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The basic architecture of a MEMS oscillator combines a MEMS resonator die together with a oscillator IC. Both are packaged together in industry standard plastic packages. As shown on the left side of the diagram below, SiTime has developed different types of MEMS resonators for different applications needs. The output frequency is configured by using a phase locked loop (PLL) that is located on the analog oscillator die. |
MEMS resonators are connected to the MEMS-specific circuit blocks on the analog IC and are driven through electrostatic excitation. A MEMS bias generator is used to bias the electrostatic transducers that are built in the MEMS die. The resonator sustaining circuit brings the resonator into mechanical oscillation.
Since MEMS devices have an inherent temperature coefficient (stability varies with temperature), MEMS timing devices have to be compensated to meet precision timing specifications. A temperature sensor, a temperature to digital converter and a Frac-N PLL are used to perform temperature compensation, which result in devices that meet 0.1 PPM to 50 PPM frequency stability over temperature. In addition, the Frac-N PLL also generates the output frequency that can range from 1 Hz to 650 MHz, depending on the specific device. On-chip one time programmable (OTP) memory is used to store the compensation and configuration parameters. Output drivers usually offer configurable drive strength, for best matching of transmission line impedances and to reduce system EMI.
SiTime's world class analog design team has the expertise to develop MEMS timing products with the best performance and features available in the market today.
