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A short class with Sarah and her students. The other ways are under More.
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Welcome class! Today we'll discuss feedback in amplifier circuits. Can anyone tell me what feedback means in this context?
I think it means using some of the output to influence the input?
Exactly! We're going to focus on how it affects voltage gain and current gain. What do you think happens to these gains when feedback is applied?
Maybe they decrease?
Great insight! This phenomenon is known as 'desensitization'. Can anyone remember why we want to use feedback if it decreases gains?
To improve stability and control, right?
Absolutely right! Feedback improves performance stability. In summary, feedback can both decrease gains but enhance overall system stability.
Moving on, let’s talk about trans-conductance. Can anyone define it?
Isn't trans-conductance the ratio of current output to voltage input?
Exactly! So, when we apply feedback, how do we think trans-conductance influences the circuit?
It might decrease because of increased output resistance?
Right again! When we have higher resistance, it impacts the current gain. Recall that G, the trans-conductance, is important to understand the feedback effects. Can you all summarize what we've learned about it?
Trans-conductance helps us understand how feedback affects current and overall amplifier performance.
Well said! Now let’s remember that the impact of feedback can be quantitatively described by our equations.
To wrap up our discussion, let's examine the voltage and current gain specifically. How do we calculate voltage gain in a feedback circuit?
I think it involves G and the feedback circuit parameters…
Correct! The voltage gain A = G × R, right? And after feedback is applied, the gain decreases by a factor we call desensitization factor. Can anyone state that factor?
Is it D = (1 + G'β)?
Exactly! And what does a similar analysis show concerning current gain?
It remains unchanged, yes?
Spot on! Remember, while voltage gain changes, current gain maintains under feedback. Let’s summarize the benefits of feedback once more at the end.
The output to input voltage ratio in amplified signals.
The ratio of output current to input current that remains mostly unchanged under feedback.
The current driven per unit input voltage change in an amplifier.
A negative impact on gains due to feedback designed for stability improvements.
Feedback helps keep things in line, gains may drop, but stability will shine.
Imagine a librarian who must keep the library quiet (stability) while whispering (feedback) to book readers. Some noise (gain) may reduce, but the library remains peaceful.
To remember the key feedback effects, think 'Gains Down, Resistance Up, Stability Found'.
Remember 'F.I.G.S.' - Feedback Increases Gain Stability.
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What is Voltage Gain?
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What is Current Gain?
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What is Desensitization Factor?
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The ratio of output voltage to input voltage in a circuit, often influenced by feedback.
The ratio of output current to input current in a circuit, remains constant under feedback in certain configurations.
The measure of output current change per change in input voltage, important for characterizing amplifiers.
A factor that represents how feedback can decrease voltage gain while enhancing system stability.
The process of feeding back a portion of the output signal to modify the input, affecting overall circuit performance.
This section delves into the interactions of voltage and current gain in amplifier circuits under feedback conditions.
In this section, we explore the implications of feedback in amplifier circuits, particularly focusing on voltage gain and current gain. The concepts of input and output resistance are introduced, along with the effects of series-series feedback and desensitization factors.
In this section of the chapter on Analog Electronic Circuits, we investigate the effects of feedback on voltage gain and current gain in amplifier circuits. Feedback can fundamentally change these gains, often described in terms of what's known as the desensitization factor, which denotes how feedback influences system parameters.
The discussion begins with an overview of the types of feedback—specifically series-series feedback—where the input signal is voltage, and the output signal is current. The section delineates how voltage gain and current gain are modified under feedback conditions. The relationship between input and output resistance is also highlighted, demonstrating how the feedback loop can lead to increased resistance values, thereby affecting overall circuit performance.
The use of various examples, practical models, and equations reinforces the theoretical aspects by providing calculations related to trans-conductance, voltage gain, current gain, and trans-impedance. By the end of this section, readers should achieve a comprehensive understanding of how feedback configuration impacts the performance of amplifier circuits.