A 3.58 nJ/Node Dual Cross Correlation Analog-Front-End Circuit With ADC for Mutual

Abstract

This article presents a dual cross correlation analog- front-end (DCC-AFE) circuit for a mutual capacitive panel. The DCC-AFE circuit solves the problem of reduced recognition abil- ity owing to the phase difference variation between the transmit- ted and received signals for a large load panel. A sparse collection algorithm is adopted to reduce the number of analog-to-digital converter (ADC) collections and microcontroller unit (MCU) operations in the proposed touch system. Only a 12-bit successive- approximation-register voltage-controlled-oscillator (SAR-VCO) ADC could meet the requirement. Based on this algorithm, both the power consumption and die area of the proposed analog- front-end (AFE) are significantly reduced. Moreover, we propose a calibration algorithm to improve the accuracy of the ADC. The proposed state-of-art touch integrated circuit (IC) was fabricated via a 110 nm CMOS process. The proposed AFE achieves 46.1 and 50.2 dB signal-to-noise ratio (SNR) with 384 and 128 Hz frame rates, respectively. The active area of the 64-channel AFE with ADC on the chip is 0.988 mm 2, which only occupies a small area. The touch IC has an energy consumption of 3.58 nJ/node.