Quadrature Bridge Measures Harmonic Distortion in Capacitors

This article considers the measurement of harmonic distortion in capacitors using a bridge circuit. Each arm of the bridge consist of one resistor and one capacitor. The bridge is driven in quadrature, such that both the differential and common-mode output voltage are nominally zero. The article introduces a procedure to construct a capacitor with very low distortion contribution, which is used in the reference arm of the bridge. The resolution of the bridge is estimated to exceed −150 dB.  Measurement results for various capacitor types are presented. These show that parts with ceramic C0G dielectric have more consistent, and generally speaking also lower, distortion than Polyester, Polypropylene or Polystyrene film capacitors.