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Penfold
03-20-2009, 12:55 PM
I have seen on a couple of PCBs such as a SDRAM chip and the DIY FM transmitter that is being worked on by WVENGINEER that there appears to be some traces that go in a type of zig-zag configuration before it gets to the designated termination point on the board. I was just wondering if anyone knew why you would want to do that? I could understand a direct path, but a zig-zag has me confused. I'm scratching my head here. If anyone knows I would be very interested in learning the secret to this trick.

Thanks :-)

omzig
03-20-2009, 01:25 PM
I'm not sure why it's done on the transmitter board, but the SDRAM or other high-speed data circuitry, this is done to ensure that certain signal traces are the same length as others. If they are significantly different lengths, the timing of the signals can be screwed up.

ukewarrior
03-20-2009, 02:15 PM
It saves etchant.
Some DIY home etchers try to keep the PCB filled with copper.
It conserves etchant and is also more friendly to the environment.

They may be other reasons too.

n1ist
03-20-2009, 02:28 PM
On transmitters and RF boards, those are usually inductors or antennas made out of PCB traces. For much higher frequencies, they may also be filters, mixers, or other RF parts (yep, RF is black magic). In the digital world, as Omzig said, they are used as delay lines to adjust signal timing.

Thieving (usually crosshatch or an array of little round or square pads not connected to anything) is used mainly to ensure uniform plating, but also saves echant.

wvengineer
03-31-2009, 09:17 PM
On transmitters and RF boards, those are usually inductors or antennas made out of PCB traces. For much higher frequencies, they may also be filters, mixers, or other RF parts (yep, RF is black magic). In the digital world, as Omzig said, they are used as delay lines to adjust signal timing.

Exactly what they are. rf is its own animal and has a whole different set of rules it follows. the technique is called length matching. important in rf and high speed differential devices.....


in high speed digital signal it is used to match traces so that the signal arrives at a precise time.... used to reduce jitter in clocked digital signals



here is an application note on why....
www.nxp.com/acrobat_download/applicationnotes/AN10798_1.pd