Implementation of a Fully Differential Low Noise Current Source for Fluxgate Sensors

Abstract

In this paper the implementation of a fully differ-ential low-noise current source is presented. It was designed to be used in the feedback path of a fluxgate magnetometer, however, the concept is applicable wherever a low noise and precise current is required. The current source is driven by a transimpedance amplifier that buffers the output of a current-steering DAC. To meet the mandatory precision as well as the required noise level a detailed analysis of the proposed circuit was carried out. The complete feedback path is integrated on chip using a 180 nm CMOS technology and occupies a total area of 2 mm2. The proposed design results in a signal-to-noise ratio of more than 104 dB for a bandwidth of 512 Hz, requiring only a supply voltage of 3.3 V. Moreover the current source is capable of driving currents of more than 18 mA into fluxgate sensors with an inductance of up to 9 mH while consuming 70 mW of power. To the best of the authors' knowledge the designed current source offers the best performance in terms of noise for fluxgate sensor front ends.