A 14-Cell Battery Monitoring AFE with 1mV Total Measurement Error and Integrated Electrochemical Impedance Spectroscopy

Given the widespread use of Li-ion batteries in consumer electronics, electric vehicles, and energy storage applications, the study of battery monitoring systems (BMS) has received increasing attention [1]–[2]. Battery voltage has been the primary indicator for assessing battery state of charge (SoC) and state of health (SoH) in previous work. However, there are several remaining key challenges in optimizing BMS measurement accuracy and extending its functionalities under electrically and environmentally hostile conditions. Firstly, the discharge curve of Li-ion batteries is flat, so battery voltage detection with minimal total measurement error (TME) becomes an essential prerequisite for high-accuracy SoC evaluation. This requires careful control of all potential error sources in the analog front-end (AFE) circuit to achieve high accuracy over a wide temperature range. In addition, connecting multiple Li-ion cells in series generates high common-mode (CM) DC voltages, making high-precision AFE design even more challenging. High-voltage (HV)-tolerant DMOS transistors can be used at the input to withstand high CM voltages [2], and the high input impedance of DMOS can also suppress the gain error caused by filter resistors (Fig. 1). However, this solution requires a charge pump to generate an even higher voltage (7.5V higher than the top cell voltage) for the amplifier, making the supply rail design even more complicated. Furthermore, voltage measurement alone is not sufficient to promptly assess the SoH of battery cells [3]. By the time voltage or temperature anomalies become apparent, it is too late to avert the consequences of irreversible heating or even explosion. Last but not least, electrochemical impedance spectroscopy (EIS) has been proposed as a new paradigm for evaluating battery SoH [3], but existing EIS techniques in BMS rely on additional equipment and do not provide real-time monitoring capabilities.