MEMS oscillator

A MEMS (Micro Electrical Mechanical System) consists of electrodes on a Si substrate and a vibrator made of silicon. By applying an AC voltage to the vibrator, the vibrator resonates, and by applying a DC voltage to the electrodes, the capacitance between the vibrator and the electrodes changes, converting mechanical vibration into an electrical signal. Because it can be generated on silicon, the oscillator itself can be made smaller than a crystal.

A MEMS-based oscillator is converted to the required output frequency with a Fractional-N PLL. Since Si-MEMS oscillators have large frequency fluctuations due to temperature, ranging from 20 to 30ppm/°C, a temperature sensor is used to adjust the voltage to suppress the oscillation of the oscillator. This makes it possible to improve the temperature characteristics, but recently, deep dope Si oscillators with less temperature fluctuation have also appeared.

Since Fractional-N PLL is used, the increase in Jitter at the point where decimal division occurs causes Phase Noise to rise, but in the latest devices, along with the development of Fractional-N PLL technology , Low Phase Noise products are also available. Because it uses Fractional-N PLL, any frequency can be created with a single oscillator. There is no need to create a new oscillator, just write the program to the internal ROM, depending on the frequency like a crystal, so development time can be greatly reduced.

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