[SI-LIST] Re: Measuring Power supply noise
- From: Oscar Lang <design97@xxxxxxxxx>
- To: David Instone <dave.instone@xxxxxxxxxx>, si-list@xxxxxxxxxxxxx
- Date: Mon, 20 Mar 2006 09:28:12 -0800 (PST)
Well I'm trying not to use all these passives and just
ONE ADC chip to measure noise.
Again original question remains, Any critic to this
idea?
--- David Instone <dave.instone@xxxxxxxxxx> wrote:
---------------------------------
Whats inside a modern scope?
Oscar Lang wrote:
Has anyone tried a ADC (analog to digital converter)to
measure this noise? They come with
finegranularity.Then one needs to allocate a clean /
quiet ground andmeasure 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-contactoptical, perhaps) alwaysaffects the
circuit. There is always some loading(voltage
divider), andother 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 bothprobes at the sametime.You could also
try experimenting with a passiveprobe by inserting a
smallseries resistor between the pad and your coax
cable. For example, 450 ohmsgives you a pretty good
10:1 probe with 10 times theinput impedance, ifyou're
careful with the layout.
http://www.emcesd.com/1ghzprob.htm andother places
have tips on this.Use the scope (e.g., bandwidth
controls) to see whatkind of noise you aregetting.Be
careful about the maximum input voltage at thescope.
Some are rated forless than 2V before damage may
occur.Regards,Andy
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