Ken,
Again, there is no generic answer, it depends on the circuit you feed.
Generic low speed logic can be fairly tolerant to noise, but today's
high-speed digital chips also have a lot of analog-like circuits: PLL,
oscillators, SerDes drivers and receivers. Dependent on their
construction, their tolerance to noise can be very different. If we are
lucky, we get that requirement from the device's data sheet, so that we
can decide about acceptable limits rail by rail and device by device.
Dips usually dont kill a device, it may cause 'only' functional errors.
A spike can cause damage to the chips, but only if it appears on the
semiconductor itself. But we do not have direct access to the
semiconductor to measure the voltage, and as opposed to signal
integrity, where we can deembed the package and can reliably infer the
waveform on the silicon from a waveform measured at the pin and from a
package model, we almost never have a model for the power path of the
package to do the same deembedding with power noise.
Regards,
Istvan Novak
Ken Javor wrote:
Re: [PSES] Power Integrity Question Then let’s slightly rephrase the
question. What sort of ripple causes problems? Is it dips - how much?
Spikes – again, how much? Let’s confine this to digital logic. Analog
is easier because there is defined power supply ripple rejection for
parts plus the noise sources aren’t high speed.
Ken Javor
Phone: (256) 650-5261
------------------------------------------------------------------------
*From: *John Woodgate <[email protected]>
*Date: *Sun, 8 Apr 2018 08:09:47 +0100
*To: *Ken Javor <[email protected]>,
<[email protected]>
*Subject: *Re: [PSES] Power Integrity Question
A specific target would typically be 'less than 1/3 of the value known
to just provoke trouble'.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk <http://www.woodjohn.uk>
<http://www.woodjohn.uk>
Rayleigh, Essex UK
On 2018-04-08 04:25, Ken Javor wrote:
Re: [PSES] Power Integrity Question If the answer to how much
ripple is too much, or how little ripple is good enough is in all
cases, “it depends,” then does that mean that the pursuit of power
integrity has a purely functional pass/fail criteria; i.e., that
the unit operates properly, as opposed to a specific target on
ripple level?
Ken Javor
Phone: (256) 650-5261
------------------------------------------------------------------------
*From: *John Woodgate <[email protected]> <mailto:[email protected]>
<mailto:[email protected]>
*Date: *Sat, 7 Apr 2018 17:58:36 +0100
*To: *Ken Javor <[email protected]>
<mailto:[email protected]>
<mailto:[email protected]> ,
<[email protected]> <mailto:[email protected]>
<mailto:[email protected]>
*Subject: *Re: [PSES] Power Integrity Question
I don't think that there is a general rule that doesn't have so
many exceptions as to be useless. Even a 'simple' audio power
amplifier can show this. A conventional linear amplifier can have
very good PSRR (power supply rejection ratio) but a Class D
amplifier has zero dB PSRR - none at all.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
<http://www.woodjohn.uk> <http://www.woodjohn.uk>
<http://www.woodjohn.uk> <http://www.woodjohn.uk>
Rayleigh, Essex UK
On 2018-04-07 17:41, Ken Javor wrote:
Power Integrity Question There are many learned
books/papers/discussions on how to achieve proper power
integrity by way of proper PCB layout and proper capacitor
decoupling techniques, but what is the goal? I don't mean the
functional goal, which is obvious, but rather what is the
metric? Is it ripple voltage peak-to-peak, maximum excursion,
minimum excursion, some rms value, or...?
This question is decoupled from achieving PI for the purpose
of controlling radiated emissions: just asking how close to
pure unadulterated dc a dc rail must be in order to be
considered properly functional.
Understand the answer will be different for an analog rail
vs. a digital one, and for different digital rails, but
appreciate insight into what constitutes acceptable power
quality for all dc rails used in a typical piece of electronics.
Thank you,
Ken Javor
Phone: (256) 650-5261
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