97.2.3 - Finding Suitable Feedback Network
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Introduction to Feedback Configurations
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To start, let’s discuss what feedback configurations are. Feedback in amplifier circuits can modify output characteristics based on input signals. Can anyone tell me some basic feedback configurations?
I remember voltage-shunt and current-shunt are types of configurations.
Exactly! We have voltage-shunt, current-shunt, voltage-series, and current-series configurations. These play a crucial role in amplifier design. Remember them as V, C, V, C for easy recall.
What does each configuration do to the gain and resistance?
Great question! Each configuration affects gain and resistances differently. For example, shunt-shunt reduces both input and output resistance, while series-series tends to increase them.
So, understanding these effects helps in selecting the right configuration?
Absolutely! Selecting the right configuration depends on whether you want to stabilize voltage, current, or trans-impedance gains.
Let’s summarize: We have four basic configurations, each affecting amplifier performance differently. Keep V, C, V, C in mind for recalling them!
Impact of Feedback on Gain and Resistance
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Now, let's explore how feedback affects amplifiers. If I mention a shunt-shunt configuration, what changes do you think we will see?
I think the input and output resistances go down?
Correct! And it scales down the current gain as well. Would you like to take a guess about what happens with voltage gains?
I guess it stays the same?
Good thought! The voltage gain can remain unchanged because of the relationship between the input and output resistances being effectively balanced.
And what about if we take the series-series configuration?
In this case, both input and output resistances increase. This configuration is typically for boosting the voltage gain while providing good stability.
In summary, each configuration changes gain and resistance differently, making it essential to consider the desired performance.
Practical Selection of Feedback Networks
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Let’s shift gears and talk about the practical selection of feedback networks. What factors do you think we should consider?
I think we need to look at the gain parameters?
Correct! We need to ensure that the feedback factor β is meaningful and that loading effects of the feedback network on the amplifier are minimal.
How do we ensure that?
Generally, we need the relationship of A and β such that A′β should be considerably greater than 1. This checks if the feedback is effective.
What happens if we don’t satisfy these conditions?
If we don’t, the relationships may be inaccurate, affecting performance. Therefore, consider the impact on both A and the chosen configuration.
To summarize, selection involves checking gain parameters and making sure approximations hold to keep the network effective.
Consequences of Feedback Configuration Changes
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Finally, let's sweat over the consequences when changing feedback configurations. Could be potential changes to consider?
What if we reduce input resistance? Does that always impact current gain?
Great observation! Reducing input resistance can enhance current gain under specific configurations, whereas the output resistance may become less stable.
Does this mean configurations interact with each other?
Exactly! Changing one part changes others. Understanding these relationships is crucial. For instance, maintaining stable Z is often a goal.
I see how important this is in design choices.
Absolutely! It’s all about balancing the interactions based on what characteristics you wish to stabilize or optimize.
To summarize, configurations influence each other. Designers must navigate these complexities diligently.
Introduction & Overview
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Quick Overview
Standard
This section delves into the applications of feedback within amplifier circuits, focusing on different feedback configurations such as voltage and current sampling. It highlights how each configuration affects amplifier characteristics like gain and resistance, along with guidance on selecting suitable feedback networks to fulfill design requirements.
Detailed
Finding Suitable Feedback Network
The section discusses essential feedback configurations used in amplifier circuits, aimed at achieving specific performance characteristics. Firstly, it reviews the basic feedback configurations — voltage-shunt (shunt-shunt), current-shunt (series-shunt), voltage-series (shunt-series), and current-series (series-series). Each configuration interacts with the amplifier’s gain and input/output resistances in varying ways.
The feedback mechanisms discussed include:
1. Voltage Sampling and Shunt Feedback (Shunt-Shunt): This configuration reduces the input and output resistances simultaneously, impacting current gain while stabilizing trans-impedance.
2. Current Sampling and Series Mixing (Series-Series): This typically increases input resistance while decreasing output resistance, optimizing voltage gains.
3. Voltage Series Feedback (Shunt-Series): This affects voltage gain directly while also adjusting input and output resistances differently.
Additionally, it emphasizes the significance of the feedback factor (β) and provides guidelines to ensure that the feedback network effectively stabilizes necessary parameters while keeping the amplifier’s performance intact. Understanding these configurations allows circuit designers to rationally choose feedback networks that align closely with application requirements.
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Understanding Feedback Configurations
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Chapter Content
So, the concept, so, we are planning to cover today it is listed here. So, we shall see how we can deploy or how do we decide different feedback configuration in BJT circuits BJT amplifiers. And there we will be talking about specifically three different configurations, which you will be giving us fair idea how to deploy the feedback configuration.
Detailed Explanation
In this chunk, we are introduced to the primary focus which revolves around deploying feedback configurations in BJT amplifiers. The discussion will center on three configurations that help guide how feedback is utilized, giving us insights into their practical applications in circuits. By understanding these configurations, one can better tailor feedback systems for different operational needs in amplifier design.
Examples & Analogies
Imagine a teacher giving a student feedback on their exam performance. Depending on the subject, the feedback can be specific to areas that need improvement – for example, desiring better mathematical reasoning might require just focusing on algebra, while other subjects could need a completely different approach. Similarly, in electronic circuits, choosing the right feedback configuration is akin to providing the right kind of feedback to enhance amplifier performance.
Feedback Configuration Types
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These are the three possible configurations we are talking about of course, one more configuration it is skipped due to the shortage of time. So, we will be talking about voltage sampling and shunt feedback referred as shunt-shunt feedback. And then current sampling and a series mixing referred as series-series feedback and then the third one it is voltage series feedback or shunt-series feedback.
Detailed Explanation
This chunk explains the three primary feedback configurations. The first is 'voltage sampling and shunt feedback,' identified as shunt-shunt feedback. This configuration is significant in stabilizing output voltage while monitoring the feedback. The second, 'current sampling and series mixing,' is termed series-series feedback, which focuses on stabilizing current behavior. Lastly, 'voltage series feedback' or shunt-series feedback is used to stabilize voltage gains in application's context. Understanding these configurations helps designers choose the appropriate type based on desired outcomes.
Examples & Analogies
Think of these configurations like choosing different tools for a carpentry project. If you need to smooth a surface, a sander would be more effective (voltage sampling), while if you need to shape wood, a saw might be necessary (current sampling). Similarly, in amplifiers, the configuration chosen will suit specific requirements based on the type of feedback needed to enhance performance.
Objective of Stabilizing Parameters
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Chapter Content
So, the basic objective of having this -ve feedback system it is to stabilize this A whether it is Z, A, A or G.
Detailed Explanation
In this section, the focus is on the goal of implementing negative feedback—stabilizing certain parameters of the amplifier. This includes stabilizing the trans-impedance (Z), current gain (A), voltage gain (A), or trans-conductance (G). By applying negative feedback, designers can effectively manage and control the amplifier's performance, lessening the variations that might occur due to other factors in a circuit.
Examples & Analogies
Consider a thermostat controlling a heater. The thermostat measures the room temperature and adjusts the heater’s output to maintain a stable temperature. In a similar way, negative feedback acts to stabilize an amplifier's performance by regulating its output, ensuring it remains consistent regardless of external conditions.
Adjusting for Desired Characteristics
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Chapter Content
So, while we are trying to stabilize this, we should be aware that the corresponding input and output resistance they are also getting decreased.
Detailed Explanation
This chunk explains that stabilizing the amplifier’s main parameters (like gain) often leads to changes in input and output resistances. Specifically, in negative feedback configurations, typically when gain is stabilized, input and output resistances will also decrease which may affect the circuit’s overall response. Understanding this relationship is crucial for designing an efficient feedback network tailored to specific requirements.
Examples & Analogies
Imagine trying to keep a car on a steady course while facing headwinds or changing terrains. In doing so, you’ll access different speeds and fine-tune your steering, impacting fuel efficiency (akin to resistance). In electronics, when you stabilize certain aspects (like gain), you must be aware of how other characteristics, such as input and output resistances, are affected.
Selecting the Appropriate Configuration
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Chapter Content
So, to achieve this property namely the A solely defined by the feedback network we need to have meaningful selection of this β.
Detailed Explanation
This section emphasizes the importance of selecting suitable feedback configurations. Here, it’s highlighted that to ensure the gain is primarily influenced by the feedback network, the selection of the feedback factor (β) needs to be meaningful. This means that designers must choose values to keep β high enough so that gain is predominantly determined by the feedback design rather than other circuit components.
Examples & Analogies
Choosing the right spice for a dish can significantly affect its flavor. If you use just the right amount of salt, the dish tastes balanced and well-seasoned. Similarly, in feedback networks, the choice of β influences the amplifier’s performance, ensuring that it performs as intended within a desired range of parameters. Using too much or too little could lead to undesirable outcomes.
Key Concepts
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Feedback Types: Different configurations impact amplifier performance.
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Desensitization: Understanding how feedback can stabilize gain.
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Loading Effects: The need to consider how connections impact amplifier operation.
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Configuration Selection: Choosing feedback depends on application goals.
Examples & Applications
In a shunt-shunt feedback configuration, both input and output resistance drop while the current gain stabilizes.
In a series-series feedback configuration, the input resistance increases while voltage and trans-impedance features are optimized.
Memory Aids
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Rhymes
Feedback effects are neat and clean, shunt-shunt configuration reigns supreme!
Stories
Imagine a designer juggling amplifiers, selecting configurations just right to keep all parameters on a pedestal, stabilizing and managing them for the perfect sound.
Memory Tools
Remember V, C, V, C to recall the feedback configurations easily.
Acronyms
Use 'PVC' for remembering Positive Voltage Changes in amplifiers when feedback is applied.
Flash Cards
Glossary
- Feedback Configuration
A method of connecting output back to input in amplifiers to control performance.
- Voltage Gain
The ratio of output voltage to input voltage within an amplifier.
- Current Gain
The ratio of output current to input current in an amplifier.
- Transimpedance
The relationship between output voltage and input current (Ohms).
- Desensitization Factor
A factor affecting gain reduction in feedback systems, calculated as (1 + βA).
- Loading Effect
The impact of connected circuitry on the characteristics of the primary amplifier.
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