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Figure 4 Excessive jitter causes sampling and hold problems leading to lost or corrupted data. (Source: IDT)
necessary to perform careful analysis using instrumentation to determine the root cause of the problem. Jitter is commonly specified in root mean square (RMS) values of the timing increment (pico- or femtoseconds) because it is assumed that it has a Gaussian distribution. The calculated result is the standard deviation of the jitter measurements, which are typically performed using a high-speed digital oscilloscope. These instruments are particularly suited to measuring data-dependent jitter (JTIE, Jper, and Jcc) for high- or low-frequency clock signals. Once raw jitter measurements have been collected, the value for RMS jitter is post-processed. This value is then be converted to a peak-to-peak value by performing a “crest factor” calculation which assumes an accepted typical bit error rate (BER) of 10-12. For this value of BER, the crest factor is 14.069 meaning that 1ps of RMS jitter equates to peak-to-peak jitter of 14.069ps. Once the source of problematic jitter in the clock tree has been identified, some standard design techniques can be used to overcome it. These include the use of single multi-output buffers (instead of several instances of a single buffer), choosing higher performance components and performing rerouting and better matching of the lengths of metal traces. In a system where random jitter is the major contributor to timing problems, the most logical approach is to reduce the number of components to as few as possible and then replace each component in turn with a higher specification part until the timing budget is met.
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In exceptional circumstances, it may not be possible to meet the jitter specification simply even after all other attempts at troubleshooting have failed. In these scenarios, the only remaining option is to use jitter attenuators in the clock tree such as IDT’s 8V19N407 or Silicon Lab’s Si5317. These devices filter noise from the input clock signal to produce a low jitter clock output.
CONCLUSION
Jitter on clock signals is a major contributor to timing problems in electronic circuits and has several causes. In this article, we investigated the types and sources of jitter in clock trees and showed how a combination of good design practice and careful component selection can help to limit its impact.
Mouser Electronics
www.mouser.co.uk
August 2022. With more than 1,200 manufacturer brands, Mouser now offers an even wider range of product options for its global customer base of design engineers, component buyers, procurement agents, educators and students. “Engineers look to Mouser for the latest, most innovative products for their designs, and we strive to meet their expectations by connecting them with leading component manufacturers in our ever-expanding line card,” says Jeff Newell, Mouser Electronics’ senior vice president of Products. In the face of semiconductor shortages and other supply chain disruptions, Mouser's longstanding strategy to invest in and maintain strong inventory is helping meet the component needs of manufacturers around the globe. As the New Product Introduction Leader, Mouser handles a massive inventory of more than one million unique SKUs at its Global Distribution Centre, offering semiconductors and electronic components across all product categories, including embedded, connectors, optoelectronics, passives and more. Among the new manufacturer partners Mouser has added in 2022 are:
M
Solidigm, a leading supplier of NAND flash and SSD technology that offers QLC storage technology based on Intel technology.
Amphenol PCB Piezotronics focuses on the development and application of integrated circuit technology to piezoelectric sensors and rapidly expanded to include vibration and force sensors. In today’s market, their sensors support testing in aerospace and defence, transportation, automotive, civil engineering, and general R&D industries.
The Modal Shop offers structural vibration and acoustic sensing systems for various applications in design and test laboratories as well as manufacturing plants. Their precision calibration systems and modal and vibration shakers are designed to simplify test phases and help manufacturers provide 100 per cent quality inspection of components.
Allegro MicroSystems, a global leader in power and sensing solutions for motion control and energy-efficient systems.
Labforge Inc., a designer and developer of smart cameras.
Mouser Electronics
www.mouser.co.uk November 2022 Instrumentation Monthly
ouser Electronics continues to expand its line card by adding 36 new manufacturers through the end of
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