Question

(a) Draw the circuit diagram for studying the characteristics of a transistor in common emitter configuration. Explain briefly and show how input and output characteristics are drawn.
(b) The figure shows input waveforms A and B to a logic gate. Draw the output waveform for an OR gate. Write the truth table for this logic gate and draw its logic symbol.

Answer 1

(a) Circuit diagram of transistor in common emmiter configuration:

(1) Input charcteristics : The input charactecteristics of the transistor are obtained by plotting the base current $I_B$ versus base emitter voltage $V_{BE}$ for fixed collector emitter voltage $V_{CE}$. The observations of $I_B$ versus $V_{BE}$ are repeated for fixed values of $V_{CE}$. The figure given below represents the input characteristics curves.

(2) Output characteristics : These characteristics are obtained by plotting collector current $I_c$ versus collector emitter voltage $V_{CE}$at a fixed value of base current $I_B$. The base current is changed to some other fixed value and the observations of $I_C$ versus $V_{CE}$ are repeated. The figure given below represents the output characteristic curves.


truth table :
$\begin{array}{ccc}\text{A}& \text{B}& \text{Y}\\ 0& 0& 0\\ 0& 1& 1\\ 1& 0& 1\\ 1& 1& 1\end{array}$