Despite length-matching traces between a distributor-stage and the individual output-stages on my pulse distribution amplifier there remains a 2-300 ps peak-to-peak output skew between the channels.
Here's a test where a 50 pF or 10 pF trimmer-cap is added just before the input of the output-stage. I found that tuning the cap results in a variable delay of 60-80 ps/pF, so if initially the channels are within 300 ps of each other the 500 ps tuning-range of the 10 pF trimmer-cap is sufficient.
As a test I first tuned all channels to within 20 ps peak-to-peak, then verified this the following day and got 52 ps peak-to-peak. BNC-connectors might not be the greatest for picosecond level repeatability.
Although the PCB was designed with equal-length traces for the output stages it appears that channels 3-4 and 5-6 are consistently late, and some shortening of the traces would improve things. I tried this on one PCB (blue data points) with moderate success.
Measurement setup: 1PPS source to 50-ohm splitter. One output of the splitter drives CH1(start) of a time interval counter (HPAK 53230A), the other output drives the input of the pulse distribution amplifier. Outputs wired to CH2(stop) of the counter and measured for 100 s or more (delay is average of 100 pulses). Counter inputs DC-coupled, 50 Ohms, trigger level 1.0 V.
A new pulse distribution amplifier for 1PPS distribution.
The input is fed to a LT1711 comparator triggering at 1.0 V (set by reference ADR423). This edge is buffered by 74AC14 before 1:8 fan-out to output-stages with three 74AC04 inverters in parallel driving the outputs.
Preliminary measurements show around 200ps channel-to-channel propagation skew - to be improved on by further trace-length matching or tuning. More measurements to follow.
A new distribution amplifier design featuring a 1PPS pulse distribution amplifier (PDA) and a 5/10 MHz frequency distribution amplifier (FDA).
1U 150mm deep rack-enclosure from Schaeffer. Prototype PCBs without soldermask or silkscreen from Prinel. Both the FDA and PDA boards have 1:8 fan-out with 9 BNC (optionally SMA) connectors spaced 16mm apart. The boards fit comfortably side-by side on a 19" rack panel. Some funky BNC-cables with unusually large connectors may not fit side-by-side 16mm apart - a price to pay for the compact design. The plan is to use an +/-12 AC/DC brick power-supply (not shown) which fits in the back of the enclosure.
Detailed posts on the PDA and FDA boards to follow.