1. 1 Magnetometer Front-end ASIC (MFA) Magnes, W. 1), H. Hauer 2), A. Valavanoglou 1), M. Oberst 2), H. Neubauer 2), W. Baumjohann 1) and P. Falkner 3) 1) Space Research Institute, Austrian Academy of Sciences, Graz, Austria 2) Fraunhofer, Institute for Integrated Circuits, Erlangen, Germany 3) European Space Research and Technology Centre (ESA/ESTEC), Noordwijk, The Netherlands AMICSA 2006 Xanthi, Greece, 3 rd Oct. 2006

2. 2 Overview MFA…  Project goals  System level block diagram  Basic integration idea  Analog and digital realization  Test results of MFA1 chip  Noise performance  Total ionization dose (TID)  Single event effects (SEE)  Temperature  Chip and instrument summary

3. 3 Project goals MFA…  Development of an instrument front-end ASIC for an external fluxgate (magnetic field) sensor  Reduction of mass and power dissipation  Instrument performance as good as of a standard fluxgate electronics (Venus Express, Themis, etc.)  Reduction of instrument costs (e.g. procurement of rad- hard components)  Radiation tolerant ASIC  Manufacturing on a European chip process (which was found with the 0.35µm austriamicrosystems CMOS process)

4. 4 System level block diagram MFA…

5. 5 Merging and integration idea MFA…

6. 6 Merging and integration idea MFA…

7. 7 Analog part MFA…

8. 8 Analog realization MFA… Linearized model of the modified 2-2 cascaded  modulator R FB …External feedback resistor (= 12.5 kOhm if range of ±2000 nT) S FB … Coil factor of the feedback coil (= 10nT/μA) S SE … Sensitivity of the sense (secondary) coil (= 2μV/nT) G IA … Input amplifier gain at 2f 0 (= 10-20) G A SD … Rectification factor G’’ 11 … Time discrete gain of first integrator f 0 … Excitation frequency (= 16.384 kHz) f I … Integrator one switching frequency (= 16F0=262.144 kHz) Gain calculation for the  modulator:

9. 9 Digital part MFA…

10. 10 Digital realization MFA… Digital filter structureSynchronous serial INTERFACE  Simple 4 wire interface  CMD (start/16bit data/parity/stop)  TLMH/L (start/16bit data/.../stop)  TLMH always 128Hz data output  TLML 128Hz…2Hz command able  32 Status bits included in data frame

11. 11 SNDR voltage channel MFA test results …

12. 12 80dB/dec = 4 th order Power spectral density  Characteristic noise shaping behavior of delta-sigma modulators  FS = ±2,000nT fluxgate channel  FS = ±1.25V voltage channel  Fluxgate channel limited by sensor noise  Flicker noise in first integrator (=1/f noise)  Correlated double sampling in MFA2 will solve this problem MFA test results …

13. 13 Total ionisation dose (TID)  Co-60 gamma ray, Noordwijk (ESTEC), Nov. 2005  Altogether four MFA chips of the same lot were tested upon TID Device Name Test Cycle Test Board Type of Operation Dose Rate Max. Radiation Level MFA1021voltagebiased98 rad (Si) /min129.4 krad (Si) MFA1042voltagebiased 93 rad (Si) /min 261.5 krad (Si) MFA112 1housekeepingbiased65 rad (Si) /min81.0 krad (Si) 2housekeepingbiased56 rad (Si) /min144.2 krad (Si) MFA1093housekeepingbiased90 rad (Si) /min88.6 krad (Si)  All chips showed full functionality in terms of command ability, data transmission as well as modulator and test bus operation throughout the entire test run as well as after the irradiation.  An increase of the supply current on the 3.3 V digital supply as well as a decrease of the Signal-to-Noise and Distortion Ratio (SNDR) was measured for all four devices under test. MFA test results …

14. 14 TID example MFA104  Test parameters: Dose rate: 93rad (Si) /min; Total dose: 261.5krad (Si)  Current analog: constant at approx. 10mA  Current digital: increases 2.55mA – 4.13mA => +61%  SNDR: drops 72dB-62dB (4-5dB per 100krad) Irradiation time [h] Missing data interpolated using linear interpolation SNDR of HK-channel [dB] red curve: PSD @ beginning; blue curve: PSD @ end noise floor: increase 15 to about 65 μV/√Hz fundamental sine 10 Hz and 30Hz harmonics: unchanged all the other harmonics: larger – increase as noise floor MFA test results …

15. 15 Singel event effects (SEE)  Two MFA chips (MFA110 and MFA 118) from the same lot were irradiated at HIF Cyclotron Université Catholique de Louvain, Dec. 2005  19 cycles with 4 different ion spices within a LET range of 2.97 – 34 MeV*cm²/mg  MFA is susceptible to latch-ups beginning at a LET of 14.1 MeV*cm²/mg  Both chips showed full functionality after the irradiation, no permanent damage occured.  SEL without protection => I Amax 99 mA, I Dmax 240 mA no permanent damage occured  Results correspond with results from Mullard Space Science Laboratory, University College London. AMS 0.35 µm ‘opto’-process with a 20 µm thick epitaxial layer MFA test results …

16. 16 Cross-section MFA test results …

17. 17 Temperature behavior MFA test results …  Scale factor drift in MFA1 design is too high : > 130pp/°C  Drift is caused by  Pad resistor (ESD)  On-resistance of output switches  Feedback buffer amplifier  Changes in MFA2 design:  0-Ohm pad resistance  Lager output switches (less on-resistance)  Matched buffer amplifiers

18. 18 Chip and instrument summary MFA… Chip Type: CMOS 0.35µm Layers: 2P4M Chip area: 20mm² Gate Equivalent: 25,000 FAB: austraimicrosystems Package: CQFP-100 Supply: 3.3VA/3.3VD Total power: 46mW TID test up to: 260krad SEL: >LET 14MeV/cm²mg -1

19. 19 Chip and instrument summary  3-axis fluxgate magneto- meter with external sensor  Full synchron design  4 wire interface (CLK, CMD, TLMH, TLML)  Range: +/- 2000nT  Data rate: 128Hz..2Hz  Resolution: 22bit  DR: 92dB  SNDR: 86dB  Housekeeping  Range: +/-1.25V  Data rate for 1 chan: 128Hz  Data rate for 8:1 MUX: 2Hz  Resolution: 22bit  DR: 98dB  SNDR: 92dB MFA…

20. 20 Acknowledgements The authors would like to thank the European Space Agency Science Payload and Advanced Concepts Office for funding this project under contract no. 18391/04/NL/HB and, the Fraunhofer Institute for Integrated Circuits for the cooperation as sub-contractor for the chip integration and, the Institute of Meteorology and extraterrestrial Physics of the Technical University in Brunswick for supplying a high- quality fluxgate sensor.