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A short class with Sarah and her students. The other ways are under More.
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Today, we're focusing on feedback configurations in common emitter amplifiers. Can anyone tell me what a feedback configuration is?
Is it the way we connect feedback to the amplifier to control its gain?
Exactly! There are primarily two types: voltage feedback and current feedback. In our case, we're looking at the voltage-shunt configuration. Can anyone explain why we use this one?
Because it stabilizes the output voltage and ensures consistent gain?
Right! This setup samples the output voltage to control the input current effectively.
So, does that mean we can control the trans-impedance with this configuration?
Good question! Yes, precisely! The trans-impedance Z becomes defined by the feedback network, ensuring stability. In feedback circuits, we often remember: Z = A * R_f, where A is the gain.
To summarize, feedback configurations like voltage-shunt help stabilize our amplifiers by controlling how feedback from the output informs the input.
Now let's discuss how to calculate input and output resistance in our circuit. Can someone tell me about the role of feedback resistors here?
Are they used to determine how much current flows through the circuit?
Absolutely! They help define the input resistance, which can be seen as R_in = r + R_f, where R_f is the feedback resistor. What's crucial is knowing when to ignore those biases.
So, when do we ignore them?
You generally ignore bias resistance in small signal analysis when it is negligible compared to R_f. This results in simplified calculations.
Can anyone tell me the implications on the output resistance?
It gets reduced when using feedback, right?
Correct! The output resistance is also impacted, guiding how we design the feedback network effectively.
Quick recap! Remember, R is used in calculating Z and helps us stabilize trans-impedance, influenced by our feedback network.
Today, let's explore how we choose our feedback resistor values. Why do you think it’s important?
To ensure the circuit performs optimally without distortion?
Exactly! We aim for R_f to be over ten times greater than any load resistance to avert loading effects. How can we represent this mathematically?
R_f should be greater than 10 * R?
Right! And we also need to ensure that the product of beta and Z' exceeds one for stability.
What happens if we don't meet those limits?
If those limits aren't met, we could face instability, fluctuating gain, or increased distortion. Quickly, let's review: always check that our feedback resistors fit within suitable ranges to maintain effective performance.
Finally, let’s apply what we've learned to a numerical example. Can anyone recall our ideal resistor configurations?
We learned R_f has to be much higher than R to avoid loading issues.
Precisely! When we set R to 50kΩ, we satisfy both upper and lower limits of resistance. What result do we get regarding the output resistance?
It becomes lower than the original values, right?
Exactly! So, in summary, choosing the right feedback resistor helps stabilize and optimize gain while managing output effectively. Be sure to apply these principles in real-world circuits!
The feedback configuration influences the forward amplifier's gain (A) and the trans-impedance (Z) is stabilized by the feedback network.
The shunt configuration allows for the mixing of output and input signals. The voltage sampled from the output is mixed at the input to ensure stability.
The detailed equations for input and output resistance of the circuit are derived, highlighting the importance of bias and feedback resistors.
Criteria for selecting the resistance values that avoid loading effects, ensuring robustness, and maintaining circuit performance are discussed.
The section provides numerical examples illustrating how to determine the suitable range of feedback resistors, considering real-world parameters such as load and gain requirements.
The effect of feedback on voltage and current gains, and the calculation of individual resistances after feedback are also tackled, emphasizing that certain parameters remain unchanged while others are significantly influenced.
Through systematic approaches and detailed calculations, the section aims to equip students with a clear understanding of the interactions between feedback resistors, gain, and stability within analog electronic circuits.
Feedback helps stabilize, oh so fine, / Without loading, our circuits shine.
Imagine a carpenter measuring lengths. If his measuring tape is off, every cut will be wrong. Resistors are like that tape—they ensure accurate cuts in voltage and current.
Remember: F.A.C.E (Feedback, Amplifier, Circuit, Efficiency) represents the essentials of amplifier stability.
R.S.V.P (Resistance Should Validate Performance) to remind us that resistor values need to help performance.
Term
Trans-Impedance (Z)
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Term
Feedback Resistor (R_f)
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Stability Criteria
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Term
Input/Output Resistance
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A parameter representing the relationship between output voltage and input current in an amplifier.
Resistor used in feedback circuits to regulate the signal and improve amplifier performance.
The combined resistance that the input sources observe at the input terminal of the amplifier.
The resistance seen by the load connected to the output of the amplifier.
The ratio of output current to input current in an amplifier.
This section explores the appropriate range for feedback resistors in amplifier circuits to achieve desired performance and stability.
The section discusses the significance of selecting suitable feedback resistors in common emitter amplifiers, emphasizing the relationship between feedback configurations, input and output resistances, and the overall trans-impedance of the amplifier. Key criteria for selection and formulas for calculating effects on gain and resistance are presented.
In this section, we delve into the essential role of feedback resistors in amplifier circuits, particularly in common emitter configurations. We aim to stabilize trans-impedance, denoted as Z, using negative feedback. The narrative begins with understanding how feedback networks can stabilize amplifier performance by appropriately defining the feedback configuration (voltage-shunt or shunt-shunt).
Through systematic approaches and detailed calculations, the section aims to equip students with a clear understanding of the interactions between feedback resistors, gain, and stability within analog electronic circuits.