Patent Publication Number: US-9836172-B2

Title: Touch apparatus, capacitive touch sensing circuit thereof, and touch sensing method using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 104137107, filed on Nov. 11, 2015. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     Field of Invention 
     The invention relates to a capacitive touch sensing circuit, and more particularly, to a 1-bit sigma delta capacitive touch sensing circuit. 
     Description of Related Art 
     With the popularity of electronic products, a well-functioned human-machine interface has become indispensible in every electronic apparatus, and capacitive touch panels are commonly applied in the existing electronic apparatuses. 
     According to the related art, equipping the capacitive touch panel with a 1-bit sigma delta capacitive touch sensing circuit has been proposed, so as to perform touch sensing actions. In terms of the dimension of the circuit, the power consumption, or the immunity to noise interference, the 1-bit sigma delta capacitive touch sensing circuit is superior to the conventional analog-to-digital touch sensing circuit. However, since the 1-bit sigma delta capacitive touch sensing circuit provides the feedback circuit with constant charge dissipation according to the related art, the 1-bit sigma delta capacitive touch sensing circuit cannot guarantee both of the high resolution and the large detectable range while detecting variations of capacitance, thus lessening the efficiency. 
     SUMMARY 
     The present invention is directed to a capacitive touch sensing circuit and sensing method thereof, which are able to effectively increase the sensing resolution and the detectable range while variations of capacitance are being detected. 
     The present invention is further directed to a touch apparatus using the capacitive sensing circuit and the touch sensing method of the capacitive touch sensing circuit, so as to effectively increase the sensitivity and the detectable range while variations of capacitance are being detected. 
     In an embodiment of the present invention, a capacitive touch sensing circuit that includes a switching capacitor integrating circuit, an encoding circuit, a feedback circuit, and a decoding circuit is provided. The switching capacitor integrating circuit is coupled to a to-be-tested capacitive touch unit that receives an input signal, and the switching capacitor integrating circuit integrates the input signal to generate an output signal. The encoding circuit is coupled to the switching capacitor integrating circuit to receive the output signal and encode the output signal to generate an encoded result. The feedback circuit is coupled to the switching capacitor integrating circuit and the encoding circuit and provides the switching capacitor integrating circuit with a charge dissipation path for discharging charges from the switching capacitor integrating circuit, and the feedback circuit receives the encoded result and adjusts a charge dissipation ability provided by the charge dissipation path according to the encoded result. The encoding circuit is coupled to the switching capacitor integrating circuit to receive the output signal and decode the output signal to generate a touch detecting result. 
     In an embodiment of the present invention, a touch display apparatus includes a display panel and at least one capacitive touch sensing circuit described above. The touch panel includes a plurality of capacitive touch units. The at least one capacitive touch sensing circuit is coupled to the to-be-tested capacitive touch unit of one of the capacitive touch units. 
     In an embodiment of the present invention, a capacitive touch sensing method includes: receiving an input signal by a to-be-tested capacitive touch unit, providing a switching capacitor integrating circuit, and integrating the input signal by the switching capacitor integrating circuit, so as to generate an output signal; encoding the output signal to generate an encoded result; providing the switching capacitor integrating circuit with a charge dissipation path for discharging charges from the switching capacitor integrating circuit and adjusting a charge dissipation ability provided by the charge dissipation path according to the encoded result; decoding the output signal to generate a touch detecting result. 
     In view of the above, the encoding circuit provided herein encodes the output signal and thereby generates the encoded result. The charge dissipation ability of the charge dissipation path provided by the feedback circuit can be dynamically adjusted according to the encoded result. That is, the charge dissipation mechanism provided herein can be dynamically adjusted in response to the load current, and the capacitive touch sensing circuit can detect minor variations in the capacitance even in case of significant transfer capacitance; as such, the requirements for highly sensing resolution and large detectable range can be satisfied. 
     Several exemplary embodiments accompanied with figures are described in detail below to further describe the disclosure in details. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic view illustrating a capacitive touch sensing circuit according to an embodiment of the present invention. 
         FIG. 2  is a schematic view illustrating a capacitive touch sensing circuit according to another embodiment of the present invention. 
         FIG. 3  is a schematic view illustrating a capacitive touch sensing circuit according to still another embodiment of the present invention. 
         FIG. 4  is a schematic view illustrating a capacitive touch sensing circuit according to still another embodiment of the present invention. 
         FIG. 5  illustrates waveforms of encoding actions of an encoding circuit according to an embodiment of the present invention. 
         FIG. 6  is a schematic view illustrating a touch apparatus according to an embodiment of the present invention. 
         FIG. 7  is a flowchart of a capacitive touch sensing method according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS 
       FIG. 1  is a schematic view illustrating a capacitive touch sensing circuit according to an embodiment of the present invention. The capacitive touch sensing circuit  100  includes a switching capacitor integrating circuit  110 , a decoding circuit  120 , a feedback circuit  130 , and an encoding circuit  140 . The switching capacitor integrating circuit  110  is coupled to one terminal of a to-be-tested capacitive touch unit TUNT. The other terminal of the to-be-tested capacitive touch unit TUNT receives a signal VIN. When a touch detecting action is performed on the to-be-tested capacitive touch unit TUNT, the signal VIN may be a clock signal, and the to-be-tested capacitive touch unit TUNT may generate an input signal IN and provide the input signal IN to the switching capacitor integrating circuit  110 . The switching capacitor integrating circuit  110  integrates the input signal IN received by the switching capacitor integrating circuit  110 , so as to generate an output signal OUT. 
     In the present embodiment, the capacitance of the to-be-tested capacitive touch unit TUNT may be changed according to whether the to-be-tested capacitive touch unit TUNT is touched or not, and the input signal IN may also be changed in response to variations in the capacitance of the to-be-tested capacitive touch unit TUNT. Since the switching capacitor integrating circuit  110  integrates the input signal IN, the integrated result can effectively reflect the changes to the input signal IN, and whether the to-be-tested capacitive touch unit TUNT is touched or not can be determined according to the integrated result. On the other hand, the switching capacitor integrating circuit  110  may determine a reference voltage and compare the integrated result with the reference voltage, so as to generate the output signal OUT. In an embodiment of the present invention, the output signal OUT may be a digital signal, and a voltage level of the output signal OUT may stay unchanged or may be different in a plurality of continuous time cycles. 
     The encoding circuit  140  is coupled to the switching capacitor integrating circuit  110  and receives the output signal OUT. The encoding circuit  140  encodes the output signal OUT to generate an encoded result ER. The encoding circuit  140  may sequentially generate the encoded result ER in a plurality of time cycles according to variations in a voltage of the output signal OUT in two successive time cycles. Particularly, the encoding circuit  140  may determine whether a logic level of the voltage of the output signal OUT remains constant (i.e., logic high or logic low in both time cycles); if yes, the encoding circuit  140  gradually increases the encoded result ER by 1. By contrast, if the logic level of the voltage of the output signal OUT is switched from high to low or from low to high in the two successive time cycles, the encoding circuit  140  gradually decreases the encoded result ER by 1. For instance, if the high logic levels of the output signal OUT in plural successive time cycles are sequentially 1, 1, 1, 1, 0, 1, and 0, the encoded results ER generated by the encoding circuit  140  are sequentially 0, 1, 2, 3, 2, 1, and 0 (the default value is 0). Here, the minimum encoded result ER is 0. 
     The feedback circuit  130  is coupled to the switching capacitor integrating circuit  110  and the encoding circuit  140 . The feedback circuit  130  provides the switching capacitor integrating circuit  110  with a charge dissipation path for discharging charges from the switching capacitor integrating circuit  110 . Here, the feedback circuit  130  receives the encoded result ER and adjusts a charge dissipation ability provided by the charge dissipation path according to the encoded result ER. The feedback circuit  130  also receives the output signal OUT and determines to perform the charging action or the discharging action according to the output signal OUT. 
     In the present embodiment, the feedback circuit  130  can adjust the charge dissipation ability of the charge dissipation path provided to the switching capacitor integrating circuit  110  according to the encoded result ER. If the encoded result ER is a 3-bit numeral value, the feedback circuit  130  is able to offer eight (2 3 ) different charge dissipation abilities. If the charge dissipation ability provided by the feedback circuit  130  is rather small, the sensing resolution of the capacitive touch sensing circuit  100  can be enhanced; if the charge dissipation ability provided by the feedback circuit  130  is rather large, the capacitive touch sensing circuit  100  can expand its detectable range of variations in the capacitance. 
     The decoding circuit  120  is coupled to the switching capacitor integrating circuit  110 . The decoding circuit  120  receives the output signal OUT and decodes the output signal OUT to generate a touch detecting result DR. In detail, the decoding circuit  120  sequentially generates a plurality of numeral values in a plurality of time cycles according to variations in a voltage of the output signal OUT in two successive time cycles and obtains the touch detecting result DR through adding up the numeral values. 
     In light of the foregoing, the feedback circuit  130  of the capacitive touch sensing circuit  100  can adjust the charge dissipation ability of the provided charge dissipation path according to the output signal OUT generated by the switching capacitor integrating circuit  110 . The capacitive touch sensing circuit  100  can, according to its operating conditions, make necessary modifications to satisfy the requirements for high resolution and the large detectable range, respectively, so as to optimize the performance of the capacitive touch sensing circuit  100 . 
       FIG. 2  is a schematic view illustrating a capacitive touch sensing circuit according to another embodiment of the present invention. The capacitive touch sensing circuit  200  includes a switching capacitor integrating circuit  210 , a decoding circuit  220 , a feedback circuit  230 , and an encoding circuit  240 . The switching capacitor integrating circuit  210  is coupled to a capacitive touch unit TUNT. In the present embodiment, the capacitive touch unit TUNT receives a signal VIN generated by alternately switching on or off switches S 1  and S 2 , and an input signal IN is correspondingly generated. The signal VIN may be a periodic signal transiting between a voltage of a reference ground terminal GND and a reference voltage Vref. 
     The switching capacitor integrating circuit  210  includes an operational amplifier OP 1 , a capacitor Cop, a switch Sop, a comparator CMP 1 , and a latch LA 1 . The operational amplifier OP 1  receives the input signal IN and integrates the input signal IN through the switch Sop and the capacitor Cop. An integrated result is generated by an output terminal of the operational amplifier OP 1  and transmitted to the comparator CMP 1 . The comparator CMP 1  compares the integrated result with a reference signal VR to generate a comparison result, and the latch LA latches the comparison result generated by the comparator CMP 1 , so as to generate an output signal OUT. The latch LA performs the data latching action according to a clock signal CK. 
     The output signal OUT is transmitted to the decoding circuit  220 , the encoding circuit  240 , and the feedback circuit  230 . The decoding circuit  220  receives the output signal OUT and accordingly generates a detecting result DR. The encoding circuit  240  receives the output signal OUT and encodes the output signal OUT to generate an encoded result ER. 
     The feedback circuit  230  includes a switching capacitive circuit  231 . The switching capacitive circuit  231  receives the output signal OUT, and a first terminal of the switching capacitive circuit  231  is coupled to an end point of the switching capacitor integrating circuit  210  receiving the input signal IN. The switching capacitive circuit  230  includes a weighted capacitance adjuster  232 . The weighted capacitance adjuster  232  provides a capacitance Cfbv that can be adjusted according to the encoded result ER. 
     Based on the capacitance Cfbv provided by the weighted capacitance adjuster  232 , the charge dissipation ability of the charge dissipation path provided by the feedback circuit  230  can be adjusted, and the capacitive touch sensing circuit  200  can satisfy the requirements for both the highly sensing resolution and the large detectable range of variations of the capacitance. 
     As to other details of the switching capacitive circuit  231 , the switching capacitive circuit  231  further includes switches S 3 , S 4 , S 5 , and S 6 . A first terminal of the switch S 3  receives the input signal IN, and a second terminal of the switch S 3  is coupled to a first terminal of the switch S 4 . A second terminal of the switch S 4  is coupled to a first terminal of the switch S 5  and a first terminal of the switch S 6 , and a second terminal of the switch S 5  and a second terminal of the switch S 6  are respectively coupled to the reference ground terminal GND and the reference voltage Vref. The weighted capacitance adjuster  312  is serially coupled between the second terminal of the switch S 4  and the reference ground terminal GND. The switches S 5  and S 6  may be switched on or off according to the same control signal, and the switches S 3  and S 4  are switched on or off according to the output signal OUT. While the switch S 3  is switched on, the switch S 4  is switched off, and vice versa. 
     In the present embodiment, the switches S 5  and S 6  may controlled by the control signal CTR and may thus be switched on or off, and the switches S 3  and S 4  are switched on or off according to the output signal OUT. While the switch S 3  is switched on, the switch S 4  is switched off, and vice versa. If the switch S 4  is controlled by the output signal OUT and is switched on, the feedback circuit  230  provides the switching capacitor integrating circuit  210  with a charge dissipation path for discharging charges from the switching capacitor integrating circuit  210 . 
     In detail, the decoding circuit  220  sequentially generates a plurality of numeral values in a plurality of time cycles according to variations in a voltage of the output signal OUT in two successive time cycles and obtains the touch detecting result DR through adding up the numeral values. 
     The encoding circuit  240  sequentially generates the encoded result ER in a plurality of time cycles according to variations in a voltage of the output signal OUT in two successive time cycles. Particularly, the encoding circuit  240  may determine whether a logic level of the voltage of the output signal OUT remains constant; if yes, the encoding circuit  240  gradually increases the encoded result ER by 1. By contrast, if the logic level of the voltage of the output signal OUT is switched from high to low or from low to high in the two successive time cycles, the encoding circuit  240  gradually decreases the encoded result ER by 1. 
     Note that the decoding circuit  220  and the encoding circuit  240  can both be implemented in form of a digital circuit. That is, according to the aforesaid principles of circuit operations, the decoding circuit  220  and the encoding circuit  240  can be implemented in form of any digital design commonly known to people having ordinary skill in the pertinent art, such as a hardware description language (HDL), a conventional truth table, a Karnaugh map, a Mealy finite state machine or a Moore finite state machine, and so on. Hence, the decoding circuit  220  and the encoding circuit  240  do not have any fixed configuration. If the decoding circuit  220  and the encoding circuit  240  are implemented in form of HDL, the database of the circuit synthesizer software and the basic logic gate of the circuit employed by the designer determine the type and the number of logic gates in the circuit, and the type and the number of logic gates may not remain constant. 
       FIG. 3  is a schematic view illustrating a capacitive touch sensing circuit according to still another embodiment of the present invention. The capacitive touch sensing circuit  300  includes a switching capacitor integrating circuit  310 , a decoding circuit  320 , a feedback circuit  330 , and an encoding circuit  340 . The feedback circuit  330  provided herein not only receives the output signal OUT but also receives the encoded result ER. Different from the feedback circuit  230  provided in the aforementioned embodiment, the feedback circuit  330  provided herein includes the switching capacitive circuit  331  and a weighted voltage adjuster  332 . The switching capacitive circuit  331  includes switches S 3 -S 6  and a capacitor Cfb. One terminal of the switch S 3  receives the input signal IN, and the other terminal of the switch S 3  is coupled to one terminal of the switch S 4 . The other terminal of the switch S 4  is coupled to a first terminal of the switch S 5  and a first terminal of the switch S 6 , and a second terminal of the switch S 5  and a second terminal of the switch S 6  are respectively coupled to the reference ground terminal GND and the weighted voltage adjuster  332 . The capacitor Cfb is serially connected between the reference ground terminal GND and the terminal where the switches S 3  and S 4  are coupled to each other. 
     The weighted voltage adjuster  332  provides a weighted voltage WV to the second terminal of the switch S 6  and is able to adjust the weighted voltage WV according to the encoded result ER. Through adjusting the weighted voltage WV, the feedback circuit  330  is able to effectively adjust the charge dissipation ability of the charge dissipation path provided by the feedback circuit  330 . 
     For instance, if 8 different 3-bit hexadecimal encoded results ER (0-7) are provided, the weighted voltage WV can be adjusted within the range 1/8 *Vref−8/8 *Vref. That is, the feedback circuit  330  is able to make 8-phase modifications to the charge dissipation ability of the charge dissipation path. 
     Certainly, the bit number of the encoded result ER is not limited herein; if it is intended to increase the sensing resolution of variations in the capacitance, the bit number of the encoded result may also be increased. The feedback circuits can also make modifications to the charge dissipation ability of the charge dissipation path in more phases. 
       FIG. 4  is a schematic view illustrating a capacitive touch sensing circuit according to another embodiment of the invention. The capacitive touch sensing circuit  400  includes a switching capacitor integrating circuit  410 , a decoding circuit  420 , a feedback circuit  430 , and an encoding circuit  440 . Different from the feedback circuits provided in the aforementioned embodiments, the feedback circuit  430  provided herein includes current sources I 1  and I 2  and switches S 3  and S 4 . A first terminal of the switch S 3  and a first terminal of the switch S 4  are commonly coupled to an input end point of the switching capacitor integrating circuit  410 , and a second terminal of the switch S 3  and a second terminal of the switch S 4  are respectively coupled to the current sources I 1  and I 2 . Note that the current source I 2  drains the current from the switch S 4  and transmits the drained current to the reference ground terminal GND. 
     Note that the switches S 3  and S 4  are controlled by the output signal OUT, and the current sources I 1  and I 2  are controlled by the encoded result ER. When the switch S 3  is switched on, the switch S 4  is switched off, and vice versa. Here, the amount of the current drained from the current sources I 1  and I 2  or the time frame during which the charges are discharged can be adjusted according to the encoded result ER and the output signal OUT. Thereby, the charge dissipation path provided by the feedback circuit  410  is dynamically adjusted, e.g., the charging/discharging ability of the charging/discharging path may be adjusted. 
       FIG. 5  illustrates waveforms of encoding actions of an encoding circuit according to an embodiment of the invention. The voltage level of the output signal OUT is periodically detected; at the time point T 1  and the time point T 2 , the output signal OUT has the same logic high level, and the encoding circuit can gradually increase the encoded result ER from 0 to 1 at the time point T 2 . At the time point T 3 , the encoding circuit detects that the voltage level of the output signal OUT remains logic high, and thus the encoding circuit gradually increases the encoded result ER from 1 to 2 at the time point T 3 . At the time point T 4 , the encoding circuit continues to detect the voltage level of the output signal OUT and finds out that the voltage level of the output signal OUT remains logic high, and thus the encoding circuit gradually increases the encoded result ER from 2 to 3 at the time point T 4 . 
     At the time point T 5 , the encoding circuit detects that the voltage level of the output signal OUT is changed to logic low, and thus the encoding circuit gradually decreases the encoded result ER from 3 to 2 at the time point T 4 . Similarly, at the time point T 6 , the encoding circuit detects that the voltage level of the output signal OUT is changed to logic high from logic low; at the time point T 7 , the encoding circuit detects that the voltage level of the output signal OUT is changed to logic low from logic high. Hence, the encoding circuit gradually decreases the encoded result ER from 2 to 1 at the time point T 6  and gradually decreases the encoded result ER from 1 to 0 at the time point T 7 . 
       FIG. 6  is a schematic view illustrating a touch apparatus according to an embodiment of the present invention. The touch apparatus  600  includes a touch panel  610  and at least one capacitive touch sensing circuit  620 , and the touch panel  610  may be a self-capacitive touch panel or a mutual-capacitive touch panel. The touch panel  610  includes a plurality of capacitive touch units, and the to-be-tested capacitive touch unit TUNT of the capacitive touch units is coupled to the capacitive touch sensing circuit  620  to detect variations in the capacitance of the to-be-tested capacitive touch unit TUNT and thereby obtain the touched condition of the to-be-tested capacitive touch unit TLTNT. In the present embodiment, the touch panel  610  may be an in-cell touch display panel. However, in other embodiments, the touch panel  610  may be an out-cell touch panel or any other touch panel capable of performing the touch function. 
     The capacitive touch sensing circuit  620  may be implemented by any of the capacitive touch sensing circuits  200 ,  300 , and  400  depicted in  FIG. 2 ,  FIG. 3 , and  FIG. 4 , and the implementation details of the capacitive touch sensing circuits  200 ,  300 , and  400  are already elaborated in the aforementioned embodiments and therefore will not be provided herein. 
       FIG. 7  is a flowchart of a capacitive touch sensing method according to an embodiment of the present invention. In step S 710 , a to-be-tested capacitive touch unit receives an input signal and provides a switching capacitor integrating circuit to integrate the input signal, so as to generate an output signal; in step S 720 , the output signal is encoded to generate an encoded result; in step S 730 , a charge dissipation path is provided to the switching capacitor integrating circuit for discharging charges from the switching capacitor integrating circuit and adjusting a charge dissipation ability provided by the charge dissipation path according to the encoded result; in step S 740 , the output signal is decoded to generate a touch detecting result. 
     The implementation details of each step are already elaborated above and thus will not be repeated. 
     To sum up, the encoding circuit provided herein encodes the output signal, and the encoded result is provided to the feedback circuit. The feedback circuit dynamically adjusts the charge dissipation ability of the charge dissipation path provided by the feedback circuit according to the encoded result; thereby, the capacitive touch sensing circuit need not sacrifice the detectable range of variations in the capacitance for the highly sensing resolution nor sacrifice the resolution for the large detectable range of variations in the capacitance. That is, the capacitive touch sensing circuit provided herein can function while taking the requirements for both the resolution and the detectable range into consideration, and the performance can therefore be enhanced. It will increase the sensitivity of touch apparatus using the capacitive sensing circuit according to the embodiments of the present invention. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.