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 transmit a PAM4 symbol test pattern, which is captured as a signal waveform. The test pattern includes at least one rising signal sequence having a PAM4 symbol pattern of at least three −1 PAM4 symbols followed by at least three +1 PAM4 symbols and at least one falling signal sequence having a PAM4 symbol pattern of at least three +1 PAM4 symbols followed by at least three −1 PAM4 symbols. A voltage modulation amplitude (VMA) level for each of a −1 and +1 PAM4 signal level is measured for at least one rising signal sequence and falling signal sequence to derive 20% and 80% VMA levels. A rise transition time is then determined by measuring the time interval between when a rising signal crosses the 20% and 80% VMA levels, and a fall transition time is determined by measuring the time interval between when a falling signal crosses the 80% and 20% VMA levels.