Transistor Feedback Circuits Unit 2 – Series Feedback
Exercise 3 – Effect of Feedback on Impedance
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to describe the effect of series feedback
on input impedance by using a typical series feedback circuit. You will verify your results with
an oscilloscope.
DISCUSSION
- Simple input impedance is the sum of all series elements and the transistor base input
impedance including effects of any bias resistors. - Adding series negative feedback to a common emitter amplifier increases input impedance.
- VR1 = Vi - Vb
- Ii = VR1/R1
- Zi = Vi/Ii