Input impedance,output impedance,voltage gain,current gain of ce amplifier using small signal analysis
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Input Impedance, ZIN or Input Resistance as it is often called, is an important parameter in the design of a transistor amplifier and as such allows amplifiers to be characterized according to their effective input and output impedances as well as their power and current ratings.
An amplifiers impedance value is particularly important for analysis especially when cascading individual amplifier stages together one after another to minimise distortion of the signal.
The input impedance of an amplifier is the input impedance “seen” by the source driving the input of the amplifier. 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.
Some types of amplifier designs, such as the common collector amplifier circuit automatically have high input impedance and low output impedance by the very nature of their design. Amplifiers can have high input impedance, low output impedance, and virtually any arbitrary gain, but were an amplifiers input impedance is lower than desired, the output impedance of the previous stage can be adjusted to compensate or if this is not possible then buffer amplifier stages may be needed.
In addition to voltage amplification ( Av ), an amplifier circuit must also have current amplification ( Ai ). Power amplification ( Ap ) can also be expected from an amplifier circuit. But as well as having these three important characteristics, an amplifier circuit must also have other characteristics like high input impedance ( ZIN ), low output impedance ( ZOUT ) and some degree of bandwidth, ( Bw ). Either way, the “perfect” amplifier will have infinite input impedance and zero output impedance.
An amplifiers impedance value is particularly important for analysis especially when cascading individual amplifier stages together one after another to minimise distortion of the signal.
The input impedance of an amplifier is the input impedance “seen” by the source driving the input of the amplifier. 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.
Some types of amplifier designs, such as the common collector amplifier circuit automatically have high input impedance and low output impedance by the very nature of their design. Amplifiers can have high input impedance, low output impedance, and virtually any arbitrary gain, but were an amplifiers input impedance is lower than desired, the output impedance of the previous stage can be adjusted to compensate or if this is not possible then buffer amplifier stages may be needed.
In addition to voltage amplification ( Av ), an amplifier circuit must also have current amplification ( Ai ). Power amplification ( Ap ) can also be expected from an amplifier circuit. But as well as having these three important characteristics, an amplifier circuit must also have other characteristics like high input impedance ( ZIN ), low output impedance ( ZOUT ) and some degree of bandwidth, ( Bw ). Either way, the “perfect” amplifier will have infinite input impedance and zero output impedance.
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