[SI-LIST] Re: Injecting noise into a plane
- From: "WEBB,JEREMY (A-Sonoma,ex1)" <jeremy_webb@xxxxxxxxxxx>
- To: "'ahmed.alokby@xxxxxxxxx'" <ahmed.alokby@xxxxxxxxx>
- Date: Mon, 16 Jul 2001 17:45:40 -0600
Ahmed,
I have actually done this. All you have to do is design a passive bias tee
to the desired frequency that you want to introduce
into your 3.3V Power Plane, and that should be sufficient for the
experiment.
Here is an example:
DC
|
C
C L
C
C |
AC ----||---------- AC + DC
F = 10kHz
L = 1000uH
C = 4.7uF
DC = +3.3V from Power Supply.
AC = 10kHz or whatever frequency you want to introduce into your system.
AC+DC = the voltage that is used to supply your board with +3.3V.
Hope this helps.
Sincerely,
Jeremy Webb
==========================================================================
Have you thought of injecting noise into the summing node of the feedback
loop in the power supply. Tie a resistor to the node and drive the signal
of interest into the resistor. You will have to inspect the schematic of
the supply to compute the value of R. It is likely that the supply itself
has very slow frequency response so you will not get fast variation on the
output voltage but you can get the magnitude you need.
Tom Dagostino
Modeling Manager
Mentor Graphics Corp.
SAE
tom_dagostino@xxxxxxxxxx
503-685-1613
-----Original Message-----
From: Alokby, Ahmed [mailto:ahmed.alokby@xxxxxxxxx]
Sent: Monday, July 16, 2001 2:21 PM
To: 'si-list@xxxxxxxxxxxxx'
Subject: [SI-LIST] Injecting noise into a plane
Dear SI subscribers,
I am looking to correlate and quantify the power supply noise that exist on
the VDD pins of a system clock generator to the output clocks cycle to cycle
jitters. I like to be able to induce controlled noise (or ripples) on the
3.3V rail, and directly measure the phase noise. I am sure you all know
there are difficulties in injecting noise from say a function generator
directly into the power plane. To overcome this I think it might be easier
to mock with the power supply it self to generate this noise. (For example
one idea is place a set of power transistors across the rail and gate em
with the desired noise waveform).
Does any one know of a computer power supply that has feature for adding
noise to one of its rails? Or if any one know of a simple modification to a
standard supply that will add controlled ripples to one of the rails? I
would really appreciate any comments or feedback.
Thanks
AA
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