Scientific instruments for challenging and cost-optimized space missions have to reduce their resource requirements while keeping the high performance levels of conventional instruments. In this context the development of an instrument front-end ASIC (0.35 μm CMOS from austriamicrosystems) for magnetic field sensors based on the fluxgate principle was undertaken. It is based on the combination of the conventional readout electronics of a fluxgate magnetometer with the control loop of a sigma-delta modulator for a direct digitization of the magnetic field. The analogue part is based on a modified 2-2 cascaded sigma-delta modulator. The digital part includes a primary (128 Hz output) and secondary decimation filter (2, 4, 8, . . . , 64 Hz output) as well as a serial synchronous interface. The chip area is 20 mm 2 and the total power consumption is 60 mW. It has been demonstrated that the overall functionality and performance of the magnetometer front-end ASIC (MFA) is sufficient for scientific applications in space. Noise performance (SNR of 89 dB with a bandwidth of 30 Hz) and offset stability (< 5 pT • C −1 MFA temperature, < ±0.2 nT within 250 h) are very satisfying and the linear gain drift of 60 ppm • C −1 is acceptable. Only a cross-tone phenomenon must be avoided in future designs even though it is possible to mitigate the effect to a level that is tolerable. The MFA stays within its parameters up to 170 krad of total ionizing dose and it keeps full functionality up to more than 300 krad. The threshold for latch-ups is 14 MeV cm 2 mg −1 .

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switches in the capacitor network in Fig. 21.5.3, which can be The read-out electronics of a state-of-the-art fluxgate mnagne-ativated by a digta comad tometer (including ADC) for scientific measurements of DC and a g low-frequency AC magnetic fields (<100H-z) in space and geo-The chip contains 3 modified 2-2 cascaded modulators (fluxgate physics, which requires a >1,OOOnT measurement range and a channels) for a 3D measurement of the magnetic field plus an SNR of more than 90dB, is normally placed on a large PCB additional conventional 2-2 cascaded modulator (voltage channel) (100cm2) and consumes more than 350mW. It is essential for with an 8:1 multiplexer for auxiliary measurements. The digital future space applications, especially onboard miniaturized satelpart contains a 4h-order sinc-filter for each channel (OSR = 64) lites and landing units, that the size and power of the read-out with an output data rate of 128Hz. In addition, the data rate can circuit be reduced while keeping a suitable SNR and radiation be further lowered by factors of 2 down to 2Hz by using boxcar filhardness.ters. The command and telemetry interface is realized with a Figure 21.5.1 shows how the traditional control loop of a fluxgate serial synchronous interface. magnetometer can be combined with the control loop of a 2nd-The PSD plots of the voltage (range: ±1.25V) and fluxgate chanorder AL modulator [1]. A fluxgate sensor is usually made with a nels (range: +2,O0OnT) are depicted in Fig. 21.5.4. Both the voltsoft-magnetic core (ring or rod) placed in the center of a solenoid age and fluxgate channels (with G =0.5) show 4th-order noise pick-up coil. The core is wrapped with a single layer of drive shaping, but the noise floor of the fluxgate channel below 1OOHzwindings, which are then periodically driven by current pulses is 6dB higher due to the noise from the fluxgate sensor and the with a frequency f0 of 5 to 20kHz in order to periodically saturate input stage of the modified AIM. The noise densities of both chanthe magnetic material. The output signal from the pick-up coil nels increase at lower frequencies because of the flicker noise in then contains induced even harmonics of f0 that are proportional the first integrator. The 4th-order performance of the fluxgate to the external magnetic field [2]. The readout electronics channel decreases significantly when the G,J-factor is off by about extracts the magnetic field information by synchronously con-10%. The SNDR of the voltage channel, which was calculated verting and integrating the 2nd-harmonic term (2f0). Normally, the with the output data of the sinc-filter (-3dB at 30Hz) and an input fluxgate sensor operates as a zero detector since the output voltsine at 10Hz, is shown in Fig. 21.5.5. The SNDR and DR are 92dB age is fed back via a resistor to either the pick-up coil or a sepa-and 98dB, respectively. The DR of the decimated output of the rate feedback coil in order to increase the overall linearity. When fluxgate channel in a bandwidth of 0.1 to 30Hz measured 92dB combining...