Agilent Technologies 4294A Specifications download pdf (Page 22)

2-4. Key measurement functions

The following discussion describes the key measurement functions for advanced impedance mea-

surement instruments. Thoroughly understanding these measurement functions will eliminate the

confusion sometimes caused by the measurement results obtained.

2-4-1. OSC level

The oscillator output signal is output through the Hc terminal and can be varied to change the test

signal level applied to the DUT. The specified output signal level, however, is not always applied

directly to the DUT. In general, the specified OSC level is obtained when the High terminal is open.

Since source resistor Rs is connected in series with the oscillator output, as shown in Figure 2-6,

there is a voltage drop across Rs. So, when the DUT is connected, the applied voltage Vx depends on

the value of the Source resistor and the DUT’s impedance value, Zx. This must taken into considera-

tion especially when measuring low values of impedance (low inductance or high capacitance). The

OSC level should be set as high as possible to obtain a good S/N ratio for the vector ratio detector

section. A high S/N ratio improves the accuracy and stability of the measurement. In some cases,

however, the OSC level should be decreased, such as when measuring cored-inductors, and when

measuring semiconductor devices in which the OSC level is critical for the measurement and to the

device itself.

Figure 2-6. OSC level divided by source resistor (Rs) and DUT impedance (Zx)

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Agilent Technologies 4294A Specifications Page 22