Development of chopper-stabilized ASIC preamplifier for improving noise equivalent magnetic induction of search coil magnetometer probing space plasma waves

Abstract

AbstractSpace-based search coil (SC) magnetometers connected to preamplifiers have been used to investigate magnetic field vectors of plasma waves from 100 mHz to 10 kHz for understanding magnetospheric dynamics. However, flicker noise below several 100 Hz of typical preamplifiers degrades the noise equivalent magnetic induction (NEMI) of SCs and affects the probing of plasma waves from 100 mHz to 100 Hz. In this study, we developed a chopper-stabilized preamplifier using application-specific integrated circuit (ASIC) technology for improving the NEMI below 100 Hz while maintaining miniaturization and a low power consumption. The chopper ASIC preamplifier fits into a layout size of 2.3 × 3.4 mm in a bare chip. We used two SC sensors with different (20 cm and 5 cm) lengths to evaluate the NEMI with the prototype of the chopper ASIC preamplifier. At 100 mHz, the NEMI values of the 20-cm length and 5-cm length SCs were 0.1 nT/Hz1/2 and 1.9 nT/Hz1/2, respectively, which can detect typical electromagnetic ion cyclotron waves in the magnetosphere. The NEMI value at 100 mHz for the 5-cm-length SC was improved by approximately 19 dB compared with that for a previous ASIC preamplifier without chopping. We conducted temperature tests for the chopper ASIC preamplifier to evaluate the behavior for under a wide temperature range from − 40 to + 100 °C. The temperature coefficient of the gain was approximately − 0.02 dB/°C, which is a sufficiently low temperature-dependence. The use of ASIC technology achieved high stability under the wide temperature range and radiation tolerance. Thus, the chopper ASIC preamplifier with high robustness and ultra-low noise characteristics is suitable for plasma wave observations in harsh space environments for future missions. Graphical Abstract