Specifications

A.2.3 Open offset error
The term, Yo x Zx x 100 is called open offset error. If Zx is multiplied to this term, then ΔY = Yo. This
term affects the absolute admittance error, by adding an offset. Open repeatability, Yo, is determined
from the variations in multiple admittance measurements of the test fixture in the open condition.
After performing open compensation, the measured values of the open condition will distribute
around 0 S in the complex admittance plane. As shown in Figure A-3, the maximum value of the
admittance vector in the complex admittance plane is defined as open repeatability. The larger open
repeatability is, the more difficult it is to measure large impedance values. Open repeatability is
made up of a stray conductance and a stray capacitance part, which become larger as the frequency
becomes higher.
Figure A-3. Definition of open repeatability
A.3 New market trends and the additional error for test fixtures
A.3.1 New devices
Recently, the debut of extremely low ESR capacitors, and the trend to use capacitors at much higher
frequencies, have increased demand for low impedance measurements. As a result, the test fixture’s
short repeatability has become increasingly important. In Figure A-4, the relationship between
proportional error, short offset error, and frequency are shown when measuring low impedance of
100 mΩ and 10 Ω. Notice that when the measured impedance is less than 100 mΩ, short offset error
influences the entirety of the test fixture’s inherent error. As shown in the Figure A-4, when the
DUT's impedance is 100 mΩ and the test fixture’s short repeatability is 10 mΩ, the short offset error
will be 10 percent. Since the proportional error is minimal in low frequencies, the additional error
will also be 10 percent.
Figure A-4. Relationship between proportional error, short offset error, and frequency when measuring low impedance
A-3