99.6.3. Predicted Effects on Circuit Parameters

In feedback, both circuit gain and trans-conductance are affected. Specifically, the trans-conductance of the circuit defined by the feedback network is anticipated to decrease.

In feedback circuits, adding feedback typically reduces the overall gain of the amplifier. It modifies the trans-conductance (G) of the amplifier, creating a desensitization effect. This means the circuit becomes less sensitive to variations in component properties like temperature or manufacturing tolerances, as the feedback stabilizes the gain.

Think of feedback like a coach guiding an athlete. If the coach provides constant advice (feedback), the athlete can refine their skills and perform reliably, reducing the variability in their outputs.

When feedback is applied, both the input resistance and output resistance increase for the circuit. This is essential for maintaining circuit stability and performance.

With feedback, the input resistance of an amplifier tends to increase. This is advantageous because a higher input resistance means that the amplifier will draw less current from the previous stage, minimizing its loading effect. Similarly, output resistance also increases, which helps to preserve the desired voltage output under various load conditions.

Imagine you are using a water hose to water your garden. If you place a narrow nozzle at the end (representing increased resistance), it restricts how much water can flow out but maintains pressure effectively throughout. Similarly, increased resistance in an amplifier can help maintain the desired output characteristics.

The gain parameters, such as current gain and voltage gain, can show no change due to feedback, as changes in input and output resistance can offset each other.

It's interesting to note that in many feedback configurations, while individual parameters (gain levels) may decrease, the overall current gain and voltage gain often remain stable. This stability arises from the balance between the decrease in trans-conductance and the corresponding increases in resistance, which work against each other.

Think about the balance of weight on a seesaw. If you add weight on one side (simulating gain reduction), but also improve the structure (increase resistance), the seesaw can remain level. Just as with the seesaw, various parameters can counterbalance each other to maintain steady performance.

As feedback is introduced, a desensitization factor is defined. This factor determines how the feedback modifies the input and output resistances, as well as the overall parameters.

The desensitization factor can be derived from the feedback configuration. It often quantifies how feedback affects the circuit parameters like input resistance and gain. As a mathematical construct, it helps in designing circuits to achieve desired stability and performance characteristics by calculating necessary resistor values and configurations.

Consider this like tuning a musical instrument. As you adjust the tension (analogous to feedback), the pitch stabilizes and holds steady across various temperatures and conditions—this tuning factor helps ensure consistent output from the instrument regardless of the environment.

In practical scenarios, such as in amplifier circuit design, one can assess the impact of resistor choices on the circuit’s performance by utilizing numerical examples.

Through specific resistor values and operating conditions, one can observe firsthand how feedback affects circuit parameters. For example, calculating changes in input and output resistance helps to verify the theoretical predictions about circuit performance.

It's akin to maintaining a garden. If you change your watering schedule (akin to adjusting the resistor values), you can directly observe how the health of your plants improves or suffers over time. Monitoring allows the gardener to make informed decisions based on numerical outcomes—similarly, engineers assess feedback values to optimize design.

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