Common Source JFET Amplifier

AIM: To Study the common source amplifier and to find 1. Cut off frequencies. 2. Bandwidth. 3. Gain. APPARATUS: 1. CS(FET) Amplifier Kit 2. CRO 3. Function Generator 4. BNC Probes 5. Patch Chords THEORY: The common-source (CS) amplifier may be viewed as a transconductance amplifier or as a voltage amplifier. (See classification of amplifiers). As a transconductance amplifier, the input voltage is seen as modulating the current going to the load. As a voltage amplifier, input voltage modulates the amount of current flowing through the FET, changing the voltage across the output resistance according to Ohm's law. However, the FET device's output resistance typically is not high enough for a reasonable transconductance amplifier (ideally infinite), nor low enough for a decent voltage amplifier (ideally zero). Another major drawback is the amplifier's limited highfrequency response. Therefore, in practice the output often is routed through either a voltage follower (common-drain or CD stage), or a current follower (common-gate or CG stage), to obtain more favorable output and frequency characteristics.