Capacitive Sensing and Terminal CPU Solutions in Mobile Phones 1

In the mid-range smartphone industry, improving the user interface is key to the success of new models. If no one is willing to use a phone, what good is it, no matter how great it is! Considering this, manufacturers are focusing on developing innovative technologies to replace larger buttons and switches without compromising the performance of the user interface (CPUI). Capacitive sensing is an effective technique for reducing size, offering low cost, robustness, flexibility, and an intuitive CPUI while remaining compatible with the form factor and functionality of existing devices. Capacitive sensing can also be combined with other standard smartphone features like white LED drivers and battery charging to further reduce costs. Cypress's PSoC mixed-signal array with CapSense technology enables manufacturers to easily incorporate capacitive sensing into their phones.  A typical mid-range CPUI consists of several buttons, switches, and a display. For basic functionality, a CPUI only needs an alphanumeric keypad, display, and perhaps a power switch. However, current phone designs allow browsing the web, sending text messages, taking photos, and even storing and playing background music. These features are key factors in attracting most consumers in the consumer market. To support these functions, manufacturers need to enhance CPUI capabilities. For CPUIs, increased functionality leads to two outcomes: either larger size or greater complexity. Unfortunately, consumers also favor simpler, more compact phones. How can phone manufacturers solve this dilemma? One possible solution is to replace traditional buttons and switches with capacitive sensors. Capacitive sensors can easily substitute the most commonly used digital switches and linear sliders in current CPUIs.  The basic form of a capacitive sensor is a pair of adjacent plates. There is inherent capacitance between these plates, proportional to their thickness and inversely proportional to the distance between them. In an ideal scenario, this is the only measurable capacitance. When a conductor (such as a finger) is placed near the plates, it adds a parallel capacitance to the inherent capacitance. The measurable capacitance is then the sum of the inherent value and the coupling capacitance from the finger to the sensor. When a finger is placed on the capacitive sensor, the capacitance increases. Removing the finger causes the capacitance to decrease. By intelligently measuring these capacitance changes, the presence of a finger can be detected. diode