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Old 9th February 2013, 12:14 PM   #521
EUVL is offline EUVL  Europe
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We have good experiences with both FKPs and PPS caps.
We use PPS where we want a compact layout and small values (like 150p).
We find silver mica a touch bright for analog filters.
Where space is not a restriction, we want best properties and larger values, we use FKP, or MKP.
Best is still styroflex.


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Last edited by EUVL; 9th February 2013 at 12:16 PM.
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Old 9th February 2013, 12:48 PM   #522
qusp is offline qusp  Australia
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yep, if it werent for the odd pckage I would use the relcap styrenes in place of the FKP, but the diagonal lead placement makes them a pita to work with.
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Old 9th February 2013, 01:57 PM   #523
qusp is offline qusp  Australia
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Quote:
Originally Posted by curryman View Post
qusp, how to measure and design the source and receiver resistors? My old 10 MHz Hameg might help for LRCLK but for MCLK (e.g. 49.152 MHz) even a 100 MHz scope only shows 1st and 2nd harmonic? I guess not many will be able to test and design suitable values for their specific application

And what about the effect of having 0R resistors compared to just a trace?

If I want to have 50 Ohm impedance for the clock lines, TXline gives me 0.75mm trace width (1mm FR4, 35m, 0.15mm gap) if I have a solid ground plane on bottom layer and surround the lines with GND on top layer. Would you agree?

Just as a small upgrade another version
well we kind of need more information than the above and its difficult, because the exact thickness and dielectric constant of the FR4 vary from batch to batch and the dielectric constant also varies depending on frequency. You need to use Duroid or some other higher quality Rogers PTFE or ceramic substrate to get something more stable and allow more arbitrary rules of thumb.

.75 doesnt seem thick enough to me. for example with a trace thickness of 35m, with 150m gap and 1mm board which leaves us 815m substrate. if we just give an estimation of Er = 4, I get 1.6mm trace width for 49Ω (1.555mm for exactly 50Ω)

here is a good calculator (use microstrip for this calc), which PCB layout package are you using? Eagle? does it have the ability to handle these calculations for you?

the zero ohm resistor.. hmm yeah I nearly mentioned those, I would think they are problematic, but I cant suggest an alternative, this is where flip-flops/clock buffers with 2 inputs might be handy?

Last edited by qusp; 9th February 2013 at 02:16 PM.
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Old 10th February 2013, 06:17 PM   #524
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I assumed a grounded coplanar waveguide (see attached diagram). It is not available in the online calculator in your link but i found a tool here. Does not yet correspond to my board, however thought about adding a second groundplane on toplayer (with lots of vias). By the way: I am using Target! as design tool (just got used to it).

Having said that, I am not really sure if it makes sense to go too deep into those things. As you said, to make it really good you have to control many parameters which will be quite hard in a hobby project like this. I'll try to make some good estimations to come close to 50Ohm and that should be enough

I'll try to order pcb's this week. Any special recommendation? makePCB was very cheap, but communication and quality were not really top-notch...
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Old 11th February 2013, 08:04 AM   #525
vzs is online now vzs  Europe
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Hi! I just became aware of this thread...
Very nice work! I Really like the clean schematics and your strive for a good PCB layout on a two layer board. If you intend to order multiple PCBs (even for beta testing) please count me in for one.
Thanks!
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Old 13th February 2013, 01:52 PM   #526
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Hello all. I did some more rework. Please find attached the latest version.

When I order boards, some will be left for a few beta tester if there is interest

Best regards, Daniel
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Old 13th February 2013, 02:15 PM   #527
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Thanks for the offer - and your work Daniel! Count me in for a board :-)
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Old 15th February 2013, 06:13 AM   #528
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Hello all, please find attached the latest version, which I will order this weekend. Those who asked for prototypes are on my list and will be contacted by PM.

Best regards, Daniel
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Old 15th February 2013, 08:36 AM   #529
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Do you have the BOM on hands?
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Old 15th February 2013, 11:39 AM   #530
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Hi Daniel, waiting some news from you when the boards are ready, they look great
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