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This paper presents a voltage controlled oscillator (VCO) for application in chip-scale atomic frequency references. At 3.4GHz (half of the Rubidium atom ground-state hyperfine transition frequency), the VCO demonstrates low phase noise (-33dBc@100Hz and -92dBc@10kHz) at 4.5mW power consumption with a circuit footprint <0.5cm2. The temperature stability is 0ppm/°C at room temperature, and does not exceed -40ppm/°C over the range of -5°C to +65°C. Locking to the coherent population trapping (CPT) resonance of a NIST Rb clock is enabled by a weakly-coupled varactor diode which provides ∼3MHz of tuning range. The oscillator is implemented using low-cost off-the-shelf surface-mount components, including a micro-coaxial resonator. To the authors' knowledge, this VCO has the lowest simultaneous size, phase noise, DC power consumption and thermal drift published in the literature.
Date of Conference: 12-17 June 2005