Day 3: Dependent Sources and MOSFETs

Lab 3: Dependent Sources and MOSFETs

Procedure

Materials used in lab (Not pictured, laptop)

Schematic to build for testing MOSFET behavior

Testing actual resistance of 100 Ohm resistor

Breadboard of circuit including MOSFET and ANALOG Discovery

After building the circuit, we needed to test the relation of the dependency on the MOSFET in order to properly analyze it.

Beginning test for threshold by adding applying voltage to MOSFET gate until current increases.

Left DMM is for gate voltage applied, Right DMM is for current through MOSFET 

Increasing V(gate)

Huge spike in Current once threshold of approx 2.20V(gate) is acheived.

Increasing to higher V(gate) does very little in comparison.

It can be deduced that the threshold for which the MOSFET allows current to flow is approx. 2.20V on the Gate. This can be further seen in the data chart and graph of said data.

After obtaining a threshold voltage to begin a more aware procedure, we begin testing increments of 0.5V from 2 to 5.

Beginning procedure to characterize gate voltage and drain current.

V(gate) will begin at 2.00V for collection of data.

Increments of 0.5V were added to V(gate) for smoother plots.

Until a maximum of 5V is achieved by the Analog Discovery unit.

Analysis/Summary:

 The transistor is behaving in the manner that a Voltage Controlled Current Source would. In other words, the MOSFET will not allow any current through itself unless a specific magnitude of Voltage is applied to its Gate.

To calculate the value of g, we need to use the following formula for a Field Effect Transistor.

Where I(d) is the drain current, V(gs) is the voltage to the gate from the source, and V(t) is the threshold voltage we found. Using the last row as our values:

g = 2(35.6)/(5.00 - 2.20) = 71.2/2.80 = 25.43 milliSiemens