Agilent Technologies 4294A Specifications download pdf (Page 69)

Conceptually, there are two methods of defining the short bar’s impedance: One is to assume the

impedance to be zero. This has been a primordial method of defining the short impedance. In this

definition method, measurement result is a relative value of the DUT to the short bar.

The other method is to define the short bar’s inductance as xx H. (Residual resistance is negligible

for small short bar.) In this method, the measurement result is deemed as the absolute value of the

DUT. The residual inductance of the short bar is estimated from physical parameters (size and

shape) and is used as a reference. To estimate the inductance, the short bar needs to meet condi-

tions, where theoretical derivation is possible.

The measurement results from both definition methods are correct. The difference in measurement

result is attributable to only the difference in the definition. Practically, because of these incompati-

ble definitions, a problem will emerge when yielding correlation. To avoid this type of problem, it is

necessary to establish an agreement on the short bar’s size, shape and the definition method of the

residual inductance.

Note: Each of the 16196A/B/C/D coaxial test fixtures has a short device whose value is theoretically definable. Since a

50 Ω coaxial configuration is established for the whole signal flow path including the short device placed in the

fixture, the theoretical inductance value of the short device can be calculated from the length and physical constants

by using a transmission line formula. Its reference value is documented; however, the use of the 16196A/B/C/D is

not subject to execution of the compensation based on the reference value. You need to select the definition method

of short inductance that agrees with your measurement needs.

The chip type short devices and load devices are readily available from the working-standard set

supplied for Agilent RF I-V measurement instruments. Otherwise, you can substitute appropriate

devices for the short and load chips by accurately determining (or properly defining) their charac-

teristics. Method of calibrating the load device follows.

4-6-6. Calibrating load device

To determine the values of a load device, you can utilize the same instrument that will be used to

measure DUTs. Appropriate procedure for calibrating the load device is described below:

(1) Perform open/short/load calibration at the instrument’s test port. In addition, for a capacitive

or an inductive load device, it is recommended that low loss capacitor calibration be performed.

(2) Connect a direct-mounting type test fixture to the test port. It is recommended that the

16196A/B/C/D coaxial test fixtures be used to insure the best measurement accuracy.

(3) Perform open and short compensation. For short measurement, the method of minimizing

short impedance must be employed. (To do this, contact the terminals directly together if possi-

ble.) When the 16196A/B/C/D is used, consider inputting the reference value of the residual

inductance of furnished short device to the instrument. (Using the reference value is contin-

gent upon how the reference of short inductance needs to be defined for your measurement.

Agilent chooses to take the historic approach to let short=0 H, but the actual user of the test fix-

ture can choose either approach.)

(4) Connect the load device to the test fixture, select parameters available for instrument’s load cal-

ibration function (typically R-X, L-Q, L-Rs and C-D) and measure the device. Set the measure-

ment time, test signal level and averaging so that the instrument can measure the load with a

maximum accuracy (or use the specified test signal level of the device if required).

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Agilent Technologies 4294A Specifications Page 69