Low-power gps-disciplined oscillator module for distributed wireless sensor nodes

Many sensor systems, such as distributed wireless sensor arrays, require high-accuracy timing while maintaining low power consumption. Although the capabilities of chip-scale atomic clocks have advanced significantly, their cost continues to be prohibitive for many applications. GPS signals are commonly used to discipline local oscillators in order to inherit the long-term stability of GPS timing; however, commercially available GPS-disciplined oscillators typically use temperature-controlled oscillators and take an extended period of time to reach their stated accuracy, resulting in a large power consumption, usually over a watt. This has subsequently limited their adoption in low-power applications. Modern temperature-compensated crystal oscillators now have stabilities that enable the possibility of duty cycling a GPS receiver and intermittently correcting the oscillator for drift. Based on this principle, a design for a GPS-disciplined oscillator is presented that achieves an accuracy of 5 µs rms in its operational environment, while consuming only 45 mW of average power. The circuit is implemented in a system called geoPebble, which uses a large grid of wireless sensors to perform glacial reflectometry.