Question 17.SG.Q.1: A bipolar transistor is operating in the active region with ......
A bipolar transistor is operating in the active region with a collector current of 1 mA. Assuming that the β of the transistor is 100 and the thermal voltage (V_T) is 25 mV, the transconductance (g_m) and the input resistance (r_π ) of the transistor in the common emitter configuration, are
(a)g_{\mathrm{m}}=25 \mathrm{~mA} / \mathrm{V} \text { and } r_\pi=15.625 \mathrm{k} \Omega
(b) g_{ m }=40 mA / V \text { and } r_\pi=4.0 k \Omega
(c) g_{ m }=25 mA / V \text { and } r_\pi=2.5 k \Omega
(d) g_{ m }=40 mA / V \text { and } r_\pi=2.5 k \Omega
g_{ m }=\frac{I_{ C }}{V_{ T }}
Therefore,
g_{ m }=\frac{1 \times 10^{-3}}{25 \times 10^{-3}} A / V =40 mA / V
Also, \beta=g_{ m } r_\pi.Therefore,
r_\pi=\frac{100}{40 \times 10^{-3}} \Omega=2.5 k \Omega
Ans. (d)