91.1. Feedback System (Part B)

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

And how do we name this configuration? This type of sampler and type of mixer.

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.

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.

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