12/30/2023 0 Comments 3 resistor npn transistor amplifierThe reactance of emitter bypass capacitor C E for any given input frequency is so small that parallel combination of R E and C E can be considered as a short circuit.The bias resistors R 1 and R 2 are very large in comparison to h ie.1/h oe is so large that it can be considered as an open circuit.h re is so small that the voltage source h re V out can be neglected.Analysis:įor drawing approximate model of the circuit shown in Fig. Thus the overall gain shall be less than the product of the gains of four stages. However, the gain of final or last stage (4th stage in this case) which has no loading effect of subsequent stage, remains unaffected. For example, in a 4-stage amplifier the gains of first three stages will be reduced due to loading effect of the subsequent stage. This reduces the gain of the stage which is loaded by the next stage. This is because whenĪ second stage is made to follow the first one, the effective load resistance of the first stage is reduced because of the shunting effect of the input resistance of the second stage. It may be mentioned here that the overall gain is less than the product of the gains of individual stages. The phase of output is the same as that of input because the phase is reversed twice by two transistors as they are in CE configuration. Thus the cascade stages amplify the signal and thus the overall gain is considerably increased. This is further amplified by the next stage and so on. The amplified signal developed across R C is transmitted to the base of next stage of the amplifier through coupling capacitor C C. When ac signal is applied to the base of the first amplifier, it appears in the amplified form across collector load R C. Operations of RC Coupled Transistor Amplifier: For this reason, the coupling capacitor C C is also called the blocking capacitor. Thus the dc biasing of the next stage is not interfered with. The coupling capacitor C C transmits ac signal but blocks the dc voltage of the first stage from reaching the base of the second stage. If it is not present, then the voltage drop across R E will reduce the effective voltage available across the base-emitter terminals (the input voltage) and thus reduces the gain. The emitter bypass capacitor C E, offers low reactance path to the signal. Thus the function of C in is to allow only the alternating current from signal source to flow into the input circuit. In the absence of C in the signal source will be in parallel with resistor R 2 and the bias voltage of the base will be affected. The input capacitor C in couples ac signal voltage to the base of transistor Q 1. As the coupling from one stage to the next is obtained by a coupling capacitor followed by a connection to a shunt resistor, therefore, such amplifiers are called Resistance-capacitance coupled or RC Coupled Transistor Amplifier. In this arrangement, the signal developed across collector resistor R C of the first stage is coupled to the base of the second stage through the coupling capacitor C C. The resistors R 1, R 2 and R E form the biasing and stabilization network. The two transistors used are identical and use a common power supply V CC. RC Coupled Transistor Amplifier – Operations, Derivation and Applications:Ī two-stage RC Coupled Transistor Amplifier using N-P-N transistors in CE configuration is shown in Fig.
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