|
|
|
|
|
||||||||||||||||||||||||||||||||||
| Specifications | How can I improve system performance when using multiple clocks? Analog Devices : Rarely Asked Questions \Watch for Those Multiple Clocking Edges!\ Rarely Asked Questions, RAQs, Multiple Clocking Edges, system performance, Rob Reeder Analog Devices |
| Business section |
| Specifications | How can I improve system performance when using multiple clocks? Analog Devices : Rarely Asked Questions \Watch for Those Multiple Clocking Edges!\ Rarely Asked Questions, RAQs, Multiple Clocking Edges, system performance, Rob Reeder Analog Devices |
| Suggested Link Details/Purchase | |
| Content | RAQ’s SPECIAL ADVERTISING SECTION Strange stories from the call logs of Analog Devices SPONSORED BY Contributing Writer Rob Reeder is a senior converter applications engineer working in Analog Devices high- speed converter group in Greensboro, NC since 1998. Rob received his MSEE and BSEE from Northern Illinois University in DeKalb, IL in 1998 and 1996 respectively. In his spare time he enjoys mixing music, art, and playing basketball with his two boys. Have a question involving a perplexing or unusual analog problem? Submit your question to: www.analog.com/ askrob For Analog Devices’ Technical Support, Call 800-AnalogD Watch for Those Multiple Clocking Edges! Q. How can I improve system performance when using multiple clocks? A. A common problem that arises when using multiple clocks generated from the same source is noise—usually a spur popping out of the noise floor—because the sin- gle clock source is multiplied or divided into several versions of the same clock. Skewing the adjacent edges of each clock allows you to reduce the noise spur, or get rid of it completely, depending on the system’s timing margin. This phenom- enon indicates a time-variant system, in which corruption on the clock signal is related to the location of the inter- ference in the time domain. The loca- tion of the interference is fixed, so the degree of clock corruption is propor- tional to the magnitude of the interfer- ence, just like in a linear system. As an example, let’s take two outputs of the AD9516 clock generator. One output, at 100 MHz, is connected to an ADC; the other, at 25 MHz (1/4×fSAMPLE), clocks an FPGA. Rising and falling edges occur on both output clocks at nearly the same time. The result is a coupling effect, because two fast mov- ing, high-bandwidth edges occur every 10 ns instead of one as desired. During this transition period, the noise—intrin- sic or extrinsic—must be low, as jitter or noise can only corrupt the ADC’s tim- ing when present during the transition region of the clock. Making the edge faster (and hence the threshold region smaller) by increasing the slew rate will inevitably reduce the amount of time that noise can be present during the threshold period, effectively reducing the amount of rms (root-mean-square) jitter introduced to the system. During the steady-state period of the clock— the high and low levels—the clock noise is irrelevant. Therefore, simply delaying either the 25 MHz or 100 MHz clock will spread them apart in time, moving the location of the interference. In other words, arrange for the transi- tion edges of one clock to happen dur- ing the steady-state period of the other clock. In essence, what is happening here is crosstalk-induced jitter (noise) from one trace to an adjacent trace. If one trace carries a signal, and a nearby parallel trace carries a varying current, a voltage will be induced in the signal trace; if it is a clock signal, the time at which the clock edge occurs will be modulated. This causes problems if these edges are taking place at nearly the same time. To Learn More About Clock Distribution http://dn.hotims.com/27753-101 |
| Suggested Link Details/Purchase | |
| Following Datasheets | RAQ_comparatorsOpAmp_1 (1 pages) RAQ_converterFront-end_1 (1 pages) RAQ_crosstalkin_converters (1 pages) RAQ_datasheets (1 pages) RAQ_DC_Parameters_1 (1 pages) RAQ_dieTemperature_1 (1 pages) RAQ_diffAmps-1 (1 pages) RAQ_diodes_1 (1 pages) RAQ_FeedbackPin_1 (1 pages) RAQ_filters_1 (1 pages) |
Check in e-portals |
World-H-News Products Extensions Partners Automation Jet Parts |
| Sitemap Folder | group1 group2 group3 group4 group5 group6 group7 group8 group9 group10 group11 group12 group13 group14 group15 group16 group17 group18 group19 group20 group21 group22 group23 group24 group25 group26 group27 group28 group29 group30 group31 group32 group33 group34 group35 group36 group37 group38 group39 group40 group41 group42 group43 group44 group45 group46 group47 group48 group49 group50 group51 group52 group53 group54 group55 group56 group57 group58 group59 group60 group61 group62 group63 group64 group65 group66 group67 group68 group69 group70 group71 group72 group73 group74 group75 group76 group77 group78 group79 group80 group81 group82 group83 group84 group85 group86 group87 group88 group89 group90 group91 group92 group93 group94 group95 group96 group97 group98 group99 group100 Prewious Folder Next Folder |
