[SI-LIST] Re: Single crystal driving two different inputs of a chip
- From: "Tom Dagostino" <tom@xxxxxxxxxxxxx>
- To: <JYWANG@xxxxxxxxxx>, <Rohan.Hubli@xxxxxxxxxxxxxxxx>, <ray.anderson@xxxxxxxxxx>
- Date: Tue, 28 Jun 2005 15:39:02 -0700
This sounds like one of those situations where you really should simulate
the circuit you propose routing on your board. If not done properly you
could have mis-terminated lines with the associated reflections interacting
causing apparent jitter on the clock inputs.
Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
tom@xxxxxxxxxxxxx
www.teraspeed.com
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Joseph Wang
Sent: Tuesday, June 28, 2005 3:02 PM
To: Rohan.Hubli@xxxxxxxxxxxxxxxx; ray.anderson@xxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Single crystal driving two different inputs of a
chip
Should not be a problem. In my previous board design, we connect four
clock inputs together to a signal oscillator, running 33MHz.
Well, you have to know what you are doing. In rare case, the oscillator
has very weaker drive strength. The clock inputs pins on the chip
should be close enough, not to rise up SI issue, etc.
Anyway, the concern about the jitter is too pessimistic to me. Any
reason why and failing case?
Regards,
Joseph Wang
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Rohan Hubli
Sent: Tuesday, June 28, 2005 2:46 PM
To: ray.anderson@xxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Single crystal driving two different inputs of a
chip=20
I am talking about onnecting a single quartz
oscillator to two clock inputs
-----Original Message-----
From: Ray Anderson [mailto:ray.anderson@xxxxxxxxxx]
Sent: Tuesday, June 28, 2005 2:42 PM
To: si-list@xxxxxxxxxxxxx
Cc: Ray Anderson
Subject: [SI-LIST] Re: Single crystal driving two different inputs of a
chip=3D20
Are you asking about connecting a single crystal resonator to two
oscillators within a chip (I hope not...) or connecting a single quartz
oscillator to two clock inputs?
-Ray
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Rohan Hubli
Sent: Tuesday, June 28, 2005 2:38 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Single crystal driving two different inputs of a chip
Folks,=3D3D3D20
Can a single crystal be driving two different inputs of a chip that feed
=3D3D3D
into=3D3D3D20
two sensitive analog blocks within a chip. Has anyone had any experience
=3D3D3D
doing this kind of a thing on the board ?=3D3D3D20
We are facing an issue where a 27Mhz crystal clock needs to be hooked up
=3D3D3D
to drive=3D3D3D20
two sensitive analog cores.=3D3D3D20
If we make the connection internal to the chip then the jitter due to =
=3D
=3D3D
=3D3D3D
(trace delay + buffer delay + process variations)=3D3D3D20
has significant impact on the audio quality.
Not to mention the fact that any issues that surface and subsequent =3D
=3D3D3D
fixes with this approach will have significant=3D3D3D20
respin costs for the chip.=3D3D3D20
Your inputs would be greatly appreciated.=3D3D3D20
Thanks
Rohan=3D3D3D20
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