Patent Publication Number: US-2023133003-A1

Title: Stylus communicating with a device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2020/100071, filed on Jul. 3, 2020, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a stylus, a method for communicating by the stylus with a device, and an input system including the device and the stylus. The stylus is capable of communicating with the device. For example, the device may be a mobile phone, a smart phone, a tablet computer, a personal computer, or the like. 
     BACKGROUND 
     In recent years, various devices such as a mobile phone, a smart phone, a tablet computer, a personal computer are equipped with a touch sensor below a display thereof for detecting a touch position of a finger and/or a stylus on the display. For example, the touch sensor detects the touch position of the stylus based on a strength of a signal transmitted by an electrode located in a tip of the stylus. Also, there exists a stylus having a first electrode located in a tip of the stylus and a second electrode located in a portion apart from the tip of the stylus. In this case, the touch sensor receives a first signal from the first electrode and a second signal from the second electrode, and may detect a tilt angle of the stylus based on a distance between received positions of the first and second signals. Although such two electrodes structure enables to provide functions using both the tip position and the tilt angle of the stylus, but there is room for improvement of a writing performance. 
     SUMMARY 
     Embodiments provide a stylus, a method for communicating by the stylus with a device, and an input system including the device and the stylus. The device may be a mobile phone, a smart phone, a tablet computer, a personal computer, or the like. 
     A first aspect of the embodiments provides a stylus capable of communicating with a device. In a first possible implementation form of the first aspect, the stylus comprises: a first electrode used for transmitting a first signal to the device, where the first electrode is located at a tip portion of the stylus; a second electrode used for transmitting a second signal to the device, where the second electrode is located apart from the first electrode; and a third electrode used for receiving a third signal from the device. In some examples, the third signal is used for triggering transmission of the first and second signals. 
     According to the first possible implementation form of the first aspect, the device may receive the first signal from the first electrode and the second signal from the second electrode, thereby detecting a tilt angle of the stylus based on received positions of the first and second signals. Further, the device may transmit the third signal triggering transmission of the first and second signals, so that the device may accurately recognize transmission periods of the first and second signals following the third signal. This may make it possible to certainly receive the first and second signals at the device even though an interval between adjacent transmission periods of the first and second signals is around 5 µs or less. Accordingly, three electrodes structure of the stylus mentioned above may provide high temporal resolution on detection of the tip position and the tilt angle of stylus, thereby improving a writing performance. 
     A second possible implementation form of the first aspect provides: the stylus according to the first possible implementation form of the first aspect, where the third signal carries information including at least one of frequency information and an identifier of a specific stylus corresponding to the device. 
     For example, the frequency information may include information indicating frequencies for transmission of the first and second signals respectively. Using the frequency information, the device may change at least one of the frequencies corresponding to the first and second signals, thereby avoiding that a frequency of noise is close to the frequencies for the transmission of the first and second signals. The identifier may be used for limiting a usable stylus for the device and/or to distinguish between two or more styluses used simultaneously. 
     A third possible implementation form of the first aspect provides: the stylus according to the first or second possible implementation form of the first aspect, where the third electrode is located between the first electrode and the second electrode. According to the third possible implementation form of the first aspect, the third electrode may reduce interference between the first and second signals during transmission of the first and second signals, thereby improving a signal to noise ratio (SNR) during downlink transmission from the stylus to the device. 
     A fourth possible implementation form of the first aspect provides: the stylus according to any one of the first to third possible implementation forms of the first aspect, where the second electrode has a ring shape, and the stylus further comprises a ground shield configured to be inside the second electrode. According to the fourth possible implementation form of the first aspect, the ground shield may reduce interference between the first and second signals during the transmission of the first and second signals, so that reduction of the interference between the first and second signals improves the downlink SNR and makes it possible to lower transmission voltages applied to the first and second electrodes that are required for an adequate performance. 
     A fifth possible implementation form of the first aspect provides: the stylus according to any one of the first to fourth possible implementation forms of the first aspect, where during reception of the third signal from the device, the first electrode acts as a floating electrode. According to the fifth possible implementation form of the first aspect, the first electrode acting as the floating electrode enhances the third signal from the device, thereby improving a SNR during uplink transmission from the device to the stylus. 
     A sixth possible implementation form of the first aspect provides: the stylus according to any one of the first to fifth possible implementation forms of the first aspect, where during reception of the third signal from the device, the first electrode acts as an electrode for receiving the third signal from the device. According to the sixth possible implementation form of the first aspect, the third signal is received by the first electrode located in a closer position than the third electrode as well as the third electrode and enhanced, thereby improving the uplink SNR. 
     A seventh possible implementation form of the first aspect provides: the stylus according to the sixth possible implementation form of the first aspect, further comprising: a transmitter configured to transmit the first signal; a receiver configured to receive the third signal; and a switch set configured to connect the first electrode with the transmitter during transmission of the first signal to the device, and to connect the first electrode with the receiver during reception of the third signal from the device. 
     According to the seventh possible implementation form of the first aspect, the transmitter may transmit the first and second signals via the first and second electrodes respectively during the downlink transmission, and the receiver may receive the third signal via the first and third electrodes during the uplink transmission, thereby improving the uplink SNR. 
     A eighth possible implementation form of the first aspect provides: the stylus according to any one of the first to seventh possible implementation forms of the first aspect, where the first signal is used for detection of a position at which the tip portion of the stylus touches a touch panel of the device, and the second signal is used for detection of a tilt angle of the stylus. According to the eighth possible implementation form of the first aspect, various functions using both the tip position and the tilt angle of the stylus may be implemented on the device. 
     A ninth possible implementation form of the first aspect provides: the stylus according to any one of the first to eighth possible implementation forms of the first aspect, where a first period for transmission of the first and second signals is separated from a second period for reception of the third signal. According to the ninth possible implementation form of the first aspect, the first period for the downlink transmission is separated from the second period for the uplink transmission, thereby avoiding interference between uplink and downlink signals. 
     A tenth possible implementation form of the first aspect provides: the stylus according to any one of the first to ninth possible implementation forms of the first aspect, where a first frequency at which the first signal is transmitted is different from a second frequency at which the second signal is transmitted. According to the tenth possible implementation form of the first aspect, the first and second signals are transmitted at different frequencies from each other, thereby reducing interference between the first and second signals and improving the downlink SNR. 
     A second aspect of the embodiments provides a method for communicating by a stylus with a device. In a first possible implementation form of the second aspect, the method comprises: receiving, by a third electrode of the stylus, a third signal from the device during uplink transmission periods; transmitting, by a first electrode of the stylus, a first signal to the device during downlink transmission periods, wherein the first electrode is located at a tip portion of the stylus; transmitting, by a second electrode of the stylus, a second signal to the device during the downlink transmission periods, wherein the second electrode is located apart from the first electrode. In some examples, the third signal is used for triggering transmission of the first and second signals. 
     According to the first possible implementation form of the second aspect, the device may receive the first signal from the first electrode and the second signal from the second electrode, thereby detecting a tilt angle of the stylus based on received positions of the first and second signals. Further, the device may transmit the third signal triggering transmission of the first and second signals, so that the device may accurately recognize transmission periods of the first and second signals following the third signal. This may make it possible to certainly receive the first and second signals at the device even though an interval between adjacent transmission periods of the first and second signals is around 5 µs or less. Accordingly, three electrodes structure of the stylus mentioned above may provide high temporal resolution on detection of the tip position and the tilt angle of stylus, thereby improving a writing performance. 
     A second possible implementation form of the second aspect provides: the stylus according to the first possible implementation form of the second aspect, where the third signal carries information including at least one of frequency information and an identifier of a specific stylus corresponding to the device. 
     For example, the frequency information may include information indicating frequencies for transmission of the first and second signals respectively. Using the frequency information, the device may change at least one of the frequencies corresponding to the first and second signals, thereby avoiding that a frequency of noise is close to the frequencies for the transmission of the first and second signals. The identifier may be used for limiting a usable stylus for the device and/or to distinguish between two or more styluses used simultaneously. 
     A third possible implementation form of the second aspect provides: the method according to the first or second possible implementation form of the second aspect, where the receiving is specifically performed by the third electrode located between the first electrode and the second electrode. According to the third possible implementation form of the second aspect, the third electrode may reduce interference between the first and second signals during transmission of the first and second signals, thereby improving the downlink SNR. 
     A fourth possible implementation form of the second aspect provides: the method according to any one of the first to third possible implementation form of the second aspect, further comprising: managing the first electrode to act as a floating electrode during the uplink transmission periods. According to the fourth possible implementation form of the second aspect, the third signal is received by the first electrode located in a closer position than the third electrode as well as the third electrode and enhanced, thereby improving the uplink SNR. 
     A fifth possible implementation form of the second aspect provides: the method according to any one of the first to fourth possible implementation forms of the second aspect, further comprising: managing the first electrode to act as an electrode for receiving the third signal from the device during the uplink transmission periods. According to the fifth possible implementation form of the second aspect, the third signal is received by the first electrode located in a closer position than the third electrode as well as the third electrode and enhanced, thereby improving the uplink SNR. 
     A sixth possible implementation form of the second aspect provides: the method according to the fifth possible implementation form of the second aspect, further comprising: controlling a switch set of the stylus to connect the first electrode with a transmitter of the stylus during the downlink transmission periods, and to connect the first electrode with a receiver of the stylus during the uplink transmission periods. According to the sixth possible implementation form of the second aspect, the transmitter may transmit the first and second signals via the first and second electrodes respectively during the downlink transmission, and the receiver may receive the third signal via the first and third electrodes during the uplink transmission, thereby improving the uplink SNR. 
     A seventh possible implementation form of the second aspect provides: the method according to any one of the first to sixth possible implementation forms of the second aspect, where the first signal is used for detection of a position at which the tip portion of the stylus touches a touch panel of the device, and the second signal is used for detection of a tilt angle of the stylus. According to the seventh possible implementation form of the second aspect, various functions using both the tip position and the tilt angle of the stylus may be implemented on the device. 
     A eighth possible implementation form of the second aspect provides: the method according to any one of the first to seventh possible implementation forms of the second aspect, where a first frequency at which the first signal is transmitted is different from a second frequency at which the second signal is transmitted. According to the eighth possible implementation form of the second aspect, the first and second signals are transmitted at different frequencies from each other, thereby reducing interference between the first and second signals and improving the downlink SNR. 
     A third aspect of the embodiments provides an input system including a device and a stylus capable of communicating with the device. In a first possible implementation form of the third aspect, the stylus comprises: a first electrode used for transmitting a first signal to the device, wherein the first electrode is located at a tip portion of the stylus; a second electrode used for transmitting a second signal to the device, wherein the second electrode is located apart from the first electrode; and a third electrode used for receiving a third signal from the device. In some examples, the third signal is used for triggering transmission of the first and second signals. 
     According to the first possible implementation form of the third aspect, the device may receive the first signal from the first electrode and the second signal from the second electrode, thereby detecting a tilt angle of the stylus based on received positions of the first and second signals. Further, the device may transmit the third signal triggering transmission of the first and second signals, so that the device may accurately recognize transmission periods of the first and second signals following the third signal. This may make it possible to certainly receive the first and second signals at the device even though an interval between adjacent transmission periods of the first and second signals is around 5 µs or less. Accordingly, three electrodes structure of the stylus mentioned above may provide high temporal resolution on detection of the tip position and the tilt angle of stylus, thereby improving a writing performance. 
     A second possible implementation form of the third aspect provides: the stylus according to the first possible implementation form of the third aspect, where the third signal carries information including at least one of frequency information and an identifier of a specific stylus corresponding to the device. 
     For example, the frequency information may include information indicating frequencies for transmission of the first and second signals respectively. Using the frequency information, the device may change at least one of the frequencies corresponding to the first and second signals, thereby avoiding that a frequency of noise is close to the frequencies for the transmission of the first and second signals. The identifier may be used for limiting a usable stylus for the device and/or to distinguish between two or more styluses used simultaneously. 
     A third possible implementation form of the third aspect provides: the system according to the first or second possible implementation form of the third aspect, where the third electrode is located between the first electrode and the second electrode. According to the third possible implementation form of the third aspect, the third electrode may reduce interference between the first and second signals during transmission of the first and second signals, thereby improving the downlink SNR. 
     A fourth possible implementation form of the third aspect provides: the system according to any one of the first to third possible implementation forms of the third aspect, where the second electrode has a ring shape, and the stylus further comprises a ground shield configured to be inside the second electrode. According to the fourth possible implementation form of the third aspect, the ground shield may reduce interference between the first and second signals during the transmission of the first and second signals, so that reduction of the interference between the first and second signals improves the downlink SNR and makes it possible to lower transmission voltages applied to the first and second electrodes that are required for an adequate performance. 
     A fifth possible implementation form of the third aspect provides: the system according to any one of the first to fourth possible implementation forms of the third aspect, where during reception of the third signal from the device, the first electrode acts as a floating electrode. According to the fifth possible implementation form of the third aspect, the first electrode acting as the floating electrode enhances the third signal from the device, thereby improving a SNR during uplink transmission from the device to the stylus. 
     A sixth possible implementation form of the third aspect provides: the system according to any one of the first to fifth possible implementation form of the third aspect, where during reception of the third signal from the device, the first electrode acts as an electrode for receiving the third signal from the device. According to the sixth possible implementation form of the third aspect, the third signal is received by the first electrode located in a closer position than the third electrode as well as the third electrode and enhanced, thereby improving the uplink SNR. 
     A seventh possible implementation form of the third aspect provides: the system according to the sixth possible implementation form of the third aspect, where the stylus further comprises: a transmitter configured to transmit the first signal; a receiver configured to receive the third signal; and a switch set configured to connect the first electrode with the transmitter during transmission of the first signal to the device, and to connect the first electrode with the receiver during reception of the third signal from the device. 
     According to the seventh possible implementation form of the third aspect, the transmitter may transmit the first and second signals via the first and second electrodes respectively during the downlink transmission, and the receiver may receive the third signal via the first and third electrodes during the uplink transmission, thereby improving the uplink SNR. 
     A eighth possible implementation form of the third aspect provides: the system according to any one of the first to seventh possible implementation forms of the third aspect, where the first signal is used for detection of a position at which the tip portion of the stylus touches a touch panel of the device, and the second signal is used for detection of a tilt angle of the stylus. According to the eighth possible implementation form of the third aspect, various functions using both the tip position and the tilt angle of the stylus may be implemented on the device. 
     A ninth possible implementation form of the third aspect provides: the system according to any one of the first to eighth possible implementation forms of the third aspect, where a first period for transmission of the first and second signals is separated from a second period for reception of the third signal. According to the ninth possible implementation form of the third aspect, the first period for the downlink transmission is separated from the second period for the uplink transmission, thereby avoiding interference between uplink and downlink signals. 
     A tenth possible implementation form of the third aspect provides: the system according to any one of the first to ninth possible implementation forms of the third aspect, where a first frequency at which the first signal is transmitted is different from a second frequency at which the second signal is transmitted. According to the tenth possible implementation form of the third aspect, the first and second signals are transmitted at different frequencies from each other, thereby reducing interference between the first and second signals and improving the downlink SNR. 
     A fourth aspect of the embodiments provides a non-transitory computer readable storage medium storing a program to cause a computer to implement the method of the second aspect. A fifth aspect of the embodiments provides a computer program to cause a computer to implement the method of the second aspect. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    shows an example of an input system including a device and a stylus according to an embodiment of the present disclosure. 
         FIG.  2    is a schematic diagram for describing electrodes of the stylus according to the embodiment of the present disclosure. 
         FIG.  3    is a schematic diagram for describing a method for detecting a tilt angle of the stylus according to the embodiment of the present disclosure. 
         FIG.  4    is a schematic block diagram for describing elements of the stylus according to the embodiment of the present disclosure. 
         FIG.  5    is a schematic block diagram for describing elements of the device according to the embodiment of the present disclosure. 
         FIG.  6    is a schematic diagram for describing configuration of uplink and downlink transmission periods according to the embodiment of the present disclosure. 
         FIG.  7    is a schematic diagram for describing addition of a ground shield to the stylus according to the embodiment of the present disclosure. 
         FIG.  8 A  shows an example of a TX1 signal from a TX1 electrode, and; 
         FIG.  8 B  shows an example of a TX2 signal from a TX2 electrode. 
         FIG.  9 A  is a schematic diagram for describing a method to enhance an uplink signal according to the embodiment of the present disclosure, and; 
         FIG.  9 B  is a schematic diagram for describing another method to enhance an uplink signal according to another embodiment of the present disclosure. 
         FIGS.  10 A and  10 B  show switching mechanism for changing a path to the TX1 electrode according to said another embodiment of the present disclosure. 
         FIG.  11    is a schematic diagram for describing configuration of uplink and downlink transmission periods according to said another embodiment of the present disclosure, and; 
         FIG.  12    is a flowchart for describing a communication method between the stylus and the device according to said another embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes technical solutions of embodiments, referring to the accompanying drawings. It will be understood that the embodiments described below are not all but just some of embodiments relating to the present disclosure. It is to be noted that all other embodiments which may be derived by a person skilled in the art based on the embodiments described below without creative efforts shall fall within the protection scope of the present disclosure. 
     Following describes an input system including a device and a stylus according to one embodiment of the present disclosure. For example, the device may be a mobile phone, a smart phone, a tablet computer, a personal computer, or the like. The stylus is an input apparatus used for operating the device. 
       FIG.  1    shows an example of an input system including a device and a stylus according to the embodiment of the present disclosure. An input system  5  shown in  FIG.  1    is an example of the input system according to the embodiment of the present disclosure. 
     In an example of  FIG.  1   , the input system  5  comprises a stylus  10  and a device  20 . The stylus  10  is an example of a pen-type input apparatus. Also, the stylus  10  is capable of communicating with the device  20 . The device  20  may be a mobile phone, a smart phone, a tablet computer, a personal computer, or the like. The device  20  comprises a touch panel  20   a  capable of detecting a tip position and a tilt angle of the stylus  10  through communication with the stylus  10 . 
     The device  20  includes processing circuitry. The processing circuitry may be an integrated circuit (IC) so called Touch IC implemented in a touch panel, or a processor such as a central processing unit (CPU), a field-programmable gate array (FPGA) or an application specific integrated circuit (ASIC). The processor is connected to a memory such as a read-only memory (ROM) or a random access memory (RAM), a flash memory, or the like. The memory may store a program to cause the processor to control operation of the device  20 . Likewise, the stylus  10  may also comprise processing circuitry such as the processor or an IC chip and the memory which may store a program to cause the processor to control operation of the stylus  10 . In some examples, the program may be provided via a non-transitory computer readable storage medium to the stylus  10  and/or the device  20 . 
     Following describes an electrodes structure of the stylus  10  with reference to  FIG.  2   .  FIG.  2    is a schematic diagram for describing electrodes of the stylus according to the embodiment of the present disclosure. 
     In an example of  FIG.  2   , the stylus  10  comprises a first electrode  11  (TX1) used for transmitting a first signal to the device  20 . The first electrode  11  is located at a tip portion of the stylus  10 . Also, the stylus  10  comprises a second electrode  12  (TX2) used for transmitting a second signal to the device  20 . The second electrode  12  is located apart from the first electrode  11 . Also, the second electrode  12  may have a ring shape placed around a core of the stylus  10 . The stylus  10  further comprises a third electrode  13  (RX) used for receiving a third signal from the device  20 . 
     The device  20  may receive the first signal from the first electrode  11  and the second signal from the second electrode  12 , and the device  20  may detect the tilt angle of the stylus  10  based on a distance A received positions P 1  and P 2  on the touch panel  20   a  of the first and second signals, as shown in  FIG.  3   .  FIG.  3    is a schematic diagram for describing a method for detecting a tilt angle of the stylus according to the embodiment of the present disclosure. 
     In addition, the device  20  may transmit the third signal triggering transmission of the first and second signals. Using the third signal enables the device  20  to accurately recognize transmission periods of the first and second signals following the third signal, so that the device  20  may certainly receive the first and second signals even though an interval between adjacent transmission periods of the first and second signals is around 5 µs or less. Accordingly, three electrodes structure of the stylus  10  mentioned above may provide high temporal resolution on detection of the tip position and the tilt angle of stylus  10 , thereby improving a writing performance. 
     In addition, the device  20  may transmit the third signal carrying information including at least one of frequency information and an identifier of a specific stylus usable for the device  20 . 
     For example, the frequency information may include information indicating frequencies for transmission of the first and second signals respectively. Using the frequency information, the device  20  may change at least one of the frequencies corresponding to the first and second signals, thereby avoiding that a frequency of noise is close to the frequencies for the transmission of the first and second signals. This may provide improvement of a signal to noise ratio (SNR) during downlink transmission from the stylus  10  to the device  20 . 
     The identifier may be used for limiting a usable stylus for the device  20 . For example, the stylus  10  may transmit the first and second signals if the stylus  10  determines that an identifier of the stylus  10  is identical to the identifier carried by the third signal from the device  20 . This function may be usable for preventing fraud use of the device  20 . In addition, the identifier may be used to distinguish between two or more styluses used simultaneously. This may extend functionality of the device  20 . 
     Referring back to  FIG.  2   , the third electrode  13  may be located between the first electrode  11  and the second electrode  12 . According to this electrodes layout, the third electrode  13  may reduce interference between the first and second signals during transmission of the first and second signals, thereby improving the downlink SNR. 
     The first electrode  11  may be made from a non-conductive material or a conductive material such as a metal or a conductive polymer. However, the downlink SNR may be improved when applying the conductive material to the first electrode  11 . Further, the downlink SNR may be improved when the first electrode  11  is configured to act as a floating electrode. The second electrode  12  may be configured to be grounded or floated. However, the downlink SNR may be improved when the second electrode  12  is configured to be grounded. Following table shows comparison of the downlink SNR between four conditions on the first electrode  11  and the second electrode  12 . 
     
       
         
          TABLE
           
               
               
               
               
               
             
               
                 Comparison of the downlink SNR 
               
               
                   
                 Condition 1 
                 Condition 2 
                 Condition 3 
                 Condition 4 
               
             
            
               
                 TX1 Driving 
                 Grounded 
                 Floated 
                 Floated 
                 Floated 
               
               
                 TX1 Material 
                 Non-conductive 
                 Non-conductive 
                 Conductive 
                 Conductive 
               
               
                 TX2 Driving 
                 32 
                 35 
                 48 
                 52 
               
               
                 DL SNR [db] 
                 32 
                 35 
                 48 
                 52 
               
            
           
         
       
     
     Following describes functions of the stylus  10  with reference to  FIG.  4   .  FIG.  4    is a schematic block diagram for describing elements of the stylus according to the embodiment of the present disclosure. In an example of  FIG.  4   , the stylus  10  comprises the first electrode  11 , the second electrode  12 , the third electrode  13 , a TX driver  14 , a receiver  15  and a processor  16 . The TX driver  14  is an example of a transmitter configured to apply voltage pulses to the first electrode  11  and the second electrode  12 , to transmit the first and second signals to the device  20 . The receiver  15  is configured to receive the third signal from the device  20  via the third electrode  13 . The processor  16  is configured to control the TX driver  14  to transmit the first and second signals during downlink transmission periods and to control the receiver  15  to receive the third signal during uplink transmission periods. 
     Following describes functions of the device  20  with reference to  FIG.  5   .  FIG.  5    is a schematic block diagram for describing elements of the device according to the embodiment of the present disclosure. In an example of  FIG.  5   , the device  20  comprises a receiver  21 , a transmitter  22 , and a processor  23 . The receiver  21  and the transmitter  22  may be implemented in the touch panel  20   a . The receiver  21  is connected with a receiving electrode (not shown in the figure) and is configured to receive the first and second signals from the stylus  10  via the receiving electrode. The transmitter  22  is connected with a transmitting electrode (not shown in the figure) and is configured to transmit the third signal to the stylus  10  via the transmitting electrode. 
     The processor  23  is configured to control the receiver  21  to receive the first and second signals during the downlink transmission periods, and to control the transmitter  22  to transmit the third signal during the uplink transmission periods. Also, the processor  23  is configured to determine received positions (e.g. P 1  and P 2  of  FIG.  3   ) on the touch panel  20   a  of the first and second signals, to calculate a distance between the determined positions, and to detect the tilt angle of the stylus  10  based on the distance. 
     Following describes configuration of uplink and downlink transmission periods with reference to  FIG.  6   .  FIG.  6    is a schematic diagram for describing configuration of uplink and downlink transmission periods according to the embodiment of the present disclosure. 
     In an example of  FIG.  6   , each RX block indicates a period for reception of the third signal by the third electrode  13  of the stylus  10 , and corresponds to the uplink transmission period (e.g. t1 and t7 of  FIG.  6   ). In each uplink transmission period, a predetermined number of signal pulses may be transmitted to the stylus  10 . 
     Each TX1 block indicates a period for transmission of the first signal by the first electrode  11  of the stylus  10 , and each TX2 block indicates a period for transmission of the second signal by the second electrode  12  of the stylus  10 . The TX1 and TX2 blocks correspond to the downlink transmission period (e.g. t2 to t5 and t7 of  FIG.  6   ). In each downlink transmission period, a predetermined number of signal pulses may be transmitted to the device  20 . 
     The transmitter  22  of the device  20  transmits the third signal to the stylus  10  during the uplink transmission period, and the receiver  21  of the device  20  receives the first and second signals from the stylus  10  during the downlink transmission period. As shown in  FIG.  6   , the downlink transmission period is separated from the uplink transmission period, thereby avoiding interference between the third signal (an uplink signal) and each of the first and second signals (downlink signals). 
     Arrangement of the uplink and downlink transmission periods may be predetermined, and a sequence of the downlink transmission periods begins after the downlink transmission period as shown in  FIG.  6   . Also, there exists a predetermined number of the downlink transmission periods between the adjacent two uplink transmission periods. Therefore, when the device  20  determines an initial downlink transmission period and informs it to the stylus  10 , the stylus  10  transmits the first and second signals during uplink transmission periods following the initial downlink transmission period. Accordingly, the device  20  can accurately recognize reception timing of the first and second signals following transmission of the third signal, thereby certainly receiving and processing the first and second signals even though an interval between adjacent transmission periods is around 5 µs or less. This makes it possible to implement high temporal resolution on detection of the tip position and the tilt angle of stylus, thereby improving a writing performance. 
     Following describes one variation of the electrodes structure of the stylus  10  with reference to  FIG.  7   .  FIG.  7    is a schematic diagram for describing addition of a ground shield to the stylus according to the embodiment of the present disclosure. 
     As shown in  FIG.  7   , the stylus  10  further comprises a ground shield  17 . In an example of  FIG.  7   , the ground shield  17  has a ring shape like the second electrode  12 , and at least a part of the ground shield  17  is placed inside the second electrode  12 . This configuration of the ground shield  17  is merely one example, various shapes and arrangements may be applied to the ground shield  17  as variations of the embodiment. Addition of the ground shield  17  may reduce interference between the first and second signals, thereby improving the downlink SNR. Also, improvement of the downlink SNR makes it possible to lower transmission voltages applied to both the first electrode  11  and the second electrode  12  that are required for an adequate performance. 
     Following describes waveforms of the first and second signals with reference to  FIGS.  8 A and  8 B .  FIG.  8 A  shows an example of a TX1 signal from a TX1 electrode, and  FIG.  8 B  shows an example of a TX2 signal from a TX2 electrode. As shown in  FIG.  8 A , each of the first signal (TX1) and the second signal (TX2) has a waveform in which pulses are arranged at equal intervals. In examples of  FIGS.  8 A and  8 B , the interval of the first signal is set to be larger than that of the second signal, that is, a frequency of the first signal is set to be smaller than that of the second signal. This frequency setting may reduce interference between the first and second signal, thereby improving the downlink SNR. 
     Following describes a first method to enhance an uplink signal with reference to  FIG.  9 A .  FIG.  9 A  is a schematic diagram for describing a method to enhance an uplink signal according to the embodiment of the present disclosure. 
     As shown in  FIG.  9 A , a sensing module in the touch panel  20   a  of the device  20  generates an electric field for transmission of an uplink signal (the third signal). If the first electrode  11  (TX1) is configured to be grounded, a portion of the electric field is cut by the first electrode  11  and a strength of the third signal received by the third electrode  13  is reduced. Therefore, in the first method according to the embodiment of the present disclosure, the TX driver  14  of the stylus  10  controls the first electrode  11  to act as a floating electrode during the uplink transmission period. According to the first method, the first electrode  11  acting as the floating electrode enhances the third signal as shown in  FIG.  9 A , thereby improving the uplink SNR. 
     Following describes a second method to enhance an uplink signal with reference to  FIG.  9 B .  FIG.  9 B  is a schematic diagram for describing another method to enhance an uplink signal according to another embodiment of the present disclosure. 
     In the second method according to the embodiment of the present disclosure, the TX driver  14  of the stylus  10  controls the first electrode  11  to act as an electrode for receiving the third signal from the device  20  during the uplink transmission period. In this case, the third signal received via the first electrode  11  is transferred to the receiver  15 . Accordingly, the receiver  15  may receive the third signal via both the first electrode  11  and the third electrode  13 . In the second method, the third signal is received by the first electrode  11  located in a closer position than the third electrode  13  as well as the third electrode  13  and enhanced, thereby improving the uplink SNR. 
     It should be noted that configuration of the stylus  10  shown in  FIG.  4    should be changed to add a path connecting the first electrode  11  with the receiver  15  in order to implement the second method. Following describes switching mechanism for changing a path to the first electrode  11  with reference to  FIGS.  10 A and  10 B .  FIGS.  10 A and  10 B  show switching mechanism for changing a path to the TX1 electrode according to said another embodiment of the present disclosure. 
     As shown in  FIG.  10 A , the stylus  10  further comprises a switch set including switches  101 ,  102  and  103 . During the downlink transmission periods, the switch  101 ,  102  and  103  are set to be ON, OFF and OFF, respectively, and the first electrode  11  is connected with the TX driver  14 . In this case, the first electrode  11  is used for transmission of the first signal (DL Signal#1). 
     On the other hand, during the uplink transmission periods, the switch  101 ,  102  and  103  are set to be OFF, ON and ON, respectively, and the first electrode  11  is connected with the receiver  15  as shown in  FIG.  10 B . In this case, the first electrode  11  is used for reception of the third signal (UL Signal), and the third signal received via the first electrode  11  closer to the touch panel  20   a  than the third electrode  13  strongly enhances the third signal received via the third electrode  13  and the enhanced third signal is transferred to the receiver  15 . Accordingly, the second method described above may further improve the uplink SNR. 
     In the second method described above, configuration of the uplink and downlink transmission periods are changed to that shown in  FIG.  11   .  FIG.  11    is a schematic diagram for describing configuration of uplink and downlink transmission periods according to said another embodiment of the present disclosure. In an example of  FIG.  11   , RX blocks at periods t1 and t6 are added to a sequence of blocks including TX1 blocks that indicate transmission periods of the first signal. In this case, the stylus  10  receives the third signal from the device  20  by using both the first electrode  11  and the third electrode  13  at the periods t1 and t6. 
     Following describes a communication method between the stylus  10  and the device  20  according to the second method mentioned above with reference to  FIG.  12   .  FIG.  12    is a flowchart for describing the communication method between the stylus and the device according to another embodiment of the present disclosure. 
     At a step S 11 , before receiving the third signal from the device  20 , the stylus  10  controls the switches  101 ,  102  and  103  to connect the first electrode  11  with the receiver  15  and also cut off a path between the TX driver  14  and the first electrode  11 . 
     At a step S 12 , the device  20  transmits the third signal triggering transmission of the first and second signals to the stylus  10 , and the stylus  10  receives the third signal from the device  20  via both the first electrode  11  and the third electrode  13 . 
     At a step S 13 , the stylus  10  determines the downlink transmission periods for transmission of the first and second signals according to reception of the third signal from the device  20 . 
     At a step S 14 , the stylus  10  controls the switches  101 ,  102  and  103  to connect the first electrode  11  with the TX driver  14  and also cut off a path between the receiver  15  and the first electrode  11 . 
     At a step S 15 , the stylus  10  transmits the first and second signals via the first electrode  11  and the second electrode  12  respectively during the determined downlink transmission periods. Since the device  20  can accurately recognize reception timing of the first and second signals during the downlink transmission periods, the device  20  may certainly receive and process the first and second signals even though an interval between adjacent downlink transmission periods is around 5 µs or less. This makes it possible to implement high temporal resolution on detection of the tip position and the tilt angle of stylus, thereby improving a writing performance. 
     The foregoing disclosure merely discloses exemplary embodiments, and is not intended to limit the protection scope of the present invention. It will be appreciated by those skilled in the art that the foregoing embodiments and all or some of other embodiments and modifications which may be derived based on the scope of claims of the present invention will of course fall within the scope of the present invention.