Projected capacitive sensors are often incorporated in touch screens, touch pads or buttons. Similar sensors are used in non-touching three-dimensional position detection sensor arrangements. These sensors use receiving electrodes and in some embodiments also emitting electrodes. When using two electrodes, one electrode acts as a transmitter and the other electrode as a receiver. A matrix can be formed to allow for a plurality of keys to share transmitting and receiving lines. In practice, the measurement system connected to the receiving electrodes is then often used in a time multiplexing manner. To keep a good responsiveness to user inputs, projected capacitive devices must scan quickly several locations of a mesh of electrodes.
For example, the standardized test “IEC61000-4-6 Immunity to Conducted Disturbances” reveals a common problem of projected capacitive sensors: to acquire a weak signal from the receive electrode at a given frequency when a disturbing noise overlaps the signal with a slightly different frequency. Furthermore, the requirement for short scan time exacerbates this problem of distinguishing signal and noise occupying nearby frequencies.
USPTO Backgrounds
USPTO Backgrounds