Specifications

2-9
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. Oscillator (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 2-7,
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. This must be taken into
consideration especially when measuring low values of impedance (low inductance or high capaci-
tance). The OSC level should be set as high as possible to obtain a good signal-to-noise (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 2-7. OSC level divided by source resistor (Rs) and DUT impedance (Zx)