A Pen-Pressure-Sensitive Capacitive Touch System Using Electrically Coupled Resonance Pen

Abstract

A touch system sensing pen-pressure of the proposed electrically coupled resonance (ECR) pen is implemented, which can replace costly digitizer system containing electro magnetic resonance (EMR) and capacitive touch system. The proposed system detects the location of the ECR pen and finger using proposed position sensor, and senses pen-pressure of ECR pen using proposed pen-pressure sensor. For the position sensor, to detect even small variation of the mutual capacitance on touch screen panel (TSP) of the pen, a simultaneous driving scheme is proposed with modified Hadamard matrix, resulting in highly increased dynamic range and SNR. In the proposed pen-pressure sensor, the resonant frequency of the ECR pen is measured by a frequency to voltage converter based sensor. The measured SNR for the pen position is 49 dB with 1 mm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\mmb\varphi}$</tex> </formula> metal pillar, and 6.5-bit resolution is achieved for pen-pressure sensor in <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$6\sigma$</tex> </formula> criteria.