Transistors

Part 3

Transistor Parts 3

• Field Effect Transistors (FETs) are Unipolar transistors with current carried by one type of charge carries – holes or electrons depending on the type of semiconductor being used.

• FETs are Voltage Controlled Devices

• Input impedance is high, low noise and good temperature stability.

Transistor Parts 3

• A JFET is a FET with a single P-N junction. It has 3 external connections: Gate (G), Source (S) and Drain (D).

• Schematic symbols of P and N Channels

Transistor Parts 3

• The Source (S) connection provides the source of charge carriers for the channel current. The Drain (D) acts as the place where the charge carriers are removed (or drained) from the device. This is the same for a P-Channel or an N-Channel, the charge carriers flow from the source to the drain connection.

Transistor Parts 3

• A typical circuit using a P-Channel JFET is:

Transistor Parts 3

• There is a dc voltage source, VDD, between the source and the drain connected so the positive terminal is connected to the drain and the negative is to the source connection. A second voltage is VGG connected between the gate and the source and it controls the amount of current that flows through the channel. This area is known as the depletion region.

Transistor Parts 3

Transistor Parts 3

• Amplification

Transistor Parts 3

• With a CS Common Source JFET there is a 180 degree phase reversal between the input and the output signals.

• CD Common Drain has voltage gains less than 1 and provides high current and power gains.

• CG Common Gate JFETs has Current gains less than 1 and high output impedance.

Transistor Parts 3

• MOSFETS-Metal Oxide Semiconductor FETs

Transistors Part 3

• FET Parameters:

Transistors Part 3

• Transistors Part 4 - Silicon Controlled Rectifiers (SCRs) - Class of Operation (Load-Line Analysis) - Class A - Class B - Class AB - Class C