More Tweaks on Amanero USB Board
Still striving for unlock-free behavior, I implemented what Mr. Abraxalito recommended:
Be careful with ultra-fast CMOS logic – it does require extremely good decoupling. Inside CMOS devices the transistors crowbar the supplies (quite literally) every clock transition. I discovered this with 74AC chips many years ago – even there I was using a multilayer PCB. I suspect the Potato chips are considerably faster! Get the smallest package size you can solder, decouple with 0603s and use a ferrite bead on the positive supply to reduce the bounce on the GND. Even with these precautions you’ll get some jitter from the bounce on the positive supply. Good luck! [link]
After the mods:
Basically I added a ferrite to Vcc and a capacitor to GND. Effectively, including with the previous bypass capacitor, it is a CLC filter which is symmetric from either side of the supply line (meaning it should filter noise coming into the flip flop and noise coming out of the flip flop through the power line). I also paired the bit clock line with a ground wire to provide some shielding. Pretty standard and common sense tweaks.
Unfortunately I messed my my clean and professional looking implementation :-). If I were to do it again, I would put those components under the board.
Based on feedback from readers, I’ve replaced the “magic red cap” :-)) with a much smaller ceramic cap
Seems very positive: I did the first interval for the unlock test, from midnight to 8:00 AM and there were Zero unlocks. It “survived” the “morning hiccup” where at the start of the day, electrical activity would cause one or more unlocks… We will see what happens in the afternoon.
Unlocks after: (8 hrs play time)
after 20 hours, the results are really good. Have never gotten this kind of performance in the past: ZERO unlocks (except, of course for the warm up time). Here is the plot showing the full 20 hours of play time. Well, there is really nothing to show 🙂
This turned out a very effective mod, even with much less than ideal components. If done correctly (proper PCB with ground plane, proper bypass, compact layout, etc), the results would be even better (and finally beyond my “measurements” – not really, I just use higher sample rate material). Anyone wants to develop a small PCB?