Explanation of Output Form Transistor Amplifier

Output form Transistor Amplifier

The below fig shows the common emitter transistor amplifier. There are two ways of taking output from the transistor amplifier. The output can be taken either across R_C or across terminals 1 and 2. In either case the magnitude of output is the same.

Suppose if we take the output across load resistor R_C in the collector circuit i.e.

Output = Voltage across R_C = I_CR_C      …………………… (4)

This method of taking output from collector load is used only in single stage amplifiers. The output can also be taken across terminals 1 and 2

V_CE = V_CC – I_CR_C            …………………. (5)

From this V_CC is a D.C. Voltage and cannot pass through capacitor C_C therefore only varying voltage I_C R_C will appear across terminals 1 and 2.

 Output = I_CR_C

From expression (4) and (5) it is clear that the magnitude of output is the same whether takes output across collector load or terminals 1 and 2. The minus sign in expression (5) simply indicates the phase reversal. The second method of taking output is used in multistage amplifiers.

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