1. What is Input Resistance With Feedback?

Input Resistance with Feedback (R_inf) 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:

Where:

• \( R_{inf} \) — Input Resistance with Feedback (Ohm)
• \( R_{in} \) — Input Resistance (Ohm)
• \( A\beta \) — Loop Gain (dimensionless)

Explanation: The formula shows how feedback increases the input resistance of an amplifier by a factor of (1 + loop gain).

3. Importance of Input Resistance Calculation

Details: Calculating input resistance with feedback is crucial for designing amplifier circuits, impedance matching, and ensuring proper signal transfer between stages in electronic systems.

4. Using the Calculator

Tips: Enter the input resistance in Ohms and the loop gain value. Both values must be positive numbers for valid calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is loop gain in amplifier circuits?
A: Loop gain (Aβ) is the product of the amplifier gain (A) and the feedback factor (β). It determines the amount of feedback applied to the circuit.

Q2: How does feedback affect input resistance?
A: Negative feedback typically increases the input resistance of voltage amplifiers, making them less loading on the preceding stage.

Q3: What are typical values for input resistance?
A: Input resistance values vary widely depending on the amplifier type, from a few ohms in power amplifiers to megaohms in operational amplifiers.

Q4: Can this formula be used for all amplifier types?
A: This formula is specifically for feedback voltage amplifiers. Different formulas apply for current amplifiers or other amplifier configurations.

Q5: Why is high input resistance desirable?
A: High input resistance minimizes loading effects on the signal source, preserving signal integrity and ensuring accurate signal transfer.