A 78.2-dB Dynamic Range Shunt-Based Current Sensor for BLDC Motor Control With 2.75-μs Conversion Time and 0.4-mm² Active Area

Abstract

This article presents a shunt-based current sensor (CS) designed for brushless dc (BLDC) motor control. The proposed sensing system digitizes the current flowing through an external 12-m $\Omega $ resistor by sampling the resulting voltage drop by means of an accumulation-based sample-and-hold (S/H) circuit followed by a SAR-assisted $\Sigma \Delta $ incremental analog-to-digital converter (ADC). The employment of an accumulation technique within the S/H circuit allows to amplify the input signal while effectively mitigating the $kT/C$ noise contribution, leading to a significant improvement to the dynamic range (DR) of the readout. The proposed ADC architecture, on the other hand, allows achieving the target resolution in a relatively fast conversion time, essential feature needed to meet the stringent latency requirement imposed by the considered application. The sensor was fabricated in a standard 130-nm CMOS process, occupies a silicon area of 0.4 mm2, and draws 6.7 mA from a 1.5-V supply. Over a ±4-A input current range and a $- 20~^{\circ }$ C to $100~^{\circ }$ C temperature range, it achieves a worst case gain error of ±0.8%. Moreover, the sensor features a DR of 78.2 dB and a 2.75- $\mu $ s conversion time, resulting in a state-of-the-art 0.21-fW/Hz figure of merit (FoM).