## What is the input impedance of a transistor?

## Is there a formula for output impedances and output resistance?

- There do not appear to be any simple formulas for the output impedances. However, R. Victor Jones develops expressions for output resistance. [RVJ] Amplifier characteristics, adapted from GE
**Transistor**Manual, Figure 1.21.

## What are the different types of impedances in an amplifier?

- A common theoretical model has total 4 impedances for an amplifier:
**Input impedance**, output**impedance**, transfer**impedance**and feedback**impedance**. Those impedances are complex numbers in equations which describe how**input**signal current and voltage depend on each other and on signal current and voltage in output.

## Can a transistor be used as an amplifier?

**Transistor**is a common part which can act as an amplifier. To design a proper circuit around a**transistor**to make a working amplifier one needs those theoretical impedances. The impedances depend on frequency and on the applied dc voltages and currents.The manufacturer publishes them in the datasheet**of**the**transistor**.

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