A transistor is usedin common emitter mode in an amplifier circuit. It is found that when a signal of 20 mV (millivolt) is added to base-emitter voltage the basecurrent changes by `20 muA` (micro ampere) nd collector current changes by 1.5 mA (milli ampere). Determine the current gain b, Input resistance Ri, transcondutance and voltage gain. Give load resistance `R_l = 6kW` (kilo ohm).

Explanation

`V_(i)= 20mV= 20 xx 10^(-3)V, Delta I_(b)= 20mu A= 20 xx 10^(-6) A`
`Delta I_(c)= 1.5mA = 1.5 xx 10^(-3)A`
`beta`= ?, `R_(i)= ?, R_(L)= 6 k Omega= 6000Omega`
Transconductance `=g_(m)`= ? `A_(v)`= ?
`beta_(ac)= (Delta I_(c))/(Delta I_(b))= (1.5 xx 10^(-3))/(20 xx 10^(-6))= (1500)/(20)`
`beta_(ac)= 75`
`R_(i)= (V_(i))/(Delta I_(b))= (20 xx 10^(-3))/(20 xx 10^(-6))`
`R_(i)= 1000Omega=1k Omega`
`A_(v)= beta_(ac)xx (R_(L))/(R_(i))`
`=75 xx (6000)/(1000)= 450`
`g_(m)= (beta_(ac))/(R_(i))= (75)/(100)`
`0.075 Omega^(-1)`