Patent ID: 8363033
Filing Date: 2013-01-29
Classification: G06F

Abstract:
1. A capacitance sensing circuit, comprising: an analog capacitance-detecting circuit configured to detect a touch capacitance of a touch panel when a touch action occurs according to a charging current and convert a detected value of the touch capacitance into a pulse width modulation (PWM) control signal; a PWM-to-digital circuit configured to convert the PWM control signal into a sensing count value according to a clock signal; and a self-calibration counter configured to adjust the charging current or the clock signal according to a difference between the sensing count value and a predetermined detecting range, thereby adjusting the predetermined detecting range for matching a range of the sensing count value; wherein the analog capacitance-detecting circuit comprises: a first switch controlled by the PWM control signal and including: a first end for receiving the charging current; a second end; and a control end for receiving the PWM control signal; a second switch controlled by a first control signal and including: a first end coupled to the second end of the first switch; a second end coupled to the panel for providing a ramp voltage corresponding to the touch capacitance; and a control end for receiving the first control signal; a third switch controlled by a second control signal and including: a first end coupled to the second end of the second switch; a second end coupled to a negative bias voltage; and a control end for receiving the second control signal, wherein the first control signal and the second control signal have opposite phases; and a comparator configured to generate the PWM control signal according to the ramp voltage and a reference voltage, the comparator including: a first input end for receiving the reference signal; a second input end coupled to the first end of the second switch; and an output end coupled to the control end of the first switch for providing the PWM control signal.