Abstract :
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This paper describes a low-noise, 900-MHz, voltage controlled oscillator (VCO) fabricated in a 0.6m CMOS technology. The VCO consists of four-stage fully differential delay cells performing full switching. It utilizes dual-delay path techniques to achieve high oscillation frequency and obtain a wide tuning range. The VCO operates at 750 MHz to 1.2 GHz, and the tuning range is as large as 50%. The measured results of the phase noise are 101dBc/Hz at 100-kHz offset and 117dBc/Hz at 600-kHz offset from the carrier frequency. This value is comparable to that of LC-based integrated oscillators. The oscillator consumes 10 mA from a 3.0-V power supply. A prototype frequency synthesizer with the VCO is also implemented in the same technology, and the measured phase noise of the synthesizer is 113dBc/Hz at 100-kHz offset. In order to increase the linearity of the VCO, a resonant circuit is proposed that consists of four parallel p-n junction varactor pairs. The VCO operate at a bias current of 3.13 mA and a supply voltage of 3.0 V with a corresponding DC power consumption of about 9.3 mW. The VCO gain changes from 214 MHz/V to 271 MHz/V. The CMOS VCO shows a fine frequency tuning range of 786 MHz. In addition, a low phase noise of-120.976 dBc/Hz at 1 MHz offset was obtained.
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