Field Effect Transistors

Field Effect Transistors:

FET Amplification : Consider the n-channel FET Amplification circuit in Fig. 9-26. Note that drain-source terminals are provided with a dc supply (VDD), connected via the drain resistor (R1). The gate-source junctions are reverse-biased by the gate voltage (VG). An ac signal generator (with voltage vf) is connected in series with the gate terminal. As already discussed, field effect transistors are voltage-operated devices. The drain current is controlled by the gate-source voltage. A change in gate-source voltage (ΔVGS) produces a change in …


FET Datasheet Specifications : Maximum Ratings – A portion of a FET Datasheet Specifications is reproduced in Fig. 9-17. As with other device data sheets, a device type number and brief description is usually given at the start. Maximum ratings follow, and then the electrical characteristics are stated for specific bias conditions. From Fig. 9-17, the maximum drain-source voltage (VDS) for the 2N5457 through 2N5459 devices is 25 V, and the maximum drain-gate voltage (VDG) is also 25 V. This means, for example, that …


JFET Characteristics : An n-channel JFET Characteristics block representation is shown in Fig. 9-6. With a drain-source voltage applied as illustrated, ID flows in the direction shown producing voltage drops along the channel. Consider the voltage drops from the source terminal (S) to points A, B. and C within the channel. Point A is positive with respect to the source: alternatively, it can be stated that S is negative with respect to A. Because the gate blocks are connected to S, the …


Junction Field Effect Transistor Theory : n-Channel JFET – The operating principle of an n-channel Junction Field Effect Transistor Theory (JFET) is illustrated by the block representation in Fig. 9-1(a). A piece of n-type semiconductor material, referred to as the channel, is sandwiched between two smaller pieces of p-type (the gates). The ends of the channel are designated the drain (D) and the source (S), and the two pieces of p-type material are connected together and their terminal is named the gate …


MOSFET Construction and Characteristics : Figure 9-28 shows the MOSFET Construction and Characteristics of a metal oxide semiconductor FET (MOSFET), also known as an insulated gate FET. Starting with a high-resistive p-type substrate, two blocks of heavily-doped n-type material are diffused into the substrate, and then the surface is coated with a layer of silicon dioxide. Holes are cut through the silicon dioxide to make contact with the n-type blocks. Metal is deposited through the holes for source and drain terminals, as …