DISTORTION IN BJT AMPLIFIERS
For an ideal transistor amplifier, the output must be an exact replica of input except that the required characteristics(Voltage, Power) is increased according to the gain of amplifier.
In the otherhand For a practical amplifier the ideal conditions may not be achieved. Some of the changes take place in the output wave form other than the amplitude increases. Such a change can be termed as DISTORTION.
DISTORTION is undesirable because it may affect the information carried by the signal.
Non-linear distortion occurs when the transistor operates in the Non-linear region of its output.
2. When the signal is considered under Frequency domain, it is known as Harmonic distortion
occurs when the active device operates on the Linear part of its output with small signal inputs. It is mainly due to Frequency dependent reactances associated with the active device itself and occurs if the input signal is composite (speech- contains too many Frequency)
AMPLITUDE DISTORTION IN AMPLIFIERS
For a small swing of input signal, only a small part of the transconductance curve, this small part is almost linear and operation over this curve is Linear Operation because the changes in the output Current is proportional to the changes in the input Voltage. In such a case, the shape of the input waveform is almost similar to output wave and therefore no Distortion occurs.
But for large input signal, the Operation became Non-linear.
HARMONIC DISTORTION IN AMPLIFIERS
The Frequency domain of Non-linear Distortion (HARMONIC Distortion) is shown in the Figure below:-
The input is a single Frequency(f1) signal and the output consist of dc component and different harmonics. These harmonics are the integral multiples of the output signal Frequency. The result is Distorted output. The magnitude depends on the the strength and number of These harmonics.
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