Sensing circuit for capacitive touch panel
First Claim
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1. A sensing circuit for a capacitive touch panel, comprising:
- a sensing signal part for generating a sensing signal according to a capacitance of the capacitive touch panel and a noise which is received by the sensing signal part, wherein the capacitance of the capacitive touch panel at a touched condition is different from the capacitance of the capacitive touch panel at an untouched condition, wherein the sensing signal part comprises;
a sensing unit for receiving the noise through a parasitic capacitance, the sensing unit having a first equivalent capacitance or a second equivalent capacitance, wherein the first equivalent capacitance is an equivalent capacitance of the capacitance of the capacitive touch panel at the touched condition and the parasitic capacitance, and the second equivalent capacitance is an equivalent capacitance of the capacitance of the capacitive touch panel at the untouched condition and the parasitic capacitance; and
a sensing signal generating unit coupled to the sensing unit, for generating the sensing signal according to the first equivalent capacitance and the noise or according to the second equivalent capacitance and the noise;
a reference signal part for receiving the noise and outputting a reference signal, the reference signal part having the same electrical conditions as the sensing signal part, wherein the reference signal part comprises;
a reference unit, for receiving the noise, the reference unit having a third capacitance, wherein the third capacitance simulates the capacitance of the capacitive touch panel at the untouched condition and the parasitic capacitance; and
a reference signal generating unit coupled to the reference unit, for outputting the reference signal according to the third equivalent capacitance and the noise,wherein the reference unit has the same circuits as the sensing unit, and the reference signal generating unit has the same circuits as the sensing signal generating unit; and
an integrator for receiving the sensing signal and the reference signal, subtracting the reference signal from the sensing signal to generate an output signal.
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Abstract
A sensing circuit for a capacitive touch panel is disclosed. By adding a path for a noise to pass through, the noise is differentially processed through two paths which have the same electrical conditions with each other. The noise is then decreased significantly, and a sensing signal can be detected correctly.
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Citations
18 Claims
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1. A sensing circuit for a capacitive touch panel, comprising:
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a sensing signal part for generating a sensing signal according to a capacitance of the capacitive touch panel and a noise which is received by the sensing signal part, wherein the capacitance of the capacitive touch panel at a touched condition is different from the capacitance of the capacitive touch panel at an untouched condition, wherein the sensing signal part comprises; a sensing unit for receiving the noise through a parasitic capacitance, the sensing unit having a first equivalent capacitance or a second equivalent capacitance, wherein the first equivalent capacitance is an equivalent capacitance of the capacitance of the capacitive touch panel at the touched condition and the parasitic capacitance, and the second equivalent capacitance is an equivalent capacitance of the capacitance of the capacitive touch panel at the untouched condition and the parasitic capacitance; and a sensing signal generating unit coupled to the sensing unit, for generating the sensing signal according to the first equivalent capacitance and the noise or according to the second equivalent capacitance and the noise; a reference signal part for receiving the noise and outputting a reference signal, the reference signal part having the same electrical conditions as the sensing signal part, wherein the reference signal part comprises; a reference unit, for receiving the noise, the reference unit having a third capacitance, wherein the third capacitance simulates the capacitance of the capacitive touch panel at the untouched condition and the parasitic capacitance; and a reference signal generating unit coupled to the reference unit, for outputting the reference signal according to the third equivalent capacitance and the noise, wherein the reference unit has the same circuits as the sensing unit, and the reference signal generating unit has the same circuits as the sensing signal generating unit; and an integrator for receiving the sensing signal and the reference signal, subtracting the reference signal from the sensing signal to generate an output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A sensing circuit for a capacitive touch panel, comprising:
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a sensing signal path for generating a sensing signal according to a capacitance of the capacitive touch panel and a noise which is received by the sensing signal path, wherein the capacitance of the capacitive touch panel at a touched condition is different from the capacitance of the capacitive touch panel at an untouched condition, wherein the sensing signal path comprises; a sensing unit for receiving the noise through a parasitic capacitance, the sensing unit having a first equivalent capacitance or a second equivalent capacitance, wherein the first equivalent capacitance is an equivalent capacitance of the capacitance of the capacitive touch panel at the touched condition and the parasitic capacitance, and the second equivalent capacitance is an equivalent capacitance of the capacitance of the capacitive touch panel at the untouched condition and the parasitic capacitance; a sensing signal generating unit coupled to the sensing unit, for generating the sensing signal according to the first equivalent capacitance and the noise or according to the second equivalent capacitance and the noise, a first resistor having a first end coupled to the sensing signal generating unit and a second end coupled to an inverting input of the first differential amplifier; and a first capacitor having a first end coupled to the inverting input of the first differential amplifier and a second end coupled to an output of the first differential amplifier; a reference signal path for receiving the noise and outputting a reference signal, the reference signal path having the same electrical conditions as the sensing signal path, wherein the reference signal path comprises; a reference unit for receiving the signal, the reference unit having a third capacitance, wherein the third capacitance simulates the capacitance of the capacitive touch panel at the untouched condition and the parasitic capacitance; a reference signal generating unit coupled to the reference unit, for outputting the reference signal according to the third equivalent capacitance and the noise; a second resistor having a first end coupled to the reference signal generating unit and a second end coupled to a non-inverting input of the first differential amplifier; and a second capacitor having a first end coupled to the non-inverting input of the first differential amplifier and a second end coupled to a ground, wherein the reference unit has the same circuits as the sensing unit, the reference signal generating unit has the same circuits as the sensing signal generating unit, a resistance of the second resistor is the same as a resistance of the first resistor, and a capacitance of the second capacitor is the same as a capacitance of the first capacitor; and a first differential amplifier for receiving the sensing signal and the reference signal, subtracting the reference signal from the sensing signal to generate an output signal. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
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Specification