19.5 A 2.4GHz RF fractional-N synthesizer with 0.25fREF BW

The loop bandwidth of conventional RF fractional-N synthesizers has been limited to about f
_REF
/10 despite the use of methods that suppress the ΔΣ-modulator quantization noise [1-4]. The trade-off between the loop bandwidth and the ΔΣ noise peaking becomes more serious if the synthesizer employs a ring oscillator to achieve multiband operation, less unwanted coupling, and greater design flexibility than LC oscillators [5]. This paper proposes a simple, robust fractional-N architecture that reduces the ΔΣ noise peak at fREF/2 by 62dB without significant bandwidth penalty. The synthesizer can thus incorporate a ring oscillator while achieving a performance commensurate with WiFi receivers and transmitters.