Abstract
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.
Highlights
Providing accurate timing for electronic sensors has been a necessary and difficult problem for a long time [1,2] and is necessary for distributed wireless sensor applications, such as tracking items or targets of interest [3], network communication [4,5], or reflectometry
The excessive power consumption of typical highaccuracy frequency sources has limited their use in wireless sensor nodes due to the size of the required battery pack needed for long duration operations
A system called geoPebble [13,14], which uses a large grid of wireless sensors to perform glacial reflectometry, has been developed at The Pennsylvania State University
Summary
Providing accurate timing for electronic sensors has been a necessary and difficult problem for a long time [1,2] and is necessary for distributed wireless sensor applications, such as tracking items or targets of interest [3], network communication [4,5], or reflectometry. Since a typical high-accuracy frequency source would account for the largest average power consumption in the system, a method of frequency counting and GPS receiver duty cycling has been developed that allows for a timing accuracy of 5 μs rms, while consuming less than 45 mW average power. This reduction in power usage significantly extends the operational time of the deployed geoPebbles from about one day to almost a week and reduces the logistical costs of constant retrieval and deployment of the units for recharging.
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