Re: Relative merits of various logic families in not generating RFI
You might find the following website from Intel useful for this question. It'll give edge rates, input and output construction, ... >From there, you can make some conclusions. http://focus.ti.com/docs/logic/catalog/resources/selectionmatrix.jhtml?fileN ame=seltree_by_volt Regards, Doug McKean --- 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...@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://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
RE: Relative merits of various logic families in not generating RFI
I generally agree, although your comment that double sided PCBs are about to disappear is rather premature. Way over half of the PCBs manufactured in the world today are SINGLE sided (look in any piece of high volume electronics). Double sided PCBs still will be used in volume for many years to come. Many 4 layer PCBs are simply the result of lack of designer layout skill, or (in particular) a result of the use of autoplace and autoroute programs that would otherwise "ventilate" a 2-sided board with an absurd number of vias and serpentine tracks snaking willy-nilly all over the place. The "solution" to the need for actual skill in board layout is often to let the machine do it, and suffer the cost of more layers. Time to market is, it seems, more important than cost or quality. At least here in North America. Bob Wilson TIR Systems Ltd. Vancouver. -Original Message- From: Cortland Richmond [mailto:72146@compuserve.com] Sent: March 19, 2002 4:02 PM To: Robert Macy; ieee pstc list Subject: Re: Relative merits of various logic families in not generating RFI Probably, you won't get much choice. I've often found older, slower, quieter logic impractical or even uneconomical to use. It may be made only by one (thus off limits single-source) manufacturer, or it may be built using older, more expensive technologies and cost an arm and a leg. And it may happen one day that a manufacturer lets you know production is simply ending, and with no chance of an equivalent substitute. I am rather afraid that the best solution in these cases is to go with later, even if noisier devices -- and then design for them. Then too, if you use current devices, you may escape being blind-sided when they go to a smaller fabrication technology without letting you know. Even spting advertised an spe'd as an older device may in fact be a newer one. Who, after all, specifies devices by the fastest they go? It's always a minimum guaranteed speed. Yes, that means even MHz and KHz clock-rates with nanosecond transitions. You have to deal with it. Slew rate limiting is available, sometimes, built-in. If not, you have to add it externally. I've seen a 30 dB difference at 147 Mhz from a single 33 ohm resistor on a 1 Mhz clock. You have to be more careful with layout. You have to avoid inadvertent peaking networks - DON'T let anyone just throw HF bypasses willy-nilly on logic signals; you'd be AMAZED where the high frequencies can end up. And it means the end, really of 2-layer boards, at least as the old engineers know them. They have to be redesigned for RF, even if we weren't dealing with RF. But in the end, we get reliable boards, cheaper, that won't have to be replaced when the foundry discovers shorter-wavelength lithography. And your totem-pole short circuit? Yes, they know about that. Don't DO it. (grin) If you MUST have that kind of output, put a charge reservoir right at the device power pins, faster than a speeding junction, able to leap tall short circuits at a single bound, with enough charge to keep the transient local. But you already KNEW that! Cheers, 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...@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://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...@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://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
Re: Relative merits of various logic families in not generating RFI
Thank you for the prompt reply. Yes, faster rise time would lend the "signal" and its generation to create energetic RFI, but just in case there were some internal states that blew power out, or high impedance return paths through the substrate that caused all the outputs to dance in common mode horror would be examples of the "gotchas" I was looking for. - Robert - -Original Message- From: peter.pou...@invensys.com To: Robert Macy List-Post: emc-pstc@listserv.ieee.org Date: Tuesday, March 19, 2002 8:23 PM Subject: Re: Relative merits of various logic families in not generating RFI > >Robert, > >I suggest you have a look at the logic selection guides and application >notes from the major semiconductor logic manufacturers. > >As a starting point, check out page 13 to 15 of >http://www.fairchildsemi.com/ms/MS/MS-520.pdf for a rule-of-thumb guide on >how to assess EMI generation from the manufacturer's specs for the logic. > >Generally the slower the rise & fall time, the lower the emissions. > > > > > > >"Robert Macy" > To: >Sent by: cc: >owner-emc-pstc@majordomFax to: >o.ieee.org Subject: Relative merits of various logic families in not > generating RFI > >20/03/02 08:49 >Please respond to >"Robert Macy" > > > > > > > >Group, > >What are the relative merits of the various logic families HCT, HC, AC, ACT >with regard to generating RFI? > >I remember one time we replaced an HCT which made more noise than Schottky >TTL due to an internal overlap in the switching causing a power rail >"shorting" spike. > >I'm sure by now that most IC vendors have addressed the EMC problems >associated with poorly designed chips, but what's the status on these now? > >What's the order of preference? Which one's best? > > - 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 > > > >--- >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...@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://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...@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://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
Re: Relative merits of various logic families in not generating RFI
Probably, you won't get much choice. I've often found older, slower, quieter logic impractical or even uneconomical to use. It may be made only by one (thus off limits single-source) manufacturer, or it may be built using older, more expensive technologies and cost an arm and a leg. And it may happen one day that a manufacturer lets you know production is simply ending, and with no chance of an equivalent substitute. I am rather afraid that the best solution in these cases is to go with later, even if noisier devices -- and then design for them. Then too, if you use current devices, you may escape being blind-sided when they go to a smaller fabrication technology without letting you know. Even spting advertised an spe'd as an older device may in fact be a newer one. Who, after all, specifies devices by the fastest they go? It's always a minimum guaranteed speed. Yes, that means even MHz and KHz clock-rates with nanosecond transitions. You have to deal with it. Slew rate limiting is available, sometimes, built-in. If not, you have to add it externally. I've seen a 30 dB difference at 147 Mhz from a single 33 ohm resistor on a 1 Mhz clock. You have to be more careful with layout. You have to avoid inadvertent peaking networks - DON'T let anyone just throw HF bypasses willy-nilly on logic signals; you'd be AMAZED where the high frequencies can end up. And it means the end, really of 2-layer boards, at least as the old engineers know them. They have to be redesigned for RF, even if we weren't dealing with RF. But in the end, we get reliable boards, cheaper, that won't have to be replaced when the foundry discovers shorter-wavelength lithography. And your totem-pole short circuit? Yes, they know about that. Don't DO it. (grin) If you MUST have that kind of output, put a charge reservoir right at the device power pins, faster than a speeding junction, able to leap tall short circuits at a single bound, with enough charge to keep the transient local. But you already KNEW that! Cheers, 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...@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://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"