Sub-10 picosecond differential TDR and TDT pulse source

A 9 ps differential time domain reflectometry (TDR) and time domain transmission (TDT) source has been built and characterized. This new differential pulse source is capable of producing both positive and negative pulses for differential and common mode analysis. The module connects to a trigger source, such as a slower commercial TDR/TDT plug-in, and uses nonlinear-transmission-line (NLTL) circuits to reduce the pulse risetime. TDR pulses captured with a 70 GHz sampling plug-in have a measured risetime of approximately 12 ps and an amplitude of 200 mV. Deconvolving the effects of timing jitter and sampler risetime yields a TDR risetime of approximately 9 ps. TDR measurements of a test circuit board show two-event resolution of less than 1.5 mm. Calculations suggest a resolution limit of around 0.5 mm on alumina. TDT pulses measured with a 70 GHz sampling plug-in have a risetime of approximately 10 ps (7 ps deconvolved) with an amplitude of over 2 V. The larger pulse amplitude of the TDT signal enables improved signal margin for far-end cross talk measurements.