Capacitance detecting apparatus and capacitive touch control system using the same
A capacitance detecting apparatus, coupled to a capacitor to be measured, includes a first capacitor, a second capacitor, a control module and a judging module. The first and second capacitors are coupled to the capacitor to be measured via an input node. The control module provides a first voltage-drop variation to the first capacitor and a second voltage-drop variation to the capacitor to be measured to introduce a third voltage-drop variation to the second capacitor. The first and second voltage-drop variations cause charge flowing from the first capacitor to the input node have a same sign with charge flowing from the input node to the capacitor to be measured. The judging module determines capacitance of the capacitor to be measured according to capacitance of the first and second capacitors as well as the first, second and third voltage-drop variations.
1. A capacitance detecting apparatus, coupled to a capacitor to be measured, the apparatus comprising:
a first capacitor and a second capacitor, coupled to the capacitor to be measured via an input node;
a control module, for providing a first voltage-drop variation to the first capacitor and a second voltage-drop variation to the capacitor to be measured to introduce a third voltage-drop variation to the second capacitor; wherein the first voltage-drop variation and the second voltage-drop variation cause charge flowing from the first capacitor to the input node to have a same sign with charge flowing from the input node to the capacitor to be measured; and
a judging module, for determining capacitance of the capacitor to be measured according to capacitance of the first capacitor, capacitance of the second capacitor, the first voltage-drop variation, the second voltage-drop variation and the third voltage-drop variation,
wherein the capacitor to be measured is connected to the capacitance detecting apparatus via a connecting wire formed on a circuit board, the circuit board has a shielding layer, and the first capacitor comprises parasitic capacitance between the connecting wire and the shielding layer, and the control module controls the shielding layer to provide the first voltage-drop variation of the first capacitor.
2. The capacitance detecting apparatus according to claim 1 , wherein the circuit board is a flexible circuit board or a printed circuit board.
3. The capacitance detecting apparatus according to claim 1 , wherein the first capacitor is coupled between the input node and a control node, and the second capacitor is coupled between the input node and an output node; at a first time point, the control module provides a first input voltage to the input node and the output node, and provides a first control voltage to the control node; at a second time point, the control module provides a second input voltage to the input node, and provides a second control voltage to the control node; a difference between the first input voltage and the second input voltage is smaller than a difference between the first control voltage and the second control voltage.
4. The capacitance detecting apparatus according to claim 3 , wherein the control module comprises:
an operational amplifier, comprising a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is the input node and the output terminal is the output node;
a first switch, coupled between the first input terminal and the output terminal, being turned on at the first time point and turned off at the second time point;
a second switch, coupled between the second input terminal and a second input voltage supply, being turned off at the first time point and turned on at the second time point;
a third switch, coupled between the second input terminal and a first input voltage supply, being turned on at the first time point and turned off at the second time point;
a fourth switch, coupled between the control node and a ground terminal, being turned on at the first time point and turned off at the second time point; and
a fifth switch, coupled between the control node and a first control voltage supply, being turned off at the first time point and turned on at the second time point.
5. The capacitance detecting apparatus according to claim 1 , wherein the capacitor to be measured is coupled between the input node and a driving node, the first capacitor is coupled between the input node and a control node, the second capacitor is coupled between the input node and an output node; at the first time point, the control module provides a reference voltage to the input node and the output node, provides a first voltage to the control node, and provides a second voltage to the driving node; at the second time point, the control module provides the reference voltage to the input node, provides the second voltage to the control node, and provides the first voltage to the driving node; wherein the first voltage is different from the second voltage.
6. The capacitance detecting apparatus according to claim 5 , wherein the control module comprises:
an operational amplifier, comprising a first input terminal, a second input terminal and an output terminal; wherein the first input terminal is the input node, the output terminal is the output node, and the second input terminal is coupled to a reference voltage supply;
a first switch, coupled between the first input terminal and the output terminal, being turned on at the first time point and turned off at the second time point;
a second switch, coupled between the driving node and a second input voltage supply, being turned on at the first time point and turned off at the second time point;
a third switch, coupled between the driving node and a first input voltage supply, being turned off at the first time point and turned on at the second time point;
a fourth switch, coupled between the control node and the first voltage supply, being turned on at the first time point and turned off at the second time point; and
a fifth switch, coupled between the control node and the second voltage supply, being turned off at the first time point and turned on at the second time point.
7. A capacitive touch control system, comprising:
a display device;
a plurality of sensing capacitors, respectively corresponding to a plurality of physical positions on the display device;
a first capacitor and a second capacitor, coupled to one of the plurality of sensing capacitors via an input node; wherein the one sensing capacitor is a capacitor to be measured;
a control module, for providing a first voltage-drop variation to the first capacitor and a second voltage-drop variation to the capacitor to be measured to incur a third voltage-drop variation of the second capacitor; wherein the first voltage-drop variation and the second voltage-drop variation cause charge flowing from the first capacitor to the input node to have a same sign with charge flowing from the input node to the capacitor to be measured; and
a judging module, for determining capacitance of the capacitor to be measured according to capacitance of the first capacitor, capacitance of the second capacitor, the first voltage-drop variation, the second voltage-drop variation and the third voltage-drop variation,
wherein the first capacitor and second capacitor are coupled to the capacitor to be measured via a connecting wire formed on a circuit board, the circuit board comprises a shielding layer, the first capacitor comprises a parasitic capacitance between the connecting wire and the shielding layer, and the control module controls the shielding layer to provide the first voltage-drop variation of the first capacitor.
8. The capacitive touch control system according to claim 7 , wherein the circuit board is a flexible circuit board or a printed circuit board.
9. The capacitive touch control system according to claim 7 , wherein the first capacitor is coupled between the input node and a control node, and the second capacitor is coupled between the input node and an output node; at a first time point, the control module provides a first input voltage to the input node and the output node, and provides a first control voltage to the control node; at a second time point, the control module provides a second input voltage to the input node, and provides a second control voltage to the control node; wherein a difference between the first input voltage and the second input voltage is smaller than a difference between the first control voltage and the second control voltage.
10. The capacitive touch control system according to claim 9 , wherein the control module comprises:
an operational amplifier, comprising a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is the input node and the output terminal is the output node;
a first switch, coupled between the first input terminal and the output terminal, being turned on at the first time point and turned off at the second time point;
a second switch, coupled between the second input terminal and a second input voltage supply, being turned off at the first time point and turned on at the second time point;
a third switch, coupled between the second input terminal and a first input voltage supply, being turned on at the first time point and turned off at the second time point;
a fourth switch, coupled between the control node and a ground terminal, being turned on at the first time point and turned off at the second time point; and
a fifth switch, coupled between the control node and a first control voltage supply, being turned off at the first time point and turned on at the second time point.
11. The capacitive touch control system according to claim 7 , wherein the capacitor to be measured is coupled between the input node and a driving node, the first capacitor is coupled between the input node and a control node, the second capacitor is coupled between the input node and an output node; at the first time point, the control module provides a reference voltage to the input node and the output node, provides a first voltage to the control node, and provides a second voltage to the driving node; at the second time point, the control module provides the reference voltage to the input node, provides the second voltage to the control node, and provides the first voltage to the driving node; the first voltage is different from the second voltage.
12. The capacitive touch control system according to claim 11 , wherein the control module comprises:
an operational amplifier, comprising a first input terminal, a second input terminal and an output terminal; wherein the first input terminal is the input node, the output terminal is the output node, and the second input terminal is coupled to a reference voltage supply;
a first switch, coupled between the first input terminal and the output terminal, being turned on at the first time point and turned off at the second time point;
a second switch, coupled between the driving node and a second input voltage supply, being turned on at the first time point and turned off at the second time point;
a third switch, coupled between the driving node and a first input voltage supply, being turned off at the first time point and turned on at the second time point;
a fourth switch, coupled between the control node and the first voltage supply, being turned on at the first time point and turned off at the second time point; and
a fifth switch, coupled between the control node and the second voltage supply, being turned off at the first time point and turned on at the second time point.