Input Resistance With Feedback Of Feedback Transconductance Amplifier (Series-Series) Calculator

Formula Used:

\[ R_{inf} = (1 + A \cdot \beta) \cdot R_{in} \]

Open Loop Gain of an Operational Amplifier (A):

Feedback Factor (β):

Input Resistance (R_in):

Ohm

Input Resistance with Feedback (R_inf):

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1. What is Input Resistance with Feedback?

The input resistance with feedback of a feedback amplifier is equal to the source impedance for which loop gain would drop to unity. It represents the effective input resistance when feedback is applied to the amplifier circuit.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ R_{inf} = (1 + A \cdot \beta) \cdot R_{in} \]

Where:

\( R_{inf} \) — Input Resistance with Feedback (Ohm)
\( A \) — Open Loop Gain of an Operational Amplifier
\( \beta \) — Feedback Factor
\( R_{in} \) — Input Resistance (Ohm)

Explanation: The formula shows how feedback increases the input resistance of an amplifier by a factor of (1 + Aβ), which is a fundamental property of series-series feedback configurations.

3. Importance of Input Resistance Calculation

Details: Calculating input resistance with feedback is crucial for designing amplifier circuits, ensuring proper impedance matching, and predicting circuit behavior in feedback configurations.

4. Using the Calculator

Tips: Enter the open loop gain, feedback factor, and input resistance values. All values must be positive numbers with input resistance greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What is the significance of input resistance with feedback?
A: It determines how much the amplifier loads the signal source and affects the overall circuit performance in feedback configurations.

Q2: How does feedback affect input resistance?
A: Series-series feedback increases the input resistance by a factor of (1 + Aβ), making the amplifier appear as a higher impedance to the source.

Q3: What are typical values for these parameters?
A: Open loop gains can range from 10^4 to 10^6, feedback factors are typically between 0.01-0.1, and input resistances vary based on amplifier design.

Q4: When is this calculation most important?
A: This calculation is critical when designing precision amplifiers, instrumentation circuits, and any application where input impedance matching is important.

Q5: Are there limitations to this formula?
A: This formula assumes ideal amplifier characteristics and may need adjustment for real-world components with finite output impedance and other non-ideal characteristics.