Capacitance sensing circuit
First Claim
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.
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Accused Products
Abstract
A capacitance sensing circuit for a touch panel includes an analog capacitance-detecting circuit, a PWM-to-digital circuit and a self-calibration circuit. The analog capacitance-detecting circuit detects the capacitance of the touch panel based on a charging current, and converts the detected capacitance into a PWM control signal. The PWM-to-digital circuit converts the PWM control signal into a sensing count value based on a clock signal. The self-calibration circuit adjusts the value of the charging current or the frequency of the clock signal according to the difference between the range of the sensing count value and a predetermined detecting range. The predetermined detecting range can thus be adjusted for matching the range of the sensing count value.
15 Citations
9 Claims
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
- 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;
Specification