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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 61 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 costeffective integration with the digital back-end onto a single silicon die. The demonstrator test chip has been fabricated in a digital 0.13-m 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.

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We propose and demonstrate the first RF digitally controlled oscillator (DCO) for cellular mobile phones. The DCO is part of a single-chip quad-band fully compliant GSM transceiver realized in a 90 nm digital CMOS process. Wide and precise linear frequency tuning is achieved through digital control of a large array of standard n-poly/n-well MOSCAP devices that operate in flat regions of their C-V curves. The varactors are partitioned into binary-weighted and unit-weighted banks that are sequentially activated during frequency locking and tracking. The finest varactor step size is 12 kHz at the 1.6-2.0 GHz high-band output. To attenuate the quantization noise to below the natural oscillator phase noise, the varactors undergo high-speed second-order 61 dithering. We analyze the effect of the 61 dithering on the phase noise and show that it can be made sufficiently small. The measured phase noise at 20 MHz offset in the GSM900 band is 165 dBc/Hz and shows no degradation due to the 61 dithering. The 3.6 GHz DCO core consumes 18.0 mA from a 1.4 V supply and has a very wide tuning range of 900 MHz to support the quad-band operation.