In a common emitter (CE) amplifier having a voltage gain G, the transistor used has transconductor 0.03 mho and current gain 25. If the above transistor is replaced with another one with transconductance 0.02 mho and current gain 20, the voltage gain will

Options

A. `1/3 G`
B. `5/4G`
C. `2/3 G`
D. `1.5 G`

Answer

C

Explanation

Voltage gain = Current gain `xx` Resistance gain
`A_(v)=betaxx(R_("out"))/(R_("in"))`
Transconductance, `g_(m)=(beta)/(R_("in")) or R_("in")=(beta)/(g_(m))`
`therefore A_(v)=g_(m)R_("out")`
For first case, `A_(v)=G, g_(m)="0.03 mho, "beta=25`
`therefore G=0.03R_("out")" ...(i)"`
For second case, `A_(v)=G.,g_(m)="0.02 mho, "beta=20`
`therefore" "G.=0.02R_("out")" ....(ii)"`
Divide (ii) by (i), we get
`(G.)/(G)=(2)/(3) or G.=(2)/(3)G`