[SI-LIST] Re: Measuring Power supply noise

  • From: Oscar Lang <design97@xxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Mon, 20 Mar 2006 08:57:01 -0800 (PST)

Has anyone tried a ADC (analog to digital converter)
to measure this noise? They come with fine
granularity.
Then one needs to allocate a clean / quiet ground and
measure the noisy ground.

Any critic to this idea?

--- Andrew Ingraham <a.ingraham@xxxxxxxx> wrote:

> > a)       By using a 50Ù probe, did I create a
> voltage divider?
> 
> Adding a probe of any kind (except non-contact
> optical, perhaps) always
> affects the circuit.  There is always some loading
> (voltage divider), and
> other things that affect what you see.
> 
> > To check the sanity of my measurement, Instead of
> my 50Ù probe, I used a
> > standard 1MÙ probe and carried out the
> measurement.
> 
> Check the sanity check experiment by connecting both
> probes at the same
> time.
> 
> You could also try experimenting with a passive
> probe by inserting a small
> series resistor between the pad and your coax cable.
>  For example, 450 ohms
> gives you a pretty good 10:1 probe with 10 times the
> input impedance, if
> you're careful with the layout. 
> http://www.emcesd.com/1ghzprob.htm and
> other places have tips on this.
> 
> Use the scope (e.g., bandwidth controls) to see what
> kind of noise you are
> getting.
> 
> Be careful about the maximum input voltage at the
> scope.  Some are rated for
> less than 2V before damage may occur.
> 
> Regards,
> Andy
> 
> 
>
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