A 700-kHz bandwidth /spl Sigma//spl Delta/ fractional synthesizer with spurs compensation and linearization techniques for WCDMA applications

• Published in: IEEE journal of solid-state circuits Vol. 39; no. 9; pp. 1446 - 1454
• Main Authors: Temporiti, E., Albasini, G., Bietti, I., Castello, R., Colombo, M.
• Format: Journal Article
• Language: English
• Published: IEEE 01-09-2004
• Subjects: Bandwidth; CMOS technology; Filters; Frequency synthesizers; Linearization techniques; Multiaccess communication; Phase locked loops; Phase noise; Prototypes; Voltage-controlled oscillators
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2004.831598

A /spl Sigma//spl Delta/ fractional-N frequency synthesizer targeting WCDMA receiver specifications is presented. Through spurs compensation and linearization techniques, the PLL bandwidth is significantly extended with only a slight increase in the integrated phase noise. In a 0.18-/spl mu/m standard digital CMOS technology a fully integrated prototype with 2.1-GHz output frequency and 35 Hz resolution has an area of 3.4 mm/sup 2/ PADs included, and it consumes 28 mW. With a 3-dB closed-loop bandwidth of 700 kHz, the settling time is only 7 /spl mu/s. The integrated phase noise plus spurs is -45 dBc for the first WCDMA channel (1 kHz to 1.94 MHz) and -65 dBc for the second channel (2.5 to 6.34 MHz) with a worst case in-band (unfiltered) fractional spur of -60 dBc. Given the extremely large bandwidth, the synthesizer could be used also for TX direct modulation over a broad band. The choice of such a large bandwidth, however, still limits the spur performance. A slightly smaller bandwidth would fulfill WCDMA requirements. This has been shown in a second prototype, using the same architecture but employing an external loop filter and VCO for greater flexibility and ease of testing.