1. What is Input Resistance in Small-Signal Operation?

Input resistance is the resistance value seen at the input of a voltage amplifier in small-signal operation. In current mirrors, it represents the resistance that the input signal encounters when entering the circuit.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( R_i \) — Input resistance (Ohm)
• \( g_m \) — Transconductance (Siemens)

Explanation: The input resistance is inversely proportional to the transconductance of the device. Higher transconductance results in lower input resistance.

3. Importance of Input Resistance Calculation

Details: Accurate input resistance calculation is crucial for impedance matching, signal transfer efficiency, and overall circuit performance in amplifier design and small-signal analysis.

4. Using the Calculator

Tips: Enter transconductance value in Siemens. The value must be greater than zero for valid calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is transconductance?
A: Transconductance is the ratio of the change in drain current to the change in gate/source voltage with constant drain/source voltage.

Q2: Why is input resistance important in current mirrors?
A: Input resistance affects how the current mirror interacts with preceding stages and influences the accuracy of current replication.

Q3: What are typical values of transconductance?
A: Transconductance values typically range from microsiemens to millisiemens depending on the transistor size and biasing conditions.

Q4: Does this formula apply to all transistor types?
A: This formula primarily applies to MOSFETs and JFETs in saturation region. For BJTs, the input resistance calculation differs.

Q5: How does temperature affect input resistance?
A: Temperature affects carrier mobility and threshold voltage, which in turn affects transconductance and consequently the input resistance.