Thus, a weak signal (0.1V) applied to the input circuit appears in the amplified form (10V) in the collector circuit. This pair of transistors will buffer the signal from Q3s collector, and provide a high gain as the signal goes to the final stage.
Q11 is a common collector and Q12 is a common emitter. Q11 and Q12 are part of the second stage. When collector current flows through such a high resistance, it produces a large voltage drop across it. These transistors help to form the input differential stage of the amplifier. In the collector circuit, a load resistor R C of high value is connected. This change is almost the same in collector current because of the transmitter action. When a weak signal is applied to the input, a small change in signal voltage causes a change in emitter current (or we can say a change of 0.1V in signal voltage causes a change of 1mA in the emitter current) because the input circuit has very low resistance.
The DC voltage V EE keeps the emitter-base junction under the forward biased condition regardless of the polarity of the input signal and is known as a bias voltage. The DC voltage V EE is applied to the input circuit along with the input signal to achieve the amplification. The input signal or weak signal is applied across the emitter base and the output is obtained to the load resistor R C which is connected in the collector circuit.
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