Thursday, October 29, 2020

Important Formula of Multistage Transistor Amplifiers

 

( 1 ) Gain of amplifier

        G = G1 × G2 × G3

        Where

        G1 = Gain of first stage

        G2 = Gain of second stage

        G3 = Gain of third stage

( 2 ) Relation between “Bel” and “dB”

        1 Bel = 10 dB

( 3 ) Gain of Amplifier in dB

        G = G1 + G2 + …… + Gn

        Where

        G1 = Gain of first stage ( dB )

        G2 = Gain of second stage ( dB )

        Gn = Gain of nth stage ( dB )

( 4 ) Power gain

                  = 10 Log10 ( Pout / Pin ) dB

( 5 ) Voltage gain

                 = 20 Log10 ( Vout / Vin ) dB

( 6 ) Current gain

                = 20 Log10 ( Iout / Iin ) dB

( 7 ) Bandwidth of amplifier

              BW = f2 – f1

              Where f2 = Upper cut off frequency

                          f1 = Lower cut off frequency

  • f1 and f2 is called as 3 dB frequency or half power frequency.

( 8 ) Voltage gain of RC Coupled Amplifier

        Voltage gain = β ( Rac / Rin )

        Where Rac = Effective load of first stage

                          = Rc ‖ Rin

( 9 ) The load reflected at the primary side of the transformer coupled amplifier

        RL’ = ( NP / NS ) RL

        Where RL = Load resistance

                   NP = Primary turns

                    NS = Secondary turns

                                OR

                  RL’ = ( IS / IP )2 RL

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