FreeLists / si-list / [SI-LIST] Re: Article discussion on bad packages - core powermeasurments

[zhangkun 29902 <zhang_kun@xxxxxxxxxx>]

Dear Charles

The 50 ohm input impedance of SA would not affect the PDS. Normally, the 
impedance of PDS is below 1 ohm, which is little compared with 50ohm. If the 
freqeuncy domain is extended above 3GHz, my method is not useful. There are 
some point to suggust.

1.There is a dc-block. If the frequency domain is below 2GHz, a very cheap 
dc-block could be made by PCB and discrete capacitor, which is about of $1.00:) 
A commerical dc-block is about of $100:(
2.The "pigtail" effect should be awared. The pigtail should be as short as 
possible.

I hope this is helpful.

I am also trying to corelate the measurement in time domain and frequency 
domain. I have not get any success:( In SA maesurement, there is no phase 
information. Another problem is "what is measured by SA?" I have found that 
some kinds of noise could not be caught by SA.

Best Regards

Zhangkun
2005.1.5

----- Original Message -----
From: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>
Date: Wednesday, January 5, 2005 10:38 pm
Subject: RE: [SI-LIST] Re: Article discussion on bad packages - core power 
measurments

> Dear Zhangun
> 
> I am intrigued by your last email. In it you mentioned that:
> "I measured the CORE power ground noise by spectrum analyzer...."
> 
> I very interested in your experiences as I have tried to correlate
> SA power measurements with scope measurements with minimal success.
> One problem I think is that a SA has a 50ohm input impedance that
> can load the PDS and the coax needed to hook up the SA will add
> how hf filtering, 
> 
> Would you share with us some thoughts on how to use a SA for
> power measurements ??
> 
> Thanks!
> 
> Best Regards
> Charles Grasso
> Senior Compliance Engineer
> Echostar Communications Corp.
> Tel:  303-706-5467
> Fax: 303-799-6222
> Cell: 303-204-2974
> Pager/Short Message:  3032042974@xxxxxxxx
> Email: charles.grasso@xxxxxxxxxxxx;  
> Email Alternate: chasgrasso@xxxxxxxx
> 
> 
> 
> -----Original Message-----
> From: zhangkun 29902 [zhang_kun@xxxxxxxxxx] 
> Sent: Wednesday, January 05, 2005 7:29 AM
> To: weirsp@xxxxxxxxxx
> Cc: hmurray@xxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Article discussion on bad packages - core
> 
> 
> Steve:
> 
> I agree with you according to my experience. In some product in my 
> company,I measured the CORE power ground noise by spectrum 
> analyzer. There is some
> great power consuming for several MHz to dozens of MHz. This kind 
> of power
> ground noise give rise to system failure. The solvment is to add a 
> lot of
> discrete decoupling capacitor, which is very simple:)
> 
> If there is any problem with IO power, it is very difficult to 
> solve them.
> There is also critical SSN problem.
> 
> Larry:
> 
> Why do you seperate the SSN and PI problem? I think they should be
> considered together.
> 
> Best Regards
> 
> Zhangkun
> 2005.1.5
> 
> ----- Original Message -----
> From: steve weir <weirsp@xxxxxxxxxx>
> Date: Wednesday, January 5, 2005 7:07 pm
> Subject: [SI-LIST] Re: Article discussion on bad packages - core
> 
> > Hal, I have generally found that the FPGA core power is not a
> > serious 
> > challenge.  In general ( beware generalizations! ) I have found 
> > the I/O 
> > rails tend to suffer much more percentage bounce and need much 
> > more care 
> > and attention than the core, even though the core is lower 
> > voltage.  There 
> > are a number of reasons for this:  fewer attachments, little in-
> > package / 
> > on-die capacitance for I/O, sparse ground chevron, tendency to 
> cut-
> > up I/O 
> > power planes, etc, etc.  The single most important design issue 
> in 
> > my mind 
> > is planning I/Os to contain the peak value of simultaneous 
> > switching di/dt 
> > within the package capabilities.
> > 
> > For your toolbox code, you might consider using the clock
> > multiplexers 
> > available for several years now.
> > 
> > For I/O rather than build a special test load, I suggest including
> > a 
> > multiplexor to all output IOBs that has as its second input a 
> > simple 
> > pattern generator as part of the production design.  Attaching 
> the 
> > mux 
> > control to a scan chain, or host register makes probing with 
> > otherwise 
> > realistic conditions much easier, and avoids code maintenance 
> > headaches.  You can stay as simple or get as fancy as you like 
> > with this 
> > technique without consuming much area, or imposing much timing 
> > penalty.
> > I don't have a good answer for CPU code.
> > 
> > Steve.
> > 
> > At 01:55 AM 1/5/2005 -0800, Hal Murray wrote:
> > 
> > > > The most crucial piece of information from the chip
> > manufacturer is
> > > > the maximum and minimum currents that can be drawn from the
> > PCB PDS.
> > > > This establishes the dI or transient current that the PCB must
> > supply.> >  The rise time (dt) is determined by the low pass
> > filter associated
> > > > with the chip/package resonant frequency.  Generally, customer
> > code> > will determine the current waveform and therefor the
> > frequency profile
> > > > of the current drawn by the chip, so I don't believe it is
> > fair to ask
> > > > chip vendors for the power spectrum.  However, they should 
> be 
> > > > obligated to give their customers the maximum and minimum
> > current that
> > > > their chip will ever draw.  The minium I is probably
> > determined by
> > > > sleep mode and power saving states.
> > >
> > >Is is possible to give useful numbers for min/max currents on
> > modern chips?
> > >
> > >Consider a CPU:  What code is it running?
> > >
> > >Consider a FPGA:  A nasty design can use many times the normal
> > peak current
> > >for a short burst without cooking itself.  (Adjust duty cycle 
> to keep 
> > >temperature reasonable.)
> > >
> > >I occasionally scheme about writing some code that would try to
> > go from min
> > >to max power usage and adjust the timing to see if I can provoke
> > troubles in
> > >the PDS.  Or something else will break.  This seems like a
> > generally nasty
> > >sort of code to have in your toolbox.
> > >
> > >I'm thinking of something like keep all memories active for N
> > cycles, then do
> > >nothing for N cycles.  Repeat for a while, then try the next N.
> > Finding the
> > >really nasty cases would probably take help from one of the
> > chip/system>designers/architects.  How do you keep all the ALUs
> > and memories busy?
> > >
> > >Maybe the leakage through thin oxides will save us by making the
> > min current
> > >large enough so that the ratio of min:max is reasonable.  :)
> > >
> > >Worst case might be coming out of reset.
> > >
> > >
> > >
> > >
> > >--
> > >The suespammers.org mail server is located in California.  So are
> > all my
> > >other mailboxes.  Please do not send unsolicited bulk e-mail or
> > unsolicited>commercial e-mail to my suespammers.org address or any
> > of my other addresses.
> > >These are my opinions, not necessarily my employer's.  I hate spam.
> > >
> > >
> > >
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