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提出了一种2.4GHz 4mW的无电感RF整数N合成器架构，解决了接收机中最后一个电感问题。采用环形振荡器替代LC-VCO，实现了与传统LC振荡器相当的相位噪声和FOM，同时显著减小面积、降低耦合、拓宽调谐范围并支持多相位输出。
Recent developments in RF receiver design have eliminated all on-chip inductors except for that used in the local oscillator. This paper addresses this “last inductor” problem and proposes an integer-N synthesizer architecture that achieves a phase noise and a figure of merit (FOM) comparable to those of LC-VCO-based realizations. The use of ring oscillators instead of LC implementations offers numerous advantages: smaller area, much less coupling to and from other circuits, a much wider tuning range, straightforward generation of multiple phases, and the ability to multiplex several small rings so as to cover multiple bands with minimal area penalty. However, the far inferior FOM of rings has discouraged their use in RF synthesis. The loop bandwidth of traditional type-II PLLs is bounded by “Gardner’s limit” to fREF/10, and typically less than fREF/20 to suppress the reference spurs, thus failing to reduce the ring phase noise sufficiently.
Long Kong, Behzad Razavi
University of California, Los Angeles, CA