A Noise-Immunity-Enhanced Analog Front-End for $36\times64$ Touch-Screen Controllers With 20-$\text{V}_{\text{PP}}$ Noise Tolerance at 100 kHz

Abstract

This paper describes the design of an analog front-end (AFE) for capacitive touch-screen controllers that provide highly enhanced noise immunity. The proposed AFE mitigates severe noise interference using a multi-channel-driving (MCD) TX scheme and a noise-filtering RX structure. The MCD scheme with a frequency hopping technique modulates mutual capacitances in a touch-screen panel (TSP) using low-offset orthogonal sequences, spreading the noise interference. In the RX sensing block, a pre-filtering differential sensing method is employed to improve touch sensitivity and to reject common-mode noise. An incorporated RX modulation scheme performs the down-conversion of the capacitance signal and the multiplexing of subsequent blocks, which enables an efficient high-order noise filtering. An incremental <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \Sigma $ </tex-math></inline-formula> analog-to-digital converter is adopted to provide a high resolution and a scalable frame rate. The proposed AFE was fabricated in a 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS process. The prototype achieves 20-V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PP</sub> noise immunity against the external noise interference and provides 54-dB SNR and 120-Hz frame rate with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$36\times 64$ </tex-math></inline-formula> TSP. The prototype supports a supply voltage ranging from 2.7 to 3.3 V and consumes 94.5 mW from a 3.3-V supply.