Time Domain Reflectometer Measurements on MIPI D-PHY Protocol for Signal Integrity Analysis

As data rates continue to rise, data protocols allow engineers the bandwidth and speed necessary to utilize an ever increasing video resolution and quality. The Mobile Industry Processor Interface (MIPI) D-PHY CSI-2 protocol is one such solution. The MIPI standards utilizes High Speed (HS) and Low Power modes. These modes occupy the same data lines, making oscilloscope measurements difficult to obtain because the modes are constantly switching. In addition, the amount of data sent, during HS mode, changes with each packet. Real time oscilloscopes can recognize the HS mode data and wait for single triggered measurements to create a real time eye diagram. This process is time consuming and if the PCB is not designed for signal integrity testing, the measurements involve holding a differential probe steady on the DUT, introducing human error. In this paper, we propose to use Time Domain Reflection (TDR) measurements which can be easily made on any board as they do not require capturing live data. Using differential probes, TDR measurements also capture waveforms for each data lane and obtain an eye diagram. Results show a good correlation between real time scope and TDR eye diagrams. Also, TDR software allows S-parameters to be obtained.