Driving frequency selection method for capacitive multi-touch system

摘要

A driving frequency selection method is used in a capacitive multi-touch system. When the system operates in an idle mode, an active driving frequency is selected randomly from N candidates, and a self-capacitance driving and sensing is used to detect touch points. When there are touch points, the capacitive multi-touch system is switched to an active mode to acquire an image raw data for finding the positions of touch points. In the active mode, noise is calculated from the image raw data. When the noise exceeds a predetermined value, the system is switched back to the idle mode, and the self-capacitance driving and sensing is applied to N−1 active driving frequencies other than the previously selected active driving frequency to acquire N−1 self-capacitance image raw data. The method determines one with a minimum noise and selects the corresponding frequency as a currently active driving frequency.

主权项

1. A driving frequency selection method for capacitive multi-touch system, which is used in a capacitive multi-touch system including a capacitive touch panel, a first driving and sensing device, a second driving and sensing device, and a controller, the first driving and sensing device and the second driving and sensing device each having an idle mode and an active mode and using N driving frequencies in the idle mode and the active mode, where N is a positive integer greater than one, wherein a self capacitance driving and sensing is performed when the first and second driving and sensing devices are in the idle mode, and a mutual capacitance driving and sensing is performed when the first and second driving and sensing devices are in the active mode, the driving frequency selection method comprising the steps of:
(A) using the controller to initialize the first and the second driving and sensing devices; (B) using the controller to configure the first and the second driving and sensing devices into the active mode, and sequentially using the N driving frequencies to sense the capacitive touch panel to produce N mutual capacitance base image raw data to store in the storage unit; (C) configuring the first and the second driving and sensing devices into the idle mode, and sequentially using the N driving frequencies to sense the capacitive touch panel to produce N self capacitance base image raw data to store in the storage unit; (D) selecting one of the N driving frequencies as an active driving frequency; (E) using the active driving frequency to sense the capacitive touch panel to produce a self capacitance image raw data to store in the storage unit; (F) detecting a touch point on the capacitive touch panel according to the self capacitance image raw data and the self capacitance base image raw data, and executing step (G) when the touch point exists on the capacitive touch panel; (G) configuring the first and the second driving and sensing devices into the active mode, and sensing the capacitive touch panel based on the active driving frequency to produce a mutual capacitance image raw data and store it in the storage unit; (H) detecting a noise on the capacitive touch panel according to the mutual capacitance image raw data, and executing step (I) when there is no noise on the capacitive touch panel; and (I) calculating a coordinate of the touch point on the capacitive touch panel according to the mutual capacitance image raw data and the mutual capacitance base image raw data.