EEVblog #117 - PCB Power Plane Capacitance

Open source STF clone project.
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EEVblog #117 - PCB Power Plane Capacitance

Post by exxos » Fri Aug 31, 2018 10:18 pm

I tagged in this video in as my board uses a power plane...

It wasn't so much the capacitance, even though it will help with some high-frequency decoupling, it just keeping the resistance/inductance of the ground as low as possible between all points on the board...

It was actually one of the epic fails of a early V2.2 booster... http://www.exxoshost.co.uk/atari/last/16mhz/index.htm March 10th 2015 update..

Where basically while two ground pins on the CPU were connected together, the impedance between 0V pins on the with the frequency of the CPU, added up to about 2V bounce across the 0V points.. I still cannot really believe this even now.. Of course lesson learned, and they are all solid copper power planes now.

For example, the early V2 ground was this...
v2.jpg
v2.jpg (96.24 KiB) Viewed 158 times

And all my designs after that, the STE booster for example look like this..
ste.jpg
ste.jpg (48.33 KiB) Viewed 158 times
Of course a lot of issues on the STFM/E are due to bad grounding as already discussed a million times...

In terms of the STF remake.. It is a four layer board. Top and bottom layer of the signal traces.. And yes routing the entire board in just two layers took rather a long time even with the auto router... It failed to route it many times.. I think TerribleFire was slightly against the small tracks, but as I pointed out to him, it was only way to get the auto router to route the entire design two layers. Sure if I moved to 6 layers It could have been routed easily with wider tracks.. Of course that then doubles the price of the PCB.. So of course, some compromises had to be made.

The power rails (5V and 0v) are a dedicated layer right across the board. It is the best ground system that can be done, with the aid of the distributed capacitance, should really be a solid set up.. Of course there are huge number of ceramics on there as well..

And of course the money shot..
IMG_3252.JPG
IMG_3252.JPG (129.22 KiB) Viewed 158 times
.. and below the gnd layer..
gnd.JPG
gnd.JPG (190.55 KiB) Viewed 158 times

Maybe worth checking out Daves video... Does not cover everything but does basely point out how awesome these things are..

4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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