A low-power, low-phase-noise quadrature oscillator for Medical Implantable\nCommunications Service (MICS) transceivers is presented. The proposed quadrature oscillator\ngenerates 349~689 MHz I/Q (In-phase and Quadrature) signals covering the MICS band.\nThe oscillator is based on a differential pair with positive feedback. Each delay cell consists of a few\ntransistors enabling lower voltage operation. Since the oscillator is very sensitive to disturbances in\nthe supply voltage and ground, a self-bias circuit for isolating the voltage disturbance is proposed to\nachieve bias voltages which can track the disturbances from the supply and ground. The oscillation\nfrequency, which is controlled by the bias voltages, is less sensitive to the supply and ground noise,\nand a low phase noise is achieved. The chip is fabricated in the UMC (United Microelectronics\nCorporation) 0.18 Ã?¼m CMOS (Complementary Metal Oxide Semiconductor) process; the core just\noccupies a 28.5 Ã?â?? 22 Ã?¼m2 area. The measured phase noise is âË?â??108.45 dBc/Hz at a 1 MHz offset with a\ncenter frequency of 540 MHz. The gain of the oscillator is 0.309 MHz/mV with a control voltage from\n0 V to 1.1 V. The circuit can work with a supply voltage as low as 1.2 V and the power consumption\nis only 0.46 mW at a 1.8 V supply voltage.
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