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The input impedance of a common-base amplifier is a measure of how much resistance the amplifier presents to the input signal source. It is determined by the parallel combination of the emitter resistance and the small signal input resistance between base and emitter.
The calculator uses the formula:
Where:
Explanation: The input impedance is calculated as the parallel equivalent of the emitter resistance and the small signal input resistance, representing how the amplifier loads the signal source.
Details: Accurate input impedance calculation is crucial for impedance matching, maximizing power transfer, and ensuring proper signal coupling between stages in amplifier circuits.
Tips: Enter emitter resistance and small signal input resistance in ohms. Both values must be positive and non-zero for accurate calculation.
Q1: Why is input impedance important in amplifier design?
A: Input impedance determines how much the amplifier loads the previous stage or signal source, affecting signal transfer and overall circuit performance.
Q2: What are typical values for input impedance in common-base amplifiers?
A: Common-base amplifiers typically have low input impedance, usually in the range of tens to hundreds of ohms, making them suitable for current amplification.
Q3: How does emitter resistance affect input impedance?
A: Lower emitter resistance results in lower input impedance, while higher emitter resistance increases input impedance in a common-base configuration.
Q4: What is the significance of small signal input resistance?
A: Small signal input resistance models the dynamic resistance of the base-emitter junction when a small AC signal is applied, which varies with bias current.
Q5: How does temperature affect input impedance calculations?
A: Temperature changes affect the small signal input resistance (which is temperature-dependent) more significantly than the emitter resistance, potentially altering the overall input impedance.