[SI-LIST] Re: uper to How high the frequency to scan is sufficientfortarget impedance of Power distribution system

Hi Kong,

Generally scope probes are specified using the following equation for
a reasonable approximation:

bandwidth = risetime/0.35

This is defined as the 3db point where frequencies measured above this
point are not measured reliably.  I believe that Dr Johnson makes reference
to something similar regarding the spectral energy knee at 3db of a system
in his High Speed Digital Design book as well.

Hope this helps with your application.

Chris Jakubiec
Sun Microsystems


Kong Chuan Susanto wrote:
> 
> Hi Meng,
> 
> I have read some papers that use 'risetime/0.35' for the upper bound
> frequency. However I'm not sure where this thing comes from. Perhaps
> others can comment on this too. The lower bound basically is from DC.
> 
> Regards,
> 
> Chuan
> 
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> > [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of
> > meng.yubao@xxxxxxxxxx
> > Sent: Monday, April 26, 2004 2:52 AM
> > To: si-list@xxxxxxxxxxxxx; si-list-bounce@xxxxxxxxxxxxx
> > Subject: [SI-LIST] uper to How high the frequency to scan is
> > sufficient for target impedance of Power distribution system
> >
> >
> > HI:
> >    For a highspeed digital system PCB, we should control its
> > PDS Impedance
> > not to exceed its target Impedance from low frequency uper to high
> > frequency, but how higher the upper frequency is good enough, and how
> > lower the frequency ? Deducing from the Pulse width of the PCB
> > simultaneous switch noise or from the signal rise/fall edge
> > and its pulse
> > width ? Can anyone give me some clear equation!
> > regards
> > meng yubao
> >
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