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Importance of Accurate Zref Estimation for Transmission Line Characterization based on 2x-thru Calibration
  • Chiu-Chih Chou
Chiu-Chih Chou
National Central University

Corresponding Author:[email protected]

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Abstract

The 2x-thru calibration is frequently used in the characterization of printed circuit board (PCB) transmission lines. Since the reference impedance of the calibrated S parameters are exactly given by the characteristic impedance, ZLINE, of the trace at the center of THRU, accurate estimation of this impedance becomes crucial to the accuracy of the renormalized S parameters. In this paper, we compare three different methods of estimating ZLINE: the mid-point TDR method, the initial-value TDR method, and the analytic model fitting method. Through a simulation test case, it is demonstrated that (i) the initial-value method gives accurate high-frequency responses, but inaccurate low-frequency and time-domain responses, (ii) the mid-point TDR gives inaccurate results in both time and frequency domains, and (iii) the analytic model method produces the most accurate results.