Transmitter and Dispersion Eye Closure Quaternary (TDECQ) and its sensitivity to impairments in PAM4 waveforms

This paper presents the principles behind the transmitter and dispersion eye closure quaternary (TDECQ) test. A novel method to decompose TDECQ values is proposed where the result is separated into penalties from signal impairments that are either equalizable or nonequalizable by the reference receiver, enabling a more comprehensive study of signal quality. Moreover, the impact of selected impairments is studied in terms of their TDECQ penalty and its composition. This is achieved by producing generic test signals, where isolated impairments are applied to a high-quality reference signal. The impairments include low-pass filtering, amplitude noise, compression and eye skew. Low-pass filtering is shown to contribute mainly to increase the equalizable penalty while noise, compression and eye skew are shown to affect mainly the nonequalizable part. The results serve as a generic guideline to understand the engineering rules and parameter limits that are needed to design links using TDECQ.