Chris Cheng
Distinguished Technologist , Electrical
Hewlett-Packard Enterprise Company
+1 510 344 4439/ Tel
chris.cheng@xxxxxxx / Email
4209 Technology Dr
Fremont, CA 94538
USA
On die decoupling caps can easily be few nf to 100's of nf. Your high
performance probe loading is only in pf. If sense lines are designed properly,
the loop inductance are minimal. Why is there any concern about using them as
direct on die power measurement ?
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Iliya Zamek
Sent: Tuesday, May 8, 2018 9:34 PM
To: si-list@xxxxxxxxxxxxx; Giuseppe Selli (giselli) <giselli@xxxxxxxxx>
Subject: [SI-LIST] Re: Remote sense vs power
Your measurement results have sense. Noise source on chip die' power rail is
connected through parasitic inductance of die-package-PCB to the decoupling
capacitor; this circuit together with decoupling capacitor is filtering power
noise when you are measuring it on the capacitor directly. Noise on the sense
line differs from noise on the die in less degree, -no filtering by capacitor.
Measurements on sense line with high impedance and low capacitance measurement
device (probe with oscilloscope) will be more close to the voltage variations
on-die compared to measurements on capacitor, while still will be reduced.
To avoid the impact of parasitic you might use the method base on Jitter
measurements I designed specifically for this purpose. In this method two
switching logic domains that are sharing the same power supply are used. Using
one of them as an aggressor that creates a power noise, and measure Jitter on
other, it is possible to figure out the value of power noise behavior by
measuring Jitter. By vary switching frequency it is also possible to find the
PDN resonance frequency. The method is described in:
https://ieeexplore.ieee.org/document/4603875/metrics and in paper published in ;
DesignCon 2012
https://pdfs.semanticscholar.org/5bc2/0603dc181cc67500aa875e50e959c1a95e17.pdf
If you need more details, please, contact me offline. Thank you.Iliya Zamek
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A study of jitter effects in nm-FPGA based on various physical and elect...
Achievements in semiconductor nanotechnology have enabled the design of
advanced devices with higher performance...
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On Monday, May 7, 2018, 10:55:25 AM PDT, Giuseppe Selli (giselli)
<giselli@xxxxxxxxx> wrote:
Greetings,
Question :
we are trying to measure the noise voltage on system, we hooked up two 50 Ohm
coax cables - unshielded - one coax is connected between the VDD and GND sense
pins right at the BGA on the bottom of the PCB, while another coax cable is
connected across a decoupling cap right under the BGA on the bottom of the PCB.
The noise observed @ sense pin is approximately 50% higher than the noise
observed at decoupling.
Assuming that sense pin observe the noise at the die, since it is a very short
connection to a pair of bumps connected to the power/gnd grid on die, this
means that the noise observed at the bump is higher than the noise observed at
the BGA on the same voltage rail
Now the sense line is connected though a differential pair ~ 5-7 inches long to
the input of a controller that I think is high impedance and it appears to be
routed between GND planes quite nicely without discontinuities, it occurred to
me that perhaps the sense line might be picking some noise from other sources,
but I cannot be sure ...
Any suggestions/feedback would be greatly appreciated even on how to improve
the measurement setup itself (literature) !
Thanks,
Giuseppe
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