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Topic: Timing skew

	Timing skew - Wikipedia, the free encyclopedia
		Timing skew is a problem that can occur on many kinds of computer buses.
		When signals are transmitted down parallel paths, they will not arrive at exactly the same time due to unavoidable variations in wire transmission properties and transistor sizing, but the signals will arrive close to each other in time.
		If the timing skew is large enough, the clock signal may arrive while the data signal is still transitioning between the previous and current values.
	en.wikipedia.org /wiki/Timing_skew (159 words)

	InterOperability Laboratory: Technologies: Token Ring: Knowledge Base
		Timing Skew between channels - This simulation studied the effect of having a possible timing skew of up to 100 ps between the two channels A and B on the jitter measures.
		The FAJ time series in all the 15 measurements at most of the zero crossings was within +/-100 ps (refer to the second and third sub plot, jitter a and jitter b).
		Timing skews between channels showed up in the average of the fifteen measures for the two sets of measurements when plotted together at the top of the graph.
	www.iol.unh.edu /training/tokenring/vjs_thesis/vjthes4.php (2486 words)

	Computer bus - Wikipedia, the free encyclopedia
		This was a waste of time for programs that had other tasks to do.
		DEC noted that having two buses seemed wasteful and expensive for small, mass-produced computers, and mapped peripherals into the memory bus, so that the devices appeared to be memory locations.
		As data rates increase, the problems of timing skew and crosstalk across parallel buses become more and more difficult to circumvent.
	en.wikipedia.org /wiki/Computer_bus (1990 words)

	1.1 Parallel and Serial Links; Rate and Throughput (U.Crete, CS-534) (Site not responding. Last check: 2007-10-08)
		Currently, in the Giga-Hertz era, where bit times are shorter than a nanosecond, the primary reason is that the inevitable timing skew between any two signals carried over a distance longer than a meter or so exceeds the bit time duration.
		Alternatively or at the same time, idle periods may be squeezed out of the incoming line, with new, different idle periods added to the outgoing stream; idle periods are transmitted when no useful traffic exists to be sent, or when it is not appropriate to send traffic due to flow control (policing, shaping, backpressure, etc).
		These are both monotonically increasing functions of time, equal to the cumulative number of useful bits that have flown through the respective interface since the beginning of time; "useful" bits are the bits that are preserved from input to output, across whatever processing the node performs.
	www.ics.forth.gr /~kateveni/534/05a/s11_parSer.html (4683 words)

	Time Division Multiple Access Without a Bus Master
		After the message and gap, a guard time is allocated to accommodate timing skew among the oscillators of the nodes.
		This frame sync serves as a central time reference point and is used to resynchronize the time bases of each slave node, eliminating cumulative time skew caused by oscillator speed inaccuracies over the duration of a frame.
		The disadvantages of initial allocation of mastership with stable time bases are that logic for an initial arbitration scheme must be included, and very stable time bases must be used to minimize oscillator skew over the longest possible time between messages on the network.
	www.ece.cmu.edu /~koopman/jtdma/jtdma.html (4577 words)

	The Pregnancy Institute - PUCP
		As in humans, there are varying presentations depending on the time and duration of the stimulus along with the gestational age of the animal fetus.
		Time of observation (bedtime and 12mn-6am) may need to be included in any future study.
		Nuchal cords: Timing of antenatal diagnosis and duration.
	www.preginst.com /pucp.html (13577 words)

	about clock skew? (Site not responding. Last check: 2007-10-08)
		In circuit design, clock skew is a phenomenon in synchronous circuits in which the clock signal (sent from the clock circuit) arrives at different components at different times.
		Clock skew is the variation of arrival time (of the clock signal) to the destination logic cell using the same clock source.
		Clock skew is due to (1) variation in the RC of the clock interconnect due to the geometrical layout of the length and width, (2) process variation in permittivity and thickness (due to the actual fabrication of the interconnect), thus causes imperfection.
	www.edaboard.com /ftopic131953.html (564 words)

	Celestry : Welcome : etc : etc (Site not responding. Last check: 2007-10-08)
		Striving to eliminate clock skew, they are unaware that perfect zero-skew is not the solution for either the safest or the highest performance design.
		The zero-skew methodology leaves skews dangerously close to the brink of timing violations (a).
		Timing analysis produces permissible ranges, a set of constraints on clock delays to individual registers.
	www.celestry.com /products_clockwise.shtml (345 words)

	XAUI: Curing Internal Speed Blockages (Site not responding. Last check: 2007-10-08)
		In fact, the skewing problem on parallel buses is often the limiting factor for the data throughput rates over the bus.
		By the time the data has traveled through the loss-prone backplane media and reached the receiver, the line attenuation has shrunk the single zero closer to the ideal unit interval.
		As long as the skew from lane to lane in the channel does not exceed 30- to 40-b times, XAUI is able to re-align the lanes, re-synchronize the data, and continue communication.
	www.commsdesign.com /printableArticle?articleID=16503592 (2086 words)

	[No title] (Site not responding. Last check: 2007-10-08)
		The justification for this is that we do not use the outer pairs on the twist and flat cable and that we use only every other pair in the center section of the cable.
		This is because of the high degree of symmetry in the layout of the timing signals in the top section of the P1 backplane.
		The estimate of the maximum skew in the P1 Timing Signals reaching the THE-Card BSF FPGA will be the sum of the maximum estimate for items: #1, #3, and #5.
	www.pa.msu.edu /hep/d0/ftp/l1/framework/timing/timing_signal_skew.txt (310 words)

	11.19.98 Clock drivers ensure on-time arrival of high-speed signals
		When cycle times are approximately 50 nsec, you do not have to worry too much about skew because it is not a major factor in total cycle time.
		Board-design skew depends on a combination of factors, such as the length of the traces, capacitive loading of those traces, variations in threshold voltages, and transmission-line terminations.
		A 3-nsec clock-driver skew may be acceptable for the design and board layout of 20- to 25-MHz systems, but such skew becomes increasingly unacceptable as system clock rates increase.
	www.edn.com /archives/1998/111998/24ms434.htm (2042 words)

	Meeting Recorder: Between-channel timing skew
		In March 2001 I was looking at timing delays between the same voice being picked up by different channels in the meeting recordings.
		These delays are consistent with a fixed skew introduced when the individual channels are initialized at the start of a recording session, and should remain absolutely fixed throughout the session.
		But it does mean that you can't assume that timing skews between channels will be bounded by a few hundred samples.
	www.icsi.berkeley.edu /~dpwe/research/mtgrcdr/chanskew.html (837 words)

	Delay Matching & Skew (Site not responding. Last check: 2007-10-08)
		Timing skew may also violate setup and hold times for various gates.
		The resulting skew in the arrival of wavefronts to the various gates is unacceptable.
		With correct routing and terminating schemes, the skew is minimized.
	www.kaw.com /Solution_Services/Delay_Matching_Skew/delay_matching_skew.htm (150 words)

	Maintaining Digital Signal Integrity
		Skew is important because it sets a reference level for channel-to-channel timing uncertainty.
		Even at their highest speeds, the smallest time interval for these analyzers is several hundred picoseconds, far greater than the noise and data-dependent errors associated with low passive-probe bandwidth.
		If you consider that the resolution of a measuring instrument should be several times greater than the precision of the value being measured, a 2-GHz or 4-GHz timing-resolution logic analyzer should be used to measure events a few nanoseconds long.
	www.evaluationengineering.com /archive/articles/1299ds.htm (1058 words)

	Interconnect and Noise Immunity Design for the Pentium® 4 Processor
		In most cases, the timing of aggressors switching for noise is earlier than predicted by max delay timing analysis due to a reduced Miller Coupling Factor (MCF) in the noise case.
		Timing filtering was first implemented for the Intel® Pentium® Pro processor as the tool Crosswind [4], and it introduced the concept of valid and required time window filtering; valid window noise 'profiling' or juxtaposition of aggressor noise over the clock period; and rudimentary modeling of drive ratios with fixed thresholds for noise sensitization.
		The key to computing the next frequency of interaction is to comprehend the relative velocity of timing edge references as one slows the primary clock.
	www.intel.com /technology/itj/q12001/articles/art_5i.htm (1208 words)

	MBD > Backgrounder > Examining Rambus
		The 26 high-speed, high-quality signals must travel on controlled-impedance transmission lines that are closely matched in length to minimize timing skew.
		Because clock and data skew must be carefully matched to ensure proper operation, the 400-MHz clock and data must travel along nearly identical paths both to and from the Master.
		To verify overall system timing for the Rambus memory architecture in a design, the engineer will need to rely on the TDS 694C to verify the extremely high-speed signal characteristics single shot.
	www.tek.com /Measurement/Products/backgrounders/rambus (1194 words)

	[No title]
		The minimum bit time is an aggregate of a required minimum bit-valid timing window of a receiver and a minimum timing impact of a transmitter.
		Taking into account the impact of a transmitter and receiver clock jitter, channel skew and cross talk, the BER of an interface, power supply noise, device process, temperature, as well as EMI, then a practical data speed limitation can be derived from the minimum bit time and a specified eye diagram margin.
		In the case of a multi-channel, the channel and package skew are an important contribution to the timing margin.
	www.planetanalog.com /showArticle.jhtml?articleID=18902426 (2895 words)

	Design Guidelines and Criteria: Clocks
		In addition to setup time, which is based on a clock period, hold time analysis must be analyzed.
		While the worst-case behavior of the clock-to-out of the source chip is easily analyzed using "minimum" or "best case" timing parameters, the hold time of the sink chip must be analyzed assuming a slow path for the clock and the fast path for the data, for the same calculation.
		Also note the conditions for which the flip-flop's metastable parameters are taken, with large differences possible in resolution time when moving from nominal temperature and voltage to the extremes.
	klabs.org /DEI/References/design_guidelines/nasa_guidelines/clocks/clocks.htm (1176 words)

	[No title]
		Feeding Timing Signals from the ECL Receivers to the BSFS FPGA (and the VME Interface FPGA and the 53 MHz driver for Finisar).
		This skew is added to account for either (a) a single output driving multiple inputs, or (b) skew between parallel paths.
		Note also that the various P1 Timing Signals can be skewed with respect to each other by as much as 9 ns in the worst case (data book numbers, not measured numbers), which must be taken into account when "phasing" the 53 MHz clock.
	www.pa.msu.edu /ftp/pub/d0/l1/framework/hardware/general/characterization_of_run_ii_components.txt (1776 words)

	[No title] (Site not responding. Last check: 2007-10-08)
		Another challenge presented by signal redistribution within the multi-layer substrate 105 is that differences in routing distances tend to introduce timing skew between simultaneously transmitted signals.
		Further, because the direct-connect cable 203 may be constructed with a set of same-length conductors, timing skew resulting from different signal path lengths through the printed circuit board 205 is also avoided.
		By this arrangement, the parasitic capacitance, signal reflections and timing skew resulting from signal redistribution in the substrate layer 219 are avoided.
	www.wipo.int /cgi-pct/guest/getbykey5?KEY=03/94203.031113&ELEMENT_SET=DECL (11224 words)

	Clock Reference - Support
		Clock delay and skew can be measured at the SDRAM chips on the module and then compared against the signal at the reference net.
		Depending on the skew of the clock signals, you will either tune the feedback of the PLL or change the clock loading to balance the skew.
		Clock skew is measured by comparison of the waveform at the “clock reference net” and the clock signal at the clock pin of the SDRAM.
	www.simmtester.com /page/products/clock/clksupp.asp (1654 words)

	EETimes.com - Mixed-Signal Verification Methodology Using Nanosim Integration with VCS
		However, the behavioral models that are required for emulating the functionality of the analog blocks are the main weakness of the Verilog gate-level verification.
		Timing, voltage and power characterization, meanwhile, are particularly important in light of today's low-power/high-speed devices.
		For example, a skew in differential signals, which was not modeled properly in the behavioral model, results in successful gate-level verification but immediately fails in the transistor-level simulation due to major glitches.
	www.eetimes.com /showArticle.jhtml?articleID=18400630 (1022 words)

	DeepChip Homepage (Site not responding. Last check: 2007-10-08)
		In 4.2 we have the ability to introduce useful skew early in physical synthesis flow.
		The "run timing adjust skew $m $l" can command be used as early as after initial global placement.
		This command will estimate the actual skew that will be seen much later in the flow.
	www.deepchip.com /items/0432-06.html (1073 words)

	Timing skew: Facts and details from Encyclopedia Topic (Site not responding. Last check: 2007-10-08)
		Timing skew is a problem that can occur on many kinds of computer bus[For more info, click on this link].
		If the timing skew is large enough, EHandler: no quick summary.
		The hold time is the minimum amount of time the data signal should be held steady after the clock event so that the data is reliably sampled by the clock....
	www.absoluteastronomy.com /encyclopedia/t/ti/timing_skew.htm (460 words)

	Timing Analysis and Optimization of Sequential Circuits
		Timing Analysis and Optimization of Sequential Circuits describes CAD algorithms for analyzing and optimizing the timing behavior of sequential circuits with special reference to performance parameters such as power and area.
		The state of the art in timing analysis and optimization techniques are described for circuits using edge-triggered or level-sensitive memory elements.
		Timing Analysis and Optimization of Sequential Circuits is written for graduate students, researchers and professionals in the area of CAD for VLSI and VLSI circuit design.
	www.ateworld.com /books/view_details.cfm?id=145 (181 words)

	EETimes.com - Integrated approach lets new tech in (Site not responding. Last check: 2007-10-08)
		At the same time, the number of clock loads is increasing, which results in increased skew.
		Clock skew is difficult to control in the context of historical budgets, partly due to increased frequencies, loads, and larger die size.
		The amount of time it takes standalone point tools to analyze the impact of interconnect effects and then implement corrective action on the design is becoming prohibitive with respect to time-to-market constraints.
	www.eetimes.com /story/OEG20001016S0056 (1719 words)

	Multi-Gigabit SerDes: The Cornerstone of High Speed Serial Interconnects
		The timing skew problem encountered in a parallel bus is solved by embedding the clock signal into the data stream.
		With a bit time of 400ps, it is not a trivial task to keep a constant phase relationship between the two clocks over all the temperature, supply voltage and process corners.
		Since the bit time for PCI Express is only 400ps, the two clocks would have to track each other within as low as 100ps depending on the setup and hold time needed by the latch.
	www.us.design-reuse.com /news?id=10541&print=yes (4461 words)

	Baris Taskin (Site not responding. Last check: 2007-10-08)
		Static timing analysis is currently the prevailing methodology to verify the temporal correctness of integrated circuits due to its accuracy, relatively less computational complexity and the practically of accompanying timing models.
		Clock skew scheduling is a synchronization technique where the clock signal delays at the synchronous components (typically registers) of a circuit are manipulated in order to improve the circuit performance.
		With the optimal clock schedule, the timing reliability or the minimum clock period of the circuit is improved for higher performance.
	www.pitt.edu /~baris/research.html (2494 words)

	( ESNUG 397 Item 6 ) --------------------------------------------- [07/24/02] (Site not responding. Last check: 2007-10-08)
		This time I found something I have to respond to because it is pretty untrue.
		Dolphin timing reports are in the same format as PrimeTime with one exception.
		While in PrimeTime the timing is reported on the output pin of a cell.
	www.deepchip.com /items/0397-06.html (2541 words)

	Relative Bus Delay-Skew Mode
		When you write out the equations for bus timing, the clock skew between cards has as much to do with the cycle time as any other delay component.
		And there's a big incentive to work on the clock skew (as opposed to trying to improve the performance of any other element in the system).
		Just working on clock skew gets you up into the territory of a 30 percent bus timing ratio.
	www.sigcon.com /Pubs/misc/busarch4.htm (193 words)

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