Introduction：
Mutual capacitive touch screens are constructed by forming horizontal and vertical electrodes on the surface of the glass using ITO (indium tin oxide). Unlike self-capacitive screens, mutual capacitive screens create capacitance at the intersections of these two sets of electrodes, where each set acts as one terminal of a capacitor. When a finger touches the screen, it alters the coupling between the nearby electrodes, changing the capacitance at that location.
Mutual capacitive screens are a type of projected capacitive screen, the other type being self-capacitive screens. The mutual capacitive technology, characterized by direct, efficient, accurate, smooth, and stylish interactions, significantly enhances the efficiency and convenience of human-computer interaction, making it a likely mainstream choice for future consumer devices.
Technology Overview:
In mutual capacitive screens, the horizontal electrodes send excitation signals sequentially, while all vertical electrodes receive these signals simultaneously. This allows for the measurement of capacitance at the intersection points of the horizontal and vertical electrodes, generating a two-dimensional capacitance map for the entire touch screen. By analyzing changes in capacitance, the coordinates of each touch point can be accurately calculated, even if multiple touch points are present simultaneously.
Key Developments by FocalTech:
FocalTech is one of the pioneering companies in the research and development of mutual capacitive touch screen technology, holding numerous domestic and international patents covering the design of the touch screen body, detection circuits, touch detection algorithms, and environmental adaptation algorithms. Their proprietary technologies significantly enhance the following performance metrics of mutual capacitive touch screens:
**Electromagnetic Interference (EMI) Resistance:**
EMI resistance is crucial for capacitive touchscreen performance. Since 2007, companies have offered self-capacitive touch screen technologies, but poor EMI designs often lead to malfunctions during calls, resulting in project failures. FocalTech has implemented frequency-hopping techniques from modern wireless communication, increasing transmission power to enhance the system’s signal-to-noise ratio (SNR) and effectively suppress electromagnetic interference.
**Signal-to-Noise Ratio (SNR):**
SNR is defined as the ratio of received signal power to noise power, a critical factor that influences touch precision, linearity, and resolution. FocalTech improves SNR through three primary methods: increasing transmission power, reducing noise with superior shielding designs (e.g., grounding planes), and enhancing the capacitive change induced by touch. Their unique technology achieves capacitive changes of over 30%, surpassing the 18% typically seen in devices like the iPhone.
**Environmental Adaptability:**
Touch screens are exposed to varying environmental conditions that can affect capacitance, such as temperature and humidity. Water droplets on the surface may cause false touches. FocalTech has developed adaptive algorithms that allow the touch screen to function accurately across a wide range of environmental conditions, ensuring reliable performance even in the presence of moisture.
**Power Consumption:**
Power efficiency is critical for portable devices. Mutual capacitive technology, which employs two-dimensional detection, generally consumes 2 to 3 times more power than self-capacitive systems. FocalTech has prioritized low power consumption in its IC design, employing low-power structures, processes, and hardware accelerators. They have also developed rapid coordinate calculation methods to simplify processing and have implemented multiple power-saving modes, achieving power consumption that is approximately half that of comparable solutions.
**Self-Capacitive Touch Screens:**
Self-capacitive screens consist of horizontal and vertical electrode arrays made from ITO. These electrodes form capacitance with the ground, known as self-capacitance. When a finger touches the screen, it increases the screen’s capacitance by adding its capacitive effect. During touch detection, self-capacitive screens sequentially check the horizontal and vertical electrodes, determining the coordinates by measuring capacitance changes. However, this method can lead to “ghost points” when multiple touches occur, as it struggles to accurately register multiple simultaneous touches.
This analysis provides an in-depth look at the technology and innovations behind mutual capacitive touch screens, particularly the advancements made by FocalTech, illustrating their potential to shape the future of touchscreen technology.
