Advanced method to refine waveform smeared by jitter in waveform sampler measurement

Abstract

Mixed signal ATE (Automated Test Equipment) often integrates a waveform sampler for testing UHF signals. While performing under-sampling, slow jitter greatly influences the captured signal which is reconstructed into a meaningful waveform by manner of coherent waveform reconstruction. The purpose of this work is to remove slow jitter effects from a high-speed digital signal measured by a waveform sampler and to reconstruct a clear waveform and eye pattern. The test signal is a PRBS (Pseudo Random Binary Sequence) bit stream with slow jitter. The PRBS signal becomes an extreme wideband multi-tone from a spectrum point of view, so capturing such a signal with a waveform sampler needs a carefully organized test plan based on the coherent condition. Measured data is reconstructed into a meaningful waveform by reshuffling the sequence of the sampled points. Jitter in the signal is a kind of PM (Phase Modulation) which smears the spectrum. So the point of processing is to demodulate the PM signal and then restore the original multi-tone components. An elegant mathematical equation is introduced to perform the carrier tone recovery. Because of the multi-tone structure, processing needs to be applied to each one of the tone components. First, the PM effect is removed from each tone, and then each tone needs to be compensated amplitude loss by referencing the original tone power. Finally processing successfully reconstructs a clear PRBS waveform and a big eye opening. This paper reports the signal processing in detail with showing 7 Gbps 127-bit PRBS waveform.