High speed serial data link systems 10 are composed of a transmitter 12, a channel 14 and a receiver 16 as shown in FIG. 1. As serial data speed reaches 6 Gb/s and beyond, equalization techniques become necessary to maintain system performance in the presence of channel loss, reflection, cross talk, noise and other factors that degrade the system performance. The system performance can be measured in various ways including bit error rate, eye opening, and jitter measurements. Industry standards start defining measurements based on equalization measurement or simulation, such as methods proposed to SAS-2 6 G (Serial Attached SCSI (Small Computer System Interface)-2 6 Gigabits/sec) standard committee.
One equalization or simulation method is based on knowing a training sequence, and having the averaged sampled analog data pattern waveform to equalize. An equalization adaptation algorithm 20 uses both inputs to optimize equalizer taps as depicted in FIG. 2. However, this method doesn't explicitly take into account the signal components that are not correlated to data pattern, such as periodic and random jitter/noise for equalizer tap optimization.
Another solution for equalization simulation on oscilloscopes uses only the sampled analog waveforms for equalizer adaptation, as shown in FIG. 3. When the waveforms have very severe Inter-Symbol Interference, ISI, and large noise, the blind equalizer adaptation approach 22 would fail since there is no guarantee that the taps are optimized correctly. The bit sequence could be classified incorrectly.
The real-time oscilloscopes capture signals without aliasing, so all the frequency dependent information is preserved. When an equalizer adaptation algorithm uses the real-time samples directly, the equalizer taps are optimized in the sense that all the frequency dependent information has been taken into account. For example, when the sinusoidal noise has energy concentrated at different frequencies, the optimized taps will have different values so that the optimal system performance is achieved accordingly to the specific sinusoidal noise distribution.
Real-time oscilloscopes have the flexibility to capture any waveforms, even when triggers are difficult or impossible to obtain precisely. Without any trigger, a real-time oscilloscope can take a long record single shot acquisition to record the waveform, and then process the waveform with equalization simulation.