An ultra-low-power Low phase noise 2-stage ring voltage controlled oscillator and a frequency synthesizer adopting a spur suppression technique based-on N-path filtering

Abstract

In this dissertation, an ultra-low-power (ULP) frequency synthesizer that adopts a reference spur suppression technique is proposed. The frequency multiplication using a proposed current-shaped 2-stage ring voltage controlled oscillator (VCO) dramatically reduces the power consumption of the VCO by lowering its operating frequency. The current shaping technique in the VCO improves the phase noise performance and generates impulse-like current pulses which are synthesized into a large 2nd order voltage harmonics which are amplified to be used as rail-to-rail local oscillator (LO) signals. The large reference spur caused by using a low-power charge pump architecture is suppressed with the proposed N-path filtering-based reference spur suppression filter. Impedance peaking formed by N-path switching rejects the reference frequency component of charge pump current without any tuning circuits. The power consumption of the proposed frequency synthesizer is only 105uW while providing quadrature LO signals for a Sliding-IF receiver operating in the 900MHz ISM band. The measured phase noise of the proposed VCO at 1MHz offset is -104.1dBc/Hz at 306.67MHz while dissipating 52uW. The proposed reference spur suppression filter shows 15dB spur rejection performance and consumes only 3uW.