High-Speed Differential Pair Measurements Based on Two-Port Probe System Only

Differential pairs are popularly used in high-speed links. But they are difficult to measure, especially for PCB hoards and packagings, due to lacking properly connectable standards or expensive 4-port probe systems. In this work, a new differential analysis method based on the single trace's two-port measurement is proposed. It is theoretically derived and practically demonstrated that if the traces of a differential pair have weak couplings, their single trace's 2-port measurements with the other trace open-ended could effectively replace the complex and expensive 4-port differential measurements. To check the approximation accuracy, this paper proposes a companion testing method based on the 2-port system also. This work provides theoretical supports and experimental methods for general differential analysis using economic 2-port systems including but not limited to the probing system.