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Enabling techniques for low power, high performance fractional-N frequency synthesizers

  • Author(s): Swaminathan, Ashok
  • et al.
Abstract

Delta-sigma fractional-N phase-locked loops are used to generate high quality radio-frequency signals for use in wireless applications. To reduce the phase noise inherent to these systems, a digital-to-analog converter is used to cancel the error introduced by the fractional division process, however matching between the digital-to-analog converter and the phase-locked loop circuitry place a limit on the amount of phase noise reduction that can be achieved. Furthermore, circuit non-linearity results in the appearance of spurious tones in the phase-locked loop output. This dissertation outlines a calibration technique, and a digital quantization technique that provide solutions to these two problems. The calibration technique results in improved phase noise performance by adjusting the digital-to-analog converter gain, and thus providing better matching between the phase-locked loop circuitry and digital-to-analog converter. The digital quantization technique results in no spurious tones when specified non- linearity is applied to the quantizer output sequence and error. The calibration technique was implemented in an integrated circuit, which achieves state-of-the-art performance when compared to currently published phase- locked loops and allows for all circuitry to be integrated onto a single chip. Chapter 1 presents the calibration technique, as well as a theoretical analysis of the stability. Chapter 2 presents details on the digital quantization technique, and a mathematical proof of the absence of spurious tones. In chapter 3, results from an implemented circuit are presented, which verify the behaviour of the technique presented in chapter 1

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