Hi Cortland, What you say makes sense to me. Thanks for your feedback. I need to take another look at the decoupling.
Regards Ravinder Ajmani HGST, a Western Digital company 5601 Great Oaks Pkwy San Jose, CA 95119-1003 [email protected] CR <[email protected]> 03/22/2014 11:19 PM Please respond to [email protected] To [email protected] cc Subject Re: [PSES] Higher EMI from ASIC built with new process Ravinder, While an output waveform may be limited "in firmware"* that does not mean it is limited on the chip; my experience is that a major cause of EMI when using faster devices as replacements is that the current the replacement draws due to non-limited internal functions is switched much faster than the original, so that, due to trace or package inductance, the board's charge storage capacitance may not supply current fast enough to prevent Vcc and ground bounce -- which appears on non-risetime-limited I/O, power, control, BITE and power pins/balls. There can also be radiated coupling to non-filtered or non-shielded conductors both on the PWB and off. *(Possibly by switching in one of several output buffers with different series resistors) Cortland Richmond On 3/22/2014 9:38 PM, [email protected] wrote: I am comparing EMI from two ASICs. Both have identical rise/fall times and signal amplitude. Yet the ASIC built with the later technology not only has significantly higher radiated emissions, but also shows much broader noise spectrum. PCB stackup and layout is identical. Please help me understand what other factors can be responsible for this anomaly. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to < [email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
