A Radiated-EMI-Reduced Touch AFE IC With Pipelined Dual-Frequency Modulation and Sine² Waveform Shaping for Automotive Applications

This article presents an analog front-end (AFE) for automotive touch-screen sensors that reduces radiated emission (RE) from touch-screen panel (TSP) driving signals while maintaining touch sensing performance. The proposed touch AFE employs a sine–sine (Sine<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>) waveform shaping and a sine-chirp spread spectrum (SCSS) clocking to suppress both harmonic components and peak radiated electromagnetic interference (EMI) levels from the TSP driving signal. To address degradation of the signal-to-noise ratio (SNR) and frame rate due to the use of low driving frequencies, the touch AFE adopts a pipelined dual-frequency modulation (DFM), enhancing capacitance signal power while enabling a power- and area-efficient demodulation process. Fabricated in an 80-nm CMOS process, the prototype AFE significantly reduces radiated EMI with the proposed TSP driving signal, thereby complying with the CISPR 25 Class 5 specifications. Furthermore, the prototype AFE achieves an SNR of up to 49.6 dB and a frame rate of 200 Hz with an 8-in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$28\times 18$</tex-math> </inline-formula> TSP. The fabricated AFE consumes 10.5 mW and occupies an active area of 2.21 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>.