Means and method for detecting capacitance connected to ac power

Abstract

The present invention relates to a novel means and a novel method for detecting a capacitance connected to AC power, which detect a sensor capacitance on the basis of a charge sharing phenomenon occurring due to a difference between voltages applied to a sensor capacitor and an auxiliary capacitor connected to a detection system when an AC voltage applied to the detection system alternates. According to the present invention, since the sensitivity of a signal detected by a detection system is improved, a magnitude and a change amount of a sensor capacitance are stably acquired.

1 . A means for detecting a capacitance, comprising:
 a fixed capacitor configured to have a fixed capacitance;   a variable capacitor configured to generate a variable capacitance; and   a signal detector configured to detect a change in voltage due to a charge flowing between the fixed capacitor and the variable capacitor,   wherein the signal detector detects the change in voltage in synchronization with an alternating current (AC) voltage which is applied to the fixed capacitor, and acquires the variable capacitance on the basis of the detected change in voltage.   
     
     
         2 . The means of  claim 1 , wherein the fixed capacitor and the variable capacitor are charged with a direct current (DC) voltage, or keep a charged charge in a floating state after being charged. 
     
     
         3 . The means of  claim 1 , further comprising a switching device,
 wherein the switching device charges the fixed capacitor and the variable capacitor with a DC voltage, or keeps the fixed capacitor and the variable capacitor in a floating state to conserve a charged charge after being charged.   
     
     
         4 . The means of  claim 1 , wherein the variable capacitor includes a sensor, the sensor generating the variable capacitance with an external object approaching or contacting the sensor. 
     
     
         5 . The means of  claim 4 , wherein the variable capacitance is changed in response to an opposing distance or an opposing area between the sensor and the external object. 
     
     
         6 . The means of  claim 1 , wherein the fixed capacitor has an equivalent capacitance corresponding to a capacitance of a parasitic capacitor generated by a connection to the signal detector and a capacitance of a storage capacitor in which the charge is stored. 
     
     
         7 . The means of  claim 1 , wherein the fixed capacitor is grounded to a first ground, and
 the variable capacitor is grounded to a second ground.   
     
     
         8 . The means of  claim 7 , wherein the first ground keeps an amplitude difference of a constant size from a frequency which is in-phase with the alternating current voltage, and
 a DC voltage is applied to the fixed capacitor based on the first ground.   
     
     
         9 . The means of  claim 7 , wherein the second ground is an earth ground in which a DC voltage is zero, or a DC voltage having a constant amplitude. 
     
     
         10 . The means of  claim 7 , wherein, when the signal detector outputs a detection result, the first ground and the second ground are connected to each other and the AC voltage keeps a DC voltage having a constant amplitude. 
     
     
         11 . The means of  claim 7 , wherein the first ground and the AC voltage have a first frequency during a first duration and a second frequency during a second duration,
 wherein the first and second frequencies are different from each other, and   wherein the first and second durations are alternated with each other.   
     
     
         12 . The means of  claim 1 , wherein the variable capacitor includes a sensor,
 the sensor having a plurality of sensing surfaces opposing each other, and generating variable capacitances with a plurality of external objects approaching or contacting the plurality of sensing surfaces, respectively.   
     
     
         13 . The means of  claim 1 , wherein the variable capacitor includes a plurality of sensors generating the variable capacitance,
 the plurality of sensors generating variable capacitances with a plurality of external objects approaching or contacting the plurality of sensors.   
     
     
         14 . The means of  claim 13 , wherein the signal detector senses a first voltage of the sensor or each sensor among the plurality of sensors when the variable capacitance is not generated, and senses a second voltage of the sensor or each sensor among the plurality of sensors when the variable capacitance is generated, the signal detector acquiring the variable capacitance or the plurality of variable capacitances on the basis of a difference between the first and second voltages. 
     
     
         15 . The means of  claim 14 , wherein the first voltage is a sum of a first charging voltage which is a DC voltage having a constant amplitude and the AC voltage, and
 wherein the second voltage is a difference between the first voltage and a voltage sensed by the sensor after a flow of the charge between the fixed capacitor and the variable capacitor is completed.   
     
     
         16 . The means of  claim 15 , further comprising:
 an earth ground which is the DC voltage having the constant amplitude,   wherein the variable capacitor accumulates the charge supplied from the fixed capacitor when the AC voltage is increased based on the earth ground, and the fixed capacitor accumulates the charge supplied from the variable capacitor when the AC voltage is decreased based on the earth ground.   
     
     
         17 . A method for acquiring a variable capacitance by a means including a fixed capacitor having a fixed capacitance and a variable capacitor generating the variable capacitance, the method comprising:
 detecting, by a signal detector, a change in voltage due to a charge floating between the fixed capacitor and the variable capacitor; and   acquiring the variable capacitance on the basis of the change in voltage,   wherein the signal detector detects the change in voltage in synchronization with an alternating current (AC) voltage which is applied to the fixed capacitor.   
     
     
         18 . The method of  claim 17 , wherein the fixed capacitor and the variable capacitor are charged with a DC voltage or keep a charged charge in a floating state after being charged. 
     
     
         19 . The method of  claim 17 , further comprising charging, by a switching device, the fixed capacitor and the variable capacitor with a DC voltage or keeping the fixed capacitor and the variable capacitor in a floating state to conserve a charged charge after being charged. 
     
     
         20 . The method of  claim 17 , wherein the variable capacitor includes a sensor, the sensor generating the variable capacitance with an external object approaching or contacting the sensor. 
     
     
         21 . The method of  claim 20 , wherein the variable capacitance is changed in response to an opposing distance or an opposing area between the sensor and the external object. 
     
     
         22 . The method of  claim 17 , wherein the fixed capacitor has an equivalent capacitance corresponding to a capacitance of a parasitic capacitor generated by a connection to the signal detector and a capacitance of a storage capacitor in which the charge is stored. 
     
     
         23 . The method of  claim 17 , wherein the fixed capacitor is grounded to a first ground, and
 the variable capacitor is grounded to a second ground.   
     
     
         24 . The method of  claim 23 , wherein the first ground keeps an amplitude difference of a constant size from a frequency which is in-phase with the alternating current voltage, and
 a DC voltage is applied to the fixed capacitor based on the first ground.   
     
     
         25 . The method of  claim 23 , wherein the second ground is an earth ground in which a DC voltage is zero or a DC voltage having a constant amplitude. 
     
     
         26 . The method of  claim 23 , wherein, when the signal detector outputs a detection result, the first ground and the second ground are connected to each other and the AC voltage keeps a DC voltage having a constant amplitude. 
     
     
         27 . The method of  claim 23 , wherein the first ground and the AC voltage have a first frequency during a first duration and a second frequency during a second duration,
 wherein the first and second frequencies are different from each other, and   wherein the first and second durations are alternated with each other.   
     
     
         28 . The method of  claim 17 , wherein the variable capacitor includes a sensor,
 the sensor having a plurality of sensing surfaces opposing each other, and generating variable capacitances with a plurality of external objects approaching or contacting the plurality of sensing surfaces, respectively.   
     
     
         29 . The method of  claim 18 , wherein the variable capacitor includes a plurality of sensors generating the variable capacitance,
 the plurality of sensors generating variable capacitances with a plurality of external objects approaching or contacting the plurality of sensors.   
     
     
         30 . The method of  claim 29 , wherein the signal detector senses a first voltage of the sensor or each sensor among the plurality of sensors when the variable capacitance is not generated and senses a second voltage of the sensor or each sensor among the plurality of sensors when the variable capacitance is generated, the signal detector acquiring the variable capacitance or the plurality of variable capacitances on the basis of a difference between the first and second voltages. 
     
     
         31 . The method of  claim 30 , wherein the first voltage is a sum of a first charging voltage which is the DC voltage having a constant amplitude and the AC voltage, and
 wherein the second voltage is a difference between the first voltage and a voltage sensed by the sensor after a flow of the charge between the fixed capacitor and the variable capacitor is completed.   
     
     
         32 . The method of  claim 31 , wherein the means further includes an earth ground which is the DC voltage having the constant amplitude,
 wherein the variable capacitor accumulates the charge supplied from the fixed capacitor when the AC voltage is increased based on the earth ground, and   wherein the fixed capacitor accumulates the charge supplied from the variable capacitor when the AC voltage is decreased based on the earth ground.