Transistor Amplifier Circuits Unit 4 – Common Collector Circuit
Exercise 2 – Common Collector Circuit AC Operation
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to determine ac operating
characteristics of a common collector (CC) amplifier by using a typical CC transistor circuit.
You will verify your results with a multimeter and an oscilloscope.
DISCUSSION
- The ac input is provided by a sine wave generator.
- The ac output is taken between the emitter terminal and ground.
- Voltage gain of the common collector transistor circuit is the ratio of the ac output voltage to
the ac input voltage. The voltage gain is always less than one. - The input and output signal are in phase.
- The common collector transistor circuit is also called an emitter follower because the output
signal follows the input signal. - Input impedance (Zi) is equal to the combined parallel resistance of R1, R2, and β x (R3 +
re’). Since β x (R3 + re’) is more than 100 times as large as R1 in parallel with R2, this
parallel combination equals the input impedance. - This circuit block allows the student to measure output impedance (Zo) by connecting
potentiometer R4 in parallel with R3 and adjusting R4 until the output signal is half that of
the original.