Material parameter extraction using Time-Domain TRL (t-TRL) measurements

Characterizing materials used in printed circuit board (PCB) manufacturing is becoming increasingly important in link path analysis as the data rates are increasing. The material properties governing the performance of the signal passing through a transmission line are frequency-dependent. Using frequency-domain vector network analyzer (VNA) measurements and through-reflect-line (TRL) calibration, these parameters can be determined accurately. But a time-domain reflectometer (TDR) provides a relatively inexpensive and simple way of characterizing transmission lines, and it is easily accessible to signal integrity engineers. With the time-domain TRL (t-TRL) calibration technique, it is now possible to de-embed such discontinuities as connectors, cables, etc., in the path of the transmission line using time-domain measurements. From the calibrated results, material properties can be extracted in the same way as it is done in the frequency domain. This paper describes a t-TRL technique to obtain accurate frequency domain S-parameters from time domain measurements. The calibrated results are converted into the ABCD parameters. The propagation constant is obtained through the ABCD parameters, from which attenuation loss and phase constant are extracted. Dielectric constant is extracted from the phase constant and the total attenuation constant. Curve-fitting technique is used to split the losses into conductor and dielectric loss. Once dielectric loss is determined, loss tangent can be calculated. The results are compared for three test vehicles, and are also compared with frequency domain VNA measurements. The results from the t-TRL calibration technique are also compared with another known extraction procedure.