Transistor Amplifier Circuits Unit 9 – Direct Coupling
Exercise 2 – Direct-Coupled Amplifier AC Operation
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to determine the ac voltage gain and
the input/output phase relationship of a direct-coupled amplifier by using measured and
calculated values. You will verify your results with a multimeter and an oscilloscope.
DISCUSSION
- The sine wave generator provides the input signal. The signal enters the base of the first-
stage amplifier. - Input and output signal are in phase because each common emitter inverts the signal.
- The voltage gain of Q1 is found with these equations:
Av1 = −Vo1/Vi1 = −R4/R5 - The voltage gain of Q2 is expressed by any of these equations:
Av2 = −Vo2/Vi2 = −RL2/R6 = −R7/R6 - The overall circuit voltage gain is the product of the two amplifier gains.