DAY 1 ELECS MIDTERM

• Field Effect Transistor is a three-terminal active device that controls current flow using an electric field.
• Field Effect Transistor, has a high input impedance, making it useful in a variety of circuits.
• The Regions that make up a transconductance curve are the following: Cutoff Region, Ohmic Region, Saturation Region, and Breakdown Region
• The ordinary or BJT transistor has two main disadvantages

  1. It has a low input impedance

  2. It has considerable noise level
• To overcome this problem Field Effect transistor (FET) is introduced because of its:

  • High input impedance
  • Low noise level than BJT
• The Field Effect Transistor abbreviated as FET is an another semiconductor device like BJT which can be used as an amplifier or switch.
• The name Field Effect is derived from the fact that the flow of current through the conducting region is controlled by an electric field.
• • Junction Field Effect Transistor (JFET)
  • Metal Oxide Semiconductor Field Effect

  Transistor (MOSFET)
• FET can be classified into two types. -Junction Field Effect Transistor (JFET)

  Metal Oxide Semiconductor Field Effect

  Transistor (MOSFET)
• Cutoff Region

  The cutoff voltage is the particular gate-source voltage where the JFET begins to act like an open circuit. This is where the drain current ID which flows from the drain to the source ceases to flow and the transistor turns off.
• Ohmic Region

  This is the region where the JFET transistor begins to show some resistance to the drain current, ID that is beginning to flow from drain to source. This is the only region in the curve where the response is linear.
• Saturation Region

  This is the region where the JFET transistor is fully operation and maximum current, for the voltage, VGS, that is supplied is flowing. During this region, the JFET is On and active.
• Breakdown Region

  This is the region where the voltage, VDD that is supplied to the drain of the transistor exceeds the necessary maximum. At this point, the JFET loses its ability to resist current because too much voltage is applied across its drain-source terminals. The transistor breaks down and current flows from drain to source.
• N-Channel JFET is a JFET whose channel is composed of primarily electrons as the charge carrier.
• P-Channel JFETs, whose channel is composed primarily of holes
• When no voltage is applied to the gate of a N-Channel JFET, current flows freely through the central N-channel. This is why JFETs are referred to as "normally on" devices. Without any applied to the gate terminal of the transistor, they conduct current across from drain-source region.
• When no voltage is applied to the gate of a P-Channel JFET, current (holes) flows freely through the central P-channel. This is why JFETs are referred to as "normally on" devices. Even without any voltage, they conduct current across from source to drain.
• drain terminal is where current exits or enters the JFET, depending on the mode of operation.
• N-channel JFET, the drain is the terminal through which electrons flow from the external circuit into the semiconductor material.
• P-channel JFET, the drain is the terminal through which holes flow from the semiconductor material into the external circuit.
• gate terminal controls the conductivity of the channel between the source and drain.
• P-channel JFETs, a positive voltage applied to the gate attracts holes, thereby reducing the channel conductivity.
• N-channel JFETs, a negative voltage applied to the gate creates an electric field that repels electrons, reducing the channel conductivity.
• source terminal is where current enters or exits the JFET,depending on the mode of operation.
• N-channel JFET, the source is the terminal through whichelectrons flow from the semiconductor material to the externalcircuit.
• P-channel JFET, the source is the terminal through whichholes flow from the external circuit to the semiconductormaterial
• The source terminal is typically connected to the ground or thecommon reference point in a circuit
• body terminal is often connected to the substrate of theFET,
• In some FET designs, especially in power MOSFETs, the bodyterminal may be used for isolation purposes. By applying aspecific voltage to the body terminal, engineers can control thepotential difference between the transistor's substrate and therest of the circuit, enhancing isolation and minimizing unwantedcoupling effects
• Temperature Sensing and Thermal Management

  In certain cases, the body terminal may be connected to aheatsink to facilitate better thermal management. Thisconfiguration allows for efficient dissipation of heat generatedwithin the FET during operation
• The body terminal can also play a role in controlling parasiticdiodes that may form between the substrate and other parts ofthe transistor structure. By biasing the body terminalappropriately, engineers can minimize the impact of theseparasitic diodes on circuit performance.