A Continuous-Time Ripple Reduction Technique for Spinning-Current Hall Sensors

This paper presents a new ripple-reduction technique for spinning-current Hall sensors, which obviates the need for low-pass filtering to suppress the ripple caused by up-modulated sensor offset. A continuous-time ripple-free output is achieved by the use of three ripple reduction loops (RRLs), which continuously sense the offset ripple and then use this information to drive a feedback loop that cancels sensor offset before amplification. Since no low-pass filter is involved, the bandwidth of the resulting system can be much higher than the spinning frequency. Moreover, since the front-end no longer has to process sensor offset, the requirements on its dynamic range can be significantly relaxed. A prototype system consisting of a Hall sensor readout system realized in a 0.18 μm CMOS process was combined with three off-chip RRLs realized with off-chip electronics. At a spinning frequency of 1 kHz, the RRLs reduce the offset ripple by more than 40 dB to about 10 μT, while also achieving low offset (25 μT) and wide bandwidth (over 100 kHz).