A 3.9kHz bandwidth and 2μV offset current sensor analog front-end with a capacitively coupled amplifier using a dual frequency conversion technique

Precision current measurement with low offset and low gain error is essential for battery management systems to perform accurate State-of-Charge (SOC) estimation in battery-powered vehicles. The simultaneous sampling of current and voltage enables measurement of battery capacity and/or battery impedance to estimate battery’s State-of-Health SOH or internal properties [1]. The bandwidth of the current sensor front-end is required to be on the order of kHz for those applications. The system-level chopping CHL technique [2] is proposed to improve an analog front-end (AFE) input offset while the reset of integrator is required each time the CHL operates, which limits the signal bandwidth. To overcome this bandwidth limitation, an AFE for a current sensor with a capacitively coupled amplifier (CCA) followed by a $2^{\text {nd }}$-order $\Delta \Sigma$ modulator with correlated double sampling (CDS) and charge-preserving integration technique was proposed [3]. The CCA has a duty-cycled resistor to provide a DC bias to the o & input each time the polarity of the signal changes, and the operation causes the signal leakage, resulting in a AFE gain error. Moreover, an anti-aliasing filter (AAF) is required in automotive applications to attenuate unwanted noise as well as to protect the AFE from ESD noise. It also causes inherent gain errors due to voltage division by the impedance of the AAF and the CCA determined by the input capacitance of the CCA and sampling frequency. This paper proposes an analog front end for current sensors using a CCA with a dual frequency conversion technique in order to improve the CCA input impedance by reducing the operating frequency to half that of the $\Delta \Sigma$ modulator in the following stage. The proposed AFE shows $2 \mu \mathrm{V}$ offset and ± 0.2 % gain error with 3.9kHz bandwidth from $-50^{\circ} \mathrm{C}$ to $150^{\circ} \mathrm{C}$.