Transition time measurement of PAM4 transmitters

摘要

Methods, apparatus and systems for measuring signal transition times for a four-level pulse modulated amplitude (PAM4) transmitter. During a test procedure, a PAM4 transmitter is configured to repetitively transmitting a four-level test pattern, which is captured and digitized. The digitized data is processed to generate a linear-fitted waveform. A voltage modulation amplitude (VMA) level for each of a −1 and +1 PAM4 signal level is measured and used to derive 20% and 80% VMA levels in an eye diagram. The rise transition time is then determined by measuring the time interval between when a rising signal crosses the 20% and 80% VMA levels, and the fall transition time is determined by measuring the time interval between when a falling signal crosses the 80% and 20% VMA levels.

主权项

1. A method for measuring signal transition times for a four-level pulse modulated amplitude (PAM4) transmitter, comprising:
repetitively transmitting a test pattern with the PAM4 transmitter; capturing a waveform of the test pattern to produce digitized waveform data; generating a linear-fitted waveform based on the digitized waveform data; measuring, using the linear-fitted waveform, a voltage modulation amplitude (VMA) level for each of a −1 and +1 PAM4 signal level; deriving a 20% VMA level and an 80% VMA level as a function of the VMA levels for the −1 and +1 PAM4 signal levels; determining a rise transition time by measuring a time interval between when a rising PAM4 signal from a −1 PAM4 signal level to a +1 PAM4 signal level crosses the 20% VMA voltage level and crosses the 80% VMA voltage level; and determining a fall transition time by measuring a time interval between when a falling PAM4 signal from a +1 PAM4 signal level to a −1 PAM4 signal level crosses the 80% VMA voltage level and crosses the 20% VMA voltage level.