MEMS Differential Oscillators: A Competitive Advantage in Communications Systems
From processors to oscillators, performance improvement at the component level enables improvement at the system level. This translates to more features, higher performance and increased speed for end users of both consumer products and enterprise systems. The need for higher speed in communications systems, such as equipment used in server farms and 4G base stations, is driven by the ever increasing demand for more bandwidth. Accelerating growth in high-speed serial data transmission in networking, storage and telecom environments is driving innovation through use of new technologies such as those used in new frequency control solutions. High performance networking and communications systems require a high quality stable timing component that can support high frequencies with low noise.
As a timing reference, differential oscillators play a key role in high-performance, high-speed systems. In contrast to single-ended oscillators that support lower frequencies with a single signal, differential oscillators typically support frequencies above 100 MHz. Differential oscillators use two signals of opposite phases. This two-wire architecture reduces electrical interference because noise affects both wires equally and is canceled at the receiver. In addition to eliminating common mode noise coupling, differential oscillators are less sensitive to power supply noise (expressed as PSRR or PSNS) and they help reduce electromagnetic interference (EMI).
In communications applications, timing devices must provide good signal integrity over a long period and a wide temperature range. This requires excellent frequency stability and low drift (aging) specifications. Today’s differential oscillators are based on three main technologies: silicon MEMS, overtone quartz crystal or surface acoustic wave (SAW) quartz crystal. Each of these technologies offers different performance parameters that affect system timing margin.
Among these three technologies, SAW-based oscillators have the worst frequency stability with ±50 ppm over temperature and one-year aging of ±5-10 ppm. Overtone crystal oscillators have better frequency stability at ±20 ppm and one-year aging of ±1-3 ppm, but they only support frequencies up to 200 MHz. Overtone oscillators also have start-up issues and are less reliable than SAW oscillators due to their complexity. Silicon MEMS-based oscillators overcome these deficiencies. MEMS-based differential oscillators, with frequencies up to 800 MHz, offer ±10 ppm frequency stability across the industrial temperature range and ±1 ppm one-year aging – all with less than 1 ps integrated RMS phase jitter (12 kHz to 20 MHz). MEMS differential oscillators also have the lowest power consumption and much higher reliability.
MEMS oscillators offer other compelling advantages with a programmable all-silicon platform. System designers can select the optimal combination of features for their application when using MEMS-based devices and they can receive custom-configured product within a very short timeframe. For example, the frequency can be easily programmed with six decimal places of accuracy. Any combination of signal type (LVPECL, LVDS, HCSL or CML), operating voltages (2.5-3.3V) and package options (5.0 x 3.2 mm or 7.0 x 5.0 mm) can be selected to give designers the exact solution to optimize their system. MEMS-based differential oscillators are also available with special functions such as spread spectrum control, voltage control (VCXO) and temperature control (VCTCXO).
Increased performance in networking and communications systems is enabled by improvements realized at the component level. New technologies, such as MEMS-based differential oscillators bring technology advances that were not possible before. With industry standard footprints, MEMS oscillators can replace quartz-based oscillators and allow designers to quickly and easily upgrade their systems without changing the board layout.
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