RE: Clock Dithering - some more information
I found the report Jack refers to on the website, and I think it is well worth reading. Regards - Chris Chileshe - Ultronics Ltd -Original Message- From: Jacob Schanker [SMTP:j.schan...@worldnet.att.net] Sent: Thursday, June 21, 2001 8:39 PM To: emc-p...@ieee.org Subject:Clock Dithering - some more information I followed the recent discussion threads on this topic, but it is not in my main stream of interest. However, I just remembered an extensive report I had seen on the subject. The report is Investigation into possible effects resulting from dithered clock oscillators on EMC measurements and interference to radio transmission systems By David Lauder and James Moritz of the Univ. of Hertfordshire Regional Electronics Centre, dated 18 March 2000. It was prepared for the UK Radiocommunications Agency. Although I am looking at a paper copy, I am pretty sure that I originally downloaded it from the UK RA website, http://www.radio.gov.uk The report expresses concern about the effects of DCOs on digital TV and COFDM transmissions. Regards, Jack Jacob Z. Schanker, P.E. 65 Crandon Way Rochester, NY 14618 Phone: 716 442 3909 Fax: 716 442 2182 j.schan...@ieee.org --- 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: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall, _ This message has been checked for all known viruses by Star Internet delivered through the MessageLabs Virus Scanning Service. For further information visit http://www.star.net.uk/stats.asp or alternatively call Star Internet for details on the Virus Scanning Service. _ This message has been checked for all known viruses by Star Internet delivered through the MessageLabs Virus Scanning Service. For further information visit http://www.star.net.uk/stats.asp or alternatively call Star Internet for details on the Virus Scanning Service. --- 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: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Clock Dithering - some more information
I followed the recent discussion threads on this topic, but it is not in my main stream of interest. However, I just remembered an extensive report I had seen on the subject. The report is Investigation into possible effects resulting from dithered clock oscillators on EMC measurements and interference to radio transmission systems By David Lauder and James Moritz of the Univ. of Hertfordshire Regional Electronics Centre, dated 18 March 2000. It was prepared for the UK Radiocommunications Agency. Although I am looking at a paper copy, I am pretty sure that I originally downloaded it from the UK RA website, http://www.radio.gov.uk The report expresses concern about the effects of DCOs on digital TV and COFDM transmissions. Regards, Jack Jacob Z. Schanker, P.E. 65 Crandon Way Rochester, NY 14618 Phone: 716 442 3909 Fax: 716 442 2182 j.schan...@ieee.org --- 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: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Clock dithering
tkrepdavsml7e...@jmwa.demon.co.uk, John Woodgate j...@jmwa.demon.co.uk inimitably wrote: 4.3.2.7.2.20010618143751.00b3d...@box.tin.it, Paolo Roncone paolo...@tin.it inimitably wrote: As for interference to broadband receivers (like TV equipment) I remember a Lexmark study published a few years ago that showed no increased interference from modulated clocks vs unmodulated clocks (there was also a related discussion in this forum a while ago). That is correct, as far as it goes. Dithered clocks do not cause extra interference to *analogue* TV I honestly don't know if anything new came up recently. What came up was *digital* TV (European system). This does show unexpected sensitivity to dithered clocks. Searching for something else today, I found my original proposal to BSI for a CISPR study of the subject. It is dated 9 April 1998, and that is the date that BSI circulated it to the relevant committee. The mills of God and standards -- Regards, John Woodgate, OOO - Own Opinions Only. Phone +44 (0)1268 747839 Fax +44 (0)1268 777124. http://www.jmwa.demon.co.uk Why not call a vertically- applied manulo-pedally-operated quasi-planar chernozem-penetrating and excavating implement a SPADE? --- 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: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Clock dithering
200106182001.qaa14...@interlock2.lexmark.com, rogle...@lexmark.com inimitably wrote: According to our extensive tests in conjunction with Philips Consumer Electronics, digital TV (both COFDM and ATSC) is actually less susceptible to interference from spread spectrum clocks (ssc) than current analog TV (both PAL and NTSC). Well, I hope someone will take those results to the CISPR study, instead of declining to participate and fuming with frustration in the background, as has happened with other EMC issues in the past. -- Regards, John Woodgate, OOO - Own Opinions Only. Phone +44 (0)1268 747839 Fax +44 (0)1268 777124. http://www.jmwa.demon.co.uk Why not call a vertically- applied manulo-pedally-operated quasi-planar chernozem-penetrating and excavating implement a SPADE? --- 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: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Clock dithering
4.3.2.7.2.20010618143751.00b3d...@box.tin.it, Paolo Roncone paolo...@tin.it inimitably wrote: As for interference to broadband receivers (like TV equipment) I remember a Lexmark study published a few years ago that showed no increased interference from modulated clocks vs unmodulated clocks (there was also a related discussion in this forum a while ago). That is correct, as far as it goes. Dithered clocks do not cause extra interference to *analogue* TV I honestly don't know if anything new came up recently. What came up was *digital* TV (European system). This does show unexpected sensitivity to dithered clocks. -- Regards, John Woodgate, OOO - Own Opinions Only. Phone +44 (0)1268 747839 Fax +44 (0)1268 777124. http://www.jmwa.demon.co.uk Why not call a vertically- applied manulo-pedally-operated quasi-planar chernozem-penetrating and excavating implement a SPADE? --- 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: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Clock dithering
According to our extensive tests in conjunction with Philips Consumer Electronics, digital TV (both COFDM and ATSC) is actually less susceptible to interference from spread spectrum clocks (ssc) than current analog TV (both PAL and NTSC). Philips has stated in a letter to us that they do not consider spread spectrum clocks to be an interference threat to digital TV. One report from the University of Hertfordshire has stated that digital TV is more susceptible to ssc than non-modulated clocks, which by itself is true because of the digital filtering techniques used in digital TV. However, this report does not look at the real world potential for interference. Philips found that when an interfering ssc signal is present and the digital TV and analog TV are both at comparable levels (X dB above their respective threshold of visibility signal strength) it takes roughly 16 dB higher amplitude ssc signal to disrupt the digital TV versus the analog TV. In addition, through many contacts of both television manufacturers, television broadcasters, and discrete clock vendors we have found virtually no evidence of interference complaints due to spread spectrum clocks. Since there are no real interference problems with analog TV, and digital TV is less susceptible, there is no additional interference risk due to ssc. We are in the process formalizing these results for publication. Our previously published analog TV interference study can be found at: http://www.lexmark.com/sscg Regards, Rob Oglesbee EMC Engineer Lexmark International, Inc. rogle...@lexmark.com John Woodgate jmw%jmwa.demon.co...@interlock.lexmark.com on 06/15/2001 06:09:27 PM Please respond to John Woodgate jmw%jmwa.demon.co...@interlock.lexmark.com To: emc-pstc%majordomo.ieee@interlock.lexmark.com cc:(bcc: Rob A Oglesbee/Lex/Lexmark) Subject: Clock dithering 3b2a4fda.8c64c...@mediaone.net, David Heald davehe...@mediaone.net inimitably wrote: Con's? None that I can think of, but...I have seen somewhere (maybe here??) that the EU is considering new regulations for modulated clocks, but this is in the early stages, so use them now while you can get the most benefit from them. That's correct. Digital TV has proved rather badly susceptible to interference from dithered clocks. -- Regards, John Woodgate, OOO - Own Opinions Only. Phone +44 (0)1268 747839 Fax +44 (0)1268 777124. http://www.jmwa.demon.co.uk Why not call a vertically- applied manulo-pedally-operated quasi-planar chernozem-penetrating and excavating implement a SPADE? --- 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: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall, --- 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: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: Clock dithering
Hi Cyril, I have a very good (EMC-wise) experience with clock dithering. I started using the Spread Spectrum Clock Generation (SSCG) technique (patented by Lexmark) in 1995 when I worked for my previous company. We made printers and one of our main customers was IBM. They pushed us to use an SSCG chip (there was only one licenced vendor at that time) in order to get our impact printers pass class B emissions limits (CISPR22 and FCC part 15) with the required guardband (IBM is very strict on EMC). The SSCG worked great on reducing radiated emissions of clock and clock related signals (data, control etc.). We gained in the range of 4 to 10+ dBs (depending on the frequencies), plus we managed to make a big cost reduction by switching from 4-layer to 2-layer motherboards with the addition of SSCG and careful PCB layout (also note we had no shielding over our electronics). Before SSCG we were just failing class B by 2-3 dB (with 4-layer boards). After the SSCG chip was embedded in our motherboards we were safely belowe the limits. Also we passed class B on models with coax/twinax interface boards (typically class A products). The clock frequencies running on our electronics were in the range 20-35 MHz. Basically the SSCG slowly modulates the main clock oscillator frequency. Slowly means that the modulating periodis over many (several hundreds) clock cycles. The total amount of spread can be varied between a few tens of a percent to a few percents of the clock frequency (in our application we used +/-2.5% deviation). The higher the frequency deviation, the higher the amount of spreading and the consequent attenuation of peak emission levels because (as you say) energy is spread over the spectrum. So the minimum bandwidth of the spreaded clock (fundamental frequency) is wider than the standard 120 kHz resolution BW of EMI receivers specified for radiated emission tests. Also key is the wave shape of the modulating function of the clock signal. That's what the Lexmark patent covers. The patented waveshape is the so called Herschey kiss or Lexmark shape, that produces a FLAT spectral profile. By contrast, any sinusoidal or triangular modulating waveform spreads the spectrum of clock fundamental + harmonics but the resulting shape has two peaks (at the min/max frequencies of the spread). PLUS : big EMI reductions can be achieved without compromising system performance (clock speed/rise-fall times are unaltered). This does not mean that you don't need to control EMI. You just have many more chances to pass. Without optimized board layout we would have failed class B even with the dithered clock ! CONS: EMC-wise, increased chance of exciting resonant structures (associated with cables, PCB's geometries and other mechanical parts) because the emissions cover a wider frequency spectrum. Also the clock jitter tolerances must be thoroughly checked in order to adjust the amount of deviation allowed. In some applications (ex. clocks driving video signals as in scanners or laser printers) even the minimum clock jittering is not allowed so clock dithering cannot be used. As for interference to broadband receivers (like TV equipment) I remember a Lexmark study published a few years ago that showed no increased interference from modulated clocks vs unmodulated clocks (there was also a related discussion in this forum a while ago). I honestly don't know if anything new came up recently. Cheers, Paolo At 14:16 15/06/2001 -0400, Binnom, Cyril A wrote: Resending due to no subject listed in first e-mail. -Original Message- From: Binnom, Cyril A Sent: Friday, June 15, 2001 10:14 AM To: 'emc-pstc' Cc: McBride, James; Wismer, Sam; Massey, Doug C.; Davis, Brett A. Subject: Group, I am experiencing a EMI failure during testing and it has been isolated to the processor board in which the fundamental frequency is 66.6 MHz the 3rd harmonic that is our failure frequency is 199.8 MHz. We consulted the manufacturer of the board and they have come up with a spectrum spreading application for me to try. As I understand it, these type of applications work by essentially jittering the clock frequency in order to spread the energy over a wider band of frequencies. Thus the level at any particular frequency is reduced even though the overall amount of energy radiated is the same. The file they are sending me is a test application. If it works well enough to get the unit to pass test, they have the ability to enable the same application in the BIOS so it is always running. Does anyone have any experience using this type of application? Any opinions on its validity? To those that can attest to its validity, any pros or cons to the use of this application? Regards, Cyril A. Binnom Jr. EMI/EMC Approvals Engineer LXE, Inc. (770) 447-4224 Ext. 3240 (770) 447-6928 Fax binno...@lxe.com
Re: Clock dithering
Hi Cyril, I have a very good (EMC-wise) experience with clock dithering. I started using the Spread Spectrum Clock Generation (SSCG) technique (patented by Lexmark) in 1995 when I worked for my previous company. We made printers and one of our main customers was IBM. They pushed us to use an SSCG chip (there was only one licenced vendor at that time) in order to get our impact printers pass class B emissions limits (CISPR22 and FCC part 15) with the required guardband (IBM is very strict on EMC). The SSCG worked great on reducing radiated emissions of clock and clock related signals (data, control etc.). We gained in the range of 4 to 10+ dBs (depending on the frequencies), plus we managed to make a big cost reduction by switching from 4-layer to 2-layer motherboards with the addition of SSCG and careful PCB layout (also note we had no shielding over our electronics). Before SSCG we were just failing class B by 2-3 dB (with 4-layer boards). After the SSCG chip was embedded in our motherboards we were safely belowe the limits. Also we passed class B on models with coax/twinax interface boards (typically class A products). The clock frequencies running on our electronics were in the range 20-35 MHz. Basically the SSCG slowly modulates the main clock oscillator frequency. Slowly means that the modulating periodis over many (several hundreds) clock cycles. The total amount of spread can be varied between a few tens of a percent to a few percents of the clock frequency (in our application we used +/-2.5% deviation). The higher the frequency deviation, the higher the amount of spreading and the consequent attenuation of peak emission levels because (as you say) energy is spread over the spectrum. So the minimum bandwidth of the spreaded clock (fundamental frequency) is wider than the standard 120 kHz resolution BW of EMI receivers specified for radiated emission tests. Also key is the wave shape of the modulating function of the clock signal. That's what the Lexmark patent covers. The patented waveshape is the so called Herschey kiss or Lexmark shape, that produces a FLAT spectral profile. By contrast, any sinusoidal or triangular modulating waveform spreads the spectrum of clock fundamental + harmonics but the resulting shape has two peaks (at the min/max frequencies of the spread). PLUS : big EMI reductions can be achieved without compromising system performance (clock speed/rise-fall times are unaltered). This does not mean that you don't need to control EMI. You just have many more chances to pass. Without optimized board layout we would have failed class B even with the dithered clock ! CONS: EMC-wise, increased chance of exciting resonant structures (associated with cables, PCB's geometries and other mechanical parts) because the emissions cover a wider frequency spectrum. Also the clock jitter tolerances must be thoroughly checked in order to adjust the amount of deviation allowed. In some applications (ex. clocks driving video signals as in scanners or laser printers) even the minimum clock jittering is not allowed so clock dithering cannot be used. As for interference to broadband receivers (like TV equipment) I remember a Lexmark study published a few years ago that showed no increased interference from modulated clocks vs unmodulated clocks (there was also a related discussion in this forum a while ago). I honestly don't know if anything new came up recently. Cheers, Paolo At 14:16 15/06/2001 -0400, Binnom, Cyril A wrote: Resending due to no subject listed in first e-mail. -Original Message- From: Binnom, Cyril A Sent: Friday, June 15, 2001 10:14 AM To: 'emc-pstc' Cc: McBride, James; Wismer, Sam; Massey, Doug C.; Davis, Brett A. Subject: Group, I am experiencing a EMI failure during testing and it has been isolated to the processor board in which the fundamental frequency is 66.6 MHz the 3rd harmonic that is our failure frequency is 199.8 MHz. We consulted the manufacturer of the board and they have come up with a spectrum spreading application for me to try. As I understand it, these type of applications work by essentially jittering the clock frequency in order to spread the energy over a wider band of frequencies. Thus the level at any particular frequency is reduced even though the overall amount of energy radiated is the same. The file they are sending me is a test application. If it works well enough to get the unit to pass test, they have the ability to enable the same application in the BIOS so it is always running. Does anyone have any experience using this type of application? Any opinions on its validity? To those that can attest to its validity, any pros or cons to the use of this application? Regards, Cyril A. Binnom Jr. EMI/EMC Approvals Engineer LXE, Inc. (770) 447-4224 Ext. 3240 (770) 447-6928 Fax binno...@lxe.com
RE: Clock dithering
Hi Cyril, Have you tried reducing the current that comes out of the clock oscillator with a series-resistor ? ( a small ferrite may help also). Are you sure the clock line does only route on earth-plane covered areas on the board ? To determine if the harmonic comes from clock or other signals you may listen to the demodulated signal on your measuring receiver. Databus signal content modulated; CW signals (i.e. the clock) are silent carriers, slightly modulated with any supply humble (if any) and the emissions from data and/or address buses are modulated with a software determined signal. R/W and CE and ALE lines signal harmonics are silent too but are less dominant in the high frequency areas as they are most often lower in frequency as the clock. Good luck. Regards, Gert Gremmen, (Ing) ce-test, qualified testing === Web presence http://www.cetest.nl CE-shop http://www.cetest.nl/ce_shop.htm /-/ Compliance testing is our core business /-/ === -Original Message- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Binnom, Cyril A Sent: Friday, June 15, 2001 8:16 PM To: emc-pstc Cc: McBride, James; Davis, Brett A.; Wismer, Sam; Massey, Doug C. Subject: Clock dithering Resending due to no subject listed in first e-mail. -Original Message- From: Binnom, Cyril A Sent: Friday, June 15, 2001 10:14 AM To: 'emc-pstc' Cc: McBride, James; Wismer, Sam; Massey, Doug C.; Davis, Brett A. Subject: Group, I am experiencing a EMI failure during testing and it has been isolated to the processor board in which the fundamental frequency is 66.6 MHz the 3rd harmonic that is our failure frequency is 199.8 MHz. We consulted the manufacturer of the board and they have come up with a spectrum spreading application for me to try. As I understand it, these type of applications work by essentially jittering the clock frequency in order to spread the energy over a wider band of frequencies. Thus the level at any particular frequency is reduced even though the overall amount of energy radiated is the same. The file they are sending me is a test application. If it works well enough to get the unit to pass test, they have the ability to enable the same application in the BIOS so it is always running. Does anyone have any experience using this type of application? Any opinions on its validity? To those that can attest to its validity, any pros or cons to the use of this application? Regards, Cyril A. Binnom Jr. EMI/EMC Approvals Engineer LXE, Inc. (770) 447-4224 Ext. 3240 (770) 447-6928 Fax binno...@lxe.com --- 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: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall, attachment: Gert Gremmen.vcf
Clock dithering
3b2a4fda.8c64c...@mediaone.net, David Heald davehe...@mediaone.net inimitably wrote: Con's? None that I can think of, but...I have seen somewhere (maybe here??) that the EU is considering new regulations for modulated clocks, but this is in the early stages, so use them now while you can get the most benefit from them. That's correct. Digital TV has proved rather badly susceptible to interference from dithered clocks. -- Regards, John Woodgate, OOO - Own Opinions Only. Phone +44 (0)1268 747839 Fax +44 (0)1268 777124. http://www.jmwa.demon.co.uk Why not call a vertically- applied manulo-pedally-operated quasi-planar chernozem-penetrating and excavating implement a SPADE? --- 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: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Clock dithering
Resending due to no subject listed in first e-mail. -Original Message- From: Binnom, Cyril A Sent: Friday, June 15, 2001 10:14 AM To: 'emc-pstc' Cc: McBride, James; Wismer, Sam; Massey, Doug C.; Davis, Brett A. Subject: Group, I am experiencing a EMI failure during testing and it has been isolated to the processor board in which the fundamental frequency is 66.6 MHz the 3rd harmonic that is our failure frequency is 199.8 MHz. We consulted the manufacturer of the board and they have come up with a spectrum spreading application for me to try. As I understand it, these type of applications work by essentially jittering the clock frequency in order to spread the energy over a wider band of frequencies. Thus the level at any particular frequency is reduced even though the overall amount of energy radiated is the same. The file they are sending me is a test application. If it works well enough to get the unit to pass test, they have the ability to enable the same application in the BIOS so it is always running. Does anyone have any experience using this type of application? Any opinions on its validity? To those that can attest to its validity, any pros or cons to the use of this application? Regards, Cyril A. Binnom Jr. EMI/EMC Approvals Engineer LXE, Inc. (770) 447-4224 Ext. 3240 (770) 447-6928 Fax binno...@lxe.com --- 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: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
RE: Clock Dithering
Be careful. IBM (perhaps Lexmark now) holds a patent on certain aspects of this technology. Richard Woods -- From: Binnom, Cyril A [SMTP:binno...@ems-t.com] Sent: Friday, June 15, 2001 10:07 AM To: emc-pstc Cc: McBride, James; Wismer, Sam; Massey, Doug C.; Davis, Brett A. Group, I am experiencing a EMI failure during testing and it has been isolated to the processor board in which the fundamental frequency is 66.6 MHz the 3rd harmonic that is our failure frequency is 199.8 MHz. We consulted the manufacturer of the board and they have come up with a spectrum spreading application for me to try. As I understand it, these type of applications work by essentially jittering the clock frequency in order to spread the energy over a wider band of frequencies. Thus the level at any particular frequency is reduced even though the overall amount of energy radiated is the same. The file they are sending me is a test application. If it works well enough to get the unit to pass test, they have the ability to enable the same application in the BIOS so it is always running. Does anyone have any experience using this type of application? Any opinions on its validity? To those that can attest to its validity, any pros or cons to the use of this application? Regards, Cyril A. Binnom Jr. EMI/EMC Approvals Engineer LXE, Inc. (770) 447-4224 Ext. 3240 (770) 447-6928 Fax binno...@lxe.com --- 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: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall, --- 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: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
