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 waveform A and B to a logic. Draw the output waveform for an OR gate. Write the truth table for this logic gate and draw its logic symbol.

Answer 1

A	B	C
0	0	0
1	0	1
1	1	1
0	1	1

$\text{Input characteristics}:$

1. Connect the circuit as shown in the circuit diagram.
   
2. Keep output voltage $V_{CE}=0V$ by varying $V_{CC}$.
3. Varying $V_{BB}$ gradually, note down base current $I_B$ and base-emitter voltage $V_{BE}$.
4. Step size is not fixed because of the non-linear curve. Initially, vary $V_{BB}$ in steps of 0.1V. Once the current starts increasing very $V_{BB}$ in steps of 1V up to 12V.

Repeat above procedure (step 3) for $V_{CE}=-5V$

$\text{Output characteristics}:$

1. Connect the circuit as shown in the circuit diagram.
2. Keep emitter current IB = 20A by varying VBB.
3. Varying VCC gradually in steps of 1V up to 12V and note down collector current IC and Collector-Emitter Voltage(VCE).
4. Repeat above procedure (step 3) for IB = 60µA, 0µA.