Re: [PSES] Ground Fingers routed in CPU pin fields
Hi Charles, Having a trace shorted to ground at one end and leaving open at the other end creates a quarter-wave resonator. If for sake of example the propagation delay on the particular layer is 160ps/", 250mils has 40ps and the period at the quarter-wave resonance is 4*40ps=160ps, which is around 6GHz. At that frequency (and increasingly as we approach that frequency) the insertion loss, reflection and crosstalk will be higher. Whether this creates a problem, depends on the signaling speed and signaling budget. Best regards, Istvan Novak Samtec On 11/29/2021 1:55 PM, Charles Grasso wrote: Hello all and I hope your Thanksgiving went well! I am seeking some guidance on the effect (detrimental or otherwise) on adding short (say 250mils) ground fingers in between high speed differential pairs at their source. i.e at the IC pin field. The ground finger only has a via at the entrance to the pin field and not at the final destination 250 mils away. Does anyone know of (or have experience of ) any issues this may cause? -- Charles Grasso Dish Technologies (c) 303-204-2974 (h) 303-317-5530 (e ) charles.gra...@dish.com (e2) chasgra...@gmail.com - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas Mike Cantwell For policy questions, send mail to: Jim Bacher David Heald - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] SV: [PSES] Ground copper fill on signal layer on multilayer PCB
Hi Amund, Since your potential problem appears to be at relatively low frequencies, an alternative to edge plating would be stitching the ground planes along the board edges with closely spaced vias. We have done this at SUN Microsystems also as a preventive measure. On the other hand, you should also consider the possibility that the leaking happens not through the edge of the board but through components connected to internal traces but sitting on the top or bottom of the board. What I am saying is that it is not necessarily the edge of the board that radiates. You could check this by poking around with a close-field probe, even uncalibrated unshielded home-made small loop or monopole antennas might give you a useful hint where the noise is coming from. You could also put absorbing sheets to the edge of the board to see if it makes a difference in the overall radiation. Best regards, Istvan Novak Samtec On 2/19/2020 1:50 AM, Amund Westin wrote: Hi Ken No, I have not considered edge-plating. I’ll look into this now. We have some high frequency noise (400-500MHz) from differential lines leaking out from an inner layer of a multilayer pcb. Edge-plating might be a good solution. Thanks for the tip. BR Amund *Fra:* IBM Ken *Sendt:* 18. februar 2020 23:18 *Til:* EMC-PSTC@LISTSERV.IEEE.ORG *Emne:* Re: [PSES] Ground copper fill on signal layer on multilayer PCB Hi Amund! Have you also considered edge-plating? Are you trying to reduce radiated noise outside your product, or cross-talk within the product (or both)? On Tue, Feb 18, 2020 at 3:03 AM Amund Westin <mailto:am...@westin-emission.no>> wrote: Between two solid ground planes, we have a signal layer, routing high speed differential lines. What do you recommend: 1. fill the remaining area with copper in the signal layer 2. fill only the border of the layer (5mm ground copper trace around the layer edge) 3. no fill at all Best regards Amund - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to emc-p...@ieee.org <mailto:emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas sdoug...@ieee.org <mailto:sdoug...@ieee.org> Mike Cantwell mcantw...@ieee.org <mailto:mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher j.bac...@ieee.org <mailto:j.bac...@ieee.org> David Heald dhe...@gmail.com <mailto:dhe...@gmail.com> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to mailto:emc-p...@ieee.org>> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas mailto:sdoug...@ieee.org>> Mike Cantwell mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher mailto:j.bac...@ieee.org>> David Heald mailto:dhe...@gmail.com>> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to mailto:emc-p...@ieee.org>> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas mailto:sdoug...@ieee.org>> Mike Cantwell mailto:mcantw...@ieee.org>>
Re: [PSES] DC/DC EMI Input Filter Stability
Hi James, If you consider input filters for DC-DC converter inputs (not a must, but a good idea), you want to have one filter for each converter input.? In such a case if you design each converter with its own input filter to be stable, there will be no problem.? I have been designing computer systems with many DC-DC converters in the past 22 years (also up to a dozen converter inputs connected together without input filters) and there were no issues around this.? The key is not to save on high-ESR bulk capacitors connected across the input of each DC-DC converter.? In practice I have found the loop stability on the output side to be much more challenging to solve, but that should be handled differently. You can find a few additional considerations in http://www.electrical-integrity.com/Paper_download_files/DC12_11-MP2.pdf and http://www.electrical-integrity.com/Paper_download_files/DC17_PAPER_11_OverviewComparisonPowerConverterStability_Hartman.pdf Regards, Istvan Novak Samtec On 6/4/2019 3:45 AM, James Pawson (U3C) wrote: Morning all, I?m designing an EMI filter for a DC input power line that has four DC/DC converters all running off it. I know that the output impedance of the EMI filter needs to be much lower than the input impedance of the DC/DC converter to prevent oscillation/instability. But what happens when there are multiple DC/DC converters running in parallel from the same input? How do the input impedances interact? Do they appear in parallel or do the control loops isolate stability issues to individual converters? My understanding from this paper - http://www.ti.com/lit/an/slua929a/slua929a.pdf - is that the control loop and output filter of the DC/DC contributes to the stability analysis. If so, then *each DC/DC can be considered individually* with the filter being designed to have margin to the lowest input impedance of all of the converters. This is instead of just adding all the input impedances in parallel. Is my understanding correct? Thanks in advance, James James Pawson EMC Problem Solver ** *Unit 3 Compliance* Design for EMC / Pre Compliance / Problem Solving / EMC Testing / Consultancy / Environmental & Vibration www.unit3compliance.co.uk <http://www.unit3compliance.co.uk/> -- 07811 139957 Opening Hours: Tuesday to Friday, 0830 to 1800. Closed Monday. Connect with me on LinkedIn <https://www.linkedin.com/in/james-pawson-unit-3-compliance/> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to mailto:emc-p...@ieee.org>> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas mailto:sdoug...@ieee.org>> Mike Cantwell mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher mailto:j.bac...@ieee.org>> David Heald mailto:dhe...@gmail.com>> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] Using a TDR for Shielding Effectiveness measurements
As long as we can assume that the propagation medium and the DUT are linear and time invariant, the time-domain response can be easily transformed to frequency-response data. This is true also in the other direction: vector network analyzers today can be set to operate like TDR instruments as far as their displayed data is concerned. The dynamic range limitation is likely more relevant. Regards, Istvan Novak Ken Javor wrote: Re: [PSES] Using a TDR for Shielding Effectiveness measurements Given the few responses to date, I’ll fess up to cluelessness and curiosity. Aside from the obvious dynamic range limitation working in the time domain, if you limit yourself to the time domain, how do you map SE vs. frequency? And given the inherent wide band nature of a TDR signal, I can’t see it being radiated properly. I’m thinking you would have to use something like an ASTM 4936 coaxial test fixture in order to main signal integrity up to the reflection point where the sample material puck is installed. Ken Javor Phone: (256) 650-5261 *From: *"Grasso, Charles" <charles.gra...@dish.com> *Reply-To: *"Grasso, Charles" <charles.gra...@dish.com> *Date: *Thu, 19 Apr 2018 15:23:27 + *To: *<EMC-PSTC@LISTSERV.IEEE.ORG> *Conversation: *Using a TDR for Shielding Effectiveness measurements *Subject: *[PSES] Using a TDR for Shielding Effectiveness measurements Hello all, In lieu of using shielded chambers/spectrum analyzers and such, has anyone used a TDR for performing shielding effectiveness measurements? The simplicity is tempting – but I am dubious about the dynamic range? I have poked about in the usual place – but didn’t find any definitive studies. (I suppose that is a clue in and of itself!) Thanks Charles Grasso (w) 303-706-5467 - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org <mailto:emc-p...@ieee.org>> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org <mailto:sdoug...@ieee.org>> Mike Cantwell <mcantw...@ieee.org <mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org <mailto:j.bac...@ieee.org>> David Heald <dhe...@gmail.com <mailto:dhe...@gmail.com>> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
Re: [PSES] Using a TDR for Shielding Effectiveness measurements
Ken, Actually what I was referring to: we can transmit a pulse (or rather a step, if it is a TDR), measure the response with an oscilloscope in the time domain and as long as the DUT is linear and time invariant, we can take the time-domain data from the oscilloscope, transform it into the frequency domain with Fourier transform, and if we do it properly, the result will be exactly the same that we would get with a vector-network analyzer, minus the dynamic range. Best regards, Istvan Novak On 4/20/2018 11:00 AM, Ken Javor wrote: My response was predicated on a purely time domain measurement. If we are going to transmit a pulse but measure in the frequency domain, then there is no dynamic range limitation, assuming we have a pre-selected front end to our receiver. And if we are making a frequency domain measurement, then any set of suitable transmit antennas will do, as we are only looking at some fraction of the pulse spectrum at any one time; no need to transmit the entire pulse spectrum simultaneously. But if those are the ground rules, then any impulse generator laying around the lab, from the old days when they were used to calibrate EMI receivers, would suffice. Ken Javor Phone: (256) 650-5261 From: Istvan Novak <istvan.no...@oracle.com> Date: Fri, 20 Apr 2018 08:28:09 -0400 To: Ken Javor <ken.ja...@emccompliance.com>, <EMC-PSTC@listserv.ieee.org> Subject: Re: [PSES] Using a TDR for Shielding Effectiveness measurements As long as we can assume that the propagation medium and the DUT are linear and time invariant, the time-domain response can be easily transformed to frequency-response data. This is true also in the other direction: vector network analyzers today can be set to operate like TDR instruments as far as their displayed data is concerned. The dynamic range limitation is likely more relevant. Regards, Istvan Novak Ken Javor wrote: Re: [PSES] Using a TDR for Shielding Effectiveness measurements Given the few responses to date, I¹ll fess up to cluelessness and curiosity. Aside from the obvious dynamic range limitation working in the time domain, if you limit yourself to the time domain, how do you map SE vs. frequency? And given the inherent wide band nature of a TDR signal, I can¹t see it being radiated properly. I¹m thinking you would have to use something like an ASTM 4936 coaxial test fixture in order to main signal integrity up to the reflection point where the sample material puck is installed. Ken Javor Phone: (256) 650-5261 *From: *"Grasso, Charles" <charles.gra...@dish.com> *Reply-To: *"Grasso, Charles" <charles.gra...@dish.com> *Date: *Thu, 19 Apr 2018 15:23:27 + *To: *<EMC-PSTC@LISTSERV.IEEE.ORG> *Conversation: *Using a TDR for Shielding Effectiveness measurements *Subject: *[PSES] Using a TDR for Shielding Effectiveness measurements Hello all, In lieu of using shielded chambers/spectrum analyzers and such, has anyone used a TDR for performing shielding effectiveness measurements? The simplicity is tempting but I am dubious about the dynamic range? I have poked about in the usual place but didn¹t find any definitive studies. (I suppose that is a clue in and of itself!) Thanks Charles Grasso (w) 303-706-5467 - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org <mailto:emc-p...@ieee.org>> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://
Re: [PSES] [SI-LIST] Re: Measurement Dilema - THE EXPLANATION!
Hi Doug, It was great to chat with you. Here is a brief summary of the technical details we spoke (Doug, correct me if I cite something incorrectly). Staying with the question how could someone show and demonstrate the amount of current the oscillator pumps into the circuit, there are a couple of simple possibilities: - measuring the current flowing in the wire between the oscillator output and the probes. With this we need to be careful so that the measuring probe and instrument wont alter the setup's behavior too much. - measuring the change of DC supply current going into the oscillator between unloaded state (its output disconnected from the probes), versus when the oscillator output is connected to the probes. Here we have a better chance to create a setup that only minimally alters the original scenario: we can use a miniature battery powered current meter. We can also measure the DC supply current on the oscillator separately when we connect a tuned circuit to its output drawing approximately 40mA at specific harmonics. When we do one or both of the above tests while we rearrange the probe cables to get maximum signal on the oscilloscope input, we can notice that the AC current supplied by the oscillator has two distinct states: there is a case when the oscillator supplies several times ten milliamperes, but there is also another state, when the oscillator hardly supplies any AC current. This letter case can further be tested by inserting a very small capacitance between the oscillator output and the probe loops: we will still get about the same big signal on the oscilloscope input. When I reproduced Doug's experiment at home, this latter case was accidentally the first I stumbled across. This case corresponds to a parallel resonance instead of a series resonance, requiring only a very small amount of current feeding the circuit. The Q of the tuned circuit will amplify the small injected current, so the current flowing in the ground lead wire of the oscilloscope probe is comparable to what we get in the series resonance case. As we keep moving the probe cables, we can 'tune' the circuit through a set of series and parallel resonances. Thanks again Doug for sharing your interesting experiments! Regards, Istvan Novak Istvan Novak wrote: Great! Lets talk over the phone, will call you after work. At the end though I think SI-list readers may also be interested in ways we come up with to demonstrate further aspects of your intriguing experiment. Regards, Istvan Novak On 4/6/2018 1:49 AM, Douglas Smith wrote: Actually the oscillator is producing about the same current it would into a short circuit, 40 mA) because it is driving a very low impedance of a series resonant circuit! Istvan, let’s talk on the phone to save s lot of typing. Doug Smith Sent from my iPhone IPhone: 408-858-4528 Office: 702-570-6108 Email: d...@dsmith.org Website: http://dsmith.org On Thu, Apr 5, 2018 at 21:07, Istvan Novak <istvan.no...@verizon.net> wrote: Doug, Thank you for sharing your interesting experiments. These always trigger my curiosity to look a little further. In my basement lab I came up with a small series of experiments to separate the possible different coupling mechanisms from the oscillator to the oscilloscope input. Though I did not intend to replicate your exact setup, I believe it was conceptually and essentially similar enough that the results may apply to a large number of setups, including yours. From all of the different tests my conclusion is that the oscillator is not supplying a significant amount of current to produce the effect in question. I have not had the good fortune yet to see your full live demonstration, plus as you say you have much more data than what you publish, so it very well could be that you already have done similar experiments and came to similar conclusions. Therefore I would like to hear the thoughts of those list members who did not attend your demonstrations, what kind of experiments would they suggest to prove or disprove my conclusion. Regards, Istvan Novak On 1/30/2018 12:06 PM, Douglas Smith wrote: I did that experiment a long time ago, almost 30 years ago, when developing this experiment, which is described in my book. Reducing ground lead length to near zero eliminates the effect almost completely with no other changes in the experimental setup. You still see a little effect about 1/50 of before, due to the shield transfer impedance of the probe cables. A tiny ground lead always swamps shield transfer impedance of practical shielded cables. I do that experiment for my classes as an extension of this experiment. My live experiments are always more complete than the versions I publish both to keep published versions reasonably short and to provide extra value to live experiments. I usually have ten times the data I actually publish! Doug Smith Sent from my iPhone IPhone: 408-858-4528 Office: 702-57
Re: [PSES] Power Integrity Question
Yes and no. The coupling path was closing through the user PCB... John Woodgate wrote: That should be warned about in the data sheet. Internal EMC problems tend to be rare, which is good, but because they are rare, there should be warnings if they can occur. John Woodgate OOO-Own Opinions Only J M Woodgate and Associateswww.woodjohn.uk Rayleigh, Essex UK On 2018-04-09 13:19, Istvan Novak wrote: And examples can be even more strange: we had DC-DC converter modules failing to work properly because one of the converter's power pins feeding an internal linear regulator picked up noise from the same converter. Regards, Istvan Novak John Woodgate wrote: I agree. One particular point is keeping a trace connected to an inverting input very short, even if that means including a low-value 'stopper' resistor close to the chip. That point has quasi-infinite sensitivity but infinitesimal impedance only within the op-amp pass band. Above the pass-band, it is an antenna connected to a diode. And yes, it can pick up power rail noise. John Woodgate OOO-Own Opinions Only J M Woodgate and Associates www.woodjohn.uk Rayleigh, Essex UK On 2018-04-09 04:27, Doug Smith wrote: Hi Ken and the group, Many analog circuits, as well as the analog parts of large ICs that you mention, do have response to GHz noise even 1 MHz unity gain opamps! Low frequency op amps can generate a DC offset on their inputs from GHz digital noise or radio signals, a common problem for the last 45 years since I first observed it. Power supply rejection of op amps goes to pot pretty quickly with frequency as well. High frequency effects therefore are important even to low speed analog circuits. In some ways, one must lay out the low frequency analog circuit using microwave techniques to keep RF noise at bay. The circuit features must be keep really small,, including the bypass capacitors being kept extremely close (< 100 mils) to the op amp. 45 years ago, faced with opamp problems from RF noise I developed some techniques for keeping the op amps happy. I discuss these in my upcoming course. Doug University of Oxford, Course Tutor Department for Continuing Education Oxford, Oxfordshire, United Kingdom -- Doug Smith P.O. Box 60941 Boulder City, NV 89006-0941 TEL/FAX: 702-570-6108/570-6013 Mobile: 408-858-4528 Email: d...@dsmith.org Web: http://www.dsmith.org -- - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org <mailto:emc-p...@ieee.org>> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org <mailto:sdoug...@ieee.org>> Mike Cantwell <mcantw...@ieee.org <mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org <mailto:j.bac...@ieee.org>> David Heald <dhe...@gmail.com <mailto:dhe...@gmail.com>> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-complian
Re: [PSES] Power Integrity Question
And examples can be even more strange: we had DC-DC converter modules failing to work properly because one of the converter's power pins feeding an internal linear regulator picked up noise from the same converter. Regards, Istvan Novak John Woodgate wrote: I agree. One particular point is keeping a trace connected to an inverting input very short, even if that means including a low-value 'stopper' resistor close to the chip. That point has quasi-infinite sensitivity but infinitesimal impedance only within the op-amp pass band. Above the pass-band, it is an antenna connected to a diode. And yes, it can pick up power rail noise. John Woodgate OOO-Own Opinions Only J M Woodgate and Associates www.woodjohn.uk Rayleigh, Essex UK On 2018-04-09 04:27, Doug Smith wrote: Hi Ken and the group, Many analog circuits, as well as the analog parts of large ICs that you mention, do have response to GHz noise even 1 MHz unity gain opamps! Low frequency op amps can generate a DC offset on their inputs from GHz digital noise or radio signals, a common problem for the last 45 years since I first observed it. Power supply rejection of op amps goes to pot pretty quickly with frequency as well. High frequency effects therefore are important even to low speed analog circuits. In some ways, one must lay out the low frequency analog circuit using microwave techniques to keep RF noise at bay. The circuit features must be keep really small,, including the bypass capacitors being kept extremely close (< 100 mils) to the op amp. 45 years ago, faced with opamp problems from RF noise I developed some techniques for keeping the op amps happy. I discuss these in my upcoming course. Doug University of Oxford, Course Tutor Department for Continuing Education Oxford, Oxfordshire, United Kingdom -- Doug Smith P.O. Box 60941 Boulder City, NV 89006-0941 TEL/FAX: 702-570-6108/570-6013 Mobile: 408-858-4528 Email: d...@dsmith.org Web: http://www.dsmith.org -- - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
Re: [PSES] Power Integrity Question
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 <j...@woodjohn.uk> *Date: *Sun, 8 Apr 2018 08:09:47 +0100 *To: *Ken Javor <ken.ja...@emccompliance.com>, <EMC-PSTC@LISTSERV.IEEE.ORG> *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 <j...@woodjohn.uk> <mailto:j...@woodjohn.uk> <mailto:j...@woodjohn.uk> *Date: *Sat, 7 Apr 2018 17:58:36 +0100 *To: *Ken Javor <ken.ja...@emccompliance.com> <mailto:ken.ja...@emccompliance.com> <mailto:ken.ja...@emccompliance.com> , <EMC-PSTC@LISTSERV.IEEE.ORG> <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> *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 - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> <mailto:
Re: [PSES] Power Integrity Question
Hi Ken, Good question, and as you already suspect, there is no clear, generic answer (and for the same reason there is no such thing as typical electronics). Having practiced this art for decades, and teaching courses (up to five days in length) on the subject, the best we can do is to explain all possible factors that eventually the responsible designer has to take into account. You will find pieces of the answer in various books and on the publications posted on my website, for instance http://www.electrical-integrity.com/Paper_download_files/Ansoft_EMI_Workshop_SUN_for_22Aug07_v2.pdf Regards, Istvan Novak 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 - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org <mailto:emc-p...@ieee.org>> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org <mailto:sdoug...@ieee.org>> Mike Cantwell <mcantw...@ieee.org <mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org <mailto:j.bac...@ieee.org>> David Heald <dhe...@gmail.com <mailto:dhe...@gmail.com>> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
Re: Q on Correlation of Votage ripple with a Spectrum Analyser
Charles, Doing this kind of correlation is very difficult for the following reasons: - unless you measure a very simple and dummy system, hardware today is so complex that you cant predict for sure its activity; it is a strong function of time. -tThe spectrum analyzer and scope will look at the same signal in different ways: analog spectrum analyzers have a seep time and settling time determining the frequency and aperture of visit each frequency. If you have a spectrumn analyzer used for compliance tests, probably the CISPR filter is on. Scopes on the other hand (digital scopes) undersample the signal, whether it is called real-time or not. Memory and displey refresh rate does not allow scopes to display and process all data points of high-frequency signals. Real-time scopes do it for a given time window, but it is usually way less than the time constant of a CISPR filter on the spectrum analyzer. - connection to the source makes a big difference. I assume when you calibrated the reading with a sine wave, a coaxial cable with coax connectors at both ends was used. Presumably the product does not have a coaxial connector on the Vcc plane, so you have to make your own connection or use a hand-held probe. This is very extra noise usually gets in the path, and the scope reading becomes unrealistically high. I have found no active scope probes so far, which would give a correct reading in a noisy environment. We hopefully should not see noise on the Vcc planes more than a few hundred mV. In contrast, many scope probes can pick up spikes as big as volts from the environment. If you want to measure noise levels below 100mVpp, double-shielded coax is necessary in noisy environments. Here the 'noisy environment' refers to the close vicinity of the point you test. The simplest test is: take your present probe, and hook up a good double-shielded coax to the same points. Check both readings on the same scope at the same time, and compare. I hope this helps. Best regards, Istvan Novak SUN Microsystems From: Charles Grasso cgrassospri...@earthlink.net To: Ken Javor ken.ja...@emccompliance.com; Emc-Pstc emc-p...@ieee.org Sent: Saturday, July 26, 2003 9:11 PM Subject: RE: Q on Correlation of Votage ripple with a Spectrum Analyser Hi all, Actually I was using a good ole Spectrim Analyser so I sidestepped the windowing issue/software issues altogether. What I was(am)trying to do was match the max voltage as measured on a scope with the value as measured on a SA. I first calibrated myslef using a known source - a sine wave. The amplitudes fell in just as theory predicted. Encouraged, I then probed the Vcc plane on a product I was working on and was not so happy!! Any ideas? -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Saturday, July 26, 2003 4:19 PM To: Charles Grasso; Emc-Pstc Subject: Re: Q on Correlation of Votage ripple with a Spectrum Analyser I presented a paper on that very subject about a decade ago at one of the EMC TD magazine EMC symposia. I used a Fluke Scopemeter and some FFT software that came with it. The Fluke interfaced to the PC through an optically isolated RS-232 protocol. It worked quite well from a pre-compliance or troubleshooting point-of-view. You could use time windowing to separate the signals deriving from leading and falling edges from the signals deriving from the pulse itself. I used LISNMATE and LISNMARK mode separation devices to show that the rising/falling edge signals were common mode, while the pulse itself generated differential mode signals. From: Charles Grasso cgrassospri...@earthlink.net Reply-To: Charles Grasso cgrassospri...@earthlink.net Date: Sat, 26 Jul 2003 16:18:36 -0700 To: Emc-Pstc emc-p...@ieee.org Subject: Q on Correlation of Votage ripple with a Spectrum Analyser Hi All, Has anyone tried correlating the voltage ripple as seen on a scope with the amplitudes measured on a Spectrum Analyser? I tried doing that the other day with ..umm. minimal success. I think that due to the comples convoltions that would have to occur when FFT'ing an irregular voltage shape. Charles Grasso Echostar Communications. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web
Re: Q on Correlation of Votage ripple with a Spectrum Analyser
Charles, Instead of using the 1GHz single-ended scope probe, have you tried to connect the same coax cable that you made with the seriers 50 ohms for the SA to connect to the scope? With a 50-ohm input impedance setting on the scope, the loading of the planes would be exactly the same. As I mentioned earlier, we checked many scope probes, from Tektronix, Agilent, LeCroy, including some of the new 4-6GHz bandwidth single-ended and differential probes. They all pick up more or less noise from the environment, and not necessarily through the input connection pins or wires. You can take your scope probe, with its input pins open or shorted, and take the infinite persistance scope reading, while you move the probe close to a high-power, high-speed computer board (no connection, just put the probe an inch close). Or, just simply take a desktop light with a transformer in its base, and flip the switch a few times. You will be amased how much noise these probes can pick up through the unshielded (or poorly shielded) front-end amplifier and through the cable connecting to the scope. Best regards, Istvan From: Charles Grasso cgrassospri...@earthlink.net To: Ken Javor ken.ja...@emccompliance.com; istvan novak istvan.no...@worldnet.att.net; Emc-Pstc emc-p...@ieee.org Sent: Sunday, July 27, 2003 4:26 PM Subject: RE: Q on Correlation of Votage ripple with a Spectrum Analyser This is getting pretty intense for a Sunday!! Both Mr. Javor and Mr Novak make excellent observations. Both center on the method of measurment as a point of concern. To measure the voltage ripple I used a high badwidth (1GHz) sigle ended probe with very short leads. In order to establish the error margin, I used the null experiment technique. (I don't have a diff probe with sufficient bandwidth to hand). I then used a piece of coax with very short leads (just like Mr Javor recommends) and a 50ohm resistor in series with the signal to feed the same voltage ripple to a SA. Clearly there is a voltage division here but thats easily accounted for. My concern is that the impedance of the planes is so much lower than the 50ohm input of the SA and I wanted to match that as much as possible. I belive I have taken care of as much of the measurement problem as possible. Still, the maximum voltages between the two measurments do not come close at all. -Original Message- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Ken Javor Sent: Sunday, July 27, 2003 10:27 AM To: istvan novak; Charles Grasso; Emc-Pstc Subject: Re: Q on Correlation of Votage ripple with a Spectrum Analyser Mr. Novak makes some excellent points. I was under the assumption that the phrase voltage ripple implied conducted emission measurements at a LISN port. Hence my comments on mode separation. Across a spectrum of even 30 MHz, any normal scope probe I know of (1 or 10 M Ohm in parallel with 5/10/20 pF) will present a varying load to the measured waveform. I know there are some broadband active differential probes with low shunt capacity, but I have no experience using them. The scope should be made to look like a flat 50 Ohm load to help correlate to a spectrum analyzer. Instead of using long leads to make measurements from one point of the Vcc plane to another, I would make coaxial measurements from one point on the Vcc plane to chassis ground or the reference/image plane if one exists, and then make the same measurement at another point on the Vcc plane, and compare the waveforms, perhaps using a built-in math function if your scope has that. Of course this technique requires the reference/image plane/chassis ground to be an equipotential plane... By coaxial measurement I mean using coax rather than a scope probe, and terminating the shield at the reference point, while extending the center conductor just far enough to connect to the point of interest on the Vcc plane. Theoretically, an even better technique would be to have a place on the board where the power plane reference was available circumferentially around a Vcc via, and connect the coax shield to the reference plane and the center conductor to the Vcc contact. Given a 50 Ohm load at the other end (with a blocking cap to protect it), and an FFT capability with enough memory, I believe you could achieve correlation with the individual spectral components measured by a spectrum analyzer (which of course would also need a blocking cap with this config). From: istvan novak istvan.no...@worldnet.att.net Date: Sun, 27 Jul 2003 11:02:02 -0400 To: Charles Grasso cgrassospri...@earthlink.net, Ken Javor ken.ja...@emccompliance.com, Emc-Pstc emc-p...@ieee.org Subject: Re: Q on Correlation of Votage ripple with a Spectrum Analyser Charles, Doing this kind of correlation is very difficult for the following reasons: - unless you measure a very simple and dummy system, hardware
magnetic field measuring instruments and probes
Hi list members, Could someone suggest or refer me to pointers/manufacturers of probes and instruments to measure magnetic close field in the 10kHz to 10MHz frequency range? High accuracy is not important, values to be measured would be around 0.5mT and up. Thanks Istvan Novak SUN Microsystems
