A 92dB-DR 13mW /spl Delta//spl Sigma/ Modulator for Spaceborn Fluxgate Sensors

Abstract

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...

Highly integrated front-end electronics for spaceborne fluxgate sensors

“…It is based on a combination of the readout electronics of a conventional fluxgate magnetometer with the control loop of a delta-sigma modulator (Magnes et al 2003) in order to get a further miniaturized, robust (especially in terms of radiation hardness) and highly sensitive near sensor electronics for a triaxial sensor. Since then a first test chip (MFA-1, Magnes et al 2007) followed by a redesigned MFA-2 with an improved analogue part have been developed and carefully checked for performance compliance and radiation hardness. Both ASICs were fabricated in a 0.35 μm 2P4M (two poly and four metal layers) CMOS technology from austriamicrosystems.…”

27.9 A 200kS/s 13.5b integrated-fluxgate differential-magnetic-to-digital converter with an oversampling compensation loop for contactless current sensing

“…The offset and resolution of Hall-effect sensors is in the μT-level [1][2][3], in contrast to the nT-level accuracy of integrated-fluxgate (IFG) magnetometers [4]. Previously reported sampled-data closed-loop IFG readouts have limited BWs as their sampling frequencies (f S ) are limited to be less than or equal to the IFG excitation frequency, f EXC [5][6][7]. This paper describes a differential closed-loop IFG CCS with f S >f EXC .…”

“…I meas produces differential magnetic terms B DM along the two IFGs in contrast to stray-field B CM . To avoid their transfer curve non-linearity, the IFGs are operated in feedback magnetic compensation loops (MCL) for near-zero internal field operation [6]. A precision differential MCL, MCL DIFF , integrates the difference of the two IFG V demod voltages and drives a fully balanced current into their L comp coils to null B DM terms in their cores (Fig.…”

“…Previously reported sampled-data closed-loop IFG readouts form first-order [5] or second-order MASH [6] magnetic-domain ΔΣMs or embed a SC-ΔΣM in the sense-path of an MCL with a digital loop filter and an FIRDAC (FIR filter combined with a DAC) in the feedback [7]. A challenge with embedding oversampled data-conversion into an IFG MCL is extending the readout BW independently of f EXC .…”