[SI-LIST] Re: Traces don't cause EMI - really?
- From: Ravinder.Ajmani@xxxxxxxx
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 2 Feb 2004 09:26:22 -0800
Hi Folks,
My problem relates to this topic, although I am looking for an entirely
different solution.
My board has pads for connecting an external fixture to obtain data trace.
The 8-bit data is transferred in sync with a 160 MHz clock, which is
always active even if the trace port is not in use. The impedance matched
Microstrip clock trace is about 1.2" long, and unterminated trace acts as
a nice antenna. With the help of close-field and far-field scans, I have
concluded that this my EMI problem is due to this clock. Also,
terminating the clock at the pad has very little effect on emissions (Mr.
Ritchey please note, traces do cause EMI). However, when I cut the clock
trace near the ASIC, the emissions drop by about 10 dBs. It is too late
for the redesign of ASIC to put a tri-state buffer, and I want to insert a
tri-state buffer at the clock output. The fastest single tri-state buffer
I have found (Toshiba TC7SZ125FU) has typical propagation delay of 2.5 ns.
This delay will be too much for the synchronous data transfer.
Can anyone suggest a faster single tri-state buffer for this application,
or is there a better solution to this problem. I will appreciate your
help.
Regards, Ravinder
Server PCB Development
Hitachi Global Storage Technologies
Email: Ravinder.Ajmani@xxxxxxxx
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