Design of 2.87 GHz Frequency Synthesizer with Programmable Sweep for Diamond Color Defect based CMOS Quantum Sensing Applications

Recently, diamond color defect based quantum sensing applications such as nitrogen-vacancy (NV) center magnetometry have emerged in CMOS technology, which use optically detected magnetic resonance (ODMR) for sensing magnetic field strengths (|\tilde{\mathrm{B}}|) from different environmental physical quantities. For ODMR based sensing, CMOS quantum sensors seek an onchip 2.87 GHz microwave (MW) signal generator. Moreover, in order to sense smaller |\tilde{\mathrm{B}}|, these CMOS quantum sensors also require that MW signal should be swept with sufficiently small step-size near 2.87 GHz. In this work, we present a fractional-N synthesizer based 2.87 GHz MW-generator (MWG) with an extremely small programmable sweep step-size for improved sensitivity of |\tilde{\mathrm{B}}| measurements in CMOS NV magnetometry. The proposed MWG is implemented in 180 nm CMOS technology and simulations were done to validate the proposed design. Post-layout simulation results show that the proposed MWG achieves a minimum sweep-step size of 50 kHz, which can be used to sense |\tilde{\mathrm{B}}|\lt 0.9\;\mu \mathrm{T} and exhibits a phase noise of-114.5 dBc/Hz at an offset of 1 MHz near 2.87 GHz center frequency.