Agilent Technologies 4294A Specifications download pdf (Page 68)

Accordingly, the residual parameters have greater effects on higher frequency measurements and

become a primary factor of measurement errors. The accuracy of measurement results after com-

pensation depends on how the open/short measurements have been performed properly.

Figure 4-15. Relationship of residual parameter values to the typical impedance

measurement range of the RF I-V method

To perform optimum compensation, observe the precautions for open/short measurements as

described in paragraph 4-2-3. In high frequency region, the method of open/short compensation

dominates measurement correlation. To obtain measurement results with a good correlation and

repeatability, the compensation must be performed at the same conditions. A difference in compen-

sation method will result in a difference in measured values, leading to correlation problems on

measurement results. Short measurement is more critical in terms of increasing need for low induc-

tance measurements. The short compensation issue is discussed in the following paragraph.

4-6-5. Consideration for short compensation

To make short measurement at the contact terminals of a test fixture or of a component handler, a

short bar (chip) is usually employed. In measurement of very low impedance (inductance), the fol-

lowing problems arise from the short bar:

• Different residual impedance dependent on size and shape

• Method of defining the residual impedance

If a different size or shape of the short bar is used, it is difficult to attain a good correlation of the

measurement results. The residual impedance of the short bar is different if the size differs. Hence,

the same size of short bar must be used when making short measurement.

If the definition of the short bar’s impedance is different, it causes a difference in measured values.

To have a good correlation, it is desirable to determine the short bar’s residuals. However, it cannot

be determined only from the inherent impedance of the short bar itself. The actual impedance

depends on surrounding conditions such as contact terminals, thickness of the closely located con-

ductors, permittivity of insulators, ground conditions, etc.

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Agilent Technologies 4294A Specifications Page 68