The high phase noise of ring oscillators has generally discouraged their use in RF synthesis. This paper introduces an integer-N synthesizer that employs a type-I loop to achieve a wide bandwidth, allowing the use of ring oscillators, and a master-slave sampling loop filter along with harmonic traps to suppress spurs. A 2.4 GHz prototype fabricated in 45 nm digital CMOS technology provides a loop bandwidth of 10 MHz and a spur level of −65 dBc. The phase noise is −114 dBc/Hz at 1 MHz offset.

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... ex Terms-Frequency synthesizer, harmonic trap, phaselocked loop (PLL), reference spur, voltage-controlled oscillator (VCO), Δ modulator.