At 07:26 AM 8/13/2008, fred jones wrote:

>Hi list,
>I asked a question about low noise, high gain amplifier design a 
>couple weeks ago.  I've been doing a lot of reading on everything I 
>can find on the subject.  One thing I understand is proper PCB 
>layout is important, but most articles mention this but give no 
>detail.  Can some please explain what is meant by using a "star 
>ground" such as in this article?  I was going to use a ground plane 
>but may that is not a good idea.
>Thanks,
>FJ
>http://instruct1.cit.cornell.edu/Courses/ee476/ideas/singlesupply.pdf
>_________________________________________________________________

Ground planes and common point (star) grounds serve two distinct 
purposes. The common point ground is used to reduce the current 
between circuit nodes attached to the ground flowing through a path 
which is not common. If, for example, you have a track with several 
different connections to it and then to ground their will inevitably 
be voltages, however small, generated by currents flowing in the track segment.

In a common point ground the grounded connections are all made at at 
one place. This means that no spurious voltage drop can occur between 
the grounded points. Thus eliminating the annoying "ground loops" and 
the noise generated by the currents in the ground tracks.

This article: 
http://www.hottconsultants.com/pdf_files/june2001pcd_mixedsignal.pdf 
addresses some of the issues, but not all. I suppose many of us have 
learned the hard way! Often, in my work on even two layer boards, I 
will do a common ground point on the top side f the board around a 
low noise stage, then at the common point I will connect to the 
larger ground area on the bottom side of the PCB.

John 

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