OK, from what I can gather this is a TDC, time to digital converter scope/device. Typically these have 45 psec resolution, that is the finest binning.
Although TDCs are not as accurate as Time Interval Error (TIE) measure of jitter - it helps to understand what the plots show by describing how TIEs work?
"The time difference between a real clock and an ideal uniform time scale, after a time interval following perfect synchronization between the clock and the scale. "
That is, the scope is set to collect a huge amount of data points. (10 -200 million points).
Then the run is stopped, and the data edges are searched for. An algorithm looks at the data structure, defines the Unit Interval (UI), and from there recovers the frequency of the fundamental clock embedded in the data.
When this ideal reference fundamental clock is reconstructed then each individual edge is examined again, and the difference between it's actual crossing time & the reference crossing time is what is called TIE.
So, with a TIE plot all transition points perfectly matching up with a reference crossing time would give a spike which consist of a single line with no broadening i.e. all the transitions would be exactly at the right time. Real world clocks are not this accurate so a certain amount of short term (not long term) drift is normal.
The TDC used in Steve's plots are not as accurate as TIE so the 'reference' has at least 45 psec of jitter already in it but the following still appplies
In order of decreasing performance the following plots would apply, I believe
- a single spike with as little broadening of the spike as possible (this also means that the spike will be higher i.e. the number of hits on time will be higher)
- a broader single spike i.e. more hits are off slightly from ideal
- two spikes instead of one spike would imply that there are transition timing errors concentrating around two distinct timings. I'm not uture I follow your explanation for this "The two humps indicates that the driver pulling high has a slightly different output impedance than the drive pulling low." The transitions are either on rising or alternatively, on falling edges b, not on both - or am I wrong here?
Right, thanks
Some similar (TIE) measurements
here of an SPDIF device & PS & other changes to it some of which correlate to SQ. This guy is using A TEK 7354. 35 000 Euro, Stock, without the jitter analysis package. That can cost another 10000 in a worst case..
At this point, & looking at your plots Vs listening impressions, I'm off the opinion that a reduction in close-in phase noise results in better rendition of finer, low-level details which would mean the room ambience is better portrayed & auditory images are more solid, less diffuse. Once I sourced clocks with low close-in phase noise I was finally able to confirm this as the audible result of this improvement.
This reduction in close-in phase noise shows up in your & TIE plots as less broadening of the single spike