Lab 1
MOSFET
A Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) is a type of transistor used for amplifying or switching electronic signals. Unlike bipolar transistors, which are current-controlled, a MOSFET is voltage-controlled. This makes it very useful in applications where you want to minimize the current drawn from the input source.
A MOSFET has three terminals:
- Gate (G): The control terminal. The voltage applied here determines whether the transistor is on or off.
- Drain (D): The terminal through which the output current flows out.
- Source (S): The terminal through which the output current flows in.
The MOSFET operates in different modes depending on the voltages at these terminals:
- Cutoff Mode: When the voltage on the gate (Vg) is less than a threshold, no current flows between the drain and source.
- Saturation Mode: When the gate voltage is much higher than the threshold, the MOSFET conducts fully between the drain and the source.
- Linear or Triode Mode: This is the region between cutoff and saturation where the MOSFET is partially conducting.
NFET and PFET
MOSFETs come in two main types:
- N-Channel MOSFET (NFET): Uses electrons as the charge carriers. It is turned on when a positive voltage is applied to the gate.
- P-Channel MOSFET (PFET): Uses holes (missing electrons, effectively positive charge carriers) as the charge carriers. It is turned on when a negative voltage is applied to the gate.
Characterizing MOSFETs
In a lab or simulation environment, you often want to characterize a MOSFET to understand its behavior under different conditions. Two key voltages are:
- V<sub>GS</sub>: Voltage between the Gate and the Source. This voltage controls whether the MOSFET is on or off.
- V<sub>DS</sub>: Voltage between the Drain and the Source. This voltage impacts the current flowing through the MOSFET when it's on.
By hooking up voltage sources to generate different values for V<sub>GS</sub> and V<sub>DS</sub>, you can observe how the MOSFET behaves in different regions of operation (cutoff, triode, saturation). This is crucial for designing circuits that use MOSFETs effectively.