Transceiver Performance Improvement from Integration of Micromechanical Resonator Technology

Miniaturization is the biggest advantage for the transceiver form integration of MM resonator technology. Integration of MEMS technology into resonator will make a significant impact at the system level, by offering potential transceiver architectures capable of providing substantial reduction in power consumption and remarkable improvement in the overall performance of the transceiver. Higher level integration transistors or latest solid-state devices and alternative architectures will not only reduce cost, size, and power consumption but also eliminate the need for the offchip high-Q passive devices currently used by superheterodyne transceivers.

Spurious-free dynamic range (SFDR) of the transceiver can be affected by the presence of nonlinearity present in various components such as LNA, mixer, and A/D converter. In addition, the phase noise in the LO and electronic interference signals can desensitize the receiver by generating third-order intermodulation (IM3) distortion most likely to appear at the outputs of these components. These two problems created as a result of integration of micro-resonator technology must be carefully addressed before developing device using these resonators.

Deployment of a folded-beam comb-transduced MM resonator fully integrated with CMOS electronics would maximize the frequency stability of the oscillator against supply voltage fluctuations. System-level schematic diagram of a 16.5 kHz oscillator using folded-beam comb-transduced MM resonator technology is illustrated in Figure 8.8. Critical components ofthis oscillator including the transresistance amplifier, 3-port MM resonator, and output buffer amplifier are clearly identified in this figure. The MM resonator consists of a finger-supporting shuttle mass, which is suspended around 2 mm above the polysilicon substrate by folded flexures. The folded flexures are anchored to the substrate at two central points to provide needed mechanical support. The shuttle mass is free to move around in the direction parallel to the plane of the polysilicon substrate. The fundamental resonance frequency is largely determined by the material properties and geometrical parameters. The resonance frequency is proportional to the square root of the ratio of effective stiffness (krs) of the resonator at the shutter location to effective mass of the shuttle (mrs).

Assuming a value of 0.65 N/m for the effective stiffness of the resonator at the shutter and a value of 5.73 x 10 11 kg for the effective mass resonator at the shuttle [3], one gets the computed value of the resonance frequency as

This computed value is not too far from the design value of 16.50 kHz. The difference is due to the assumed values of the parameters involved.

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