Toward a Novel Digital Electronic Conditioning for the GMI Magnetic Sensors: The Software Defined Radio

A new high frequency and fully digital electronics was implemented for the conditioning of giant magnetoimpedance (GMI) sensors. The electronics are based on the use of a direct digital synthesizer as a high frequency source for the excitation of the sensing element and a software defined radio (SDR) that performs a direct analog-to-digital conversion, with over-sampling, and quadrature digital down conversion (DDC) of GMI voltage. This DDC includes digital mixers and digital decimation filters that ensure a low-pass filtering and a processing gain. The DDC outputs the in-phase and quadrature baseband digital signals. Except for an optional preamplifier and a voltage-to-current converter, the whole system is digital and fully programmable in real time using a high performance digital signal processor. The architecture of the developed electronics is given and the various aspects of the design are addressed. The performance and potential of the SDR are discussed throughout this paper. The dynamic range for the digital full scale output was between 95 and 120 dB. The out-of-band noise rejection was beyond our measurement instruments. The concept has been successfully applied and used for a GMI sensor and the first measurements were conducted.