Agilent Technologies 4294A Specifications download pdf (Page 87)

5-4. Diode measurement

The junction capacitance of a switching diode determines its switching speed and is dependent on

the reverse DC voltage applied to it. An internal bias source of the measurement instrument is used

to reverse-bias the diode. The junction capacitance is measured at the same time. Figure 5-22

shows the measurement setup.

For variable capacitance diodes (varactor diode) which utilize capacitance-bias characteristics, it is

important to measure capacitance accurately while applying an accurate DC bias voltage. Figure 5-

23 shows an example of measuring the C-V characteristics of a varactor diode. Use a low test signal

level (typically 20 mV rms) to trace precisely the relationship of the capacitance to the DC bias volt-

age.

The varactors for high frequency applications require Q factor or equivalent series resistance (ESR)

measurement along with capacitance at a frequency above 100 MHz. The RF I-V measurement

instrument is adequate for this measurement. It is possible to measure Q or ESR with the same

setup as for the C-V measurement, by merely selecting the desired parameter.

Figure 5-22. Reverse biased diode measurement setup

Figure 5-23. Varactor C-V characteristics

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Agilent Technologies 4294A Specifications Page 87