Current-Sensitive CMOS Preamplifier for Investigating Space Plasma Waves by Magnetic Search Coils

In order to considerably reduce circuit resources (mass, volume, and power) for the analog front ends of plasma wave measurement systems, a current-sensitive preamplifier for magnetic search coils (MSCs) is designed with standard 0.25- μm complementary metal-oxide-semiconductor (CMOS) technology. Since the input noise current determines the output noise levels around the resonant frequency of an MSC, a CMOS preamplifier operating with low noise current is suitable when combined with an MSC instead of using bipolar junction transistors. The current-sensitive CMOS preamplifier consists of a current amplifier for the detection of current flowing through the MSC and an equalizer for adjusting the transfer function. A prototype of the circuit structure was fabricated on a 1.9 × 3.3- mm²-silicon chip. The noise equivalent magnetic induction of the CMOS preamplifier combined with a 100-mm-long MSC is 3.5 pT/Hz^1/2 at 10 Hz and 30 fT/Hz^1/2 at 2 kHz with a power consumption of 4.6 mW for a 3.3-V supply. This paper is the first to examine a current-sensitive CMOS preamplifier for probing plasma waves.