[SI-LIST] Re: Plane Isolation
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: Hirshtal Itzhak <ihirshtal@xxxxxxxxxx>
- Date: Sun, 26 Jun 2011 12:08:31 -0400
Itzhak
The system required better than 75 dB isolation up to 10 MHz. This was
achieved with 1 oz copper on a very large board with traces that were
nearly 30 inches long.
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC
On 6/26/2011 4:42 AM, Hirshtal Itzhak wrote:
> Thanks, Steve.
>
> Scott, in view of Steve's remark, can you recall at what frequency was
> the 75dB attenuation achieved?
>
> Thanks
> Itzhak
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of steve weir
> Sent: Sunday, June 26, 2011 7:50 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Plane Isolation
>
> Itzhak, as the frequency goes up, the effectiveness of isolation by a
> plane of any given copper thickness improves courtesy of Lenz's Law.
> If you double the copper weight, or use two plane layers for isolation
> you will drop the minimum frequency for a given amount of attenuation by
>
> a factor of 4:1.
>
> Steve.
> On 6/25/2011 11:32 PM, Hirshtal Itzhak wrote:
>> Hello Scott,
>>
>> Thanks for the tip.
>>
>> Just one question/clarification: My concern is NOT for the Analog
> signal
>> contaminating the digital signal, but vice versa. Since the digital
>> signal has much more BW, the saturation length will be much smaller
> than
>> you have indicated, and exactly the same as for digital to digital
>> noise, e.g. on the order of several hundredths of mils or several
> inches
>> at the most.
>>
>> I assume this makes no difference as for 75dB number you have quoted.
> Am
>> I right?
>>
>> Thanks
>>
>> Itzhak Hirshtal
>>
>>
>>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]
>> On Behalf Of Scott McMorrow
>> Sent: Thursday, June 23, 2011 5:02 PM
>> To: si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: Plane Isolation
>>
>> Itzhak
>>
>> there is no one number, since you need about 1000" of trace coupling
> to
>> fully saturate crosstalk through a plane at 5 MHz. IIRC for 30" of
>> trace coupling in an analog video switch board we consulted on about
> 15
>> years ago, it took 1oz copper to achieve 75 dB of isolation. This was
>> verified through measurement and modeling. The only tool I know of
> that
>> is reasonably capable of modeling field penetration through copper for
>> traces is Ansoft 2D FEM quasi-static solver, which now a part of the
>> Ansoft 3D package. The match between measurement and modeling was
>> actually quite amazing. HFSS would also be able to do this sort of
>> modeling, you'd have to create a short coupled section, and then
>> concatenate it for the length of trace coupling that you have in your
>> system.
>>
>> regards,
>>
>> Scott
>>
>> Scott McMorrow
>> Teraspeed Consulting Group LLC
>> 121 North River Drive
>> Narragansett, RI 02882
>> (401) 284-1827 Business
>> (401) 284-1840 Fax
>>
>> http://www.teraspeed.com
>>
>> Teraspeed(r) is the registered service mark of
>> Teraspeed Consulting Group LLC
>>
>>
>> On 6/23/2011 3:07 AM, Hirshtal Itzhak wrote:
>>> Hi all,
>>>
>>>
>>> I want to route hi-speed digital signals on a layer right above some
>>> sensitive analog signals (low freq of up to 7MHz). The analog signals
>>> will be routed side-by-side with their analog GND traces along it.
>>>
>>>
>>>
>>> To eliminate the possibility of noise induced from the digital to the
>>> analog signals, I intend to separate the 2 signal layers by a number
>> of
>>> Power/GND planes.
>>>
>>>
>>>
>>> Is there a known number for the attenuation that such a plane yields
>>> between the signals? Is there a formula for calculating the
>> attenuation?
>>>
>>> Thanks
>>>
>>> Itzhak Hirshtal
>>>
>>>
>>>
>>>
>>>
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