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2005-01-24 by phlpcmicro
Hi All, Some micro's have terible radiation characteristics and are unsuitable to in radio modems with sensitive analogue frontends. ARM controllers are used in mobile phones etc. What characteristics do the LPC2000 have that lend thenselves radio modems / phones etc. ie: Sloped I/O output? Small LQFP packes.... Q Are there other EMC radiation factors to consider. Thanks in Advance. Joseph
2005-01-24 by tsvetanusunov
> Some micro's have terible radiation characteristics and are > unsuitable to in radio modems with sensitive analogue frontends. > > ARM controllers are used in mobile phones etc. > > What characteristics do the LPC2000 have that lend thenselves > radio modems / phones etc. this is very interesting topic, I can't find any info on this in LPC datasheets, but we found interesting feature: when LPC PLL is enabled if you have near by (1-2 meters) FM radio you can hear the sweep tone for about second. Our QC found this as they have radio on their desk where LPC boards are tested, no one of other microcontrollers we used make such interference to the radio. Best regards Tsvetan --- PCB prototypes for $26 at http://run.to/pcb (http://www.olimex.com/pcb) PCB any volume assembly (http://www.olimex.com/pcb/protoa.html) Development boards for ARM, AVR, PIC, and MSP430 (http://www.olimex.com/dev)
2005-01-24 by charlesgrenz
Hello, I am currently in the middle of a design for the 2138. EMI is very important in the design. Are you used multilayer boards? How about series resistors on all the lines (both input and output)? Do you have a resistor in series with the XTAL2 output? How about 100pF capacitors on all the I/O that goes off the board. What crystal frequency are you using? How about ferrites on all level transistion devices (like RS232 and such)? Thanks Charles --- In lpc2000@yahoogroups.com, "tsvetanusunov" <tusunov@m...> wrote:
> > > Some micro's have terible radiation characteristics and are > > unsuitable to in radio modems with sensitive analogue frontends. > > > > ARM controllers are used in mobile phones etc. > > > > What characteristics do the LPC2000 have that lend thenselves > > radio modems / phones etc. > > this is very interesting topic, I can't find any info on this in LPC > datasheets, but we found interesting feature: when LPC PLL is enabled > if you have near by (1-2 meters) FM radio you can hear the sweep tone > for about second. > Our QC found this as they have radio on their desk where LPC boards > are tested, no one of other microcontrollers we used make such > interference to the radio. > > Best regards > Tsvetan > --- > PCB prototypes for $26 at http://run.to/pcb > (http://www.olimex.com/pcb) > PCB any volume assembly (http://www.olimex.com/pcb/protoa.html) > Development boards for ARM, AVR, PIC, and MSP430 > (http://www.olimex.com/dev)
2005-01-24 by phlpcmicro
Hi Charles, Thanks for the suggestions - all relivant details.... However some cores do radiate abormally higher than others. Using an RF probe and a spectrum analyser over the package you CAN see the difference in radiation levels of noisy cores. Yes - there are methods to "sheild" noisy cores - but - why start with one in the 1st place. Philips did an app note 10~15years ago discussing the advantages of LQFP over DIP in relation to RF EMC radiaion characteristics. Regards Joseph --- In lpc2000@yahoogroups.com, "charlesgrenz" <charles.grenz@s...> wrote: > > Hello, > > I am currently in the middle of a design for the 2138. EMI is very > important in the design. > > Are you used multilayer boards? How about series resistors on all > the lines (both input and output)? Do you have a resistor in series > with the XTAL2 output? How about 100pF capacitors on all the I/O that > goes off the board. What crystal frequency are you using? How about > ferrites on all level transistion devices (like RS232 and such)? > > Thanks > Charles > > > --- In lpc2000@yahoogroups.com, "tsvetanusunov" <tusunov@m...> wrote: > > > > > Some micro's have terible radiation characteristics and are > > > unsuitable to in radio modems with sensitive analogue frontends. > > > > > > ARM controllers are used in mobile phones etc. > > > > > > What characteristics do the LPC2000 have that lend thenselves > > > radio modems / phones etc. > > > > this is very interesting topic, I can't find any info on this in LPC > > datasheets, but we found interesting feature: when LPC PLL is enabled > > if you have near by (1-2 meters) FM radio you can hear the sweep tone > > for about second. > > Our QC found this as they have radio on their desk where LPC boards
> > are tested, no one of other microcontrollers we used make such > > interference to the radio. > > > > Best regards > > Tsvetan > > --- > > PCB prototypes for $26 at http://run.to/pcb > > (http://www.olimex.com/pcb) > > PCB any volume assembly (http://www.olimex.com/pcb/protoa.html) > > Development boards for ARM, AVR, PIC, and MSP430 > > (http://www.olimex.com/dev)
2005-01-24 by charlesgrenz
Hi Joseph, To true. The real question is the LPC2138 one of those processors? If so, then we may have to box it. reagards, Charles --- In lpc2000@yahoogroups.com, "phlpcmicro" <joseph.goldburg@a...> wrote:
> > Hi Charles, > > Thanks for the suggestions - all relivant details.... However some > cores do radiate abormally higher than others. > > Using an RF probe and a spectrum analyser over the package you > CAN see the difference in radiation levels of noisy cores. > > Yes - there are methods to "sheild" noisy cores - but - why start > with one in the 1st place. > > Philips did an app note 10~15years ago discussing the advantages of > LQFP over DIP in relation to RF EMC radiaion characteristics. > > Regards > Joseph > > --- In lpc2000@yahoogroups.com, "charlesgrenz" <charles.grenz@s...> > wrote: > > > > Hello, > > > > I am currently in the middle of a design for the 2138. EMI is > very > > important in the design. > > > > Are you used multilayer boards? How about series resistors on > all > > the lines (both input and output)? Do you have a resistor in series > > with the XTAL2 output? How about 100pF capacitors on all the I/O > that > > goes off the board. What crystal frequency are you using? How about > > ferrites on all level transistion devices (like RS232 and such)? > > > > Thanks > > Charles > > > > > > --- In lpc2000@yahoogroups.com, "tsvetanusunov" <tusunov@m...> > wrote: > > > > > > > Some micro's have terible radiation characteristics and are > > > > unsuitable to in radio modems with sensitive analogue > frontends. > > > > > > > > ARM controllers are used in mobile phones etc. > > > > > > > > What characteristics do the LPC2000 have that lend thenselves > > > > radio modems / phones etc. > > > > > > this is very interesting topic, I can't find any info on this in > LPC > > > datasheets, but we found interesting feature: when LPC PLL is > enabled > > > if you have near by (1-2 meters) FM radio you can hear the sweep > tone > > > for about second. > > > Our QC found this as they have radio on their desk where LPC > boards > > > are tested, no one of other microcontrollers we used make such > > > interference to the radio. > > > > > > Best regards > > > Tsvetan > > > --- > > > PCB prototypes for $26 at http://run.to/pcb > > > (http://www.olimex.com/pcb) > > > PCB any volume assembly (http://www.olimex.com/pcb/protoa.html) > > > Development boards for ARM, AVR, PIC, and MSP430 > > > (http://www.olimex.com/dev)
2005-01-24 by tsvetanusunov
> Hello, > > I am currently in the middle of a design for the 2138. EMI is very > important in the design. > > Are you used multilayer boards? How about series resistors on all > the lines (both input and output)? Do you have a resistor in series > with the XTAL2 output? How about 100pF capacitors on all the I/O that > goes off the board. What crystal frequency are you using? How about > ferrites on all level transistion devices (like RS232 and such)? we use double side board, the problem is not in the crystal definitely as if PLL is not enabled this noise is not generated IIRC PLL works on 150-180 Mhz and the radio iterference is caused probably when PLL frequency pass through 108Mhz FM range Best regards Tsvetan --- PCB prototypes for $26 at http://run.to/pcb (http://www.olimex.com/pcb) PCB any volume assembly (http://www.olimex.com/pcb/protoa.html) Development boards for ARM, AVR, PIC, and MSP430 (http://www.olimex.com/dev)
2005-01-24 by Marko Pavlin (home)
It's not easy and there are only well known general rules. Use emi filters on high speed lines where possible (e.g. murata EMIFIL or similar), use ground shielding as much as possible. Avoid current flowing through shielding / ground planes. Add external shield if nothing else works. It's tough task. I had similar issues with smaller MCU (x51), which was solved with EMI filters and grounding with 4-layer PCB. M. tsvetanusunov wrote:
> > > Hello, > > > > I am currently in the middle of a design for the 2138. EMI is very > > important in the design. > > > > Are you used multilayer boards? How about series resistors on all > > the lines (both input and output)? Do you have a resistor in series > > with the XTAL2 output? How about 100pF capacitors on all the I/O > that > > goes off the board. What crystal frequency are you using? How about > > ferrites on all level transistion devices (like RS232 and such)? > > we use double side board, the problem is not in the crystal > definitely as if PLL is not enabled this noise is not generated > IIRC PLL works on 150-180 Mhz and the radio iterference is caused > probably when PLL frequency pass through 108Mhz FM range > > Best regards > Tsvetan > --- > PCB prototypes for $26 at http://run.to/pcb > (http://www.olimex.com/pcb) <http://www.olimex.com/pcb%29> > PCB any volume assembly (http://www.olimex.com/pcb/protoa.html) > <http://www.olimex.com/pcb/protoa.html%29> > Development boards for ARM, AVR, PIC, and MSP430 > (http://www.olimex.com/dev) <http://www.olimex.com/dev%29> > > > > > *Yahoo! Groups Links* > > * To visit your group on the web, go to: > http://groups.yahoo.com/group/lpc2000/ > > * To unsubscribe from this group, send an email to: > lpc2000-unsubscribe@yahoogroups.com > <mailto:lpc2000-unsubscribe@yahoogroups.com?subject=Unsubscribe> > > * Your use of Yahoo! Groups is subject to the Yahoo! Terms of > Service <http://docs.yahoo.com/info/terms/>. > >
2005-01-24 by microbit
Hi, > It's not easy and there are only well known general rules. Use emi > filters on high speed lines where possible (e.g. murata EMIFIL or > similar), use ground shielding as much as possible. Avoid current > flowing through shielding / ground planes. Add external shield if > nothing else works. It's tough task. I had similar issues with smaller > MCU (x51), which was solved with EMI filters and grounding with 4-layer PCB. > > M. > > tsvetanusunov wrote: > > we use double side board, the problem is not in the crystal > > definitely as if PLL is not enabled this noise is not generated > > IIRC PLL works on 150-180 Mhz and the radio iterference is caused > > probably when PLL frequency pass through 108Mhz FM range > > > > Best regards > > Tsvetan Your best shot I think is to try and isolate *where* the VCO signal is radiating, little chance it would radiate so strongly from the die ! Probably like Fvco/2 or thru some divider, it is leaking onto a Vdd line (or also Vss) and radiating from there. The best attack - if this signal should be a problem - is to bypass the proper track(s) as cose as possible to LPC to a solid GND, with a low inductance return path to the chip. Worst case you must find where the leakiest signlas are, and terminate them. Remember, at 100-200 MHz, 100 nF is a _very_ unsuitable bypass capacitor. Bypass caps should be as low as possible in value, I doubt that EMI filters will do much in this specific scenario, chances are that by the time the sigs get to the EMI filter, they've already been radiating galore anyway. They must be bypassed to GND, and their energy returned to LPC2000. Good luck, Kris [Non-text portions of this message have been removed]
2005-01-24 by Robert Wood
Sorry if someone's already mentioned it, but big, dobbering ground planes are the single most effective way I've found over the years for helping with this. There was one board that we struggled with for ages. I kept telling my boss we needed to go multi-layer. After wasting weeks of time and loads of money he finally agreed to trying a multi-layer board. Guess what? It passed no problem after that.
2005-01-24 by charlesgrenz
Yep, all those things we've done. Top of the board is 100% components and 99% signals and the bottom is 1% signal and 99% ground plane. Top of the board that is not used by traces is also a ground plane. Took a while to lay it out, but it's better then going multilayer. I also added CTS resistor arrays right next to the processor. They are great since they have 8 single resistors on 0.5mm centers. My capacitors on the other hand are at the connector locations which is about 3 inches away (100pF). I was just wondering if anyone of the LPC processors has EMI experience? We recently went throught this with the PXAG49 processors from Philips and found that the control lines are very noisy at 29.4xxMHz. regards, Charles --- In lpc2000@yahoogroups.com, Robert Wood <robert.wood@a...> wrote: > Sorry if someone's already mentioned it, but big, dobbering ground planes are > the single most effective way I've found over the years for helping with > this. > > There was one board that we struggled with for ages. I kept telling my boss we > needed to go multi-layer. After wasting weeks of time and loads of money he > finally agreed to trying a multi-layer board. Guess what? It passed no > problem after that.
2005-01-24 by Robert Wood
Hmmm, the only other thing I can suggest is looking at any long lines with high speed data on them (especially clock lines). I found that putting a resistor on long lines to round off the signal a bit and stop ringing really helped. Good luck, EMC's a real PITA! ------------------------------------------------------- Yep, all those things we've done. Top of the board is 100% components and 99% signals and the bottom is 1% signal and 99% ground plane. Top of the board that is not used by traces is also a ground plane. Took a while to lay it out, but it's better then going multilayer. I also added CTS resistor arrays right next to the processor. They are great since they have 8 single resistors on 0.5mm centers. My capacitors on the other hand are at the connector locations which is about 3 inches away (100pF). I was just wondering if anyone of the LPC processors has EMI experience? We recently went throught this with the PXAG49 processors from Philips and found that the control lines are very noisy at 29.4xxMHz. regards, Charles --- In lpc2000@yahoogroups.com, Robert Wood <robert.wood@a...> wrote: > Sorry if someone's already mentioned it, but big, dobbering ground planes are > the single most effective way I've found over the years for helping with > this. > > There was one board that we struggled with for ages. I kept telling my boss we > needed to go multi-layer. After wasting weeks of time and loads of money he > finally agreed to trying a multi-layer board. Guess what? It passed no > problem after that. Yahoo! Groups Links
2005-01-25 by tlarson_greatnotions
I have a board built with the LPC2214. This board has 3 LDO's, a rectifier bridge and two offboard connectors and is also two layer. It is one of the cleanest micros I have ever worked with. Without knowing more about the board (and other components) it would be very hard to say what will turn out to be the source of the interference. Throwing ferrites and cap's on the board can be counter productive without knowing the frequencies that are causing the problem. Do you have access to a spectrum analyzer? This is probably the most critical tool needed to diagnosis the problem. Also be aware, that even though your crystal is a lower frequency, edges internal to the part(s)will occur much faster, as well as harmonics of the fundamental frequency. One you have the frequencies and magnitude involved, then it's possible to formulate a strategy. I believe most all the obvious fixes have been discussed already, but I did not see anyone ask about your trace lengths, width and spacing, as well as are there traces that run along the edge of the board. Do you have any traces that change direction by more than 45 degrees? Are there any floating pins? make sure you drive or pull/up down any pin without a built in pull up/down. Are you using the A2D's? If so, is your analog ground separated from your digital ground? Just to illustrate how many different things that can go wrong in a complex system. I bring up my own "nightmare" board (non LPC cpu). In the end we were able to get all into compliance. There were several small boards and one machine casting that turned out to be a great ground plane for picking up and transmitting RF. All but one board was designed overseas, with parts purchased overseas. The main board with the CPU we designed here in the USA for our customer. The board drove several motors, Brushed-DC and a couple of Stepper Motors. Between the Brushed-DC motor and the power supply and one fast CPLD. To fix, we ended up changing the CPLD for a slower, competitive model. The motors and power supply could not be changed do to cost considerations (consumer white goods). The excess emissions were primarily broadband noise. And not a multiple of the crystal. Turns out the diode rectifier was the primary source of the broadband noise. Slight upgrade in parts here as well as a few well chosen capacitors in parallel and one ferrite bead solved most of the problems here. The rest had to do with long wires coming off the board to sensors and to the motors. Again choosing the right set of capacitors and inductors to filter the signals helped again. On a couple of stubborn traces, we changed the impedance. All in all, I think we ended up adding about $2 to the BOM. Tim Larson Great Notions BTW: Going to four layer did not help in this case... It cleaned up the lower frequencies, without much effect to the 700Mhz and beyond. Of course, YMMV > Yep, all those things we've done. Top of the board is 100% components > and 99% signals and the bottom is 1% signal and 99% ground plane. Top > of the board that is not used by traces is also a ground plane. Took a > while to lay it out, but it's better then going multilayer. I also > added CTS resistor arrays right next to the processor. They are great > since they have 8 single resistors on 0.5mm centers. My capacitors on > the other hand are at the connector locations which is about 3 inches > away (100pF). > > I was just wondering if anyone of the LPC processors has EMI > experience? We recently went throught this with the PXAG49 processors > from Philips and found that the control lines are very noisy at 29.4xxMHz.
> > regards, > Charles
2005-01-25 by microbit
Hi Tim, > knowing more about the board (and other components) it would be very > hard to say what will turn out to be the source of the interference. > Throwing ferrites and cap's on the board can be counter productive > without knowing the frequencies that are causing > the problem. Exactly, and I've seen this in practice - engineers going "the safe side" with 4 layers, and creating more bad than good. I'm not opposed to 4-layer per se, but for mixed a really careful layout with 2 layers often suffices if you know the quircks a bit. > Do you have access to a spectrum analyzer? This is > probably the most critical tool needed to diagnosis the problem. Indeed, with near field probe on speccie, you can tell a lot. > Also be aware, that even though your crystal is a lower frequency, > edges internal to the part(s)will occur much faster, as well as > harmonics of the fundamental frequency. One you have the > frequencies and magnitude involved, then it's possible to formulate > a strategy. Half indifferent, you'd have to drive the Xtal pretty hard to cause this, and premature aging/drifting/life time will be badly compromised. But nothing a good old series resistor won't fix, drive-wise. > I believe most all the obvious fixes have been discussed already, > but I did not see anyone ask about your trace lengths, width and > spacing, as well as are there traces that run along the edge of the > board. I rasied this issue a while ago on MSP430 group, and a heated discussion "fobbed" this all off, dismissing as "unnecessary" for digital < 30 MHz. Well you could have 4-8 MHz clock high slew rate bus signals on "long" tracks, that are completely the wrong impedance, terminate really poorly, and cause heaps of EMI. If this is mastered, it's almost a challenge/game to do something on 2 layers instead of 4 :-) > Do you have any traces that change direction by more than 45 > degrees? Another important one, along with NOT using vias on clock/crystal lines ! B rgds Kris [Non-text portions of this message have been removed]
2005-01-25 by charlesgrenz
Hi Tim and Kris, Thanks for the info. Already performed all those things. This particular board layout can have from 2 to 3 processors on it (LPC2138) and we have several experts in EMI in Australia looking the board over as a second opinion. We learned from other designs using the PXAG49 that separate crystals with no vias is a must. We get fundamental frequencies usually in the 110 to 150MHz range with a 29.4xxMHz clock when we had just 1 crystal line feeding the processors. We will find out soon enough when one of the designs with the new processors hits the testing range in the second week of February. In terms of equipment, no. So its testing at a lab. and us adding and subtracting parts. regards, Charles --- In lpc2000@yahoogroups.com, "microbit" <microbit@c...> wrote: > Hi Tim, > > > knowing more about the board (and other components) it would be very > > hard to say what will turn out to be the source of the interference. > > Throwing ferrites and cap's on the board can be counter productive > > without knowing the frequencies that are causing > > the problem. > > Exactly, and I've seen this in practice - engineers going "the safe side" with > 4 layers, and creating more bad than good. > I'm not opposed to 4-layer per se, but for mixed a really careful layout with > 2 layers often suffices if you know the quircks a bit. > > > Do you have access to a spectrum analyzer? This is > > probably the most critical tool needed to diagnosis the problem. > > Indeed, with near field probe on speccie, you can tell a lot. > > > Also be aware, that even though your crystal is a lower frequency, > > edges internal to the part(s)will occur much faster, as well as > > harmonics of the fundamental frequency. One you have the > > frequencies and magnitude involved, then it's possible to formulate > > a strategy. > > Half indifferent, you'd have to drive the Xtal pretty hard to cause this, > and premature aging/drifting/life time will be badly compromised. > But nothing a good old series resistor won't fix, drive-wise. > > > I believe most all the obvious fixes have been discussed already, > > but I did not see anyone ask about your trace lengths, width and > > spacing, as well as are there traces that run along the edge of the > > board. > > I rasied this issue a while ago on MSP430 group, and a heated discussion > "fobbed" this all off, dismissing as "unnecessary" for digital < 30 MHz. > Well you could have 4-8 MHz clock high slew rate bus signals on "long" > tracks, that are completely the wrong impedance, terminate really poorly, > and cause heaps of EMI. > If this is mastered, it's almost a challenge/game to do something on 2 layers > instead of 4 :-) > > > > Do you have any traces that change direction by more than 45 > > degrees? > > Another important one, along with NOT using vias on clock/crystal lines !
> > > B rgds > Kris > > > > [Non-text portions of this message have been removed]