Harmonic Distortion Optimization for Sigma-Delta Modulators Interface Circuit of TMR Sensors

Area of Science:

• Micro-sensors
• Magnetic Materials
• Electronic Circuits

Background:

• Tunneling Magnetoresistance (TMR) micro-sensors offer high sensitivity, frequency response, and reliability, finding use in military and civil applications.
• Nonlinearity in TMR sensor interface circuits causes harmonic distortion, reducing signal-to-noise-and-distortion ratio (SNDR).
• Accurate modeling of harmonic distortion sources is crucial for improving TMR sensor performance.

Purpose of the Study:

• To analyze and model harmonic distortion in closed-loop TMR micro-sensor systems.
• To develop and optimize a high-performance interface circuit for TMR sensors.
• To improve the linearity and resolution of TMR sensor systems.

Main Methods:

• Established an accurate harmonic distortion model considering non-linearities in operational amplifiers, analog switches, and capacitors.
• Optimized CMOS switches and switched-capacitor circuits, including the first-stage integrator.
• Designed a digital interface circuit using a low-noise front-end and a third-order sigma-delta modulator, implemented in 0.35μm CMOS technology.

Main Results:

• Achieved a linearity of 0.3% over a full-scale range of ±10^5 nT.
• Attained a resolution of 0.25 nT/Hz^(1/2) at 1 Hz.
• The integrated TMR sensor system occupies 3.2 x 2 mm and consumes 20 mW at a 5 V supply.

Conclusions:

• The developed interface circuit effectively minimizes harmonic distortion in TMR sensor systems.
• The optimized TMR sensor system demonstrates high performance in terms of linearity and resolution.
• This work provides a foundation for advanced digital TMR sensor integration.