Abstract:
The present disclosure relates to a method for detecting an object near an electronic system, comprising steps of: forming electrodes around a central area, on an electrically insulating medium, determining measurements representative of the capacitance of the electrodes, and comparing the measurements with a detection threshold, and deducing whether or not an object is near the central area in a detection, the electrically insulating medium on which the electrodes are formed being deposited on an electrically conductive medium forming a shield, the capacitance measurements being taken by simultaneously activating all the electrodes.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a capacitive sensor-type device for detecting the proximity of an object. The present disclosure particularly applies to screens, control keyboards, and more generally to any device wherein it is desirable to detect an object such as a user&#39;s finger or hand near the device. 
         [0003]    2. Description of the Related Art 
         [0004]    One well-known method involves using electrodes in the form of keys or in the form of bands disposed, according to a matrix configuration forming a touch pad, for detecting the presence of a user&#39;s finger on a key or on an area of the touch pad. Such a touch pad may be associated with a screen in devices such as mobile telephones, to detect the position of a finger on an area of the screen, i.e., at a distance of less than a few millimeters from the latter. 
         [0005]      FIG. 1  represents a touch pad TS comprising electrodes T 1 , . . . Tp, R 1 , . . . Rn having the form of bands, which include electrodes Ti (i being a whole number ranging between 1 and p) disposed in columns, and electrodes Rj (j being a whole number ranging between 1 and p) disposed in rows transversal to the electrodes Ti. Generally, only one of the so-called “sending” electrodes is activated at a given instant, and so-called “receiving” electrodes are scanned one after the other or simultaneously to obtain measurements representative of the capacitance of each pair of electrodes comprising the active sending electrode and the scanned receiving electrode. The column electrodes Ti (or row electrodes Rj) are connected as sending electrodes, and the row electrodes Rj (or column electrodes Ti) are connected as receiving electrodes. Using the measurements obtained, the position of an object on the touch pad may be determined, given that the presence of an object on the touch pad can change the capacitance of pairs of electrodes located near the object. 
         [0006]    Amongst the capacitance measurement methods suited to touch pads, there are particularly methods based on the measurement of a capacitor charge or discharge time into a resistor, methods based on the use of a relaxation oscillator, and methods based on the charge transfer principle. The methods using a relaxation oscillator involve generating a signal having a frequency which varies according to the capacitance to be measured, then measuring the frequency of that signal. The methods based on charge transfer involve using a “sampling” capacitor, with a high capacitance compared to the capacitances to be measured, charging the capacitance to be measured, and transferring the charge of the capacitance to be measured into the sampling capacitor, and repeating these charge and transfer operations a certain number of cycles. Certain methods based on charge transfer involve executing a fixed number of charge and transfer cycles, and measuring the voltage at the terminals of the sampling capacitor, which is representative of the capacitance to be measured, at the end of the fixed number of cycles. Other methods based on charge transfer execute charge and transfer cycles until the voltage at the terminals of the sampling capacitor reaches a threshold voltage, the number of cycles thus executed being representative of the capacitance to be measured. 
         [0007]    An example of implementation of the method based on charge transfer applied to a touch pad is described in U.S. Pat. No. 6,452,514.  FIG. 1  represents a control circuit IOC of the touch pad TS, as described in that document. The circuit IOC comprises input/output ports P 0 , P 1 , . . . Pn and output ports Pn+1 to Pn+p. Each input/output port Pj (j being a whole number ranging between 1 and n) is connected to a respective input/output stage of the circuit IOC. Each input/output stage connected to a port Pj comprises a switch I 4  controlled by a signal S 4 , and a transistor M 5  the gate of which is controlled by a signal S 5 . Each switch I 4  comprises a terminal connected to a node common to other input/output stages and a terminal connected to the port Pj and to the drain of the transistor M 5 . The source of each transistor M 5  is connected to the ground. Each output port Pn+i (i being a whole number ranging between 1 and p) is linked to a supply voltage source Vdd of the circuit through a transistor M 6  the gate of which is controlled by a signal S 6 . The port P 0  is connected to the drain of a transistor M 5  the gate of which is controlled by a signal S 5  and the source of which is grounded. The port P 0  is also connected to a logic circuit LGC supplying the control signals S 4 , S 5 , S 6  of each input/output and output stage. 
         [0008]    To control the electrodes T 1 -Tp and R 1 -Rn, the port P 0  is connected to a terminal of a sampling capacitor Cs the other terminal of which is connected to the ground. The ports P 1  to Pn are connected to the row electrodes R 1 -Rn, and the ports Pn+1 to Pn+p are connected to the column electrodes T 1  to Tp. 
         [0009]    Each row electrode Rj forms with each of the column electrodes Ti a capacitor the capacitance of which varies particularly according to the proximity of an object to an area in which the row electrode overlaps with the column electrode. The circuit LGC receives numbers (i, j) of a pair of ports to be analyzed Pn+i, Pj to locate an object on the touch pad TS, and supplies a measurement DT representative of the capacitance of the pair of electrodes Ti, Rj connected to the selected pair of ports Pn+i, Pj. The measurement representative of the capacitance of the pair of electrodes is obtained according to a number of cycles executed for charging the pair of electrodes and transferring the charge to the sampling capacitor Cs, and to the voltage at the terminals of the capacitor Cs after the number of cycles executed. 
         [0010]    The logic circuit LGC manages the control circuit IOC that has just been described in accordance with a sequence of steps summarized in Table 1 below: 
         [0000]                                                                                TABLE 1                           Port                    P0   Pj   Pn + i                Step   S5   S4   S5   S6   Description               1   1   0   1   0   Discharge of Cs and Rj       2   0   0   1   0   Dead time       3   0   1   0   1   Connection of Cs to Rj and Ti to Vdd       4   0   0   1   0   Dead time       5   0   0   1   0   Rj on 0       6   0   0   1   0   Dead time       7   0   0   1   0   Reading of the charge of Cs                    
In Table 1 and below, i and j represent whole numbers varying from 1 to p, and from 1 to n, respectively.
 
         [0011]    The sequence of steps which comprises steps 1 to 7, is executed successively for each port Pj and each port Pn+i, and thus for each pair of electrodes (Ti, Rj) connected to the circuit IOC. During the execution of this sequence, all the switches I 4  and transistors M 5 , M 6  of the circuit IOC, the control signals S 4 , S 5 , S 6  of which are not mentioned in Table 1, remain open or off. Step 1 is an initialization step during which the signals S 5  switch on the transistors M 5 , connected to the ports P 0  and Pj, to discharge the capacitor Cs and the selected electrode Rj. The next step 2 is a dead-time step during which all the transistors M 5 , M 6  are off and all the switches I 4  are open. In step 3, the switch I 4  connected to the port Pi is closed to enable a charge transfer between the electrode Rj and the capacitor Cs. In parallel, the transistor M 6  connected to the port Pn+i is switched on to charge the electrode Ti to the supply voltage Vdd. The result is a charge transfer between the electrode Rj and the capacitor Cs. The next step 4 is a dead-time step, identical to step 2. In the next step 5, the transistor M 5  connected to the port Pj is switched on to discharge the electrode Rj. The next step 6 is a dead-time step, identical to step 2. In the next step 7, all the switches I 1  remain open and only the transistor M 5  connected to the port Pj is switched on. The voltage of the port P 0 , corresponding to the voltage of the capacitor Cs, is then measured. 
         [0012]    The execution of steps 3 to 6 is repeated a certain fixed number of cycles. After executing this number of cycles, the voltage of the port P 0  is measured. The presence and the position of an object on the touch pad TS are then determined according to the measurements obtained for each pair of electrodes Ti, Rj. In practice, a finger of a user can only be detected and located on the touch pad TS if it is less than a few millimeters from an overlapping area of the electrodes of a pair of electrodes (Ti, Rj). 
       BRIEF SUMMARY 
       [0013]    It may be useful to integrate a proximity sensor into a system such as a mobile telephone, whether or not integrating the touch pad described above, to activate or deactivate the system or more generally, to activate or deactivate certain functions of the system. Therefore, the proximity sensor may be used to detect when the user moves his hand or a finger to within a distance of a few centimeters from the system or more. For example, control keyboard backlighting may be activated when the user moves his hand toward the keyboard. A proximity detector may also be integrated into a mobile telephone to lock a touch-sensitive keyboard and/or put a screen into low-energy mode during a telephone call, when the user moves the telephone close to his ear. 
         [0014]    Some embodiments relate to a method for detecting an object near an electronic system, comprising steps of: forming electrodes around a central area, on an electrically insulating medium, determining measurements representative of the capacitance of the electrodes, and comparing the measurements with a detection threshold, and deducing whether or not an object is near the central area in a detection field. According to one embodiment, the electrically insulating medium on which the electrodes are formed is deposited on an electrically conductive medium forming a shield, the capacitance measurements being taken by simultaneously activating all the electrodes. 
         [0015]    According to one embodiment, the detection threshold is defined so as to detect an object at a distance of at least several centimeters along an axis perpendicular to the central area and passing through a point of the central area, located at an equal distance from opposite pairs of electrodes of the electrodes. 
         [0016]    According to one embodiment, the method comprises a step of forming an electrically conductive edge around the set comprising the electrodes and the central area. 
         [0017]    According to one embodiment, the method comprises a step of forming an electrically insulating layer covering the electrodes. 
         [0018]    According to one embodiment, the method comprises a step of generating a voltage greater than a supply voltage of the electronic system, and of using the voltage generated to determine a measurement representative of the capacitance of the electrodes. 
         [0019]    According to one embodiment, the method comprises a step of connecting the shield to the ground. 
         [0020]    According to one embodiment, each measurement representative of capacitance comprises steps of: executing several cycles of charging the electrodes and of transferring the charge between the electrodes and a sampling capacitor, and determining the measurement representative of the capacitance of the electrodes according to the number of charge and transfer cycles, so that the voltage at the terminals of the sampling capacitor reaches a threshold voltage, or according to the voltage at the terminals of the sampling capacitor, after a fixed number of charge and transfer cycles. 
         [0021]    According to one embodiment, each measurement representative of the capacitance of the electrodes comprises steps of: (a) applying a first voltage to a first terminal of a sampling capacitor and a second intermediate voltage in between the first voltage and a third voltage greater than or equal to a ground voltage, to the second terminal of the sampling capacitor, (b) applying the third voltage to a first group of the electrodes, and the second voltage to a second group of the electrodes, not comprising the electrodes of the first group, (c) linking the electrodes of the first group to the first terminal of the sampling capacitor and applying the second voltage to the electrodes of the second group and to the second terminal of the sampling capacitor, to transfer electric charges between the electrodes and the sampling capacitor, and (d) executing several cycles each comprising steps (b) and (c), the measurement representative of the capacitance of the electrodes being determined according to the voltage at a terminal of the sampling capacitor the other terminal of which receives the third voltage, after executing a fixed number of cycles, or according to the number of cycles executed so that the voltage at a terminal of the sampling capacitor reaches a threshold voltage. 
         [0022]    Some embodiments relate to a device for detecting an object near an electronic system, comprising electrodes surrounding a central area, on an electrically insulating medium, and a control circuit for controlling the electrodes, configured for determining a measurement representative of the presence of an object near the central area. 
         [0023]    According to one embodiment, the device comprises an electrically conductive shield, on which the electrically insulating medium is deposited, the control circuit being configured for implementing the method defined above. 
         [0024]    According to one embodiment, the shield comprises an electrically conductive edge formed around the set comprising the electrodes and the central area. 
         [0025]    According to one embodiment, the device comprises an electrically insulating layer covering the electrodes. 
         [0026]    According to one embodiment, the device comprises two electrodes disposed in rows and two electrodes disposed in columns, transversal to the row electrodes. 
         [0027]    According to one embodiment, the shield is connected to the ground. 
         [0028]    Some embodiments also relate to an electronic system comprising a proximity detection device. 
         [0029]    Some embodiments also relate to a portable object comprising a proximity detection device like the one defined above. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0030]    Some examples of embodiments of the present disclosure will be described below in relation with, but not limited to, the following figures, in which: 
           [0031]      FIG. 1  described above schematically represents a touch pad and a control circuit of the touch pad, according to prior art, 
           [0032]      FIG. 2  represents a front view of a proximity detection device according to one embodiment, 
           [0033]      FIG. 3  represents a cross section of the proximity detection device in  FIG. 2 , 
           [0034]      FIG. 4  represents the proximity detection device in perspective and a detection field of the detection device, 
           [0035]      FIG. 5  schematically represents a control circuit of the proximity detection device, according to one embodiment, 
           [0036]      FIG. 6  schematically represents a control circuit of the proximity detection device, according to another embodiment, 
           [0037]      FIGS. 7A to 7D  represent various configurations of electrodes of the proximity detection device. 
           [0038]      FIG. 8  is a block diagram of a system that includes a proximity detection device, according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]      FIGS. 2 and 3  represent a proximity detection device according to one embodiment. The proximity detection device comprises four electrodes in the form of bands disposed in a same plane, two electrodes EV 1 , EV 2  of which are disposed in columns and two electrodes EH 1 , EH 2  of which are disposed in rows transversal to the column electrodes. In the example in  FIG. 2 , the electrodes EV 1 , EV 2 , EH 1 , EH 2  are rectilinear and disposed so as to surround a central area  1  rectangular in shape. Positioned in the central area  1  is a central structure  1 A that in one embodiment is simply a support structure of dielectric material, for example. Alternatively, the central structure  1 A could include control electronics, such as the controller IOC 1  of  FIG. 5 , or a detection device, such as the touch pad TS shown in  FIG. 1 . 
         [0040]    According to one embodiment, the electrodes EV 1 , EV 2 , EH 1 , EH 2  are formed on an electrically insulating layer  2 , and the layer  2  is deposited on an electrically conductive layer  4  forming a shield. It shall be noted that, in one embodiment, the layers  2  and  4  are formed solely in an area extending beneath the electrodes, excluding an area located in the center of the central area  1 . On the periphery of the layer  4  there is an edge  3  extending along the electrodes EV 1 , EV 2 , EH 1 , EH 2  and surrounding the layer  2 , the electrodes and the central area  1 . The electrodes may also be covered by an electrically insulating layer  5 . The layer  4  is grounded. It shall be noted that the layers  2 ,  4  and  5  can be formed on the entire surface area extending beneath the central area  1  and the electrodes or solely in an area extending beneath the electrodes EV 1 , EV 2 , EH 1 , EH 2 , excluding an area located in the center of the central area  1 . 
         [0041]    As shown in  FIG. 4 , the detection field FLD of the proximity detection device is delimited by a lobe extending along an axis Z perpendicular to the plane of the electrodes EV 1 , EV 2 , EH 1 , EH 2 , and passing through a point O of this plane located at an equal distance from the row electrodes EH 1 , EH 2  and at an equal distance from the column electrodes EV 1 , EV 2 . Thanks to the presence of the shield layer  4 , the detection field may extend several tens of centimeters from the electrodes. Due to the presence of the edge  3 , the detection field FLD barely extends outside the volume delimited by the plane of the electrodes and the planes perpendicular to this plane and passing through each of the electrodes. The detection field FLD therefore has a section in a plane passing through the axis OZ which is substantially parabolic in shape. Therefore, these arrangements enable both good detection directivity and a relatively high detection distance to be obtained. 
         [0042]    The column EV 1 , EV 2  (or row EH 1 , EH 2 ) electrodes may be used as sending electrodes, and the row EH 1 , EH 2  (or column EV 1 , EV 2 ) electrodes may be used as receiving electrodes. According to one embodiment, the two sending electrodes are activated simultaneously and the two receiving electrodes are scanned simultaneously, to detect an object near the electrodes in the detection field FLD. 
         [0043]      FIG. 5  represents a control circuit IOC 1  of the proximity detection device, according to one embodiment. The circuit IOC 1  is for example integrated into a processor PRC. The processor PRC is for example of microcontroller type. The circuit IOC 1  comprises input/output ports P 0 , P 1 , P 2  and output ports P 3  and P 4 . Each input/output port P 0 , P 1 , P 2  is connected to a respective input/output stage of the circuit IOC 1  comprising a transistor the gate of which is controlled by a signal S 31 , S 32 , S 33 . The source of each transistor M 31 , M 32 , M 33  is connected to the ground and the drain of these transistors is connected to one of the ports P 0 , P 1 , P 2 . The ports P 1 , P 2  are linked through a switch I 11 , I 12 , to a common node N 1  connected to the port P 0 . The switches I 11 , I 12  are controlled by two signals S 11 , S 12 . Each output port P 3 , P 4  is linked to a voltage source Vh through a transistor M 21 , M 22  the gate of which is controlled by a signal S 21 , S 22 . The port P 0  is also connected to a comparator CP the output of which is connected to a logic circuit LGC 1  supplying the control signals S 11 , S 12 , S 21 , S 22 , S 31 , S 32 , S 33  of the switches I 11 , I 12  and the transistors M 21 , M 22 , M 31 , M 32 , M 33 . 
         [0044]    To control the electrodes EV 1 , EV 2 , EH 1 , EH 2 , the port P 0  is connected to a terminal of a sampling capacitor Cs the other terminal of which is connected to the ground. The ports P 1  and P 2  are connected to the row electrodes EH 1 , EH 2 , and the ports P 3  and P 4  are connected to the column electrodes EV 1 , EV 2 . The comparator CP supplies the circuit LGC 1  with a detection signal DT. The circuit LGC 1  supplies a measurement CY representative of the capacitance formed between the electrodes EH 1 , EH 2 , EV 1 , EV 2 . The measurement representative of the capacitance of the electrodes is obtained according to a number of executed cycles of charging and transferring the charge to the sampling capacitor Cs, and to the voltage at the terminals of the capacitor Cs after the number of cycles executed. 
         [0045]    The logic circuit LGC 1  can manage the control circuit IOC 1  that has just been described in accordance with a sequence of steps summarized in Table 2 below: 
         [0000]    
       
         
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 S11, 
                 S32, 
                 S21, 
                   
               
               
                 Step 
                 S31 
                 S12 
                 S33 
                 S22 
                 Description 
               
               
                   
               
             
             
               
                 1 
                 1 
                 0 
                 1 
                 0 
                 Discharge of Cs, EH1, and EH2 
               
               
                 2 
                 0 
                 0 
                 0 
                 0 
                 Dead time 
               
               
                 3 
                 0 
                 1 
                 0 
                 1 
                 Connection of EH1, EH2 to Cs, and 
               
               
                   
                   
                   
                   
                   
                 EV1, EV2 to Vh 
               
               
                 4 
                 0 
                 0 
                 0 
                 0 
                 Dead time 
               
               
                 5 
                 0 
                 0 
                 1 
                 0 
                 EH1 and EH2 to 0 
               
               
                 6 
                 0 
                 0 
                 0 
                 0 
                 Dead time 
               
               
                 7 
                 0 
                 0 
                 1 
                 0 
                 Reading of the charge of Cs 
               
               
                   
               
             
          
         
       
     
         [0046]    The sequence of steps comprises steps 1 to 7 executed periodically. Step 1 is an initialization step during which the signals S 31 , S 32 , S 33  switch on the transistors M 31 , M 32  and M 33  connected to the ports P 0 , P 1  and P 2 , to discharge the capacitor Cs and the electrodes EH 1  and EH 2 . The next step 2 is a dead-time step during which all the transistors M 21 , M 22 , M 31 , M 32 , M 33  are off and the switches I 11 , I 12  are open. In step 3, the switches I 11 , I 12  connected to the ports P 1 , P 2  are closed to enable a charge transfer between the electrodes EH 1 , EH 2  and the capacitor Cs. In parallel, the transistors M 21 , M 22  connected to the ports P 3 , P 4  are switched on to charge the electrodes EV 1 , EV 2  to the voltage Vh. The result is a charge transfer between the electrodes EH 1 , EH 2  and the capacitor Cs. The next step 4 is a dead-time step, identical to step 2. In the next step 5, the transistors M 32 , M 33  connected to the ports P 1 , P 2  are switched on to discharge the electrodes EH 1 , EH 2 . The next step 6 is a dead-time step, identical to step 2. In the next step 7, the switches I 11 , I 12  remain open and only the transistors M 32 , M 33  connected to the ports P 1 , P 2  are switched on. The voltage of the port P 0 , corresponding to the voltage of the capacitor Cs, is then measured. 
         [0047]    According to one embodiment, the execution of steps 3 to 6 is repeated a certain fixed number of cycles. After executing this fixed number of cycles, the voltage of the port P 0  is measured in step 7. The presence and the position of an object in the detection field FLD is then determined according to the measurement of the measured voltage of the capacitor Cs. In another embodiment, the execution of steps 2 to 7 is repeated a variable number of cycles CY until the voltage of the capacitor Cs reaches a threshold voltage set by the comparator CP. 
         [0048]      FIG. 6  represents a control circuit IOC 2  of the proximity detection device, according to another embodiment. The circuit IOC 2  comprises seven input/output ports P 0 , P 1 , . . . P 6 . Each port P 0 -P 7  is connected to a respective input/output stage of the circuit IOC 2 . Each input/output stage comprises a switch I 1  controlled by a corresponding signal of signals SA 1 -SG 1 , a first transistor M 2  having a gate controlled by a corresponding signal of signals SA 2 -SG 2 , and a second transistor M 3  having a gate controlled by a corresponding signal of signals SA 3 -SG 3 . The switch I 1  comprises a terminal connected to a node common to other input/output stages and a terminal connected to the port P 0 -P 7  of the stage, to the source of the transistor M 2  and to the drain of the transistor M 3 , of the stage. The drain of the transistor M 2  receives a voltage Vh which may be the supply voltage of the circuit, and the source of the transistor M 3  is connected to the ground. The circuit IOC 2  comprises two groups of input/output stages each comprising a common node N 1 , N 2 . The switches I 1  of the ports P 0  to P 3  are connected to a first common node N 1 , and the switches I 1  of the ports P 4  to P 7  are connected to a second common node N 2 , not connected to the common node N 1 . In addition, at least one of the ports, for example the port P 4 , is connected to an output  104  connected to the input of a comparator CP 1 . The output of the comparator CP 1  is connected to a logic circuit LGC 2  supplying the control signals SA 1 -SG 3 . Each of the other ports P 0  to P 7  may also be connected to an output  100  to  107  connected to a comparator (not represented) which may be identical to the comparator CP 1 , and the output of which is connected to the circuit LGC 2 . 
         [0049]    According to one embodiment, to control electrodes EH 1 , EH 2 , EV 1 , EV 2  of the proximity detection device, one of the ports connected to a comparator, for example the port P 4  connected to the comparator CP 1 , is connected to a terminal a of a sampling capacitor Cs the other terminal b of which is connected to a port of the other group of input/output stages, for example the port P 3 . Therefore, whatever the status of the switches I 1 , the terminals of the capacitor Cs cannot be short-circuited. Furthermore, the port P 0  for example, receives a reference voltage Vrf lower than the voltage Vh, for example the voltage Vh divided by 2, and the other ports P 1 , P 2 , P 5 , P 6  are each connected to one of the electrodes EH 1 , EH 2 , EV 1 , EV 2 . In the example in  FIG. 6 , the ports P 1  and P 2  are connected respectively to the row electrodes EH 1 , EH 2 , and the ports P 5  and P 6  are connected respectively to the column electrodes EV 1 , EV 2 . 
         [0050]    Together with the column electrodes EV 1 , EV 2 , the row electrodes EH 1 , EH 2  form capacitors the capacitance of which varies particularly according to the proximity of an object. The comparator CP 1  supplies the circuit LGC 2  with a detection signal DT. The circuit LGC 2  supplies a number of cycles CY that were used to discharge the capacitor Cs below a certain threshold detected by the comparator CP 1 . This threshold is for example in the order of Vh/3. 
         [0051]    The logic circuit LGC 2  manages the control circuit IOC 2  that has just been described in accordance with a sequence of steps summarized in Table 3 below: 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                 SB1, 
                   
                   
                   
                   
                 SF1, 
                 SF3, 
                   
               
               
                 Step 
                 SA1 
                 SC1 
                 SD1 
                 SD3 
                 SE1 
                 SE2 
                 SG1 
                 SG3 
                 Description 
               
               
                   
               
             
             
               
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 0 
                 0 
                 Charge of Cs between Vh and Vrf 
               
               
                 2 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 Dead time 
               
               
                 3 
                 1 
                 1 
                 0 
                 0 
                 0 
                 0 
                 0 
                 1 
                 Charge of EH1, EH2/EV1, EV2 between 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 0 and Vrf 
               
               
                 4 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 Dead time 
               
               
                 5 
                 1 
                 1 
                 1 
                 0 
                 1 
                 0 
                 1 
                 0 
                 Charge transfer between EH1, 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 EH2/EV1, EV2 and Cs 
               
               
                 6 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 Dead time 
               
               
                 7 
                 0 
                 0 
                 0 
                 0 
                 0 
                 1 
                 0 
                 0 
                 Reading of the charge of Cs 
               
               
                   
               
             
          
         
       
     
         [0052]    The sequence of steps comprises steps 1 to 7. During the execution of this sequence, all the switches I 1  and the transistors M 2 , M 3  of the circuit IOC 2 , having control signals that are not mentioned in Table 3, remain open or off. In step 1, the switch I 1  of the stage connected to the port P 3  is closed, while the signal SE 2  switches on the transistor M 2  connected to the port P 4 , and the signal SA 1  closes the switch I 1  connected to the port P 0 . Therefore, the terminals a and b of the capacitor Cs respectively receive the voltages Vh and Vrf, to charge the capacitor Cs to a voltage equal to the difference between the voltages Vh and Vrf. The next step 2 is a dead-time step during which all the transistors M 2 , M 3  are off and the switches I 1  are open. In step 3, the electrodes EH 1 , EH 2 , EV 1 , EV 2  are charged between Vrf and the ground. For this purpose, the transistors M 3  connected to the ports P 5 , P 6  are switched on using the corresponding signals SF 3 , SG 3  to put the electrodes EV 1 , EV 2  to the ground. In parallel, the switches I 1  connected to the ports P 0 , P 1 , P 2  are open to put the electrodes EH 1 , EH 2  to the voltage Vrf. The next step 4 is a dead-time step, identical to step 2. In the next step 5, all the switches I 1  are closed simultaneously to transfer electric charges between the terminals a, b of the capacitor Cs and the electrodes EH 1 , EH 2 , EV 1 , EV 2 . Therefore, the terminal a of the capacitor Cs is linked to the electrodes EV 1 , EV 2 , and the terminal b of the capacitor Cs is linked to the electrodes EH 1 , EH 2 . Furthermore, the terminal b of the capacitor Cs is put to the voltage Vrf. The capacitor Cs is thus discharged into the capacitor formed by the electrodes EH 1 , EH 2 , EV 1 , EV 2 . The next step 6 is a dead-time step, identical to step 2. In the next step 7, the transistor M 3  of the stage connected to the port P 3  is switched on to put the terminal b of the capacitor Cs to the ground, so as to enable the voltage at the terminal a of the capacitor Cs to be read by the comparator CP 1 . 
         [0053]    The execution of steps 2 to 7 is then repeated a certain number of cycles until the signal at the input of the comparator CP 1 , corresponding to the voltage at the terminals a and b of the capacitor Cs, reaches a certain low threshold voltage value. The number of cycles of executing steps 2 to 7 varies according to the capacitance between the electrodes EH 1 , EH 2 , EV 1 , EV 2 , and thus makes it possible to determine whether or not an object such as a user&#39;s finger or hand is in the detection field FLD of the proximity detection device. The dead-time steps 2, 4, 6 make sure that the switching actions of the switches I 1  and of the transistors M 2 , M 3  are completed before controlling other switching actions. The duration of these steps may be adapted to the switching characteristics (particularly switching time) of the transistors and of the switches, and to the characteristics of the control signals SA 1 -SG 3 . When the voltage at the terminals of the capacitor Cs has reached the threshold voltage, the sequence of steps 1 to 7 is executed again to perform a new detection while the detection device is active. The processor PRC may thus determine the possible presence of an object near the electrodes, in the detection field FLD, if the number of cycles CY of executing steps 2 to 7 is lower than a detection threshold value. 
         [0054]    In another embodiment, the execution of steps 3 to 6 is repeated a certain fixed number of cycles. After executing this number of cycles, the voltage of the port P 4  is measured in step 7. In this case, the output  104  connected to the terminal a of the capacitor Cs is connected to a measuring circuit such as an analog-digital converter. The presence and the position of an object in the detection field FLD are then determined according to the measurement of the voltage of the capacitor Cs supplied by the measuring circuit. 
         [0055]    According to Table 3, it can be noted that the status of some of the transistors M 2  and M 3  never changes during the execution of the sequence of steps 1 to 7. Thus, the transistors M 2 , except for the one connected to the port P 4 , always remain off. The transistors M 3  connected to the ports P 0  to P 2  and P 4  are always off too. The circuit IOC 2  may therefore be simplified by removing these components. Furthermore, combinations of commands for controlling the switches and transistors M 2 , M 3  other than those indicated in Table 3 may enable the same results to be obtained as regards the connections of the electrodes and of the capacitor Cs between themselves, or to the ground or to the voltage sources at Vh and Vrf. 
         [0056]    Unlike the control mode described with reference to  FIG. 5  and Table 2, the control mode described with reference to  FIG. 6  and Table 3 makes it possible to avoid the capacitor Cs being charged negatively by the electrodes EH 1 , EH 2  in step 3, and thus avoids having to measure negative voltages to locate an object on the touch pad. Indeed, such voltages cannot be measured with standard microcontrollers comprising inputs of analog-digital converters. 
         [0057]    The voltage Vh may be equal to the supply voltage of the circuit IOC 1 , IOC 2 . In another embodiment, the voltage Vh may be greater than the supply voltage of the circuit, so as to increase the detection distance of the proximity detection device. Thus, the voltage Vh may be set to several tens of volts (for example 30 V), for a supply voltage of a few volts (for example 5 V). The voltage Vh can be generated by a buffer circuit  8  from the supply voltage of the circuit. 
         [0058]    Other configurations of electrodes suited to a proximity detection may easily be imagined. It is merely important that the electrodes be disposed around the central area  1 . Thus,  FIGS. 7A to 7D  represent other configurations of electrodes that may be implemented with the circuits in  FIGS. 5 and 6 . In  FIG. 7A , the electrodes EH 1 , EH 2 , EV 1 , EV 2  each have the shape of a band extending along an edge of the central area  1  and overlap at the corners of the latter. In  FIG. 7B , the electrodes EH 1 ′, EH 2 ′, EV 1 ′, EV 2 ′ each have a rectangular shape covering only a limited part of an edge of the central area  1 . In this example, the electrodes EH 1 ′, EH 2 ′, EV 1 ′, EV 2 ′ may have other shapes such as circular or elliptic for example. In  FIG. 7C , only two electrodes E 1 , E 2  surround the central area. Each of the electrodes E 1 , E 2  has the shape of a U disposed so as to cover an entire edge of the central area  1  as well as a part of the two adjacent edges of the latter. In this case, one of the electrodes E 1 , E 2  is connected to one of the ports P 1 , P 2  of the circuits IOC 1 , IOC 2  in  FIGS. 5 and 6  and the other one of the electrodes E 1 , E 2  is connected to one of the ports P 3 , P 4  of the circuit IOC 1  or to one of the ports P 5 , P 6  of the circuit IOC 2 . In  FIG. 7D , only two electrodes E 1 ′, E 2 ′ surround the central area. Each of the electrodes E 1 ′, E 2 ′ has the shape of an L disposed so as to cover two entire edges of the central area  1 . The electrodes E 1 ′, E 2 ′ may be connected to the circuit IOC 1  or IOC 2  in the same way as the electrodes E 1 , E 2 . 
         [0059]      FIG. 8  is a block diagram of a system  10  that includes a proximity detector  12  according to the present disclosure, such as either of the proximity detection devices shown in  FIGS. 2-7D . The system  10  may be any electronic device that could benefit from including the proximity detector  12 , such as a mobile phone, tablet, or other computing device. The system  10  also includes system electronics  14 , coupled to the proximity detector  12 , for implementing other functions of the system, such as telecommunications, etc. 
         [0060]    It will be understood by those skilled in the art that various alternative embodiments and various applications of the present disclosure are possible. In particular, the present disclosure is not limited to the implementation of the control circuits of the electrodes described with reference to  FIGS. 2 and 3 . Other known methods for measuring the capacitance of the electrodes EH 1 , EH 2 , EV 1 , EV 2  may be implemented, such as those mentioned above. Thus, the capacitance of the electrodes can be measured by implementing methods based on the measurement of a capacitor charge or discharge time into a resistor, methods based on the use of a relaxation oscillator, and other methods based on the charge transfer principle. 
         [0061]    The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.