Re: Grounding schemes was:A prospective s.s.t.c. input-synchronizer (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Gerry Reynolds <greynolds@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Wed, 20 Dec 2006 00:30:16 -0700
From: Gerry  Reynolds <gerryreynolds@xxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Grounding schemes  was:A prospective s.s.t.c. input-synchronizer
    (fwd)

Hi Steve,

Star grounding vs a ground plane:

Digital logic signals routed over a ground plane will result in return 
currents that follow the path of the signal route.  Any drop in the ground 
plane caused by the return current will be specific to the path the return 
current follows (for the most part assuming the conductivity of the ground 
plane is reasonably good).  For logic,  ground noise is not important up to 
a point where thresholds of switching are violated.

For analog signals, ground noise can be interpreted as a signal component 
and amplified accordingly and star grounding can help control noise 
coupling.  However, it will be important that the signal path follows the 
ground path so the return current can follow the signal path.  Otherwise, a 
"loop" is formed making the signal/gound pair subceptible to outside 
influences (like magnetic fields).  It has been my experience that ground 
planes give the best grounding experience with most situations.

Gerry R.


> Hi Ken,
>
> It may be either a grounding issue, or it could be possible that the
> noise isnt real.  Putting ceramic caps on every IC V+ and ground
> should normally be good enough.  Make sure that you dont have any high
> currents flowing through the 5V ground.  If the 5V circuit is grounded
> to anything else, be sure to use "star" grounding, and the 5V circuit
> is just a branch on the star, and not the center.
>
> You probably already know all this, but you did welcome suggestions,
> and hopefully it will get you started on figuring out the problem.
>
> Steve
>
> On 12/19/06, Tesla list <tesla@xxxxxxxxxx> wrote:
>> Original poster: Gerry Reynolds <greynolds@xxxxxxxxxx>
>>
>>
>>
>> ---------- Forwarded message ----------
>> Date: Tue, 19 Dec 2006 11:28:54 -0800
>> From: K. C. Herrick <kchdlh@xxxxxxx>
>> To: Tesla List <tesla@xxxxxxxxxx>
>> Subject: Re: A prospective s.s.t.c. input-synchronizer
>>
>> Chip, Steve Ward (& all)-
>> ----------------------------------------------------------
>>
>> Hi Ken.
>>
>> Sorry for the delay.  I got slammed at work and didn't end up on the
>> computer last night.  Here's the link.  It's just plain right now but can
>> be fixed up to have html in it later. I just wanted to get it done. 
>> Sorry
>> for the delay again.
>>
>> Chip
>>
>> http://www.pupman.com/current/kcherrick/tch-synctest4a.jpg
>> ------------------------------------------
>>
>> No problemo; looks perfect as-is.  And to all:  The above link is the 
>> replacement circuit for my synctest2.jpg that I'd posted
>> previously on hot-streamer.  This one seems to work in the hardware.
>>
>>
>> And Steve...in further response to yours of 12/18: My low-level EMI
>> problem appears to stem from a 14 MHz transient that appears on the +5V
>> bus every time the H-bridge switches.  I'm now trying to track that
>> down.  Suggestions on that from >>anyone<< are welcome!!
>>
>> KCH
>>
>>
>>
>>
>
>
>
>