Mutual Capacitive Sensing Touch Screen Controller for Ultrathin Display with Extended Signal Passband Using Negative Capacitance

Abstract

Flexible and thin displays for smart devices have a large coupling capacitance between the sensor electrode of the touch screen panel (TSP) and the display electrode. This increased coupling capacitance limits the signal passband to less than 100 kHz, resulting in a significant reduction in the received signal, with a driving frequency of several hundred kilohertz used for noise avoidance. To overcome this problem, we reduced the effective capacitance at the analog front-end by connecting a circuit with a negative capacitance in parallel with the coupling capacitance of the TSP. In addition, the in-phase and quadrature demodulation scheme was used to address the phase fluctuation between the signal and the clock during demodulation. We fabricated a test chip using the 0.35 µm CMOS process and obtained a signal-to-noise ratio of 43.2 dB for a 6 mm diameter metal pillar touch input.

ITO/SiO2/ITO Structure on a Sapphire Substrate Using the Oxidation of Ultra-Thin Si Films as an Insulating Layer for One-Glass-Solution Capacitive Touch-Screen Panels

“…Finally, a capacitive touch-screen panel was fabricated with the films exhibited the highest transmittance (i.e., ITO/SiO 2 /ITO structure annealed at 823 K) by using conducting pads with an individual pattern size of 1 × 1 mm to pattern the ITO layer, as is shown in schematic design Figure 7a. There are various shapes and structures of capacitive TSPs based on the method used to form the touch sensor electrodes [33]. Among various methods, a method of forming a touch screen pattern in a low surface of a window and an on-cell TSP method for forming a touch screen pattern in an upper surface of a display effectively increases the display area while reducing the thickness [34].…”

Strain Sensing by Electrical Capacitive Variation: From Stretchable Materials to Electronic Interfaces

“…[ 81,82 ] Thus, conductive elements for a conventional capacitive sensor are fabricated by designing the geometries of traditional materials, such as percolating network, [ 83 ] wavy geometry [ 84,85 ] serpentine [ 86 ] and helical structure, [ 87 ] and mesh shapes. [ 88 ] In addition, the flexibility of the electrode can be achieved through the incorporation of conductive materials, such as graphene, [ 89,90 ] carbon black, [ 91 ] metal nanowires, [ 60,92 ] metal nanoparticles, [ 93 ] and CNTs, [ 62,94,95 ] into a polymer matrix. Recently, some studies introduced secondary fillers to improve the mechanical, chemical, and electrical properties of the stretchable composite electrodes.…”

Readout Circuits for Capacitive Sensors

“…In addition, when using signals of other waveforms such as sine waves instead of accurate pulses such as ΔVREF in the self-capacitance readout circuit or ΔVTX in the mutualcapacitance readout circuit, there may be an error source if the accurate negative polarity of compensation voltage driving is not realized. To solve this problem, a structure that compensates for a negative capacitance circuit using an additional Op amplifier without applying a negative polarity signal has been proposed [13,14,15]. Another method of compensation uses an another sensor instead of a compensation capacitor.…”