[SI-LIST] Re: Ferrite bead in ground path
- From: Istvan Novak <istvan.novak@xxxxxxxxxxx>
- To: Christopher.Lucci@xxxxxxxxxxx
- Date: Fri, 21 Dec 2012 20:17:25 -0500
I usually prefer solid, continuous ground (or reference) throughout
the boards, but there might be cases when isolation in the ground
path may not hurt, in fact may help. In the thread I have not seen
any mention of the actual function of the analog circuit. Whatever
it is, if that circuitry is connected to the rest on the system only
inside the chip, and there is no analog or digital IO from that
circuitry to the outside of the package, this kind of isolation may
help to reduce the noise from package/silicon simultaneous
switching noise imposed on the analog circuit.
Regards,
Istvan Novak
Oracle
On 12/21/2012 8:05 PM, Lucci, Christopher wrote:
> This was Joe's point earlier in the email chain and I'd probably have to
> agree that this might be some attempt to "contain" a "HF" energy source
> instead of trying to track it down and eliminate it at the source. Perhaps
> looking at the properties of the ferrite could help Hithesh identify the
> intent of the ferrite and perhaps the source of energy.
> Regardless it is encouraging that so many people are so vocal about the
> obvious issues associated with adding inductance to return current paths.
> Now if all management and PCA designers felt the same way...
>
>
> Happy Holidays to all!
>
> C.S. Lucci
>
>
> Christopher S. Lucci
> Philips Home Healthcare Solutions
>
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of ??
> Sent: Friday, December 21, 2012 7:44 PM
> To: prashant.jaiswar@xxxxxxxxx
> Cc: hitheshn@xxxxxxxxx; garys@xxxxxxxxxxx; SI-List
> Subject: [SI-LIST] Re: Ferrite bead in ground path
>
> In my opinion, the FB is used to isolate different power supply and ground,
> such as analog power and digital one.
> Prashant Jaiswar <prashant.jaiswar@xxxxxxxxx>编写：
>
>> I think the first question is to be shot to your MCU vendor,in the first
>> place why the FB has been introduced onto the power supply? For any PSU
>> design onboard, the basic requirement is to have minimised power plane
>> impedance for the required frequency decoupling. Having FB onto the PSU line
>> will introduce increased impedance for the desired frequency of operation.
>>
>> Sent from my iPad
>>
>> On 21-Dec-2012, at 11:31 PM, Hithesh <hitheshn@xxxxxxxxx> wrote:
>>
>>> Gary,
>>> The ferrite is between the MCU analog ground(GNDA) and the circuit
>>> ground(not chassis ground). Majority of the components on the board are
>>> digital(MCU, SDRAM etc). There's also a ferrite in the power section.
>>> The MCU has 1.8V for analog circuitry (not ADC), probably PLL or some Vref
>>> circuitry. I did a quick datasheet search, didn't get any details.
>>>
>>> -Hithesh
>>>
>>>
>>> On Fri, Dec 21, 2012 at 11:16 PM, Gary Stein <garys@xxxxxxxxxxx> wrote:
>>>
>>>> Ground path between what? Beads between chassis ground and signal ground
>>>> are frequently used for emi/esd suppression, ie keep external high
>>>> frequency
>>>> transients out of signal ground and to keep any ground noise from radiating
>>>> from connectors shells and such. In such applications, chassis ground is
>>>> not a signal nor power return path.
>>>>
>>>> -----Original Message-----
>>>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>>>> On
>>>> Behalf Of Ken Wyatt
>>>> Sent: Friday, December 21, 2012 11:43 AM
>>>> To: hitheshn@xxxxxxxxx
>>>> Cc: SI-List
>>>> Subject: [SI-LIST] Re: Ferrite bead in ground path
>>>>
>>>> I've seen ferrites in series with the green wire safety ground wire.
>>>> Otherwise, I wouldn't think you'd want an impedance in the signal OR power
>>>> return path, unless you'd want to keep us consultants employed!
>>>>
>>>> Cheers, Ken
>>>>
>>>> Kenneth Wyatt
>>>> Wyatt Technical Services LLC
>>>> Woodland Park, CO
>>>> ken@xxxxxxxxxxxxxxxx
>>>> www.emc-seminars.com
>>>> (Sent from my iPad)
>>>>
>>>> On Dec 21, 2012, at 10:14 AM, Hithesh <hitheshn@xxxxxxxxx> wrote:
>>>>
>>>>> I came across an old schematic that has ferrite bead in the ground
>>>>> path. Is there any advantage of using ferrite bead in the ground path.
>>>>> The general rule is to keep the ground path at low impedance.
>>>>> -Hithesh
>>>>>
>>>>>
>>>>>
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