RichF wrote:I bring this to your attention , because I firmly believe serier termination resistors should be added to any revision/upgrade.
That's an interesting suggestion, Rich. I was trained to design a PCB with series resistors on the sending side of any digital output, and an RC network on the receiving side of any digital input. This allows ringing, overshoots, and other problems to be cleaned up without a PCB rev. The initial version starts with 0Î© jumpers on the sending side and open circuits on the receiving side where the RC network would be, if needed.
The problem with all of this is that it is a design technique for fixed connections - i.e. known situations where two specific boards are connected. I don't see how you can select the "right" resistance for every possible circuit that the OLS might be connected to. In other words, I worry that the termination resistors would skew the timing of the inputs signals under certain conditions, and thus alter the results of the logic analyzer. I suppose it might be possible to calculate values which would work with "any" possible attached circuit being analyzed, but that doesn't sound easy.
I also question whether low-pass filtering on digital sampling makes any sense. Nyquist is certainly a concern with analog sampling, but binary inputs should be Schottky-connected rather than LPFd. A low-pass filter would introduce phase delay, perhaps enough to alter timing, as mentioned above.
That said, SMD sites on the PCB populated with 0Î© jumpers would not be a bad idea. The problem is that users would not easily be able to change the resistance if needed, but at least they wouldn't need a PCB revision.