A sigma–delta fluxgate magnetometer for space applications

This paper describes the concept and development of an innovative combination of conventional fluxgate magnetometer readout electronics with the control loop of a sigma–delta modulator in order to achieve a new magnetometer design that provides direct digital output without the use of a separate analogue-to-digital converter chip. The new concept is especially aimed at the measurement of extraterrestrial magnetic fields within a dynamic range of approximately ±2000 nT aboard scientific space missions which are affected by high radiation doses. A digital domain model of the new magnetometer electronics is presented, which is essential for a successful hardware implementation, and the test results of a single-axis prototype are discussed. The test results show that the fluxgate and sigma–delta modulator control loops can be merged for dynamic ranges up to ±2000 nT without significant deterioration of the overall performance of the magnetometer. The remaining quantization noise in the signal bandwidth (10 Hz) was minimized to below the sensor's noise level (7 pT Hz−1/2 at 1 Hz) due to the noise-shaping effect of the sigma–delta principle. An offset stability of 0.25 nT over four days was achieved and the linearity error is less than ±3.3 × 10−5 even though the fluxgate sensor is not kept at near-zero field as for traditional fluxgate magnetometers. A technological model of this new fluxgate magnetometer concept will be built for a test flight aboard the NASA discovery mission DAWN.

[1]  Fritz Primdahl,et al.  DESIGN NOTE: Digital fluxgate magnetometer for the Astrid-2 satellite , 1999 .

[2]  M. H. Acuna,et al.  The MAGSAT vector magnetometer: A precision fluxgate magnetometer for the measurement of the geomagnetic field , 1978 .

[3]  E. Hogenauer,et al.  An economical class of digital filters for decimation and interpolation , 1981 .

[4]  A. Namdar,et al.  A 400-MHz, 12-bit, 18-mW, IF digitizer with mixer inside a sigma-delta modulator loop , 1999 .

[5]  F. Primdahl.  The fluxgate magnetometer , 1979 .

[6]  Bernhard E. Boser,et al.  The Design of Sigma-Delta Modulation Analog-to-Digit a 1 Converters , 2004 .

[7]  J. Candy,et al.  The Structure of Quantization Noise from Sigma-Delta Modulation , 1981 .

[8]  Shoji Kawahito,et al.  A digital fluxgate magnetic sensor interface using sigma-delta modulation for weak magnetic field measurement , 2002, IMTC/2002. Proceedings of the 19th IEEE Instrumentation and Measurement Technology Conference (IEEE Cat. No.00CH37276).

[9]  H.S. Kim,et al.  Current single event effects and radiation damage results for candidate spacecraft electronics , 2002, IEEE Radiation Effects Data Workshop.

[10]  James C. Candy,et al.  A Use of Double Integration in Sigma Delta Modulation , 1985, IEEE Trans. Commun..

[11]  Shoji Kawahito,et al.  A 2D CMOS microfluxgate sensor system for digital detection of weak magnetic fields , 1999 .

[12]  R. C. Ledzius,et al.  The basis and architecture for the reduction of tones in a sigma-delta DAC , 1993 .

[13]  Pavel Ripka,et al.  Magnetic sensors and magnetometers , 2002 .

[14]  Fritz Primdahl,et al.  Digital detection of the flux-gate sensor output signal , 1994 .

[15]  A. Lichopoj,et al.  Concept and first results of a digital fluxgate magnetometer , 1995 .

[16]  C. Russell,et al.  A spaceborne magnetometer tested under extended temperature conditions (experiment MAREMF-OS/MARS-96) , 1998 .

[17]  Fritz Primdahl,et al.  The ring core fluxgate sensor null feed-through signal , 1992 .

[18]  M. Acuna,et al.  Fluxgate magnetometers for outer planets exploration , 1974 .