Agilent Technologies 4294A Specifications download pdf (Page 88)

5-5. MOS FET measurement

Evaluating the capacitances between the source, drain, and gate of an MOS FET is important in

design of high frequency and switching circuits. Generally, these capacitances are measured while a

variable DC voltage source is connected to the drain terminal referenced to the source, and the gate

held at zero DC potential (Figure 5-24). When an instrument is equipped with a guard terminal and

an internal DC bias source, capacitances Cds, Cgd, and Cgs can be measured individually. Figure 5-

25 (a) through (c) shows the connection diagram for an instrument’s High, Low, and Guard termi-

nals. The guard is the outer conductors of BNC connectors of the UNKNOWN terminals.

Figure 5-24. Capacitance of MOS FET

Figure 5-25. MOS capacitance measurement

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Agilent Technologies 4294A Specifications Page 88