HP HP-Bench-Briefs-1990-07-12 free download

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SERVICE INFORMATION FROM HEWLETT-PACKARD 3rd & 4th Quarters 1990 rim BechtoldlEditor Introduction The field-effect transistor (or FET) is a three-terminal device that can be used in a multitude of applications ranging from signal amplification to logic and memory functions. The FET's basic principle involves using voltage between two terminals to con- trol the current flowing in the third terminal. In this wa a FET can be the 7 basis for an ampli ier or a switch. There are two fundamental types of Figure 2. Circuit symbol for n-channel JFET. FETs to look at, the junction field-ef- fect transistor (JFET) and the metal- oxide-semiconductor FET, or MOSFET. Although only one pn junction exists, operation of the JFET is dependent on The name field-effect transistor arises establishing different values of re- from the fact that current flow be- verse bias at the two ends (source and tween two of the device terminals is drain) of this junction. Because of controlled by an electric field, which this, references are sometimes made in turn is established by a voltage Figure 1. Basic structure of n-channel to gate-to-drain junction and gate-to- applied to the third terminal. FETs are JFET. ** source junction. also called unipolar transistors be- cause current is conducted by charge carriers (electrons or holes) flowing p-type region to provide the gate ter- Comparisons through one type of semiconductor minal (G). The p-channel FET works material (either n-type or p-type). This in a similar manner except for a reversal Referring to Figure 3, you see that a is in contrast to bipolar transistors of polarities of all currents and voltages. vacuum tube is voltage sensitive. By where current passes through both n- controlling the voltage on the grid, type and p-type semiconductor Figure 2 shows the circuit symbol for current flow through the tube can be materials in serie