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: [email protected] [mailto:[email protected]] Sent: April 18, 2002 4:57 AM To: [email protected] 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: [email protected] [mailto:[email protected]] Sent: Wednesday, April 17, 2002 4:50 PM To: [email protected] 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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"
