From simple RC oscillators with an accuracy of about 30,000 ppm to atomic clocks with an accuracy of better than 0.001 ppb, there are many clock options that meet the requirements of different applications. For many years, bulk acoustic wave (BAW) crystal oscillators have been used to meet most requirements, providing accuracy in the 10 ppm range. Less precise choices, such as SAW oscillators, ceramic oscillators, and IC oscillators, each have their advantage of meeting specific needs.
Quartz-based devices have long been used as a standard for comparison with most other timer components. The history of quartz as a stable, controllable, high-quality material for frequency selection and timer components is widely recognized, and frequency temperature response, aging rate, and jitter and phase noise characteristics are well documented in the industry.
Figure 1 Phase noise map
The latest introductions to MEMS-based oscillators are often accompanied by assertions that the technology offers lower cost, shorter design and production cycles, superior shock and vibration performance, and better signal quality. Ultimately replace quartz. In addition to these assertions, there have been few studies that have been made to help understand the characteristics of MEMS oscillators. This study attempts to provide a direct comparison of MEMS oscillators to conventional quartz resonator-based oscillators. For many years, the bulk acoustic crystal oscillator has met most of its requirements with its 10&TImes;10-6 accuracy range.
Research methods
The results presented here are based on the application of industry-wide measurement techniques for typical frequency control and represent the commercialization techniques gained in conducting this study in 2008. Many electrical characteristics are evaluated, including frequency temperature characteristics, phase noise/jitter, short-term stability, start-up time, current, and long-term stability (aging rate).
Due to space limitations, this paper only gives data on phase noise/jitter and short-term stability. Log in to TIon/ for a PDF copy of the full study.
All of the above products are CMOS level outputs, operating at 3.0 or 3.3V and output frequencies of 25 to 50 MHz. The tested BAW quartz crystal oscillator has a fundamental harmonic mode at 25 MHz and a third-order harmonic mode at 50 MHz. The results given here are the test values ​​of typical devices or the average of multiple devices of this model.
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