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Differential Input Resistance is defined as a single-ended "resistor" (connected between the input and ground) in the case of differential mode. It represents the opposition offered to the current passing through the differential input of a BJT amplifier.
The calculator uses the formula:
Where:
Explanation: The differential input resistance is simply twice the base-emitter input resistance in a BJT differential amplifier configuration.
Details: Differential input resistance is a crucial parameter in differential amplifier design as it determines the input impedance of the amplifier stage, affecting signal transfer and matching with preceding stages.
Tips: Enter the base-emitter input resistance value in Ohms. The value must be positive and greater than zero for accurate calculation.
Q1: Why is differential input resistance twice the base-emitter resistance?
A: In a differential pair configuration, the input signal sees two base-emitter junctions in series, resulting in twice the resistance of a single base-emitter junction.
Q2: What are typical values for base-emitter input resistance?
A: Base-emitter input resistance typically ranges from a few hundred ohms to several kilo-ohms, depending on the transistor's operating point and characteristics.
Q3: How does temperature affect the differential input resistance?
A: Since base-emitter resistance is temperature-dependent, the differential input resistance will also vary with temperature changes in the circuit.
Q4: Is this formula applicable to all BJT configurations?
A: This specific formula applies to differential amplifier configurations. Other amplifier configurations may have different input resistance calculations.
Q5: How does differential input resistance affect amplifier performance?
A: Higher input resistance generally provides better signal transfer from high-impedance sources and reduces loading effects on preceding stages.