ULPAC: A Miniaturized Ultralow-Power Atomic Clock

This article introduces a chip-scale ultralow-power atomic clock (ULPAC) in the microwave frequency region. A new suspended quantum package architecture along with a fully integrated frequency probing and locking loop implemented in CMOS technology results in a compact package and ultralow-power consumption. In addition, dedicated low-noise magnetic field and temperature control loops are incorporated for isolating and mitigating the internal and external factors affecting the frequency stability. The output frequency of a crystal oscillator is continuously compensated and stabilized by locking to the peak of a coherent population trapping signal, thereby inheriting the superior frequency stability of the atomic resonance. The proposed ULPAC system achieves a frequency stability of 2.2 × 10
^-12
at an averaging time of 10
⁵
s, while consuming 59.9 mW. The frequency probing and locking circuits implemented in a standard 65-nm CMOS process node occupy an area of 2.55 mm
²
. The prototype of this atomic clock occupies a volume of 15 cm
³
.