A 1.2-V 180-nm CMOS Low-Power Multi-Band Ring Oscillator based Frequency Synthesizer for Edge-Combining Transmitters

A wide-frequency-range low-power synthesizer based on an eight-stage differential ring oscillator (RO) regulated by a phase locked loop (PLL) is introduced. It is specially designed to be used in edge-combining transmitters and fabricated in a 180nm 1P6M CMOS process. It provides 16 symmetrical phase-shifted outputs for up to 8-times frequency-multiplication using an external edge-combiner. The oscillator is implemented as current-starved RO. It includes a biasing network with threshold regulation for close to 50% duty cycle and equal time delay in all RO stages. The lower corner-frequency is 5 bit adjustable (50MHz to 300 MHz) and the oscillator offers an additional 5 bit trimmable tuning range (20.3MHz to 97.2 MHz). The structure is optimized to operate at 216MHz and shows a phase noise of -96 dBc/Hz at 1MHz offset as well as -76 dBc/Hz in-band phase noise (with locked PLL below 100 kHz offset). With its low power demand of 1.3mW, the frequency synthesizer is suited to be used in low-power transmitters.