Measurement of Capacitance Using Spread Spectrum Time Domain Reflectometry (SSTDR) and Dictionary Matching

In this article, we present a method for estimating capacitances with SSTDR and a dictionary matching algorithm. We simulate a dictionary of simulated SSTDR reflections for a range of capacitances, based on parameters of the transmitted SSTDR signal, the SSTDR signal generator, and the transmission line. The measured SSTDR reflection data is compared with each simulated reflection through cross-correlation, and the estimated capacitance is found from the highest correlation. We validate this method with experiments on capacitors ranging from 1pF to 450pF using a 12 MHz SSTDR. The dictionary matching algorithm estimated the capacitor values within 4% to 20% in the capacitance range of 100pF to 400pF.