Reconfigurable Capacitance Readout IC With Hysteresis Loop Filtering for Enhanced 2-D Touch and 3-D Proximity Sensing

This article presents a capacitance readout (CR) IC for both 2-D touch and 3-D proximity sensing. By employing hysteresis loop (HL) filtering and an external noise-monitoring schemes, the proposed CR IC solves reduced sensitivity in mutual-capacitance proximity sensing. Based on this HL filtering, irregular movements of a proximity object between 5-mm and 20-mm hover heights are identified. Moreover, using in-phase signals on multiple Tx electrodes simplifies the 3-D proximity data post-processing. This allows the 2-D touch sensing analog-front-end (AFE) to be reused for 3-D proximity without extra circuitry, leading to a cost-effective AFE architecture appropriate for mass production. The proposed CR IC was fabricated via a 350 nm CMOS process. The proposed AFE achieves 26 dB 3-D proximity signal-to-noise ratio (SNR) with 416 Hz scan rate. The active area of the reconfigurable AFE is 6.24 mm2 while the full-chip including AFE, MCU, digital logic, and memory occupies 15.02 mm2. The power consumption with in-phase driving of 6 Tx electrodes and sensing with 4 Rx electrodes for proximity sensing is 6.7 mW.