[SI-LIST] Re: AC Coupling bandwidth Consideration for 8b/10b
- From: "Curt McNamara" <curt.mcnamara@xxxxxxxxxxx>
- To: "Scott McMorrow" <scott@xxxxxxxxxxxxx>, <wolfgang.maichen@xxxxxxxxxxxx>
- Date: Thu, 14 May 2009 13:58:30 -0500
Is this comment true for all types of dielectric?
In other words: does ESR decrease with increasing capacitance even if
dielectric changes?
Often the highest values of capacitance have the worst dielectric
characteristics.
Curt
Curt McNamara, P.E. // principal electrical engineer
Logic Product Development
411 Washington Ave. N. Suite 400
Minneapolis, MN 55401
T // 612.436.5178
F // 612.672.9489
www.logicpd.com
/ / / / / / / / / / / / / / / / / / / / / / / / /
This message (including any attachments) contains confidential information
intended for a specific individual and purpose, and is protected by law. If you
are not the intended recipient, you should delete this message and are hereby
notified that any disclosure, copying, or distribution of this message, or the
taking of any action based on it, is strictly prohibited.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Scott McMorrow
Sent: Thursday, May 14, 2009 12:57 PM
To: wolfgang.maichen@xxxxxxxxxxxx
Cc: Mike Harwood; si-list@xxxxxxxxxxxxx; si-list-bounce@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: AC Coupling bandwidth Consideration for 8b/10b
I have to disagree slightly with you Wolfgang. You are correct if you
are talking about different capacitor body styles. However, as long as
the capacitor is housed in exactly the same package style (i.e. 0603,
0402, 0201), the largest capacitance in a particular package from a
manufacturer always has the lowest series resistance and inductance.
There is a balancing act that needs to take place above 10 Gbps. At low
frequencies we are concerned with charging time constants, however, to
faithfully pass the waveform edges through a capacitor it is necessary
to design a minimum return loss transition. This depends heavily on the
location of the lowest plate in the capacitor. That location can vary
as much as 10 mils in the z-axis, which is significant when passing
energy at 20-40 GHz.
--
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
wolfgang.maichen@xxxxxxxxxxxx wrote:
> - larger capacitors tend to have larger parasitics (inductance and
> resistance), which degrades your signal fidelity.
>
> Wolfgang
>
>
>
>
>
>
>
> Mike Harwood <Mike@xxxxxxxxxxxxxx>
> Sent by: si-list-bounce@xxxxxxxxxxxxx
> 05/14/2009 01:46 AM
>
> To
> si-list@xxxxxxxxxxxxx
> cc
>
> Subject
> [SI-LIST] Re: AC Coupling bandwidth Consideration for 8b/10b
>
>
>
>
>
>
>
> As well as the longest run length you need to pay attention to the
> disparity in the number of 1's and 0's. For a 8b10b pattern of at least
> 20 bits I believe that the disparity is never greater than 2 and the
> greatest number of consecutive bits is 5. Generally 8b10b patterns are
> reasonably well behaved in this regard and that's why people put up with
> the 20% coding overhead.
>
> Rearranging V=V0 * e(-t/CR) for a 1% droop in 5 bits (5ns) gives
> CR=497ns and equates to about 10nF in a 50 Ohm environment. I'd say that
> 75nF gives a good degree of marging.
>
> Another interesting concept in choosing the DC coupling cap value is the
> type of receiver used and the channel between TX & RX. Signals
> tranmitted through long (say >18") of FR4 can take several tens of bits
> to settle fully at 1Gb/s. This is a low pass effect easily determined by
> examining the pulse response. If this effect is not corrected in the
> receiver equalizer then some level of droop in the high pass filter is
> desirable. I've seen performance improvements in higher speed SerDes
> with this correction.
>
> Mike.
>
>
> It's just a single pole HPF. Calculate C based on the longest run
> interval, the acceptable percentage droop and the line impedance.
>
> Steve.
> Neo wrote:
>
>
>>> Hi,
>>>
>>> How we calculate the necessary HPF bandwidth for a say 1Gb/s 8b10b
>>>
> coded NRZ bit stream?
>
>>> I think in some spec it is defined as 75nF and 50ohm. What's the
>>>
> theory behind this number?
>
>>> Thanks,
>>> Neoflash
>>>
>>>
>>>
>>>
>>> ------------------------------------------------------------------
>>> To unsubscribe from si-list:
>>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>>>
>>> or to administer your membership from a web page, go to:
>>> //www.freelists.org/webpage/si-list
>>>
>>> For help:
>>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>>>
>>>
>>> List technical documents are available at:
>>> http://www.si-list.net
>>>
>>> List archives are viewable at:
>>> //www.freelists.org/archives/si-list
>>> or at our remote archives:
>>>
>>>
> http://groups.yahoo.com/group/si-list/messages
>
>>> Old (prior to June 6, 2001) list archives are viewable at:
>>> http://www.qsl.net/wb6tpu
>>>
>>>
>>>
>>>
>>>
>
>
> -- Steve Weir Teraspeed Consulting Group LLC 121 North River Drive
> Narragansett, RI 02882 California office (866) 675-4630 Business (707)
> 780-1951 Fax Main office (401) 284-1827 Business (401) 284-1840 Fax
> Oregon office (503) 430-1065 Business (503) 430-1285 Fax
> http://www.teraspeed.com This e-mail contains proprietary and
> confidential intellectual property of Teraspeed Consulting Group LLC
> ------------------------------------------------------------------------------------------------------
>
>
> Teraspeed(R) is the registered service mark of Teraspeed Consulting
> Group LLC
> ------------------------------------------------------------------ To
> unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with
> 'unsubscribe' in the Subject field or to administer your membership from
> a web page, go to: //www.freelists.org/webpage/si-list For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List
> technical documents are available at: http://www.si-list.net List
> archives are viewable at: //www.freelists.org/archives/si-list or
> at our remote archives: http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
