FET Fundamentals Unit 3 – JFET Amplifier
Exercise 2 – AC Operation
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to measure ac voltage gain by using a
JFET amplifier. You will verify your results with an oscilloscope.
DISCUSSION
- This JFET amplifier is designed to amplify an input sine wave (Vi) with a minimum
distortion. - The output signal (Vo) of the amplifier is 180° out of phase.
- Coupling capacitors prevent changes in JFET bias caused by external dc voltages.
- Self bias JFET circuits reduce amplifier gain; capacitor CS, which shorts RS for the ac signal,
reduces this effect. - The JFET amplifier is a voltage controlled device; changes in the amplitude of the input
signal vary the drain current. The varying drain current produces a varying signal voltage
across the load resistor (RL). - The ac voltage gain (Av) is determined by the ratio of the output voltage (Vo) to the input
voltage (Vi).
NOTES