RE: Decoupling - capacitor values
Tim, Here is the URL to Doug Smith's web page. http://www.emcesd.com/ Regards, Ahmad Fallah -Original Message- From: Wan Juang Foo [mailto:f...@np.edu.sg] Sent: Sunday, April 21, 2002 11:47 PM To: am...@westin-emission.no; ieee pstc list Subject: Re: Decoupling - capacitor values Amund, Thanks for the info, not having a copy of the standard, may I out of curiosity ask about the measurement bandwidth for the various bands? The way I see it, I suppose you have to test Radiated Emission down to 150 kHz which is very unusual because it will bring you into the near field. The units given are in E field units so am I missing on something here. BTY I take it that the units given is 'dBuV/m' and not 'dBmV/m'. Back to the original question of decoupling capacitors values. If 100 pF as a quick fix, proves to do no good, and AFAIK in all probability it may not work for all kinds of reason, then you may have to sniff around to identify the 'radiating element'. This can be done without a chamber and your probes need not be calibrated if it is 'only' used for debugging. As I have mention earlier, train your browser search engine on Douglas Smith or DIY 1 GHz probe and you may get something useful. Does anyone out there have the URLs? sincerely Tim Foo amund@westin-emission. no To: ieee pstc list emc-p...@ieee.org Sent by: cc: (bcc: Wan Juang Foo/ece/staff/npnet) owner-emc-pstc@majordo Subject: SV: Decoupling - capacitor values mo.ieee.org 04/20/02 03:45 PM Please respond to amund Tim, The standard is IEC/EN60945:1997, Maritime navigation and radio communication equipment and systems - General requirements- Methods of testing and required test results. Almost all ship classification societies as Lloyd's Register (LR), Germanischer Lloyd (GL), American Bureau of Shipping (ABS), Bureau Veritas (BV), Det Norske Veritas (DNV), Registro Italiano Navale (RINA), Korean Register of Shipping (KR), China Classification Society (CCS) refer to IEC60945. The limits are: 150kHz-300kHz80-52dBmV/m 300kHz - 30MHz 52-34dBmV/m 30M - 156MHz 54dBmV/m 156M -165MHz 24dBmV/m 165M - 1000MHz 54dBmV/m The 156M -165MHz band is used for marine radio communication, what's why they have stringent demands on radiated emission. Amund -Opprinnelig melding- Fra: Wan Juang Foo [mailto:f...@np.edu.sg] Sendt: 20. april 2002 06:30 Til: am...@westin-emission.no Kopi: ieee pstc list Emne: Re: Decoupling - capacitor values Amund, Cortland may be right, a chamber 'may not' be needed, high ambient considerations to be put aside for the moment, even if the emission is measured to be on the 24dBuV/m @ 3m, freq.band 155MHz-165MHz. I am just curious, what are the limits (or standards) are you trying to meet? From what I read here, is it CISPR22 (or EN 55022) or something like that (Class B) scaled back to 3 m? I note that it is about 20dB below FCC limits for class B (at 3m). If it is a single frequency line emission you can use a home made E or H field probe and work in the near field. Douglas Smith (who post frequently in this forum) have some good articles on DIY 1Ghz probes. You would need a E-field probe to 'sniff' out the CM portion of the emission and a H-field 'loop' to sniff out the offending loop before you can hug a 'return wire' to the offending signal line to cut the return loop down to size. I like to use the (thinisy, i.e. small gauge) wire-wraping wires for this. Good luck and hope that EMC don't always meant that it lead to Even More Coffee for the all nighter. Tim Foo Cortland Richmond 72146.373@compuserve. To: am...@westin-emission.no am...@westin-emission.no, ieee pstc com list emc-p...@ieee.org Sent by: cc: (bcc: Wan Juang Foo/ece/staff/npnet) owner-emc-pstc@majordo Subject: Decoupling - capacitor values (ESR, layout, CM filter) mo.ieee.org 04/20/02 05:39 AM Please respond to Cortland Richmond Cortland Richmond 72146@compuserve.com 04/20/02 05:39 AM Amund, You do not HAVE to be in a chamber to keep working on this. Since there is only one Vcc pin (which processor IS this? - be SURE there is only one Vcc pin; you may have an unfiltered, unconnected Vcc pin or two) you are limited in how many capacitors you can attach to it. This doesn't matter; if you filtered power, and got 7 dB, you've done
RE: Decoupling - capacitor values
Tim, Here is the URL to Doug Smith's web page. http://www.emcesd.com/ Regards, Ahmad Fallah -Original Message- From: Wan Juang Foo [mailto:f...@np.edu.sg] Sent: Sunday, April 21, 2002 11:47 PM To: am...@westin-emission.no; ieee pstc list Subject: Re: Decoupling - capacitor values Amund, Thanks for the info, not having a copy of the standard, may I out of curiosity ask about the measurement bandwidth for the various bands? The way I see it, I suppose you have to test Radiated Emission down to 150 kHz which is very unusual because it will bring you into the near field. The units given are in E field units so am I missing on something here. BTY I take it that the units given is 'dBuV/m' and not 'dBmV/m'. Back to the original question of decoupling capacitors values. If 100 pF as a quick fix, proves to do no good, and AFAIK in all probability it may not work for all kinds of reason, then you may have to sniff around to identify the 'radiating element'. This can be done without a chamber and your probes need not be calibrated if it is 'only' used for debugging. As I have mention earlier, train your browser search engine on Douglas Smith or DIY 1 GHz probe and you may get something useful. Does anyone out there have the URLs? sincerely Tim Foo amund@westin-emission. no To: ieee pstc list emc-p...@ieee.org Sent by: cc: (bcc: Wan Juang Foo/ece/staff/npnet) owner-emc-pstc@majordo Subject: SV: Decoupling - capacitor values mo.ieee.org 04/20/02 03:45 PM Please respond to amund Tim, The standard is IEC/EN60945:1997, Maritime navigation and radio communication equipment and systems - General requirements- Methods of testing and required test results. Almost all ship classification societies as Lloyd's Register (LR), Germanischer Lloyd (GL), American Bureau of Shipping (ABS), Bureau Veritas (BV), Det Norske Veritas (DNV), Registro Italiano Navale (RINA), Korean Register of Shipping (KR), China Classification Society (CCS) refer to IEC60945. The limits are: 150kHz-300kHz80-52dBmV/m 300kHz - 30MHz 52-34dBmV/m 30M - 156MHz 54dBmV/m 156M -165MHz 24dBmV/m 165M - 1000MHz 54dBmV/m The 156M -165MHz band is used for marine radio communication, what's why they have stringent demands on radiated emission. Amund -Opprinnelig melding- Fra: Wan Juang Foo [mailto:f...@np.edu.sg] Sendt: 20. april 2002 06:30 Til: am...@westin-emission.no Kopi: ieee pstc list Emne: Re: Decoupling - capacitor values Amund, Cortland may be right, a chamber 'may not' be needed, high ambient considerations to be put aside for the moment, even if the emission is measured to be on the 24dBuV/m @ 3m, freq.band 155MHz-165MHz. I am just curious, what are the limits (or standards) are you trying to meet? From what I read here, is it CISPR22 (or EN 55022) or something like that (Class B) scaled back to 3 m? I note that it is about 20dB below FCC limits for class B (at 3m). If it is a single frequency line emission you can use a home made E or H field probe and work in the near field. Douglas Smith (who post frequently in this forum) have some good articles on DIY 1Ghz probes. You would need a E-field probe to 'sniff' out the CM portion of the emission and a H-field 'loop' to sniff out the offending loop before you can hug a 'return wire' to the offending signal line to cut the return loop down to size. I like to use the (thinisy, i.e. small gauge) wire-wraping wires for this. Good luck and hope that EMC don't always meant that it lead to Even More Coffee for the all nighter. Tim Foo Cortland Richmond 72146.373@compuserve. To: am...@westin-emission.no am...@westin-emission.no, ieee pstc com list emc-p...@ieee.org Sent by: cc: (bcc: Wan Juang Foo/ece/staff/npnet) owner-emc-pstc@majordo Subject: Decoupling - capacitor values (ESR, layout, CM filter) mo.ieee.org 04/20/02 05:39 AM Please respond to Cortland Richmond Cortland Richmond 72146@compuserve.com 04/20/02 05:39 AM Amund, You do not HAVE to be in a chamber to keep working on this. Since there is only one Vcc pin (which processor IS this? - be SURE there is only one Vcc pin; you may have an unfiltered, unconnected Vcc pin or two) you are limited in how many capacitors you can attach to it. This doesn't matter; if you filtered power, and got 7 dB, you've done
SV: Decoupling - capacitor values
Hi Tim, Yes, it's dBuV/m. The bandwidths and limits : 150kHz-300kHz 9kHz 80-52dBuV/m 300kHz - 30MHz 9kHz 52-34dBuV/m 30M - 156MHz 120kHz 54dBuV/m 156M -165MHz 9kHz24dBuV/m 165M - 1000MHz 120kHz 54dBuV/m The standard is under revision and the band 150kHz-30MHz is not included in the new standard. We have now made some sniffers and we will search for 'hot spots'. Regards Amund -Opprinnelig melding- Fra: Wan Juang Foo [mailto:f...@np.edu.sg] Sendt: 22. april 2002 08:47 Til: am...@westin-emission.no; ieee pstc list Emne: Re: Decoupling - capacitor values Amund, Thanks for the info, not having a copy of the standard, may I out of curiosity ask about the measurement bandwidth for the various bands? The way I see it, I suppose you have to test Radiated Emission down to 150 kHz which is very unusual because it will bring you into the near field. The units given are in E field units so am I missing on something here. BTY I take it that the units given is 'dBuV/m' and not 'dBmV/m'. Back to the original question of decoupling capacitors values. If 100 pF as a quick fix, proves to do no good, and AFAIK in all probability it may not work for all kinds of reason, then you may have to sniff around to identify the 'radiating element'. This can be done without a chamber and your probes need not be calibrated if it is 'only' used for debugging. As I have mention earlier, train your browser search engine on Douglas Smith or DIY 1 GHz probe and you may get something useful. Does anyone out there have the URLs? sincerely Tim Foo amund@westin-emission. no To: ieee pstc list emc-p...@ieee.org Sent by: cc: (bcc: Wan Juang Foo/ece/staff/npnet) owner-emc-pstc@majordo Subject: SV: Decoupling - capacitor values mo.ieee.org 04/20/02 03:45 PM Please respond to amund Tim, The standard is IEC/EN60945:1997, Maritime navigation and radio communication equipment and systems - General requirements- Methods of testing and required test results. Almost all ship classification societies as Lloyd's Register (LR), Germanischer Lloyd (GL), American Bureau of Shipping (ABS), Bureau Veritas (BV), Det Norske Veritas (DNV), Registro Italiano Navale (RINA), Korean Register of Shipping (KR), China Classification Society (CCS) refer to IEC60945. The limits are: 150kHz-300kHz80-52dBmV/m 300kHz - 30MHz 52-34dBmV/m 30M - 156MHz 54dBmV/m 156M -165MHz 24dBmV/m 165M - 1000MHz 54dBmV/m The 156M -165MHz band is used for marine radio communication, what's why they have stringent demands on radiated emission. Amund -Opprinnelig melding- Fra: Wan Juang Foo [mailto:f...@np.edu.sg] Sendt: 20. april 2002 06:30 Til: am...@westin-emission.no Kopi: ieee pstc list Emne: Re: Decoupling - capacitor values Amund, Cortland may be right, a chamber 'may not' be needed, high ambient considerations to be put aside for the moment, even if the emission is measured to be on the 24dBuV/m @ 3m, freq.band 155MHz-165MHz. I am just curious, what are the limits (or standards) are you trying to meet? From what I read here, is it CISPR22 (or EN 55022) or something like that (Class B) scaled back to 3 m? I note that it is about 20dB below FCC limits for class B (at 3m). If it is a single frequency line emission you can use a home made E or H field probe and work in the near field. Douglas Smith (who post frequently in this forum) have some good articles on DIY 1Ghz probes. You would need a E-field probe to 'sniff' out the CM portion of the emission and a H-field 'loop' to sniff out the offending loop before you can hug a 'return wire' to the offending signal line to cut the return loop down to size. I like to use the (thinisy, i.e. small gauge) wire-wraping wires for this. Good luck and hope that EMC don't always meant that it lead to Even More Coffee for the all nighter. Tim Foo Cortland Richmond 72146.373@compuserve. To: am...@westin-emission.no am...@westin-emission.no, ieee pstc com list emc-p...@ieee.org Sent by: cc: (bcc: Wan Juang Foo/ece/staff/npnet) owner-emc-pstc@majordo Subject: Decoupling - capacitor values (ESR, layout, CM filter) mo.ieee.org 04/20/02 05:39 AM Please respond to Cortland Richmond Cortland Richmond 72146@compuserve.com 04/20/02 05:39 AM Amund, You do not HAVE to be in a chamber to keep working on this. Since there is only one Vcc pin (which processor IS this? - be SURE
Re: Decoupling - capacitor values
Amund, Thanks for the info, not having a copy of the standard, may I out of curiosity ask about the measurement bandwidth for the various bands? The way I see it, I suppose you have to test Radiated Emission down to 150 kHz which is very unusual because it will bring you into the near field. The units given are in E field units so am I missing on something here. BTY I take it that the units given is 'dBuV/m' and not 'dBmV/m'. Back to the original question of decoupling capacitors values. If 100 pF as a quick fix, proves to do no good, and AFAIK in all probability it may not work for all kinds of reason, then you may have to sniff around to identify the 'radiating element'. This can be done without a chamber and your probes need not be calibrated if it is 'only' used for debugging. As I have mention earlier, train your browser search engine on Douglas Smith or DIY 1 GHz probe and you may get something useful. Does anyone out there have the URLs? sincerely Tim Foo amund@westin-emission. no To: ieee pstc list emc-p...@ieee.org Sent by: cc: (bcc: Wan Juang Foo/ece/staff/npnet) owner-emc-pstc@majordo Subject: SV: Decoupling - capacitor values mo.ieee.org 04/20/02 03:45 PM Please respond to amund Tim, The standard is IEC/EN60945:1997, Maritime navigation and radio communication equipment and systems - General requirements- Methods of testing and required test results. Almost all ship classification societies as Lloyd's Register (LR), Germanischer Lloyd (GL), American Bureau of Shipping (ABS), Bureau Veritas (BV), Det Norske Veritas (DNV), Registro Italiano Navale (RINA), Korean Register of Shipping (KR), China Classification Society (CCS) refer to IEC60945. The limits are: 150kHz-300kHz80-52dBmV/m 300kHz - 30MHz 52-34dBmV/m 30M - 156MHz 54dBmV/m 156M -165MHz 24dBmV/m 165M - 1000MHz 54dBmV/m The 156M -165MHz band is used for marine radio communication, what's why they have stringent demands on radiated emission. Amund -Opprinnelig melding- Fra: Wan Juang Foo [mailto:f...@np.edu.sg] Sendt: 20. april 2002 06:30 Til: am...@westin-emission.no Kopi: ieee pstc list Emne: Re: Decoupling - capacitor values Amund, Cortland may be right, a chamber 'may not' be needed, high ambient considerations to be put aside for the moment, even if the emission is measured to be on the 24dBuV/m @ 3m, freq.band 155MHz-165MHz. I am just curious, what are the limits (or standards) are you trying to meet? From what I read here, is it CISPR22 (or EN 55022) or something like that (Class B) scaled back to 3 m? I note that it is about 20dB below FCC limits for class B (at 3m). If it is a single frequency line emission you can use a home made E or H field probe and work in the near field. Douglas Smith (who post frequently in this forum) have some good articles on DIY 1Ghz probes. You would need a E-field probe to 'sniff' out the CM portion of the emission and a H-field 'loop' to sniff out the offending loop before you can hug a 'return wire' to the offending signal line to cut the return loop down to size. I like to use the (thinisy, i.e. small gauge) wire-wraping wires for this. Good luck and hope that EMC don't always meant that it lead to Even More Coffee for the all nighter. Tim Foo Cortland Richmond 72146.373@compuserve. To: am...@westin-emission.no am...@westin-emission.no, ieee pstc com list emc-p...@ieee.org
SV: Decoupling - capacitor values
Tim, The standard is IEC/EN60945:1997, Maritime navigation and radio communication equipment and systems - General requirements- Methods of testing and required test results. Almost all ship classification societies as Lloyd's Register (LR), Germanischer Lloyd (GL), American Bureau of Shipping (ABS), Bureau Veritas (BV), Det Norske Veritas (DNV), Registro Italiano Navale (RINA), Korean Register of Shipping (KR), China Classification Society (CCS) refer to IEC60945. The limits are: 150kHz-300kHz 80-52dBmV/m 300kHz - 30MHz 52-34dBmV/m 30M - 156MHz54dBmV/m 156M -165MHz24dBmV/m 165M - 1000MHz 54dBmV/m The 156M -165MHz band is used for marine radio communication, what's why they have stringent demands on radiated emission. Amund -Opprinnelig melding- Fra: Wan Juang Foo [mailto:f...@np.edu.sg] Sendt: 20. april 2002 06:30 Til: am...@westin-emission.no Kopi: ieee pstc list Emne: Re: Decoupling - capacitor values Amund, Cortland may be right, a chamber 'may not' be needed, high ambient considerations to be put aside for the moment, even if the emission is measured to be on the 24dBuV/m @ 3m, freq.band 155MHz-165MHz. I am just curious, what are the limits (or standards) are you trying to meet? From what I read here, is it CISPR22 (or EN 55022) or something like that (Class B) scaled back to 3 m? I note that it is about 20dB below FCC limits for class B (at 3m). If it is a single frequency line emission you can use a home made E or H field probe and work in the near field. Douglas Smith (who post frequently in this forum) have some good articles on DIY 1Ghz probes. You would need a E-field probe to 'sniff' out the CM portion of the emission and a H-field 'loop' to sniff out the offending loop before you can hug a 'return wire' to the offending signal line to cut the return loop down to size. I like to use the (thinisy, i.e. small gauge) wire-wraping wires for this. Good luck and hope that EMC don't always meant that it lead to Even More Coffee for the all nighter. Tim Foo Cortland Richmond 72146.373@compuserve. To: am...@westin-emission.no am...@westin-emission.no, ieee pstc com list emc-p...@ieee.org Sent by: cc: (bcc: Wan Juang Foo/ece/staff/npnet) owner-emc-pstc@majordo Subject: Decoupling - capacitor values (ESR, layout, CM filter) mo.ieee.org 04/20/02 05:39 AM Please respond to Cortland Richmond Cortland Richmond 72146@compuserve.com 04/20/02 05:39 AM Amund, You do not HAVE to be in a chamber to keep working on this. Since there is only one Vcc pin (which processor IS this? - be SURE there is only one Vcc pin; you may have an unfiltered, unconnected Vcc pin or two) you are limited in how many capacitors you can attach to it. This doesn't matter; if you filtered power, and got 7 dB, you've done there what CAN be done there and should look look at other things. Troubleshoot the board. I too have thrown solutions at problems without knowing what exactly was wrong. It takes too long and costs too much. Find the source. A small 'scope probe, with the end taped over, makes a serviceable E-field probe. snip --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Decoupling - capacitor values
Amund, Cortland may be right, a chamber 'may not' be needed, high ambient considerations to be put aside for the moment, even if the emission is measured to be on the 24dBuV/m @ 3m, freq.band 155MHz-165MHz. I am just curious, what are the limits (or standards) are you trying to meet? From what I read here, is it CISPR22 (or EN 55022) or something like that (Class B) scaled back to 3 m? I note that it is about 20dB below FCC limits for class B (at 3m). If it is a single frequency line emission you can use a home made E or H field probe and work in the near field. Douglas Smith (who post frequently in this forum) have some good articles on DIY 1Ghz probes. You would need a E-field probe to 'sniff' out the CM portion of the emission and a H-field 'loop' to sniff out the offending loop before you can hug a 'return wire' to the offending signal line to cut the return loop down to size. I like to use the (thinisy, i.e. small gauge) wire-wraping wires for this. Good luck and hope that EMC don't always meant that it lead to Even More Coffee for the all nighter. Tim Foo Cortland Richmond 72146.373@compuserve. To: am...@westin-emission.no am...@westin-emission.no, ieee pstc com list emc-p...@ieee.org Sent by: cc: (bcc: Wan Juang Foo/ece/staff/npnet) owner-emc-pstc@majordo Subject: Decoupling - capacitor values (ESR, layout, CM filter) mo.ieee.org 04/20/02 05:39 AM Please respond to Cortland Richmond Cortland Richmond 72146@compuserve.com 04/20/02 05:39 AM Amund, You do not HAVE to be in a chamber to keep working on this. Since there is only one Vcc pin (which processor IS this? - be SURE there is only one Vcc pin; you may have an unfiltered, unconnected Vcc pin or two) you are limited in how many capacitors you can attach to it. This doesn't matter; if you filtered power, and got 7 dB, you've done there what CAN be done there and should look look at other things. Troubleshoot the board. I too have thrown solutions at problems without knowing what exactly was wrong. It takes too long and costs too much. Find the source. A small 'scope probe, with the end taped over, makes a serviceable E-field probe. snip --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: SV: Decoupling - capacitor values
Amund, You do not HAVE to be in a chamber to keep working on this. Since there is only one Vcc pin (which processor IS this? - be SURE there is only one Vcc pin; you may have an unfiltered, unconnected Vcc pin or two) you are limited in how many capacitors you can attach to it. This doesn't matter; if you filtered power, and got 7 dB, you've done there what CAN be done there and should look look at other things. Troubleshoot the board. I too have thrown solutions at problems without knowing what exactly was wrong. It takes too long and costs too much. Find the source. A small 'scope probe, with the end taped over, makes a serviceable E-field probe. And you can make a small (~5 mm) shielded loop out of subminiature coax by turning it back on itself. This will allow you to sweep the board for traces that have the most current at frequencies of concern. Once you know where they are, you will be able to deal with how it is coupling. I once used such a small loop to show where clock traces went -- through a nickel-paint shielded chassis. It surprised the folks I showed it to, and got the attention of the coating people as well. We'd been throwing solutions at the product for some time without effect. If a fix doesn't work, you did not put it where it COULD work. I've done this too many times to be proud of the horror stories, but I am alert to it now! Find the problem. Good luck! Cortland --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
SV: Decoupling - capacitor values
We spend a few hours in an EMC lab today, trying to suppress the unwanted 162MHz signal. We had to suppress it approximate 5 dB. There existed 100nF caps on the Vcc pins but the caps lead was long. We went on decoupling (1nF and 100nF) with short leads (not OMF caps) on the uP Vcc pin and on other IC power pins. We reduced the 162MHz signal by 7 dB. Thereafter we went on trying to kill some loop areas, but we only won 1-2 dB. When we were kicked out, time was up We would like to check the use of ferrite beads on +5V trace and the tantalum capacitor during current switching, maybe next time. Thanks for ALL ideas on this subject. Amund, Oslo/Norway -Opprinnelig melding- Fra: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]Pa vegne av Cortland Richmond Sendt: 19. april 2002 15:31 Til: richwo...@tycoint.com; ieee pstc list Emne: RE: Decoupling - capacitor values I have found removal of inductance at power pins often REDUCES emissions. When this is so, it is because designers who put it in did not insure there was sufficient local capacitance to hold up Vcc while the isolated device switches. This has happened to me often enough that when I see series inductance at a device power pin, I question the designer, and persuade him to add capacitance or remove the inductor (sometimes both - grin). Power filtering can be estimated based on data sheets and measurements on sketch boards. But designers need to do at LEAST that much, and they often do not. I consider this important enough that when I interview engineer candidates (that's when I am not one myself!) I ask them to show me how they will calculate the capacitance needed to support a digital device driving some number of loads. This is not rocket science, but many have not thought of it at all. Cortland Richmond --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Decoupling - capacitor values
Dear Bob Just a point - smaller is not always better. AVX and maybe some others make 0612 capacitors for decoupling. They are the same size as the normal 1206 size but are metallised along their long edges. This reduces their ESL considerably, to the extent that (according to manufacturer's data I have seen) their ESR performance can be better than the same value in an 0805 style, or even in an 0603. I haven't had the opportunity to try any 0612s out yet. Has anyone any real comparative data on these decaps? All the very best! Keith Armstrong Cherry Clough Consultants www.cherryclough.com In a message dated 18/04/02 00:11:45 GMT Daylight Time, bh...@ma.ultranet.com writes: Subj:RE: Decoupling - capacitor values Date:18/04/02 00:11:45 GMT Daylight Time From:A HREF=mailto:bh...@ma.ultranet.com;bh...@ma.ultranet.com/A To:A HREF=mailto:am...@westin-emission.no;am...@westin-emission.no/A, A HREF=mailto:emc-p...@majordomo.ieee.org;emc-p...@majordomo.ieee.org/A Sent from the Internet In selecting that 820 pF capacitor, check the specifications. The self-resonance frequency is a function of the capacitor value and the physical size. Chip caps that are smaller physically will have a have a self-resonant frequency higher than the same value cap with larger physical dimensions. Regards, Bob Howland dBH Consulting -Original Message- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of am...@westin-emission.no Sent: Wednesday, April 17, 2002 4:50 PM To: emc-p...@majordomo.ieee.org Subject: Decoupling - capacitor values A microprocessor is driven by a 12MHz clock. The 5V Vcc-pin is decoupled by a 100nF capacitor with a few mm leads. We can observe an unwanted 156MHz signal on the 5V line, maybe 13th harmonic of 12MHz. We will try to suppress/decouple this 156MHz signal. Suggestion: Insert a SMD ceramic capacitor of value 820pF in parallel with the existing 100nF. The reason for the low value 820pF is because the capacitor self-resonance frequency is approximate 180MHz, and I believe it is important to choose a Cap value with a resonance frequency higher than the frequency we would like to decouple. Does it make sense? Best regards Amund Westin, Oslo/Norway
RE: Decoupling - capacitor values
I have found removal of inductance at power pins often REDUCES emissions. When this is so, it is because designers who put it in did not insure there was sufficient local capacitance to hold up Vcc while the isolated device switches. This has happened to me often enough that when I see series inductance at a device power pin, I question the designer, and persuade him to add capacitance or remove the inductor (sometimes both - grin). Power filtering can be estimated based on data sheets and measurements on sketch boards. But designers need to do at LEAST that much, and they often do not. I consider this important enough that when I interview engineer candidates (that's when I am not one myself!) I ask them to show me how they will calculate the capacitance needed to support a digital device driving some number of loads. This is not rocket science, but many have not thought of it at all. Cortland Richmond --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: Decoupling - capacitor values
I am not advocating placing an inductor in series with the cap. Circulating loop currents in the power and ground traces will create emissions, but those currents can be reduced by use of bypass capacitors or an L-type filter (capacitor and inductor) in the 5V trace. At least, according to accepted theory. Richard Woods Sensormatic Electronics Tyco International -Original Message- From: Robert Wilson [mailto:robert_wil...@tirsys.com] Sent: Thursday, April 18, 2002 11:57 AM To: emc-p...@majordomo.ieee.org Subject: RE: Decoupling - capacitor values Not sure this would be a cure in this instance. This is effectively the same as adding a lossy inductor in series with the cap, which would tend to negate any benefits of using a cap with lower self inductance. Bob Wilson TIR Systems Ltd. Vancouver. -Original Message- From: richwo...@tycoint.com [mailto:richwo...@tycoint.com] Sent: April 18, 2002 4:57 AM To: emc-p...@majordomo.ieee.org Subject: RE: Decoupling - capacitor values Consider adding a ferrite bead in the 5V trace to the microprocessor. Richard Woods Sensormatic Electronics Tyco International -Original Message- From: am...@westin-emission.no [mailto:am...@westin-emission.no] Sent: Wednesday, April 17, 2002 4:50 PM To: emc-p...@majordomo.ieee.org Subject: Decoupling - capacitor values A microprocessor is driven by a 12MHz clock. The 5V Vcc-pin is decoupled by a 100nF capacitor with a few mm leads. We can observe an unwanted 156MHz signal on the 5V line, maybe 13th harmonic of 12MHz. We will try to suppress/decouple this 156MHz signal. Suggestion: Insert a SMD ceramic capacitor of value 820pF in parallel with the existing 100nF. The reason for the low value 820pF is because the capacitor self-resonance frequency is approximate 180MHz, and I believe it is important to choose a Cap value with a resonance frequency higher than the frequency we would like to decouple. Does it make sense? Best regards Amund Westin, Oslo/Norway --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- 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: davehe...@attbi.com 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
Re: SV: Decoupling - capacitor values
Amund, I have encountered similar problems with similarly designed boards. In one interesting case, I was able to get 30 dB reduction in radiated EMI by adding a series resistor to a (fairly short) low-frequency clock line. Due to use of modern devices, its rise and fall times were less than a nanosecond. The resistor limits current in the trace, reducing also the power required of the clock driver, and slows the slew rate. Improving power distribution also made a large difference; power and ground planes were added to the board and also improved signal integrity. But I prefer to first attack problems such as yours with better decoupling. One all-nighter long ago resulted in my soldering SMD capacitors directly across pins on a device package, 1208 for the pins farther from grounds, and 805's for ones closer to grounds. This made a considerable difference but was greeted by my boss with, YOU DID WHAT?! It DID open him up to the possibility of less drastic measures previously ruled out. The suggestions you've been given about power routing are on target. If you distribute power and its return as a transmission line themselves, you can at least control where noise on it goes, reducing THAT loop size, and filters on this line may be expected to work predictably. However, do remember that once you put noise on silicon, it gets onto everything else. You must satisfy the need for current at each device: enough capacitance, able to supply current quickly enough, at enough power and ground pin pairs. If you allow device Vcc/ground to be periodically modulated by device switching current, the noise produced will be present on every trace leaving the device and you will not make it go away. That's why I first look for good decoupling when doing schematic and layout reviews. THEN I look for routing missteps and inadvertent loops. Others may prefer to approach things in a different order; that's just my preference. But it works for me. Good luck! Cortland Richmond --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: Decoupling - capacitor values
Not sure this would be a cure in this instance. This is effectively the same as adding a lossy inductor in series with the cap, which would tend to negate any benefits of using a cap with lower self inductance. Bob Wilson TIR Systems Ltd. Vancouver. -Original Message- From: richwo...@tycoint.com [mailto:richwo...@tycoint.com] Sent: April 18, 2002 4:57 AM To: emc-p...@majordomo.ieee.org Subject: RE: Decoupling - capacitor values Consider adding a ferrite bead in the 5V trace to the microprocessor. Richard Woods Sensormatic Electronics Tyco International -Original Message- From: am...@westin-emission.no [mailto:am...@westin-emission.no] Sent: Wednesday, April 17, 2002 4:50 PM To: emc-p...@majordomo.ieee.org Subject: Decoupling - capacitor values A microprocessor is driven by a 12MHz clock. The 5V Vcc-pin is decoupled by a 100nF capacitor with a few mm leads. We can observe an unwanted 156MHz signal on the 5V line, maybe 13th harmonic of 12MHz. We will try to suppress/decouple this 156MHz signal. Suggestion: Insert a SMD ceramic capacitor of value 820pF in parallel with the existing 100nF. The reason for the low value 820pF is because the capacitor self-resonance frequency is approximate 180MHz, and I believe it is important to choose a Cap value with a resonance frequency higher than the frequency we would like to decouple. Does it make sense? Best regards Amund Westin, Oslo/Norway --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Decoupling - capacitor values
Years ago in ultrasonic echocardiography instrumentation (the ultrasonics analog is a wide band receiver listening in the 1-10MHz region down to less than 10uV, so the digital had better be quiet!) which used a bit slice architecture system containing Schottky logic with a clock of 20MHz for controlling and manipulating images in real time. We're talking 4 PCBs using 10 amps each board, so you can see the opportunity for generating horrific noise that would be injected into the analog section. We found that power distributed using a tree type of distribution where traces were thick then thinner out at the extremities *and* +5 was over top of GND made for the quietest distribution. The tree technique worked much quieter than the recommended grid structure where +5 distribution on bottom layer goes one direction with GND distribution on the top going the other. This structure made little tiny loop antennas that radiated energy all around inside the box and was awful! But easier for the layout people. - Robert - Robert A. Macy, PEm...@california.com 408 286 3985 fx 408 297 9121 AJM International Electronics Consultants 619 North First St, San Jose, CA 95112 -Original Message- From: am...@westin-emission.no am...@westin-emission.no To: ieee pstc list emc-p...@ieee.org List-Post: emc-pstc@listserv.ieee.org Date: Thursday, April 18, 2002 12:49 AM Subject: SV: Decoupling - capacitor values Correct, the picture is complex. The PCB is 2-layer with signal, 5V-power and 0V-ref lines routed on both sides. There is no ground layer/plane. There must be a large number of RF current loops because the 0V-lines are routed up and down and around. Beside trying to achieve a good decoupling I assume that reducing loop area is the most important. Amund -Opprinnelig melding- Fra: Cortland Richmond [mailto:72146@compuserve.com] Sendt: 18. april 2002 00:54 Til: am...@westin-emission.no; ieee pstc list Emne: Re: Decoupling - capacitor values Yes, it makes sense. But the goal here is preventing or reducing Vcc drop during the time the microprocessor is switching. You need not only low reactance, but *also* enough capacitance to supply the current needed _while it is switching_. You have not given enough information here to tell if 820pF is sufficient. Regards, Cortland Richmond Amund Westin wrote: Insert a SMD ceramic capacitor of value 820pF in parallel with the existing 100nF. The reason for the low value 820pF is because the capacitor self-resonance frequency is approximate 180MHz, and I believe it is important to choose a Cap value with a resonance frequency higher than the frequency we would like to decouple. Does it make sense? --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: Decoupling - capacitor values
Hmmm. I've read a couple of other replies on this...good suggestions. I have also read your re-replies which suggest that you have a two layer planeless board. I understand that you are trying to get an unwanted 156Mhz off of the 5V line. A couple of thoughts come to mind. First 156Mhz would need quite a long radiator to radiate efficiently. 156Mhz is approximately a 2m wavelength. One tenth of this wavelength is still 20cm. Why does this matter? Well, I like the decoupling cap idea. Another suggestion might be to add a large bulk decoupling cap such as a 10uF tantalum (you may have to experiment with the value) right at the chip. Then cut the 5V trace (on the other side of this cap) and put a good, strong ferrite (I like PREM SPG-104's myself) in the 5V trace. The bulk cap will serve as a local bulk storage device, the ferrite will help to isolate the harmonics to the area immediately around the processor. If you can keep the harmonics within a small area, perhaps they won't radiate very effectively andmaybe your product can live for another few months. Here's hoping that you find a solution. Chris Maxwell | Design Engineer - Optical Division email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | -Original Message- From: am...@westin-emission.no [SMTP:am...@westin-emission.no] Sent: Wednesday, April 17, 2002 4:50 PM To: emc-p...@majordomo.ieee.org Subject: Decoupling - capacitor values A microprocessor is driven by a 12MHz clock. The 5V Vcc-pin is decoupled by a 100nF capacitor with a few mm leads. We can observe an unwanted 156MHz signal on the 5V line, maybe 13th harmonic of 12MHz. We will try to suppress/decouple this 156MHz signal. Suggestion: Insert a SMD ceramic capacitor of value 820pF in parallel with the existing 100nF. The reason for the low value 820pF is because the capacitor self-resonance frequency is approximate 180MHz, and I believe it is important to choose a Cap value with a resonance frequency higher than the frequency we would like to decouple. Does it make sense? Best regards Amund Westin, Oslo/Norway --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: Decoupling - capacitor values
Consider adding a ferrite bead in the 5V trace to the microprocessor. Richard Woods Sensormatic Electronics Tyco International -Original Message- From: am...@westin-emission.no [mailto:am...@westin-emission.no] Sent: Wednesday, April 17, 2002 4:50 PM To: emc-p...@majordomo.ieee.org Subject: Decoupling - capacitor values A microprocessor is driven by a 12MHz clock. The 5V Vcc-pin is decoupled by a 100nF capacitor with a few mm leads. We can observe an unwanted 156MHz signal on the 5V line, maybe 13th harmonic of 12MHz. We will try to suppress/decouple this 156MHz signal. Suggestion: Insert a SMD ceramic capacitor of value 820pF in parallel with the existing 100nF. The reason for the low value 820pF is because the capacitor self-resonance frequency is approximate 180MHz, and I believe it is important to choose a Cap value with a resonance frequency higher than the frequency we would like to decouple. Does it make sense? Best regards Amund Westin, Oslo/Norway --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
SV: Decoupling - capacitor values
Interesting articles on your web-site, Tim. BTW, how about just using a 100 pF capacitor with the 'leads' hugging close to the microprocessor package There's a mile from the Vcc pin to ground, that's another problem. No ground plane, only ground traces which is routed around on the PCB. This product is soon leaving this world (it's an old product), but we are trying to let it exits a few more months before a new version is released. New emission requirements (24dBuV/m @ 3m, freq.band 155MHz-165MHz) might let it die very soon Amund -Opprinnelig melding- Fra: Wan Juang Foo [mailto:f...@np.edu.sg] Sendt: 18. april 2002 10:01 Til: am...@westin-emission.no; emc-p...@majordomo.ieee.org Emne: Re: Decoupling - capacitor values Amund, In the absence of any layout information that can evaluate the loop inductances, I suggest you read what I wrote about placing two capacitor in parallel which can be found on Chapter 3 of my thesis. A link is available in: http://www.geocities.com/timfoo6143/index.html BTW, how about just using a 100 pF capacitor with the 'leads' hugging close to the microprocessor package. i.e. assuming you are using a leaded capacitor (on say a QFP). :-) Tim Foo --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Decoupling - capacitor values
Amund, In the absence of any layout information that can evaluate the loop inductances, I suggest you read what I wrote about placing two capacitor in parallel which can be found on Chapter 3 of my thesis. A link is available in: http://www.geocities.com/timfoo6143/index.html BTW, how about just using a 100 pF capacitor with the 'leads' hugging close to the microprocessor package. i.e. assuming you are using a leaded capacitor (on say a QFP). :-) Tim Foo amund@westin-emission. no To: emc-p...@majordomo.ieee.org Sent by: cc: (bcc: Wan Juang Foo/ece/staff/npnet) owner-emc-pstc@majordo Subject: Decoupling - capacitor values mo.ieee.org 04/18/02 04:49 AM Please respond to amund A microprocessor is driven by a 12MHz clock. The 5V Vcc-pin is decoupled by a 100nF capacitor with a few mm leads. We can observe an unwanted 156MHz signal on the 5V line, maybe 13th harmonic of 12MHz. We will try to suppress/decouple this 156MHz signal. Suggestion: Insert a SMD ceramic capacitor of value 820pF in parallel with the existing 100nF. The reason for the low value 820pF is because the capacitor self-resonance frequency is approximate 180MHz, and I believe it is important to choose a Cap value with a resonance frequency higher than the frequency we would like to decouple. Does it make sense? Best regards Amund Westin, Oslo/Norway --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
SV: Decoupling - capacitor values
Correct, the picture is complex. The PCB is 2-layer with signal, 5V-power and 0V-ref lines routed on both sides. There is no ground layer/plane. There must be a large number of RF current loops because the 0V-lines are routed up and down and around. Beside trying to achieve a good decoupling I assume that reducing loop area is the most important. Amund -Opprinnelig melding- Fra: Cortland Richmond [mailto:72146@compuserve.com] Sendt: 18. april 2002 00:54 Til: am...@westin-emission.no; ieee pstc list Emne: Re: Decoupling - capacitor values Yes, it makes sense. But the goal here is preventing or reducing Vcc drop during the time the microprocessor is switching. You need not only low reactance, but *also* enough capacitance to supply the current needed _while it is switching_. You have not given enough information here to tell if 820pF is sufficient. Regards, Cortland Richmond Amund Westin wrote: Insert a SMD ceramic capacitor of value 820pF in parallel with the existing 100nF. The reason for the low value 820pF is because the capacitor self-resonance frequency is approximate 180MHz, and I believe it is important to choose a Cap value with a resonance frequency higher than the frequency we would like to decouple. Does it make sense? --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Decoupling - capacitor values
I read in !emc-pstc that Robert Wilson robert_wil...@tirsys.com wrote (in 3FF57405336C9B4C976A1819F860A2560F696F@xng_tirsys.TIRSYS.COM) about 'Decoupling - capacitor values', on Wed, 17 Apr 2002: The main reason is that the ESR of the larger cap begins to rise to unacceptable levels as frequency rises (chiefly due to its self inductance). ESR is something quite separate from self-inductance. The effect of the inductance is to *reduce* the total impedance of the capacitor to just the ESR at the self-resonance frequency and to *increase* it above that frequency. The ESR may itself be frequency-dependent because it includes dielectric losses (in the simple CRL series model of the capacitor). -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: Decoupling - capacitor values
Capacitors can continue to function quite well above their self resonance. You should not be worrying about choosing a cap based on self resonance per se. However, it is standard practice to parallel a 0,1 uF bulk bypass cap with a much smaller NP0 or C0G type (say 470 pF or 1 nF), especially in RF work. (I'm not sure why you chose the rather odd value of 820 pF) The reason has little to do with self resonance directly. The main reason is that the ESR of the larger cap begins to rise to unacceptable levels as frequency rises (chiefly due to its self inductance). The low-value NP0 cap has much lower self inductance, hence it continues to function as a true capacitor at higher frequencies. As for as specifically using an SMT cap is concerned, you can do this if you want, but it isn't a requirement. The frequency you are concerned with (the low hundreds of MHz) is still pretty low frequency. Normal leaded devices will work just fine provided you ensure the board layout is done properly (which you need to do anyway), that the cap is inserted straight into the PCB, and that the leads are not formed so it stands above the PCB. Bob Wilson TIR Systems Ltd. Vancouver. -Original Message- From: am...@westin-emission.no [mailto:am...@westin-emission.no] Sent: April 17, 2002 1:50 PM To: emc-p...@majordomo.ieee.org Subject: Decoupling - capacitor values A microprocessor is driven by a 12MHz clock. The 5V Vcc-pin is decoupled by a 100nF capacitor with a few mm leads. We can observe an unwanted 156MHz signal on the 5V line, maybe 13th harmonic of 12MHz. We will try to suppress/decouple this 156MHz signal. Suggestion: Insert a SMD ceramic capacitor of value 820pF in parallel with the existing 100nF. The reason for the low value 820pF is because the capacitor self-resonance frequency is approximate 180MHz, and I believe it is important to choose a Cap value with a resonance frequency higher than the frequency we would like to decouple. Does it make sense? Best regards Amund Westin, Oslo/Norway --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Decoupling - capacitor values
Yes, it makes sense. But the goal here is preventing or reducing Vcc drop during the time the microprocessor is switching. You need not only low reactance, but *also* enough capacitance to supply the current needed _while it is switching_. You have not given enough information here to tell if 820pF is sufficient. Regards, Cortland Richmond Amund Westin wrote: Insert a SMD ceramic capacitor of value 820pF in parallel with the existing 100nF. The reason for the low value 820pF is because the capacitor self-resonance frequency is approximate 180MHz, and I believe it is important to choose a Cap value with a resonance frequency higher than the frequency we would like to decouple. Does it make sense? --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Decoupling - capacitor values
A microprocessor is driven by a 12MHz clock. The 5V Vcc-pin is decoupled by a 100nF capacitor with a few mm leads. We can observe an unwanted 156MHz signal on the 5V line, maybe 13th harmonic of 12MHz. We will try to suppress/decouple this 156MHz signal. Suggestion: Insert a SMD ceramic capacitor of value 820pF in parallel with the existing 100nF. The reason for the low value 820pF is because the capacitor self-resonance frequency is approximate 180MHz, and I believe it is important to choose a Cap value with a resonance frequency higher than the frequency we would like to decouple. Does it make sense? Best regards Amund Westin, Oslo/Norway --- 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: davehe...@attbi.com 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://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
