Hybrid CMOS–MEMS Tunable Oscillator Architecture for Multi-Band Cognitive Radio Systems
Keywords:
CMOS oscillators, MEMS resonators, tunable oscillators, voltage-controlled oscillators (VCO), cognitive radio, multi-band systems, RF integrated circuits, phase noise, frequency synthesis, dynamic spectrum access.Abstract
Cognitive radio systems require frequency agile local oscillators that can operate over a wide tuning range, with low phase noise, and limited energy consumption in communication bands with dynamically changing accessibility. Traditional CMOS-only VCOs suffer due to poor quality factor (Q) inductor on-chip, poor phase noise characteristics, as well as nonlinear tuning characteristics throughout large frequency bands. This paper suggests a tunable CMOS- MEMS tunable oscillator design, in which a high-Q MEMS electronically tunable resonant component is incorporated into a CMOS cross-coupled negative-resistance core to facilitate the functioning of the multi-band cognitive radio. Coarse band selection is offered by a switched capacitor array and fine frequency control with increased spectral purity by MEMS based capacitive tuning. Post-layout simulations of the design are done in 180 nm CMOS technology, which consists of parasitic extraction and phase noise simulation according to the model of Leeson. The proposed architecture has a broad tuning frequency of 1.836 GHz (66%), phase noise of -121 dBc/Hz 1 difference at 1 MHz (2.4 GHz) and a power consumption of 5.8 mW with 1.8 V of power. This foM of -187 dBc/Hz is within competition with traditional examples of LC-VCO. The hybrid integration method improves the tuning linearity and frequency stability therefore applicable in dynamic spectrum access and reconfigurable RF front-end designs in next-generation wireless systems.
