Oscilloscope tools for PAM4 (4-level) signalling analysis

October 04, 2015 // By Graham Prophet
Measurement tools from Tektronix operate on both real time and equivalent time oscilloscopes, to deliver, the company says, the lowest noise acquisitions available for the signal type.

A comprehensive set of analysis tools for emerging PAM4 modulation measurement needs, with full support for both optical and electrical interfaces, these tools operate on both DPO70000SX 70 GHz real time, and DSA8300 equivalent time, oscilloscopes.

PAM4 is being adopted in the latest 400 Gigabit Ethernet standard by the IEEE P802.3bs working group for 400G (typically 8 x 50G) electrical and optical interfaces. Compared to traditional NRZ that uses two-level signalling, the four-level scheme used in PAM4 significantly increases signal complexity and places new demands on test equipment for performance and noise sensitivity.

The ability to reliably characterise PAM4 signals from 13 GBaud to 56 GBaud with a common set of tools supporting both optical and electrical domains is key to advancing this new modulation. Analysis of multi-level signalling found in PAM4 requires an oscilloscope with low noise and good signal-to-noise ratio to accurately acquire and analyse the multiple bit states. The Tektronix DPO70000SX oscilloscope uses Asynchronous Time Interleaving (ATI) technology to deliver very low noise acquisitions, as much as 30% lower noise than conventional frequency interleaved performance oscilloscopes.

Optical PAM4 measurement analysis benefits from low noise acquisitions as well. With the optical acquisition technology available with the DSA8300 Series Sampling Oscilloscope, Tektronix now claims the lowest noise and highest sensitivity available, even with full clock recovery in place. This new level of noise performance in the Tektronix 80C15/CRTP optical module suits optical PAM4 analysis with its full complement of TDEC and SR4 conformance measurement capabilities.

Features in the PAM4 Analysis toolset include the ability to analyse full waveforms or correlated waveforms, reference level settings for pass/fail analysis of multi-level thresholds, numerical rise/fall times for every LSB, MSB level, and built-in clock recovery using PAM-specific PLL models provided by Tektronix.

PAM4 analysis solutions for Tektronix DSA8300 and DPO70000SX oscilloscope models will be available in Q4, 2015. Core analysis tools that extend existing DPOJET or 80SJNB solutions to perform PAM4 analysis