Incremental Delta-Sigma Modulators for Touch Controller Interface Circuits

• Main Authors: Huang, Ding-Yu, 黃鼎淯
• Other Authors: Wu, Jieh-Tsorng
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/2yn8aj

碩士 === 國立交通大學 === 電子研究所 === 106 === Nowadays, the applications of touch control can be seen everywhere, like the automated teller machines and the smart phones in the daily life. Touch controllers of the handheld device like the smart phones commonly require the low-power and small-area design. Low-power design can enhance the battery life of the smart phones. Small-area design will play an important role in the full screen applications of the smart phones. Touch controllers consist of touch sensing panel, analog interface circuits and digital back-end circuits. Besides the high signal-to-noise ratio, touch controllers also need to take into account the low-power and small-area demand, which make the design of the analog interface circuits become difficult. This thesis describes the analog interface circuit which is implemented with the incremental delta-sigma modulator. Analog interface circuit consists of mixer, integrators, comparator, digital-to-analog capacitors and digital accumulators. Touch sensing panel consists of transmitter electrodes, receiver electrodes and mutual capacitors. Receiver electrodes of the touch sensing panel are connected to the input of the analog interface circuits. Receiver electrodes deliver the mutual capacitance signal and the noise signal to the analog interface circuits simultaneously. Mutual capacitance signal is associate with the touch behavior. Main sources of the noise signal are the display noise and the charger noise. This interface circuit can greatly increase the sensitivity of the mutual capacitance and effectively inhibit the noise signal. While the liquid-crystal display device work, the display noise is generated. As the users tap the smart phones, the charger noise is produced. Interferences of the display noise and the charger noise sent to the analog interface circuits through their own coupling capacitors affect the mutual capacitance signal. When the noise is severe, the touch behavior may be misjudged so that the users can not operate the smart phones normally. Suppressing the noise signal is divided into three steps: first, using mixer move the noise signal by 100 kHz; second, utilizing integrators do the average processing to the noise signal in the working phase of the analog interface circuits; third, exploiting digital accumulators execute the frequency downsampling and read out the data. Analog interface circuit proposed in this thesis is a second-order fully-differential incremental delta-sigma modulator. This interface circuit is fabricated in UMC 0.18 um CMOS technology. Working environment of the interface circuit are as follows: the operating voltage is 3.3 V, the driving signal of the square wave is 100 kHz and the operating frequency of the modulator is 5 MHz. Performance of the interface circuit are as follows: the power consumption is 16.83 mW, the analog-to-digital conversion time for each transmitter electrode is 210 us, the peak signal-to-noise ratio is 20.8 and the chip area is 1 x 1 mm².