A Mutual Capacitance Touch Sensor with N-path IIR Filter for High Charger Noise Rejection

• Main Authors: Kuo, Yen-Ru, 郭彥儒
• Other Authors: Chen, Wei-Zen
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/2xe7d4

碩士 === 國立交通大學 === 電子研究所 === 106 === The target of this Thesis is to develop a high charger noise immunity analog front-end circuit for touch sensing, which can be applied in the consumer electronics products. Its transmitter employs parallel driving by code-division sensing method. It senses the projected capacitive change. In the receiver, it can be divided into two part. In front part, we use current conveyor to transform the information of capacitance to current signal, and do the adjustment for signal amplification and capacitance baseline removal. It also avoids to use large feedback capacitor to prevent from output saturation resulting in an increase of power, owing to the large parasitic capacitance in traditional charge amplifier. In back part, the narrow band bandpass filter using N-path and discrete time IIR filter suppresses the charger noise, using differential circuit to attenuate even harmonics. Different magnitude Gm cells can allow for rejection of incoming signals at 3rd and 5th harmonics. Reconstructed signal flows into operational amplifier with feedback capacitor and resistor and it transforms current to output voltage of analog front-end circuit. Besides, it filters out the out-of-band noise. The high charger noise immunity analog front-end circuit will be implemented in 180-nm CMOS technology. It includes the design of input code-division sensing method, current conveyor and high-order discrete-time switched capacitor bandpass filter. Circuit techniques will be explored to achieve the ultimate goals of high charger noise immunity, high sensitivity and low power.