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

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$\Delta \Sigma $analog-to-digital converter is adopted to provide a high resolution and a scalable frame rate. The proposed AFE was fabricated in a 0.18-$\mu \text{m}$CMOS process. The prototype achieves 20-VPPnoise immunity against the external noise interference and provides 54-dB SNR and 120-Hz frame rate with a$36\times 64$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.