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A47E_EETimes_2_37x10_875_A45.qxd 9/3/14 11:15 HIGH VOLTAGE motion and high quality factors, or resonance. ADJUSTABLE Vendors claim the structure leads to high OUTPUT MODULES long-term frequency stability and low jitter. For example, the IDT DC-DC Converters pMEMS products offer 100-1500 VDC Output sub-picosecond jitter with products operating NEW SAR SERIES! High Voltage Isolated 100 to 1500 VDC Output Adjustable, Down To 0 VDC Output Output Power 3 Watts Minature Design: 1.1” x 0.8” x 0.4” ht. 12 grams Typical Weight Surface Mount & Thru Hole Models Available Output Center Tap for Dual Output Use Input/Output and Over/Under Voltage Protection Over Temperature Protection Fully Encapsulated for Use In Rugged Environments Military Screening Options per Selected MIL-STD-883 Methods with Expanded Operating Temperatures Available, -40˚ to +85˚C For full characteristics of these and the entire PICO product line, see PICO’s Full line catalog at www.picoelectronics.com PICO ELECTRONICS, Inc. 143 Sparks Ave., Pelham, New York 10803 E Mail: info@picoelectronics.com Pico Representatives Germany ELBV/Electronische Bauelemente Vertrieb E-mail: info@elbv.de Phone: 0049 89 4602852 Fax: 0049 89 46205442 England Ginsbury Electronics Ltd. E-mail: rbennett@ginsbury.co.uk Phone: 0044 1634 298900 Fax: 0044 1634 290904 at up to 20MHz. The inverter mesa structure for AT crystals and their effective frequency range. To support use in high-frequency communications, networking and computing designs – which need sources in the 150MHz to 200MHz range – IDT took advantage of its ability to co-package the tiny MEMS resonators with signal-conditioning circuitry to provided its pMEMS products with low-voltage differential signalling (LVDS) and low-voltage positive emitter-coupled logic (LVPECL) outputs. As well as providing an alternative to quartz, MEMS technology is also creating new opportunities for the piezoelectric material. To provide greater control over frequency, Epson-Toyocom started to use micromachining techniques on quartz and developed the QMEMS range of devices to create new shapes such as the inverted-mesa – a sunken structure with steep walls and a flat bottom within a larger quartz crystal that is placed closed to the excitation electrodes. This shape allows operation at higher frequencies as it reduces the thickness of the oscillating portion of the crystal to just a few micrometres. The larger surrounding area is left as a support to maintain overall mechanical strength. The use of a thinner oscillating section also reduces the sensitivity of the device to frequency dips and thermal changes. One promise of MEMS is to facilitate high integration. In principle, the resonator structure can be integrated onto the same die as the compensation and other signalconditioning circuitry. In practice, cost and yield considerations mean that many of the MEMS products on the market are two-die solutions. Silicon Laboratories has been able to combine MEMS and commercial CMOS with its Si50x series of products. Silicon Labs’ CMEMS is a technology that enables the post-processing of MEMS structures on a silicon CMOS wafer, using poly-SiGe as the MEMS structural material. It can be deposited at temperatures comparable to those used to produce the metal wiring on conventional CMOS ICs. That means the processes used to deposit the poly-SiGe will not melt the existing CMOS and backend materials if directly deposited on top of a mainstream CMOS wafer. The etching agents, which are used to cut away material from underneath the resonator so that it can vibrate are friendlier than the hydrofluoric acid and other etchants commonly often used in dedicated MEMS processes. To stabilise the frequency output, the Si50x CMEMS oscillators employ the DSPLL technology used in Silicon Labs’ crystal-based oscillator family for a total stability of as little as ±20ppm over ten years. A further step is to move away from mechanical or piezoelectric resonators and to use an entirely electronic solution. Inductor-capacitor (LC) resonating circuits have been used as a relatively low-quality clock source for microcontrollers for some years, but their application has been limited because their jitter is on the order of tens of thousands of parts per million. Improvements to PLL technology applied to quartz and MEMS products has been used to tighten up the specification of electronic resonators, making them now usable in a much wider range of designs. Because the parts are entirely electronic and their output controlled using data stored in a lookup table, they can be programmed in the factory to provide any required frequency within their output range. Products such as Silicon Labs’ Si500, for example, can support any frequency between 900kHz and 200MHz with a total stability of ±150ppm. As they have no moving parts, the devices are practically impervious to shock and vibration effects and are unaffected by the heat generated during soldering. Thanks to developments in silicon-processing technology, the quartz clock is no longer the only option for designers seeking high-performance timing solutions. Through the use of MEMS, hybrid-MEMS or fully electronic timing control, designers now have access to a widening range of devices that can meet cost, vibration and reliability targets. www.electronics-eetimes.com Electronic Engineering Times Europe October 2014 43


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