Highly improved SNR differential sensing method using parallel operation signaling for touch screen application

摘要

In this paper, a continuous-time differential type multi-signal parallel driving architecture touch screen sensing circuit for projective capacitive type panel is presented. In order to further enhance the Signal-to-Noise Ratio (SNR), a new transmitter (TX) architecture is proposed with parallel signal processing algorithm. In this work, charge amplifiers with built-in band-pass filter are designed that filter out low frequency noise and common-mode noise simultaneously. Conventional approaches in continuous-time operation with band-pass filter suffer from a synchronization problem in the case of multi-signal parallel driving. In this work, a built-in delay calibration circuit is proposed that can align signal timing for TX signal and adjacent receiver (RX) sensing line. This proposed architecture enables multi-signal parallel driving in continuous-time operation for projective capacitive sensing circuits. The proposed work supports 16 × 8 mutual capacitive touch screen panel (TSP). TSP load is 12.5 kΩ and 40 pF with frame rate of 200 Hz and 58 dB SNR. Power dissipation is 46 mW.