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Old 9th February 2013, 02:04 AM   #11
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Wah, very cool - great skills ! What size are they ? Only those four pins ? Any tips for me about building this ? Thanks.

and Kung Hei Fat Choi !

Last edited by KlipschKid; 9th February 2013 at 02:09 AM.
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Old 9th February 2013, 08:25 AM   #12
marce is offline marce  United Kingdom
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Nice
When I do boards with these devices on, I place the decouplers there only on the other side of the board, your solution is better still, but impracticle for comercial production.
If it is a 0.8mm pitch device i would say they will be 0402 capacitors, having played with those I am impressed by your patience and dexterity. Not for the faint hearted or impatienced diyer.
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Old 9th February 2013, 11:50 AM   #13
qusp is offline qusp  Australia
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Marc, have you seen the new 10000pf thin film (GX) caps from AVX? $7 a pop for an 0201 speck lol. for those that dont know thin film usually tops out around 10-22pf except for some rather impractical bare dies for wire-bonding... per kg these could be the most expensive capacitors on earth!!

re placement, between pins seems the best (most frustrating) way forward, wouldnt being soldered on top side as close as possible always be closer than even directly under the pins if its on the other side of the substrate?

Last edited by qusp; 9th February 2013 at 11:55 AM.
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Old 9th February 2013, 02:07 PM   #14
marce is offline marce  United Kingdom
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Quite often put 0201 and 0105 on PCB's these days, but not at those prices, a single one costs more than some whole assemblies! Good to 40GHz.
The area directly under the pins is dead space, ie you cant get a via in there so for double sided placement PCB's its the best place to put the decouplers, not all chips have nice power pins next to each other as conviently as this device, and most devices of this type we see have a pin to pin spacing of 0.5mm quite often (and sometimes 0.4mm). Even with 0.65mm devices you have to get the routes out away from the device to be able to get some via fan outs, so the most efficient place is under the pins, with shared vias to the power planes with the relevant pins. You also have to consider the round trip to the plane through the board, vias arn't as inductive as a short trace length, and the capacitors have to be charged from the power planes.
A compramise like most PCB design, quite often you cant see any PCB because of components, so every bit of space is often needed.
Now the best option is using HDI PCB layout with microvias in the component pads, the top layer as a ground plane and the next plane down the most critical supply, this minimises both the loop area for the supplies (0.05 to 0.1 dialectric between layers) and stray parasitic inductance caused by a trace from the capacitor to a via (this can double the inductance for a 0402, 0201 cap). This is quite common these days especially in AISA (mobile phones etc)
and becoming more popular in the West as component size is often the deceiding factor to go to HDI.

http://www.google.co.uk/url?sa=t&rct...Wvypzn3Woj1pUw

Last edited by marce; 9th February 2013 at 02:10 PM.
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Old 11th February 2013, 03:09 AM   #15
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Quote:
Originally Posted by KlipschKid View Post
Wah, very cool - great skills ! What size are they ? Only those four pins ? Any tips for me about building this ? Thanks.

and Kung Hei Fat Choi !
Quote:
Originally Posted by marce View Post
Nice
When I do boards with these devices on, I place the decouplers there only on the other side of the board, your solution is better still, but impracticle for comercial production.
If it is a 0.8mm pitch device i would say they will be 0402 capacitors, having played with those I am impressed by your patience and dexterity. Not for the faint hearted or impatienced diyer.
the cap in the pic is 0402 size I also need magnifying glass to solder it.
It's open secret that decouple cap directly solder on the pin is the best, but impractical for commercial production, diyer have no limitation

Last edited by diyinhk; 11th February 2013 at 03:16 AM.
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Old 11th February 2013, 03:23 AM   #16
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A magnifying glass, no coffee, plenty of time, good tools... and skills. I won't be trying !

What values are you using in the lpf ? The values printed on the board don't seem that good. The 220R is fine but the cap values need to be a little different from each other and a little smaller ?

cheers
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Old 11th February 2013, 04:51 AM   #17
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Originally Posted by KlipschKid View Post
A magnifying glass, no coffee, plenty of time, good tools... and skills. I won't be trying !

What values are you using in the lpf ? The values printed on the board don't seem that good. The 220R is fine but the cap values need to be a little different from each other and a little smaller ?

cheers
The value on the pcb follows the AK4399 EVM pdf
http://www.asahi-kasei.co.jp/akm/en/...99-sb4-03e.pdf
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Old 11th February 2013, 06:27 AM   #18
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Thanks. I'll try either a slightly larger cap on the shunt or a slightly smaller cap in the feedback. It gives better impulse response etc.

Here's the EVM circuit for anyone interested :

Click the image to open in full size.
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Old 13th February 2013, 01:16 AM   #19
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Click the image to open in full size.
3rd routing issue. Bottom left corner, FB1, goes to a via, and on the other side there is a power trace that runs at 30 degrees across the MCLK line.
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Old 13th February 2013, 01:48 AM   #20
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Since its using a groundplane for both power and signal I reckon lift the signal components (at least the 6n8, 1n0 filtering caps, the 1k2, 560 resistors too) from that and give them a dedicated star earth wire.
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