Fractional-N phase-locked loops (PLLs) are widely used as RF local oscillators in wireless communication systems. Their performance is critical in such applications, so they are a subject of intensive research. This talk presents recently-developed techniques that mitigate several practical problems in fractional-N PLLs. Phase noise cancellation is presented as a means of relaxing the fundamental tradeoff between fractional-N PLL phase noise and loop bandwidth. A fast-settling adaptive calibration technique is presented that makes phase noise cancellation practical for the low reference frequencies commonly used in wireless communication systems. Various techniques that work in concert to suppress spurious tones are then presented. They include a new type of digital quantizer to replace the digital delta-sigma modulator used in conventional designs, a charge pump offset technique, and a sampled loop filter. A new type of fractional-N PLL with a digital loop filter to reduce circuit area and sensitivity to device leakage and low supply voltage is also presented. Throughout the talk, integrated circuit prototypes are presented in which the various techniques are shown to enable measured state-of-the-art performance.
Sunday, April 01, 2012
Free and open to the public