Lab 2: FET Amplifier
Name
Institution

Abstract
Field Effect transistors (FET) are devices or circuits that alter or change the amplitude of a signal while maintaining the input waveform shape. The FET amplifiers run the Field Effect Transistors in saturation or active mode. The drain current is majorly determined by a small input voltage. All FET amplifiers do not have a β but instead have a trans conductance gm. In the circuit, the output voltage is primarily determined by the input gm. in the circuit.
Introduction
When working to amplify AC voltage that is time varying, we include a capacitor at the input of the amplifier to decouple any DC component that may be in the input signal. The value of the coupling capacitance used majorly depends on the circuit being designed. The RC filter which is formed by the input impedance and the coupling capacitor, should not cut off any given input signal frequencies in the FET.
Procedure
During voltage biasing, The DC voltage needs to be set at the requisite bias point. This is achieved by the use of the coupling capacitor’s biasing network. Here the source is common to both the output and input voltages and this is referred to as common source amplifier. The gate voltage and the input voltage are in direct proportion whereby an increase in input voltage causes a corresponding increase in gate voltage. The same relationship exists between the drain current and input voltage. However, the output voltage is in indirect proportion with the input voltage.

Apparatus
Transistor (2N7000)
Resistor
Capacitor
Oscilloscope
Multimeter
Breadboard (with crocodile clip ends)
Diagram;
This is how a generalized Field Effect transistor looks like; The transconductance of a FET is given by, gm=Id/Vgs Rearranging this equation gives;
Id=gm*Vgs ...........(1)
From the above equation, it can be concluded that the output current of the transistor amplifier Id is given by the product of the trans conductance gm and the input voltage Vgs.
For a FET with ideal specifications in the equivalent circuit, the voltage gain is given by the equation:
Av=Vds/Vgs
Hence, from the equivalent circuit we get,
Vds=Id*Rd
Subsequently, from the definition of trans conductance we have,
Vgs=Id/gm
These yields,
Av=gm*Rd .........(2)

References
Turner, R. P. (2007). FET circuits (3rd ed.). Indianapolis: H.W. Sams.