91.1 - Feedback System (Part B)
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Voltage Sampling and Mixing
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Today, we’ll explore the first configuration of feedback systems: voltage sampling and mixing, specifically the shunt-series feedback system.
What do you mean by shunt sampling and series mixing?
Great question! In shunt sampling, we connect the feedback sensor in parallel to the output to derive the feedback signal. In contrast, in series mixing, the input signals are combined sequentially.
Why is it important to avoid loading effects?
Avoiding loading effects is crucial because it ensures that the devices or components don’t alter the network's behavior or measurements. How can we express this relationship mathematically?
Wouldn’t that be through a formula like v = A*v_in - β*v_f?
Exactly! The equations help in understanding how feedback affects output. In this case, we maintain ideal conditions by setting R_out to zero and R_in as infinite.
So, A and β become unitless, correct?
Yes! Both the voltage gain A and the feedback factor β are unitless under these ideal conditions. By the end of our session, remember the acronym 'VSM' for Voltage Sampling and Mixing.
Current Feedback Configuration
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Now let's shift gears to current feedback configurations. What do you think happens when both the input and feedback signals are currents?
I imagine we would have series sampling since the output needs to flow through the input!
Exactly! As you pointed out, with series sampling, the current flows along a direct path. And how do we mix these currents?
That's through parallel mixing, right?
Correct! We utilize parallel connections to ensure that both currents can mix smoothly without restriction. What significance does the nature of feedback have here?
The polarity of the signals matters! Is it still considered negative feedback?
Yes! Negative feedback is essential in stabilizing circuits. We often end up with a loop gain of -βA. Try to keep the phrase 'CFS' in mind for Current Feedback Systems.
Transconductance and Transimpedance
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Now, let’s delve into transconductance and transimpedance. Who can define what transconductance is?
I believe it's the transfer of voltage to current, right?
Correct! It’s represented by G_m. Likewise, can anyone explain transimpedance?
That's converting the current feedback to voltage, represented by Z_m!
Exactly right! Remember that both G_m and Z_m are critical in defining feedback configurations. Always link them to their respective outputs, ensuring clarity!
So, can we say that these elements also help define the feedback loop gain?
Absolutely! These factors are included in calculating the overall system behavior, where we aim for stability and performance. Let's use 'TZG' for Transconductance and Transimpedance Gains.
Overall Feedback Systems
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As we conclude today, let’s summarize overall feedback systems. What important takeaway should we have?
Loop gain is vital! It's affected by our choice of sampling and mixing methods.
Right! Loop gain directly impacts stability and performance. What formula would apply when calculating the overall transfer function?
Does it involve both A and β?
Correct again! The overall system gain is derived as A_f = A/(1+βA). Make sure to remember 'LOOP' for Loop gain and Overall feedback understandings.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
This section delves into two distinct feedback configurations utilizing voltage and current signals, detailing how samplers and mixers function within these setups. It emphasizes the importance of load resistance in maintaining ideal operational conditions, while defining terminology and providing an overview of feedback systems in analog electronics.
Detailed
Feedback System (Part B)
This section analyzes different configurations of feedback systems, which are critical in analog electronic circuits. It introduces various configurations through detailed models that focus on either voltage or current signals. The feedback system discussed is dependent on the polarity and type of samplers and mixers used.
Key Points:
- Configurations: The major configurations are based on:
- Voltage sampling and mixing (Shunt-Series feedback)
- Current sampling and mixing (Series-Shunt feedback)
- Ideal Conditions: The discussion emphasizes ideal resistances to avoid loading effects, ensuring fidelity in measurements and calculations.
- Polarity and Signs: Careful examination of input/output signals' polarity is essential, helping to determine whether the feedback is negative or positive.
- Feedback Path: Various feedback paths are compared, considering aspects like the characteristics of feedback paths (ideal vs. non-ideal) and the effects of different elements on system behavior.
- For example, the output voltage (A*v) remains directly influenced by feedback (βv).
- Transfer Functions: The notion of gain and loop gain in these configurations, often yielding a unitless result, showcases the relationship between input and output signals across different configurations.
The detailed analysis laid out in this section provides insights into effectively designing and understanding feedback systems, emphasizing their utility in maintaining desired functionality in electronic circuits.
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Introduction to Feedback Configurations
Chapter 1 of 7
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Chapter Content
Welcome back after the short break. So we are talking about different possible configurations. So, in the next slide we are going to see one of those 4 configurations.
Detailed Explanation
Here, the speaker introduces the concept of feedback configurations in electronic circuits. Feedback systems are essential in control and signal processing as they help improve performance and stability. The four configurations refer to types of feedback systems differentiated by how signals are sampled and mixed.
Examples & Analogies
Think of a thermostat in a heating system. The thermostat measures the room's temperature (sampling) and sends this information back to the heater (mixing) to adjust the temperature. The four configurations are similar to different methods a thermostat might use to achieve this.
Understanding Voltage Sampler and Mixer
Chapter 2 of 7
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Chapter Content
In this case as I said that the input signal and output signal are say voltages. So, here we consider it is voltage here also it is voltage, so the signal here it is voltage and this is also voltage. Now, since here the signal it is voltage as you can see that the sampler whenever we are sampling the signal, it should be parallel connection.
Detailed Explanation
In this configuration, both the input and output signals are voltages. A voltage sampler is used to capture the output voltage, which connects in parallel to the circuit. This design allows the sampler to measure the voltage without affecting the operation of the circuit by introducing significant resistance.
Examples & Analogies
Imagine a water level sensor in a tank. It uses a float connected parallel to the water flow to measure the water level without blocking or influencing the water flow significantly.
Voltage Mixing and Feedback Network
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Chapter Content
So, that is why we say that voltage sampler at the output port it is having a parallel port. So, we do have parallel port. On the other hand if you see signal here they are voltages, so our intention is to use these two voltages to generate this S.
Detailed Explanation
The voltage generated from the mixing of the feedback signal is crucial for creating the necessary adjustments in the system. By mixing two voltage signals (the primary input and the feedback signal), the system can produce a new signal that reflects the desired output dynamics.
Examples & Analogies
Consider two rivers flowing into a larger river; the flow from each river impacts the water level of the large river at the confluence point. Similarly, the mixed voltage reflects the contributions from both sources.
Polarity and Control Equations
Chapter 4 of 7
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So, if I say that this is v this is + and this is ‒. So, v = v ‒ v. So, if you see carefully the polarity indicates that v = v ‒ v. In fact, that is what we are looking for S = S ‒ S.
Detailed Explanation
Understanding the polarity of signals is key in feedback systems. Here, the signs (+ and ‒) indicate how the various voltage signals interact in the feedback loop. This control equation establishes the relationship between the various voltages, ensuring the system responds correctly to changes.
Examples & Analogies
Using a dimmer switch to control a light bulb: turning the switch up increases brightness (positive voltage), while turning it down decreases brightness (negative voltage). The relationship ensures that adjustments in one part lead to expected changes in another.
Ideal Model Assumptions
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So, to create that situation we have considered this ideal situation namely the resistance here it is ∞. So, I am keeping this is open so, R it is ∞. On the other hand output resistance here R , so that is equal to 0.
Detailed Explanation
The concept of an ideal model simplifies analysis by assuming certain conditions, such as infinite input resistance (R) and zero output resistance (Rₒ). These assumptions indicate no loading effect on the measurement of signals, which makes understanding their behavior easier.
Examples & Analogies
Imagine trying to measure communication in a network without considering interference—if there were no obstacles (infinite resistance), the signals would pass freely without disruption.
Feedback Enough for Control
Chapter 6 of 7
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And also here we do have the output voltage which is A v. So, I should say this A v in v representing voltage gain, so A our formula we need to replace by this A. So, if you see here the primary input to primary output transfer characteristic is.
Detailed Explanation
The output voltage in feedback systems directly relates to the voltage gain (A) of the system. This means that the system's performance can be characterized by how much output can be generated relative to the input, pivotal for determining stability and reliability.
Examples & Analogies
Consider a loudspeaker—the audio input (input voltage) leads to sound output (output voltage) through a specific gain factor. The gain defines how effectively audio signals are amplified and thus affects the overall performance.
Configuration Naming and Types
Chapter 7 of 7
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Chapter Content
And how do we name this configuration? This type of sampler and type of mixer.
Detailed Explanation
Naming conventions in feedback systems rely on how each configuration interconnects samplers and mixers. The specific arrangement of connections, whether shunt or series, defines how the feedback operates and influences the nomenclature.
Examples & Analogies
Think of naming recipes based on their ingredients and methods; a salad could be called 'Greek salad' based on its specific components (tomato, cucumber) and how they're mixed (tossed together). Similarly, configurations highlight the system's arrangement and function.
Key Concepts
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Shunt Sampling: Using parallel connections to sense feedback signals.
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Series Mixing: Combining signals in series to maintain integrity.
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Loading Effect: The impact of measurement tools on circuit performance.
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Transconductance: The conversion of voltage input to current output.
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Transimpedance: The conversion of current input to voltage output.
Examples & Applications
In a voltage feedback system, if the output is 10V and the feedback voltage is 2V, the input voltage will be 8V under ideal conditions.
In a current feedback system, if the feedback current is 0.5A and the transconductance is 2S, the output voltage would be 1V.
Memory Aids
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Rhymes
To mix in series, connect them right, avoid the load to keep the circuit tight.
Stories
Imagine a teacher monitoring students with a telescope - that is shunt sampling - observing without interfering with the learning experience.
Memory Tools
VSM is for Voltage Sampling and Mixing, a simple way to keep feedback configurations in mind!
Acronyms
CFS stands for Current Feedback Systems; remember to connect currents correctly.
Flash Cards
Glossary
- Feedback System
A system that uses its output signal to influence its input for self-regulation.
- Shunt Sampling
Connecting the feedback loop in parallel to the output to sense the feedback signal.
- Series Mixing
Combining multiple signals in a sequential fashion within a feedback system.
- Loading Effect
The influence that the resistance of a measuring instrument has on the circuit being measured.
- Transconductance
The ratio of the output current to the input voltage in an electronic device.
- Transimpedance
The ratio of the output voltage to the input current in an electronic device.
- Loop Gain
The product of the gain around a feedback loop that indicates the feedback's impact.
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