocal effects of feedback on output resistance.
Trans-Impedance: Increases under feedback, representing enhanced stability in an amplifier.
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