White Paper: Test & Measurement

Accurate Measurements of Extremely Small Capacitance Values


Increasing range of required capacitance values on both high and low ends stipulates development of new measurement tools. Increasing operating frequency leads to a need of capacitors with very low capacitance. Currently, component suppliers offer capacitors as small as 0.05 pF. Such small capacitance values are virtually impossible to measure with conventional hand-held LCR-meters due to high parasitic impedances of test cables and leads.

Even 4-wire measurements introduce a sub-pF parasitic capacitance that cannot be eliminated. Bench-top LCR-meters allow a better pre-test calibration but only for loose components, while for a soldered component, test leads are required involving non-controllable parasitics.

A solution was suggested in 2004 when integration of a digital LCR-meter, LCD, and a pair of tweezers as test leads resulted in Smart Tweezers, allowing measurement of resistance from 0.1 Ohm to 10 MOhm, capacitance from 1 pF to 5 mF, and inductance from 1 uH to 1 H.

A disadvantage of this device was a single wire connection from the device PCB to the handles and test leads introducing parasitic impedance of about 1 pf. Later a 2-wire connection was introduced in the handles decreasing the parasitic capacitance to about 0.5 pF.

Major improvements were achieved in lately developed LCR-Reader-MP/MPA where Short/Open calibration was built-in, thus entirely eliminating the impedance offset. Nevertheless, the offset depends on the distance between the test leads. This white paper presents an easy way of accurate elimination of the offset with accuracy of 1 fF/1 mOhm.

LCR-Reader-MPA features ranges of: 0.01 Ohm to 20 MOhm, 0.1 pF to 1 F and 10 nH to 100 H, and 0.1% accuracy and offers: AC/DC Voltage/Current and Frequency measurements, LED/Diode/Continuity test, Oscilloscope, Signal Generator.

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