EEVblog #117 - PCB Power Plane Capacitance
Posted: 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.exxosforum.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...
And all my designs after that, the STE booster for example look like this..
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..
.. and below the gnd layer..
Maybe worth checking out Daves video... Does not cover everything but does basely point out how awesome these things are..
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.exxosforum.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 (96.24 KiB) Viewed 2055 times
And all my designs after that, the STE booster for example look like this..
- ste.jpg (48.33 KiB) Viewed 2055 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 (129.22 KiB) Viewed 2055 times
- gnd.JPG (190.55 KiB) Viewed 2055 times
Maybe worth checking out Daves video... Does not cover everything but does basely point out how awesome these things are..