FreeLists / si-list / [SI-LIST] Re: Traces don't cause EMI - really?

[Ravinder.Ajmani@xxxxxxxx]

Steve,
Thank you very much for your help.  I have located a single bus switch 
from TI (SN74CB3T1G125), which should meet my requirement.
Regards, Ravinder
Server PCB Development
Hitachi Global Storage Technologies

Email: Ravinder.Ajmani@xxxxxxxx




steve weir <weirsp@xxxxxxxxxx>
02/02/2004 09:40 AM

 
        To:     Ravinder.Ajmani@xxxxxxxx, si-list@xxxxxxxxxxxxx
        cc: 
        From:   steve weir <weirsp@xxxxxxxxxx>
        Subject:        Re: [SI-LIST] Re: Traces don't cause EMI - really?




Ravinder,

Use a QuickSwitch type device at the ASIC.  That is a pass switch only, so 

the only penalty will be a parasitic RC for each pad.

Regards,

Steve.

At 09:26 AM 2/2/2004 -0800, Ravinder.Ajmani@xxxxxxxx wrote:
>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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