Comparison of a 100-pF Capacitor With a 12 906-Ω Resistor Using a Digital Impedance Bridge.

Mona Feige,Dean G Jarrett,Frank Seifert,Stephan Schlamminger,Shamith Payagala,Bryan C Waltrip,Andrew D Koffman,Alireza Panna,Yicheng Wang,Michael Berilla

doi:10.1109/tim.2021.3139709

Abstract

We tested a digital impedance bridge in a hybrid structure for comparison of a capacitor with a resistor where the impedance ratio was measured in two separate parts. The modulus of the impedance ratio was matched arbitrarily close to the input-to-output ratio, in magnitude, of a two-stage inductive voltage divider by adjusting the operating frequency of the bridge; the residual deviation between the two together with the phase factor of the impedance ratio was measured using a custom detection system based on a four-channel 24-bit digitizer. The ratio of the inductive voltage divider was calibrated, in situ, using a conventional four-arm bridge with two known capacitors. Fluctuations of the source voltages were largely removed through postprocessing of the digitized data, and the measurement results were limited by the digitizer error. We have achieved an overall bridge resolution and stability of 0.02 μF/F in 2 h for measuring a 100-pF capacitor relative to a 12 906-Ω resistor at 1233 Hz. The relative combined standard uncertainty (k = 1) is 0.13 μF/F, dominated by the digitizer error.

Highlights

DIGITAL techniques can be readily used to generate two synchronized ac voltages with a phase difference of π/2
We evaluated a digital impedance bridge in a hybrid structure for comparison of a capacitor with a resistor where the impedance ratio was measured in two separate parts
The modulus of the impedance ratio was matched arbitrarily close to the input-to-output ratio, in magnitude, of a two-stage inductive voltage divider (IVD) by adjusting the operating frequency of the bridge; the residual deviation between the two together with the phase factor of the impedance ratio was measured using a custom detection system based on a four-channel 24-bit digitizer

Summary

INTRODUCTION

DIGITAL techniques can be readily used to generate two synchronized ac voltages with a phase difference of π/2. When the voltage ratio of two synthesized sources is used directly as the reference for impedance ratio measurements, as described in the literature [5,6,7,8,9,10,11], the stability of the voltage ratio can become a major limiting factor for the overall bridge performance. It appears that an underexplored research area is to mimic in the digital domains some analog techniques that are commonly used in the analog bridges to correlate and combine detector voltages, enabling suppression of the effect of source fluctuations. This paper describes our research in this direction, aiming to develop a simple digital bridge for RC comparisons

BRIDGE SETUP

Digitized Bridge Voltage

TEST RESULTS AND DISCUSSIONS

Correlation Analysis and Noise Cancellation

Results and Uncertainty Analysis

CONCLUSION