Single-chip VLF magnetic field receiver [electronic resource]
Keywords: Electrical Engineering.

Electromagnetic waves in the VLF frequency band from 300 Hz to 30 kHz are used to study the atmosphere, geolocate lightning, map subterranean features and provide navigation and timing signals. These waves can be generated by man-made sources, such as the VLF transmitters operated by the US Navy to communicate with submarines while they are submerged. They can also be generated by natural phenomena. For example, a lightning strike generates an impulsive signal known as a radio atmospheric. The interaction of these natural and man-made signals with the ionosphere, the magnetosphere, and the earth's electrical environment provides valuable data for scientific research. To facilitate this research, the VLF signals must be received and stored for further analysis. Due to the unique nature of these signals, specialized receiver hardware is required to receive them. Currently the most widely deployed VLF receiver is the AWESOME receiver developed at Stanford University. This receiver offers excellent data quality, but it has a power dissipation of around 60 Watts. The high power dissipation can be a problem because some of the most desirable locations to deploy receivers are remote locations, which are far away from power-lines and other sources of electromagnetic interference. In these cases, the receiver must have a very low power dissipation as it must operate on battery power for long periods of time. Low-power VLF receivers for remote deployments have been developed, but their lower power dissipation comes at the expense of data quality. The goal and challenge of this research is to design a low-power receiver without sacrificing data quality. To accomplish this goal, the first single-chip broadband VLF magnetic field receiver has been developed. The receiver consists of a low-noise amplifier (LNA) and an analog-to-digital converter (ADC) integrated on a single-chip. The LNA is implemented using a low-impedance bipolar input stage followed by a variable gain differential instrumentation amplifier. The ADC is implemented with a third-order continuous-time delta-sigma modulator, which was selected for its implicit anti-alias filtering capability and its robustness to mismatch and other non-ideal effects. The receiver also includes an automatic biasing system that compensates for the large temperature variations that are often encountered at remote deployment sites. The receiver was fabricated in a 0.13 um BiCMOS process. The LNA achieves a sensitivity of better than 1 fT/sqrt(Hz) using a standard six-turn 4.9 meter square loop antenna. It also has a peak spurious-free dynamic range of up to 104.02 dB and a 3 dB bandwidth that extends from 170 Hz to over 100 kHz. The power dissipation of the LNA is approximately 908 uW. The on-chip delta-sigma ADC has an effective resolution of 12.40 bits and a spurious-free dynamic range of over 93 dB. The power dissipation of the ADC is roughly 640 uW. The full receiver consists of the combination of the LNA and the ADC and has a total power dissipation of approximately 1.55 mW. A side-by-side comparison of field data from the single-chip receiver and the AWESOME receiver reveals that the data quality of the single-chip receiver is at least as good. Further, the single-chip receiver has a power dissipation that is over 30 times less than the current low-power receiver. The high data quality, low power dissipation and small size make the single-chip VLF magnetic field receiver especially well suited for remote VLF data collection.