Contents
What is BJT impedance?
BJT Amplifier Input/Output Impedance Input impedance is defined as the ratio of imput voltage to input current. It is calculated from the AC equivalent circuit as the equivalent resistance looking into the input with all current cources replaced by an open and all voltage sources replaced by a short.
What does impedance do in a circuit?
Impedance reduces to resistance in circuits carrying steady direct current. The magnitude of the impedance Z of a circuit is equal to the maximum value of the potential difference, or voltage, V (volts) across the circuit, divided by the maximum value of the current I (amperes) through the circuit, or simply Z = V/I.
What is impedance level?
Impedance (Z) is the measure of the total opposition to current flow in an alternating current circuit. It is made up of the sum of two components, resistance (R) and reactance (X). Z = R + X. Resistance is essentially constant at all frequencies in an audio circuit and is measured in Ohms.
Is the input impedance of a transistor always the same?
If you had a fixed set of operational parameters for the transistor and circuit, you could calculate the input impedance from that; however, it would only be good for that specific configuration and assume that the parameters wouldn’t change. As an active device, most transistors are not used in this manner.
What are the four impedances of 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.
What happens if the input impedance of an amplifier is too low?
If it is too low, it can have an adverse loading effect on the previous stage and possibly affecting the frequency response and output signal level of that stage. But in most applications, common emitter and common collector amplifier circuits generally have high input impedances.
Is the base resistance of a transistor internal or external?
The base resistance can be both internal and external to the transistor. It is a bit more complicated for the common-emitter circuit. We need to know the internal emitter resistance r EE.