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Old 17th July 2010, 11:27 AM   #11
Mooly is offline Mooly  United Kingdom
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Print the PCB on paper directly from Diptrace and see if it's correct for the actual devices and that all the parts patterns are correct. That's what I do if in doubt. You can't beat having the actual full scale layout in front of you with the parts you are using.
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Old 17th July 2010, 03:02 PM   #12
marce is offline marce  United Kingdom
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Downloaded Diptrace and started having a little play, only with the Pattern Editor. First view is its a nice little program.

The footprint you require for the PCM2707 is the QFP-32/7x7/x1.65.
The 7x7 refers to the package dimensions 7mm square, the 1.65 is the height, and 32 is the number of pins.

The attached bit map is a screen shot from the Pattern Editor, the grid is set at 0.4mm and I've added a quick dimension to give an idea of the size.
From my initial look at the libraries that come with the package I've got to say I'm impressed with them, they look to be based on IPC-7351 standards.
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File Type: jpg qfp-32-7x7-x165.jpg (46.9 KB, 139 views)
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Old 17th July 2010, 11:03 PM   #13
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Thanks guys for the help.
I just finished the i2s part drawing. Click the image to open in full size.

However, i am seeking for more advance drawing. The question is, How/what i need to set if i wish to mount the chips and smds parts at top and the bottom of the PCB? I would like to use both of the surface to mount all of the things. The reason is because i want to minimize any possible size.
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Last edited by chchyong89; 17th July 2010 at 11:06 PM.
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Old 18th July 2010, 04:24 PM   #14
marce is offline marce  United Kingdom
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There are some problems with the layout, though without the schematic I can only point the first couple that are obvious and quite serious.
1: The input from the Xtal snakes all round the board, this is (after ground connections) the most important connection, it needs to be as short as possible and also any related capacitors should be placed near the crystal and the crystal placed next to pin 12 & 13 of the chip.
2: This type of design requires preferably a contigous ground plane on 1 side of the board, or copper pours stitched together with many via's. For a two layer device the components need to be layed out to minimise the ammount of routes that have to be dropped to the other side, allowing for max ground.
The way you have done the ground will cause EMI/EMC problems, and signal integrity problems.
Sorry to be so negative but at the moment IMO if the design works it will be plauged by EMC problems.
I would re-position the components, trying to minimise connection lengths, and as stated earlier minimise the ammount of routes that have to go on the reverse side. Decoupling capacitors placed near the device power pins. The crystal very near pins 12 & 13.
Double sided placement is possible with a two layer board, but better results are achieved by using a 4 layer board.
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Old 20th July 2010, 11:57 AM   #15
marce is offline marce  United Kingdom
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Hi Chchyong89,
I dont know whether you have taken umbrage with my comments regarding you layout, but PCB layout is critical to a circuit functioning correctly.
I invested several hours of my own time to re-search and provide some answers to your questions, including looking at Diptrace, this I did freely to help
a fellow DIYer.
And agian it was in this spirit that I looked at your layout, and what became immediatly apparent was some critical concerns with the circuit topography.
To re-iterate what I said about clock circuit layout I have attached a few application notes for your referance, regarding the critical layout requirements of crytal circuits.
The comments I made are to help you achieve you desired goal with this design, not to upset


http://www.latticesemi.com/documents/an8080.pdf

http://www.atmel.com/dyn/resources/p...ts/doc8128.pdf

Page 9 in the following app note:
http://focus.ti.com/lit/an/sdya011/sdya011.pdf
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Old 20th July 2010, 12:04 PM   #16
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Hi,
No hard feeling here, i am still on the way to learn as much as i can. And i really appreciate every of your comments. The more you guys point out my mistakes, the faster i can improve to have a better skill ain't it

However i am still drawing and redrawing the circuit before i show up myself here

Regards.
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Old 20th July 2010, 05:38 PM   #17
marce is offline marce  United Kingdom
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I've been doing PCB's as a job for 25 years, and I still make mistakes. I'm doing a layout of a class D, and the first pass at it I just dove in and threw it together. When I re-read the data sheets etc I realised I'd made a complete mess of it. So I started again, and the second time was much happier with the layout.
The Wolfson site has some good evaluation board layouts that are worth looking at, though not the same devices, the general priciples of how they are layed out will give you some idea of what you are aiming for.
The manual for this board is a good example. There is also a good layout example on this site using the same chip with a Nat chipamp layout as well, I cant find the link for that at the moment.
Evaluation Boards | WM8761EV1 | Wolfson Microelectronics

This site is a good intro to the basics of PCB design and worth a look at as well.

How to be a Circuit Board Designer

Keep playing with the component layouts, the trick is ti look at the patterns the connections make, after a while you begin to picture where the routes will go.
Marc
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