![]() Let us now introduce a battery V BB in the base circuit. This leads to unfaithful amplification as shown in the figure below. When a signal is applied at the input, the base-emitter junction of the NPN transistor gets forward biased for positive half cycle of the input and hence it appears at the output.įor negative half cycle, the same junction gets reverse biased and hence the circuit doesn’t conduct. The base-emitter junction is forward biased and the collector-emitter junction is reverse biased. In order to understand this, let us consider a NPN transistor circuit as shown in the figure below. The fulfillment of these conditions ensures that the transistor works over the active region having input forward biased and output reverse biased. Minimum proper collector-emitter voltage (V CE) at any instant. ![]() Minimum proper base-emitter voltage (V BE) at any instant.To ensure faithful amplification, the following basic conditions must be satisfied. The amplified signal thus contains the same information as in the input signal whereas the strength of the signal is increased. But for the transistor to function properly as an amplifier, its input circuit (i.e., the base-emitter junction) remains forward biased and its output circuit (i.e., collector-base junction) remains reverse biased. Hence the placement of operating point is an important factor to achieve faithful amplification. If the operation point is considered near cut off point, then the amplification will be as under. If the operating point is considered near saturation point, then the amplification will be as under. The operating point is so chosen such that it lies in the active region and it helps in the reproduction of complete signal without any loss. This can be understood as Faithful Amplification. In the above graph, the input signal applied is completely amplified and reproduced without any losses. This is done when AC signal is applied at its input. This amplification when done without any loss in the components of the signal, is called as Faithful amplification.įaithful amplification is the process of obtaining complete portions of input signal by increasing the signal strength. The process of increasing the signal strength is called as Amplification. Hence the quiescent point or Q-point is the value where the Faithful Amplification is achieved. The operating point should not get disturbed as it should remain stable to achieve faithful amplification. The following graph shows how to represent the operating point. There can be many such intersecting points, but the Q-point is selected in such a way that irrespective of AC signal swing, the transistor remains in the active region. This operating point is also called as quiescent point or simply Q-point. This line, when drawn over the output characteristic curve, makes contact at a point called as Operating point. When a line is drawn joining the saturation and cut off points, such a line can be called as Load line. Emitter Follower & Darlington Amplifier.Transformer Coupled Class A Power Amplifier.
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