Re: [SI-LIST] : Reflections on clock line

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From: Tham Kok Tong (kt_tham@uti2000.co.jp)
Date: Wed Apr 12 2000 - 17:49:19 PDT


Hi

Thanks guys.
Finally I changed my clock line to T topology and it works.
Besides the clock line I also have a lot of data lines which are connected
in daisy-chain.
Is there any other solution to solve this reflection problem for 20in
daisy-chain with 8 loads(5pF each) without termination for date line? The
rising time is about 2ns.

Regards,
KT.THAM

At 午前 11:50 00/04/06 -0700, you wrote:
>This will work only if:
>
>The branches are very short ( less than 0.5")
>
>OR
>
>if each branch has twice the impedance of its trunk.
>
>Vinu
>
>Tadashi ARAI wrote:
>
> > Howdy Tham,
> >
> > It often was occured such a reflection problem on daisy-chain
> > connection.
> >
> > Use "H" topology to solve it.
> >
> > Divide clock line with T junction at exact center of 8 loads, after that
> > devide again at exact center of each 4 loads, and after that devide at
> > center of each 2. The point is that each "branch" must be the same
> > length.
> >
> > Regards,
> > //// /// // / / / / / / / / / /
> > Tadashi Arai//Platform Developing Dept.,Desktop Prd Div. Fujitsu Limited
> > arap@paso.fujitsu.co.jp TEL:+81-42-370-7624 Inagi-shi, Tokyo, Japan
> > / / / / / / / / / / / // ///
> > On Wed, 05 Apr 2000 11:15:04 -0700
> > Mail from tham@uti2000.co.jp described as below:
> >
> > > Hi,
> > >
> > > I have a 20in long 50MHz clock line which connected to 8 loads(5.5pF per
> > > load). (Vcc=3.3)
> > > I used daisy-chain to connect all loads but the waveform of the nearest
> > > receiver (respective to the driver) only swing between 1V and 2V. The
> > > waveform of the furthest receiver overshoot above 4V.
> > > I think reflection is the main reason and I had put an end termination
> > > but
> > > there is no improvement for the nearest receiver waveform.
> > > Anybody have any ideal to solve this problem?
> > > I appreciate any advice or suggestions.
> > >
> > > Thanks.
> > >
> > > Regards,
> > > KT.THAM
> > >
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