Question

Coonsider the transistor circuit shown in the figure below:



Assuming the two transistors to be perfectly matched with the value of reverse saturation current $I_1={10}^{-12}A.V_T=26mV$ and $\eta =1$. Then the value of output voltage $V_0$ is equal to _____ mV.

• A. 622.49

Answer 1

The correct option is A 622.49
Since the transistor is acting like a diode
$I_1=I_{s}exp\left[\frac{V_{BE}}{V_T}\right]$
Since both the transistors are matched
$I_1=I_2=\frac{1}{2}=\frac{50mA}{2}=25mA$
$25\times {10}^{-3}={10}^{-12}exp\left[\frac{V_{BE}}{V_T}\right]$
$V_0=V_{BE}=V_{T}ln(25\times {10}^9)=26\times {10}^{-3}ln(25\times {10}^9)$
$=0.6224V=622.49mV$