Patent ID: 12209889

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Like features have been designated by like references in the various figures. In particular, the structural and/or functional features that are common among the various embodiments may have the same references and may dispose identical structural, dimensional and material properties.

For the sake of clarity, only the steps and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail.

Unless indicated otherwise, when reference is made to two elements connected together, this signifies a direct connection without any intermediate elements other than conductors, and when reference is made to two elements coupled together, this signifies that these two elements can be connected or they can be coupled via one or more other elements.

In the following disclosure, unless indicated otherwise, when reference is made to absolute positional qualifiers, such as the terms “front”, “back”, “top”, “bottom”, “left”, “right”, etc., or to relative positional qualifiers, such as the terms “above”, “below”, “higher”, “lower”, etc., or to qualifiers of orientation, such as “horizontal”, “vertical”, etc., reference is made to the orientation shown in the figures.

Unless specified otherwise, the expressions “around”, “approximately”, “substantially” and “in the order of” signify within 10%, and preferably within 5%.

FIG.1shows an example of an electronic device10of the type for which the embodiments described hereinafter in relation withFIGS.2to5are intended.

Device10comprises a touch sensor, that is, a circuit configured to detect the contact of a portion of a body, for example, a human body, for example, the contact of a finger16, with a region12, located in a package14.

Device10is for example a wireless device, for example, a device powered by a battery or a cell. Further, device10is for example a device capable of being inactive for long periods. Device10is for example a remote control or a switch. Device10is for example a wireless headphone.

Region12for example corresponds to a button, having its activation, that is, its contact with finger16, causing the activation of one or a plurality of functionalities of device10and/or the leaving of a low-power operating mode.

The power consumption of device10is often a significant criterion in the design of device10. Thus, during idle periods, device10enters the so-called low-power operating mode. In such an operating mode, for example, standby, certain components and circuits of device10are not operating and are not powered, to keep energy.

During low-power operating periods, the circuit of detection of the contact with region12is generally maintained active. Thus, the detection of a contact between finger16and region12is generally used as a signal commanding the leaving of the low-power operating mode.

FIG.2shows an embodiment of a touch sensor20.

Sensor20comprises a contact region22. Contact region22for example corresponds to the region12ofFIG.1. Sensor20is thus configured to detect a physical contact between a user's finger and region22, for example, a user's finger and region22.

Region22for example corresponds to a conductive layer, or pellet, covered with an insulating layer. Region22is preferably a metal pellet, for example, made of copper, covered with an electric insulator, for example, glass. Region22is, due to its forming, a portion of a capacitor Cin having a relatively low capacitance value, however sufficiently high to store charges. More particularly, the conductive pellet corresponds to a first electrode of capacitor Cin. When the user comes into contact, preferably by his/her finger, with region22, the user's part in contact with region22forms the second electrode of capacitor Cin. Capacitor Cin is thus formed by the assembly comprising region22and the user, the capacitance value of capacitor Cin then being greater than the capacitance value of capacitor Cin in the absence of a contact. Thus, the value of capacitance Cin increases when there is a contact with region22and the user. In other words, the number of charges capable of being stored in capacitor Cin increases when a user touches region22. Hereinafter, region22, be it in or not in contact with the user, may be called “capacitor22”.

Region22is coupled to a node24of application of a power supply voltage of sensor20via a switch26. Preferably, switch26is formed by one or a plurality of transistors. More particularly, the region is coupled, preferably connected, to a node27. Transistor26is coupled, preferably connected, to node27by one of its conduction terminals and to node24by its other conduction terminal.

Further, region22is coupled to a node28of application of a reference voltage of sensor20, preferably the ground, via a switch30. Preferably, switch30is formed by one or a plurality of transistors. Transistor30is coupled, preferably connected, to node27by one of its conduction terminals and to node28by its other conduction terminal.

Thus, capacitor Cin may be charged with the power supply voltage via switch26, switches26and30being respectively turned on and off during the charge. Similarly, capacitor Cin may be discharged onto node28via switch30, switches26and30being respectively turned off and on during the discharge. In other words, the charges of capacitor Cin are transferred to node28via switch30.

Sensor20further comprises a capacitive element32, for example, a capacitor. The capacitance of element32is greater than the capacitance of capacitor Cin in the presence of a contact with the user. Preferably, the capacitance of element32is equal to at least 1,000 times the maximum capacitance of capacitor Cin, for example, from 1,000 to 10,000 times the maximum capacitance of capacitor Cin. The capacitance of capacitor Cin is for example in the order of a few picofarads, for example, substantially equal to 1 pF.

Capacitive element32is coupled, preferably connected, to node28by one of its terminals, and to a node34by another one of its terminals.

Node34is coupled to node24via a switch36. Preferably, switch36is formed by one or a plurality of transistors. More precisely, transistor36is coupled, preferably connected, to node34by one of its conduction terminals and to node24by its other conduction terminal.

Further, node34is coupled to node28via a switch38. Preferably, switch38is formed by one or a plurality of transistors. Transistor38is coupled, preferably connected, to node34by one of its conduction terminals and to node28by its other conduction terminal.

Sensor20further comprises a switch40. Switch40is coupled to node27by one of its terminals and to node34by its other terminal.

According to an embodiment, sensor20may also comprise a switch41. Switch40is coupled, preferably connected, to node27by one of its terminals and to node34by its other terminal. Switches40and41are for example controlled in the same way. In other words, switches40and41are for example turned off and turned on at the same times. As a variation, switch41may be maintained on during the sensor operation.

Sensor20further comprises a comparator42. Comparator42receives at an input44the voltage of node34. Node34is thus coupled, preferably connected, to input44. Another input46is coupled, preferably connected, to a reference voltage generation circuit48. The comparator thus compares the voltage on node34with a reference voltage delivered by circuit48.

Circuit48is configured to deliver first (S1) and second (S2) reference voltages, or voltage thresholds, of different values, the value of the first voltage being smaller than the value of the second voltage. The value of the first voltage is for example in the range from 50% to 95% of the value of the second voltage, preferably from 75% to 95% of the value of the second voltage, preferably equal to approximately 90% of the value of the second voltage. The value of the first voltage threshold is for example substantially equal to the value of the power supply voltage applied to node24divided by 4 and the value of the second voltage threshold is for example, equal to the value of the power supply voltage applied to node24divided by 2.

For example, circuit48comprises a digital-to-analog converter, configured to deliver a voltage of variable value. For example, circuit48may deliver a finite number of fixed voltages.

According to an embodiment, sensor20may comprise a plurality of capacitors Cin, that is, a plurality of distinct regions having their contact with a user capable of being detected by sensor20. Each region22is coupled, like the region22shown inFIG.2, to input44by a switch40. In other words, input44is coupled to a plurality of regions22. Further, each region22is coupled to nodes24and28by switches26and30, as shown inFIG.2. In other words, according to an embodiment, sensor20comprises a plurality of regions22and as many switches26, switches30, and switches40as regions22. Preferably, sensor20implements an operating method which will be described in relation withFIG.3for the different regions22one after the others. In this case, switch41is for example maintained on.

FIG.3shows an embodiment of an operating method of the device ofFIG.2.

Sensor or device20is considered as being in a low-power operating mode (block50—LP). During the low-power operating mode, the touch sensor regularly verifies whether there is a touch contact between the device and a user.

Thus, during the low-power mode, the sensor starts a first acquisition (block52—START ACQUI1). At the beginning of the acquisition, capacitor32is preferably set to a reference charge level, preferably fully discharged. In other words, the charges contained by capacitor32are preferably all transferred to node28, that is, to ground. Preferably, capacitor22is also set to a reference charge level, preferably fully discharged. During this acquisition, capacitor22(FIG.2) is fully charged, and is then discharged into capacitor32. The steps of charge and discharge of capacitor22are repeated until capacitor32is fully charged.

During a first phase of the acquisition, capacitors22and32are discharged. In this example, switches26and36are off. Further, switch40and switch41are on. Switch30and/or switch38is turned on, to be able to discharge capacitors22and32into node28.

During a second phase of the acquisition, switch40is maintained off, to be able to modify the charge levels of capacitors22and32independently from each other. During the second phase of the acquisition, switch26is then turned on and switches30,36,38, and40are turned off. Thus, capacitor22is fully charged by node24.

During a third phase of the acquisition, capacitor22is discharged into capacitor32. For this purpose, switch40is turned on. Further, switches26,30,36, and38are turned off.

The different phases of the acquisition may be separated by idle periods, during which switches26,30,36,38, and40are all off. Such idle periods preferably have a duration shorter than a few hundreds of nanoseconds, for example, shorter than 50 ns.

Other off and on configurations of the different switches may of course be implemented to carry out the three distinct phases of the acquisition, that is, the discharge of capacitors22and32, the charge of capacitor22, and the discharge of capacitor22into capacitor32. For example, during the first phase, capacitors22and32may be discharged successively rather than simultaneously. For example, during the first phase, switch40may be off during the discharge, switches30and38then being both on.

The second and third phases of the acquisition are repeated to charge capacitor32until a voltage V32across capacitor32reaches the value of first reference voltage S1.

During the repeating of the second and third phases of the acquisition, voltage V32is compared, by comparator42, with the first reference voltage S1delivered by circuit48.

When voltage V32reaches the value of first reference voltage S1, the sensor determines the duration D of the charge of capacitor32. For example, the sensor determines the duration D between the beginning of the second initial phase and the time at which voltage V32reaches value S1.

Duration D is then compared with a threshold value of duration D1(block54→D1). Capacitor Cin has, when a user is in contact with region22, a value greater than in the case where region22is not in contact with the user. Thus, the charge of capacitor32is achieved within a smaller number of repetitions of the second and third phases when a user is in contact with region22than in the case where region22is not in contact with the user. Duration D thus has a smaller value when a user is in contact with region22than in the case where region22is not in contact with the user.

Threshold value D1is selected so that a value D greater than value D1means that there is no touch contact and a value D smaller than value D1suggests a touch contact.

If value D is greater than value D1(branch YES, block54), the device remains in low-power operating mode (block50). The method, and thus the acquisition, are carried out periodically during the low-power operating mode. Thus, the step represented by block52is carried out again after a predetermined period, for example, in the range from 200 to 300 ms, for example, substantially equal to 230 ms.

If value D is smaller than value D1(branch NO, block54), the sensor initializes a counter, for example, by assigning value 2 to a variable i (block55, INIT COUNTER) and starts a second acquisition (block56, START ACQUI2). Further, the voltage value on input46of the comparator is changed by circuit48to be equal to the value of second reference voltage S2.

During the second acquisition, the three acquisition phases are for example carried out as described in relation with the first acquisition. More particularly, the second acquisition comprises a first phase during which capacitors22and32are discharged. The second acquisition further comprises second and third phases, repeated until voltage V32across capacitor32is equal to the value of second reference voltage S2. As previously, the second phase corresponds to the charge, preferably complete, of capacitor22and the third phase corresponds to the discharge, preferably complete, of capacitor22into capacitor32.

The turning-on and the turning-off of the different switches are for example such as described in relation with the first acquisition.

When voltage V32reaches the value of second reference voltage S2, the sensor determines a duration D′ of the charge of capacitor32. For example, the sensor determines the duration D′ between the beginning of the second initial phase of the second acquisition and the time at which voltage V32reaches value S2.

Duration D′ is then compared with a threshold value D2(block58→D2). Capacitor Cin has, when a user is in contact with region22, a value greater than in the case where region22is not in contact with the user. Thus, the charge of capacitor32is performed within a smaller number of repetitions of the second and third phases when a user is in contact with region22than in the case where region22is not in contact with the user. Duration D′ thus has a smaller value when a user is in contact with region22than in the case where region22is not in contact with the user.

Threshold value D2is selected so that a value D′ greater than value D2means that there is no touch contact and a value D′ smaller than value D2suggests a touch contact.

If value D′ is greater than value D2(branch YES, block58), the device remains in low-power operating mode (block50).

If value D′ is smaller than value D2(branch NO, block58), this suggests a touch contact at the level of region22. Preferably, the second acquisition is carried out a plurality of times, preferably three times, to ascertain that the detection is correct and that it is not a false measurement, in other words, a false positive. The value assigned to variable i during the use of the counter is equal to the desired number of acquisitions minus 1. For this purpose, the value of variable i of the counter is compared with the desired number of successive second acquisitions, here three acquisitions (block60, COUNTER NULL?).

If variable i has a value greater than zero (branch NO, block60), that is, if less than three second acquisitions have been carried out, the value of the variable is decremented by one unit, for example, by a value ‘1’ (block61, DECREMENT COUNTER) and a new second acquisition is implemented.

If variable i has a value equal to zero (branch YES, block60), this means that, for the three successive second acquisitions, duration D′ is shorter than threshold value D2. The sensor thus considers that there effectively is a touch contact at the level of region22(block62—DETECT). Preferably, the device then leaves the low-power operating mode and elements of the device may then be turned back on.

If, during one of the second acquisitions, value D′ is greater than threshold value D2, the touch contact detection step is over until the next iteration of the first acquisition.

The determination of the different durations D and D′ and the comparison of durations D, D′ with threshold values D1and D2may for example be performed digitally, for example, by software provided for this purpose. For this purpose, as shown inFIG.6, the device for example comprises touch sensor80having comparator42providing a touch sensor signal to a microcontroller82configured to carry out these operations. Otherwise, as shown alternatively inFIG.6, such operations may be performed analogically, the sensor80for example comprising a counting circuit84to determine durations D and D′ and a comparator86to compare the durations with threshold values D1and D2. The touch sensor signal may be provided directly by an output of comparator42as shown inFIG.2, or by switches75,77as shown inFIG.5.

Similarly, the control signals of switches26,30,36,38, and40may be determined digitally, for example, by software provided for this purpose, for example, by the microcontroller82, or in analog fashion.

FIG.4shows an example of variations of a voltage of the device20ofFIG.1over time. More particularly,FIG.4shows an example of variations of voltage V32across capacitor32(FIG.2).

At the origin of the shown time range, that is, at a time to, the device is in the low-power operating mode. Further, there is no touch contact at the level of region22. During the low-power operating mode, first acquisitions are periodically carried out.

At time to, sensor20starts a first acquisition (block52,FIG.3). Voltage V32thus increases along the charge of capacitor32via capacitor22. At a time t1subsequent to time to, comparator42determines that voltage V32has reached value S1. Duration D, here equal to the difference between t1and t0, is compared with threshold value D1and the sensor determines that, in the present example, duration D is longer than threshold value D1.

No touch contact is thus detected and the device thus remains in the low-power operating mode.

At a time t2, subsequent to time t1, sensor20starts another first acquisition. Voltage V32thus increases along the charge of capacitor32. At a time t3subsequent to time t2, comparator42determines that voltage V32has reached value S1. Duration D, here equal to the difference between t3and t2, is compared with threshold value D1and the sensor determines that, in the present example, duration D is greater than threshold value D1.

No touch contact is thus detected and the device thus remains in the low-power operating mode.

At a time t4, subsequent to time t3, another first acquisition is started by the sensor. Voltage V32thus increases along the charge of capacitor32. At a time t5subsequent to time t4, comparator42determines that voltage V32has reached value S1. Duration D, here equal to the difference between t5and t4, is compared with threshold value D1and the sensor determines that, in the present example, duration D is shorter than threshold value D1. Such a result suggests that there has been a touch contact at the level of region22. In the example ofFIG.4, it is a false positive. Indeed, there has been no touch contact. Such a false positive is at least partially due to value S1, which is relatively low and thus likely to be reached relatively fast, even when there has been no touch contact. Indeed, the sensitivity of the sensor when the threshold is threshold S1is relatively high, higher than when the threshold is threshold S2.

At time t5, after duration D has been compared with the threshold value and the result of this comparison has suggested the presence of a contact, a second acquisition (block56,FIG.3) is started by the sensor.

During the second acquisition, capacitor22is charged and discharged into capacitor32, during second and third phases, to reach value S2. In the present example, the comparator determines that value S2has been reached at a time t6. Duration D′, here equal to the difference between t6and t5, is compared with threshold value D2and the sensor determines that, in the present example, duration D′ is longer than threshold value D2. Thus, although the value of duration D of the first acquisition, between times t4and t5, suggests that there is a touch contact at the level of region22, the value of duration D′ indicates that this is not true. Value S2is higher, and thus the determination is less sensitive and more accurate. The sensor thus remains in low-power operating mode.

Another first acquisition is carried out between times ty and t8subsequent to time t6. The duration D of this acquisition implies that there is no touch contact at the level of region22.

At a time T subsequent to time t8, a touch contact is performed. For example, a user's finger comes into contact with region22. The finger remains in contact with region22for all the times ofFIG.4subsequent to time T.

At a time t9, subsequent to time T, a first acquisition is implemented. Voltage V32reaches value S1at a time t10. The value of duration D, here equal to the difference between time t10and time t9, is smaller than the value of threshold D1, which suggests that there is a touch contact at the level of region22.

At time t10, a second acquisition is implemented. The value of voltage V32reaches threshold S2at a time t11, subsequent to time t10. Duration D′, equal during this acquisition to the difference between time t11and time t10, is shorter than threshold D2.

At time t11, another second acquisition is implemented. The value of voltage V32reaches threshold S2at a time t12, subsequent to time t11. Duration D′, equal during this acquisition to the difference between time t12and time t11, is shorter than threshold D2.

At time t12, a second acquisition is implemented. The value of voltage V32reaches threshold S2at a time t13, subsequent to time t12. Duration D′, equal during this acquisition to the difference between time t13and time t12, is shorter than threshold D2.

To confirm the detection of the touch contact, three second acquisitions are successively carried out. The sensor considers that the touch contact is confirmed when the durations D′ of the third second acquisitions are shorter than threshold D2. If the duration D′ of one of the three acquisitions is longer than threshold D2, the sensor considers that there is no contact and the device remains in low-power operating mode. The succession of second acquisitions stops when the duration D′ of one of the three second acquisitions is longer than threshold D2. For example, if the second one of the three successive second acquisitions has a duration D′ greater than value D2, the last acquisition is not carried out.

More generally, the number of successive second acquisitions may be different. At least one second acquisition is carried out, preferably three second acquisitions. The larger the number of second acquisitions, the more certain the contact detection. However, the increase of the number of second acquisitions also causes an increase of the energy cost of the detection, and of the duration of the detection. The smaller the number of second acquisitions, the less the detection is power consuming and the less time is taken by the detection. However, the smaller the number of second acquisitions, the less certain the result. Thus, decreasing the number of second acquisitions increases the risk of having a false positive, that is, of detection of a contact while there is no contact.

In the example ofFIG.4, capacitor32is discharged after each acquisition. The value of voltage V32thus recovers a low value at times t1, t3, t5, t6, t8, t10, t11, t12, and t13. The low value corresponds to a reference value, preferably the value of the voltage on node28, preferably equal to 0 V.

Although the duration between times t1and t2, between times t3and t4, between times t6and t7, and between times t8and t9, is shown as being shorter than the duration of one of the acquisitions, such durations between these times are preferably substantially equal to one another. Further, the durations between these times are preferably greater than ten times the duration of a first acquisition. The durations between these times are for example in the range from 200 to 300 ms, for example, substantially equal to 230 ms.

Although it is considered, inFIG.4, that the second acquisitions start at the time at which the first or second previous acquisition ends, that is, at time t5, t10, t11, or t12, it is possible for them to be separated by a duration D1, not shown. Duration D1for example corresponds to the duration of comparison of the duration value with threshold D1or D2. Duration D1is preferably shorter than 5 ms.

FIG.5shows another embodiment of a touch sensor70. Sensor70comprises elements identical to the elements of the sensor20ofFIG.2, referenced in the same way. These elements will not be detailed again.

Sensor70differs from sensor20in that sensor70comprises a comparison circuit comprising comparator42and an additional comparison element72. An input of element72is coupled, preferably connected, to node34, and thus receives voltage V32.

An output of element72is coupled to an output node73of sensor70via a switch77. Similarly, the output of comparator42is coupled to node73via a switch75.

Comparison element72compares the voltage value at its input with a fixed threshold value, specific to the selected comparison element and to its characteristics. For example, element72is a Schmitt trigger.

In the example ofFIG.5, circuit48supplies a threshold value, for example, a single threshold value. Preferably, the threshold value supplied by circuit48is smaller than the fixed threshold of element72. The threshold value supplied by circuit48is for example in the range from 75% to 95% of the value of the fixed threshold of element72, preferably equal to approximately 90% of the value of the fixed threshold of element72.

The operation of sensor70is similar to the operation of the sensor20described in relation withFIGS.3and4. During first acquisitions, voltage V32is compared with the threshold supplied by circuit48and with the threshold of element72. Since the value of the threshold delivered by circuit48is smaller than the value of the threshold of element72, voltage34first reaches this value. When the value supplied by circuit48has been reached, the first acquisition is finished. Further, during the first acquisition, switch75is on and switch77is off.

During second acquisitions, switch75is turned off and switch77is turned on. Thus, the comparison of element42has no further effect and only the comparison with the threshold of comparator72has an impact on the sensor. As a variation, during the second acquisitions, comparator42may be configured:to receive from circuit48a value greater than the threshold value of element72; ornot to compare the voltage on node34with a reference voltage. For example, comparator42may be deactivated.

Thus, each second acquisition ends when the voltage on node34reaches the threshold value of element72.

As in the case of sensor20, a touch contact is detected when a first acquisition and at least one second acquisition, preferably three second acquisitions, have been successively carried out, and when the duration D of the first acquisition and the duration D′ of the at least one second acquisition are below thresholds, respectively D1and D2.

Although the embodiments are described in the context of the leaving of a low-power operating mode, that is, the detection of a touch contact causes the leaving of the low-power mode, it should be understood that the detection of a contact may be used in other situations without modifying the described embodiments. For example, region22may form a button activating, when a touch contact is detected, one or a plurality of functionalities of device10.

It could have been chosen to compare the voltage on node34with a single threshold value, for example, with a fixed threshold of a Schmitt trigger. Thus, in low-power operating mode, acquisitions would be performed regularly. During each of the acquisitions, capacitor32would be charged to reach the threshold value. However, the threshold value would then be relatively significant, for example, equal to the second threshold described in relation withFIG.2, to avoid too large a number of false positives. Thus, acquisitions during the low-power operating mode would be more power consuming than the first acquisitions described in relation withFIGS.2and5.

An advantage of the described embodiments thus is that the power consumption is decreased with respect to a sensor only comparing the voltage on node34with a single value, for example, equal to the value of the second threshold.

Another advantage of the embodiments is that the sensor is more accurate and has less risks of false positive than a sensor only comparing the voltage on node34with a single value, for example, equal to the value of the first threshold.

Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these embodiments can be combined and other variants will readily occur to those skilled in the art.

Finally, the practical implementation of the described embodiments and variants is within the abilities of those skilled in the art based on the functional indications given hereinabove.

Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only as defined in the following claims and the equivalents thereto.