Abstract:
A study of current-mode cross-shaped Hall effect sensors with detailed analyses of each building block of Hall effect sensor microsystems including analog front-end com ponents, and readout circuitry is presented. These include 4-phase current spinning, chopper amplifier, switched capcitor low-pass filter, and single-slope analog-to-digital converters. Significant e↵ort is devoted to eliminate the o↵set and 1/f noise of current mode Hall sensors. In addition, current-to-voltage conversion using chopper amplifiers is also investigated. The noise magnitude around 1 kHz is reduced from 65 nv to 8 nv using the chopping technique. The optimum W/L ratio of a cross-shaped Hall sensor is found to be 2.55 which provides a sensitivity of 239 nA/T by biasing at 10 µA. A switched capacitor 5th order elliptic low-pass filter is designed to remove the unwanted noise components that appear at odd harmonics of the chopping frequency. A 10-bit single-slope ADC is designed to digitally represent the magnetic field data. The designs presented are made using UMC 180 nm CMOS technology.
