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A novel digitally controlled oscillator (DCO)-based architecture for frequency synthesis in wireless RF applications is proposed and demonstrated. It deliberately avoids any use of an analog tuning voltage control line. Fine frequency resolution is achieved through high-speed ΣΔ dithering. Other imperfections of analog circuits are compensated through digital means. The presented ideas enable the employment of fully-digital frequency synthesizers using sophisticated signal processing algorithms, realized in the most advanced deep-submicrometer digital CMOS processes which allow almost no analog extensions. They also promote cost-effective integration with the digital back-end onto a single silicon die. The demonstrator test chip has been fabricated in a digital 0.13-μm CMOS process together with a DSP, which acts as a digital baseband processor with a large number of digital gates in order to investigate noise coupling. The phase noise is -112 dBc/Hz at 500-kHz offset. The close-in spurious tones are below -62 dBc, while the far-out spurs are below -80 dBc. The presented ideas have been incorporated in a commercial Bluetooth transceiver.
Circuits and Systems II: Analog and Digital Signal Processing, IEEE Transactions on (Volume:50 , Issue: 11 )
Date of Publication: Nov. 2003