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The timing is right for crystal-free oscillators to replace Quartz
Sundar Vanchinathan, Senior Director, Integrated Device Technology
being exposed. Higher frequencies and smaller form factors are forcing designers to use expensive, power hungry, smaller SMD crystal-based clocks that also often need additional circuitry to enable them to meet the performance requirements of the system. Furthermore, the proliferation of portable electronics equipment that is typically exposed to harsh operating conditions that include shock and vibration, has exposed the susceptibility of crystal oscillators to physical damage. This article discusses the emergence of crystal- free
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oscillators, and in particular, CMOS-based parts as an alternative to traditional timing solutions.
Crystal oscillators hit their limits Crystals are quite unique compared to other components used in electronic circuits in that the basis of their operation is essentially mechanical. The piezoelectric effect that causes the mechanical resonance of a vibrating quartz crystal was discovered as early as 1880, and the fi rst quartz crystal oscillator was built and patented in 1917. While most other electronic components have continued to evolve rapidly to meet the demands of the latest products by shrinking in form factor, supporting high- speed operation, having reduced power consumption and becoming integrated with other devices, crystals and crystal oscillators have reached practical limits in many aspects of their evolution, construction and application.
20 EIU
s electronics technology continues to advance at a fast pace, the limitations of crystals and crystal oscillators as a practical approach to timing are
As we share and exchange larger and more complex
pieces of information, applications in both the consumer and industrial space are typifi ed by ever-increasing data rates to meet demand for bandwidth. In order to meet this requirement, system designers are forced to use higher frequency oscillators. When using crystals alone, the maximum frequency of oscillation possible is in the region of 50 MHz; this is limited by the impracticality of manufacturing crystals to achieve higher frequencies. For frequencies over 50 MHz – which accounts for most current and next generation high speed applications – an ineffi cient approach that uses a crystal combined with a dedicated circuit to multiply the output frequency is required. While this approach allows the ‘heartbeat’ requirements of most products to be met, it also causes a number of other issues and challenges to become prevalent, the main one being power consumption which increases signifi cantly as crystal oscillator output frequency rises. Multiplication of fundamental frequency to achieve higher frequencies also leads to increased jitter. These factors have made the emergence of power effi cient ‘crystal-free’ all-silicon CMOS based oscillators that generate accurate frequencies on-chip without relying on a piezo-electric or mechanical resonator all the more welcome for designers. All-silicon CMOS oscillators such as Integrated Device Technology’s IDT 3C Series have been developed to offer a viable alternative to conventional oscillators that also address the shortcomings and problems encountered when incorporating crystal- based devices into the latest fi xed location and portable equipment applications. These include smart phones, laptops and tablet PCs, and datacom and connectivity interfaces such as 1 Gb Ethernet, SAS, SuperSpeed USB (USB 3.0) and
www.electronicscomponentworld.com /
www.electronicproductionworld.com September 2011
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