Sensor controller, position indicator, and position detecting system

A sensor controller is provided for use in a position detector for detecting a position of a position indicator on a touch surface. The sensor controller includes a microprocessor for outputting a value of a symbol to be sent to the position indicator. The sensor controller includes a transmitter coupled to the microprocessor for generating a transmission signal including a chip string CN1 produced by cyclically shifting a code string PNa having autocorrelation characteristics by a shift quantity based on the value of the symbol to be sent, and sending the generated transmission signal to the position indicator via the touch surface. A higher bit rate can be obtained for a given chip rate compared with the prior art in which only 1 bit can be expressed by one code string.

BACKGROUND

Technical Field

The present disclosure relates to a sensor controller, a position indicator, and a position detecting system, and more particularly to a sensor controller for use in a position detector that detects the position of a position indicator on a touch surface, a position indicator capable of receiving signals sent by such a position detector, and a position detecting system that is provided with such a position detector and a position indicator.

Description of the Related Art

There is known a position detecting system, in which bidirectional communication is performed between a position indicator as a pen-type device and a position detector as a device having a touch surface such as a tablet or the like, or in which unidirectional communication is carried out from the position detector to the position indicator. Patent Document 1 discloses an example of the latter position detecting system.

Patent Document 2 discloses use of the direct sequence spread spectrum (DSSS) technique (hereinafter described as “direct spread technique”) for communication between a position indicator and a position detector that make up a position detecting system.

PRIOR ART DOCUMENT

Patent Documents

BRIEF SUMMARY

Technical Problems

A communication method that is resistant to noise can be realized by using a direct spread technique for a method of communication between a position indicator and a position detector, as is the case with the disclosure described in Patent Document 2.

For example, a transmission-side device can be configured to encode a plurality of bits (a transmission bit string) that make up transmission data, bit by bit, using a known code string having autocorrelation characteristics (a code string where a peak correlation value appears only at a shift quantity 0 when a correlation value is calculated between the code string and a code string produced by cyclically shifting the code string or its inverted signal by an arbitrary shift quantity).

FIG. 16depicts an example of a chip string generated by the transmission-side device according to an encoding process. In the example depicted inFIG. 16, “00010010111” having a length of 11 chips is used as the known code string having autocorrelation characteristics. A transmission bit string is given as “10110.” As depicted inFIG. 16, if a bit to be sent has a value of “1,” then the above code string directly becomes a transmission chip string. On the other hand, if a bit to be sent has a value of “0,” then an inverted code string from the above code string becomes a transmission chip string.

When a reception-side device receives the transmission chip string sent by the transmission-side device, the reception-side device inputs the chip string, chip by chip, successively into a first-in, first-out shift register that has a capacity of 11 chips, and calculates on each input occasion a correlation value between a chip string of 11 chips temporarily accumulated in the shift register and the above known code string. Since the code string has autocorrelation characteristics, the calculated correlation value is a maximum value (+11 in this example) when the chip string stored in the shift register is precisely “00010010111,” and a minimum value (−11 in this example) when the chip string stored in the shift register is precisely “11101101000” (an inverted code string from the known code string). On the other hand, the correlation values for other chip string values are values close to 0 (+1 or −1 in this example). The reception-side device is configured to extract transmission data sent by the transmission-side device from the received chip string, using such features of correlation values.

However, the communication method using the above direct spread technique suffers from a problem that it is difficult to obtain a high bit rate. Specifically, in the example depicted inFIG. 16, since 11 chips are required to express one bit (two values), only a value of 1/11 of the chip rate can be achieved as a bit rate. As it is not easy to increase the chip rate, it is difficult to obtain a high bit rate as a result.

Consequently, one aspect of the present disclosure is directed to providing a sensor controller, a position indicator, and a position detecting system which are able to obtain a high bit rate compared with the background art.

Technical Solution

A sensor controller according to an aspect of the present disclosure is a sensor controller for use in a position detector for detecting a position of a position indicator on a touch surface. The sensor controller includes a controller that outputs a value of a symbol to be sent to the position indicator. The sensor controller includes a transmitter that generates a transmission signal including a first chip string produced by cyclically shifting a spread code having autocorrelation characteristics by a shift quantity based on the value of the symbol to be sent, and sends the generated transmission signal to the position indicator via the touch surface.

A position indicator according to the aspect of the present disclosure is a position indicator configured to be able to receive a signal sent by a sensor controller through a position detector having a touch surface. The position indicator includes a receiver that receives a signal, demodulates the value of a symbol included in the signal based on a cyclic shift quantity for a code string having autocorrelation characteristics which is included in the signal, and restores a sent command based on the demodulated value of the symbol. The position indicator includes a controller that controls the transmission of a signal to the sensor controller based on the command.

A position detecting system according to the aspect of the present disclosure is a position detecting system including a position indicator and a position detector for detecting a position of the position indicator on a touch surface. The position detector includes a controller for outputting a value of a symbol to be sent to the position indicator, and a transmitter for generating a transmission signal including a first chip string produced by cyclically shifting a code string having autocorrelation characteristics by a shift quantity based on at least a portion of the value of the symbol to be sent, and sending the generated transmission signal to the position indicator via the touch surface. The position indicator includes a receiver for successively inputting a series of chips generated by receiving the transmission signal to a first-in, first-out shift register, and each time a chip is input, calculating correlation values between the chip string temporarily accumulated in the shift register and a plurality of code strings produced by cyclically shifting a predetermined code string having autocorrelation characteristics by an arbitrary shift quantity, thereby detecting a bit string included in the series of chips.

Advantageous Effects

According to the present disclosure, since the cyclic shifting of a code string is used in generating a chip string, it is possible to express 2 bits or more with one code string. Accordingly, it is possible to obtain a high bit rate at the same chip rate, compared with the background art where only 1 bit can be expressed by one code string.

DETAILED DESCRIPTION

FIG. 1is a diagram depicting an arrangement of a position detecting system1according to an embodiment of the present disclosure. The position detecting system1is provided with a stylus2and a position detector3.

The stylus2is a position indicator of the active ES (electrostatic) type configured to be able to receive signals that are successively sent by the position detector3. As depicted inFIG. 1, the stylus2has a core20, an electrode21, a pen pressure detection sensor23, a circuit unit24, and a power supply25. A cylindrical AAAA cell, for example, is used as the power supply25. In the present embodiment, an example in which the present disclosure is applied to the stylus2of the active ES type will be described. However, the present disclosure is also suitably applicable to a stylus of another type such as the electromagnetic induction type, for example.

The core20is a rod-shaped member disposed such that its longitudinal direction is aligned with the pen axis direction of the stylus2. The core20has a distal end20awhose surface is coated with an electrically conductive material, providing the electrode21. The core20has a proximal end held against the pen pressure detection sensor23. The pen pressure detection sensor23is used to detect a pressure (pen pressure) applied to the distal end20aof the core20.

The circuit unit24has a function to receive uplink signals US (a first control signal US_c1and a second control signal US_c2) sent by the position detector3through the electrode21, and a function to send downlink signals DS (a position signal DS_pos and a data signal DS_res) through the electrode21to the position detector3. These signals will be described in detail later.

The position detector3has a sensor30that provides a touch surface3a, a sensor controller31, and a host processor32that controls various parts of the position detector3which include the sensor30and the sensor controller31.

The sensor controller31has a function to receive the downlink signals DS (the position signal DS_pos and the data signal DS_res) sent by the stylus2through the sensor30, and a function to send the uplink signals US (the first control signal US_c1and the second control signal US_c2) through the sensor30to the stylus2.

FIG. 2is a diagram depicting an arrangement of the position detector3. As depicted inFIG. 2, the sensor30includes a matrix of line-shaped electrodes30X and line-shaped electrodes30Y, and is capacitively coupled to the stylus2through the line-shaped electrodes30X,30Y. The sensor controller31has a transmitter60, a selecting section40, a receiver50, a logic unit70, and an MCU80(controller).

The transmitter60is a circuit for sending the uplink signals US (the first control signal US_c1and the second control signal US_c2) depicted inFIG. 1. Specifically, the transmitter60includes a first control signal supply section61, a switch62, a spread processor63, a code string hold section64, and a transmission guard section65. Of these components, the first control signal supply section61will be described as being included in the transmitter60according to the present embodiment. However, the first control signal supply section61may be included in the MCU80.

The first control signal supply section61holds a detection pattern c1, and has a function to repeatedly output a signal (or a bit string) corresponding to the detection pattern c1successively during a successive transmission period TCP (e.g., 3 msec.) depicted inFIG. 5to be described later, as instructed by a control signal ctrl_t1supplied from the logic unit70. The first control signal supply section61also has a function to output a predetermined delimiter pattern STP successively at least twice immediately after the end of the successive transmission period TCP or at the time of starting to send the second control signal US_c2. The first control signal US_c1is made up of the detection pattern c1and the delimiter pattern STP thus output from the first control signal supply section61.

The detection pattern c1is a pattern of the values of symbols used for the stylus2to detect the existence of the sensor controller31, and is known to the stylus2in advance (before the stylus2detects the sensor controller31). A symbol is a unit of information used for modulation in a transmission process (a unit of information represented by a transmission signal), and a unit of information obtained by demodulating one symbol as a reception signal in a reception process. The values of symbols may include a value that is converted into a bit string by the stylus2having received the symbol (hereinafter described as “bit string associated value”) and a value that is not converted into a bit string (hereinafter described as “bit string unassociated value”). As depicted in Table 1 to be described later, a symbol corresponding to the former value may take one of values, wherein a total number of such values is indicated by a power of 2, and is associated with a bit string, such as “0001.” The bit length of each symbol represented by a bit string is determined by the specifications of the spread processor63. On the other hand, a symbol corresponding to the latter value takes one or more (e.g., two) values not associated with a bit string, such as “P” and “M” as depicted in Table 1 to be described later. According to an example depicted in Table 1 to be described later, “P” and “M” are associated respectively with a predetermined spread code string and an inverted code string.

The detection pattern c1can be represented by a pattern of bit string unassociated values, and may include a repetition of two bit string unassociated values “P” and “M,” such as “PMPMPM . . . ,” for example.

The delimiter pattern STP is a pattern of symbols for notifying the stylus2of the end of the successive transmission period described above, and includes a pattern of symbols that does not appear in the repetition of the detection pattern c1. For example, if the detection pattern c1includes a repetition of two bit string unassociated values “P” and “M,” such as “PMPMPM . . . ,” then the delimiter pattern STP may include a pattern “PP” made up of two consecutive bit train unassociated values “P.” The delimiter pattern STP and the detection pattern c1may be switched around such that the delimiter pattern STP includes a pattern “PM” and the detection pattern c1includes a pattern “PP.”

The switch62has a function to select either the first control signal supply section61or the MCU80based on a control signal ctrl t2supplied from the logic unit70, and supply an output signal from the selected one to the spread processor63. If the switch62selects the first control signal supply section61, then the spread processor63is supplied with the detection pattern c1or the delimiter pattern STP. If the switch62selects the MCU80, then the spread processor63is supplied with control information c2.

The control information c2includes information including a command that represents the content of an instruction for the stylus2, and is generated by the MCU80and sent on the second control signal US_c2as depicted inFIG. 10. The control information c2includes values (for example, 0 through 15) of symbols associated with a variable-length bit string, and is different from the detection pattern c1in that its values are not shared with the stylus2in advance. The control information c2is different from the detection pattern c1that includes the values “P” and “M” in that it is indicated by value “D” that can take any one of a number of values (e.g., 8 values, 16 values) that can be indicated by a power of 2 having a predetermined bit length described above. As depicted inFIG. 10, the second control signal US_c2includes a delimiter pattern STP “PP” as a preamble followed by a transmission signal (chip string) corresponding to three items of control information c2which are indicated by D1through D3.

The code string hold section64has a function to generate and hold a spread code PN (second code string) which is 11 chips long that has autocorrelation characteristics based on a control signal ctrl_t3supplied from the logic unit70. The spread code PN held by the code string hold section64is supplied to the spread processor63. Specific details of the spread code PN will be described later.

The spread processor63has a function (chip string acquiring function) to obtain a code string which is 12 chips long (a chip string CN2depicted in Table 1,FIG. 6to be described later, a second chip string) by performing primary modulation (cyclic shifting or inversion to be described later) on the spread code PN held by the code string hold section64based on the values of symbols (information represented by a transmission signal according to the processing of the spread processor63) supplied via the switch62. The chip string acquiring function (primary modulation process) will be described briefly below though it will be described in greater detail later with reference toFIGS. 5 through 9A, 9B.

Each of the detection pattern c1, the delimiter pattern STP, and the control information c2according to the present embodiment includes a combination of bit string associated values 0 through 15 (associated bit strings “0000” through “1111”) and bit string unassociated values “P” and “M.” The spread code PN supplied from the spread code hold section64is “00010010111.”

According to the primary modulation performed by the spread processor63, the values (0 through 15, P, and M) of symbols are converted into respective corresponding chip strings CN2. Table 1 depicts specific examples of the associated relationship between the values of symbols and generated chip strings CN2obtained by the chip string acquiring function.

As depicted in Table 1, one symbol represents multiple values, and the value of a symbol is associated with any one of the chip strings CN2in Table 1, which are obtained by cyclically shifting the spread code PN by a shift quantity based on the value of the symbol and non-inverting or inverting, respectively, the cyclically shifted spread code PN. The value of a symbol takes one of the values (“0 through 15”), in a total number (e.g., 16) indicated by a power of 2 represented by a bit string having a predetermined bit length, or takes either one of the values (“P” and “M”) which are not associated with a bit string and which are different from any of the values in the total number indicated by a power of 2 as described above. The former value (“0 through 15”) is used to send the control information c2, and the latter value (“P” and “M”) is used to send the delimiter pattern STP such as a preamble or the like.

Each of the rows of the table will be described in detail below. The value “P” of a symbol is a bit string unassociated value, and is converted into a code string including the spread code PN “00010010111” having autocorrelation characteristics with a fixed chip “1” added to the beginning thereof. The bit string unassociated value “M” is converted into a code string including an inverted code “11101101000” produced by inverting the polarity of the spread code PN “00010010111,” with a fixed chip “0” added to the beginning thereof.

Each of the bit string associated values 0 through 7 is converted into a code string including a code produced by cyclically shifting the spread code PN by a shift quantity depicted in Table 1, with “1” assigned to the beginning thereof. For example, the value “4” of a symbol is converted into a code string including a code produced by cyclically shifting the spread code PN to the right by 9 (to the left by 2), with “1” assigned to the beginning thereof. Each of the bit string associated values 8 through 15 is converted into a code string including a code produced by cyclically shifting an inverted code “11101101000” produced by inverting the polarity of the spread code PN, by a predetermined shift quantity based on the value of the symbol, with “0” assigned to the beginning thereof. For example, the value “12” of a symbol is converted into a code string including a code produced by inverting the spread code PN and cyclically shifting the inverted spread code to the right by 9 (to the left by 2), with “0” assigned to the beginning thereof.

The difference between the closest shift quantities among the shift quantities of the bit string associated values 0 through 7 for use in a command is 1. On the other hand, the difference between the shift quantity of the value “P” of a symbol for use in the delimiter pattern STP such as a preamble or the like (i.e., 0), and the closest shift quantity of the bit string associated value “2” (2 to the right) or the closest shift quantity of the bit string associated value “4” (2 to the left) among the bit string associated values 0 through 7, is 2, which is larger than the smallest difference among the differences between the shift quantities of the bit string associated values 0 through 7. Since the difference between the shift quantity (“0”) of the values “P” and “M” of symbols for use in the delimiter pattern such as a preamble or the like and the shift quantity (+2, −2) of the values (“0,” “4” and “8,” “12”) for use in a command is thus larger than the smallest difference between the shift quantity for a certain value used in a command and the shift quantity for another value used in a command, the probability that the delimiter pattern such as a preamble or the like will be determined in error to be any of predetermined values corresponding to a command is reduced.

A shift quantity is determined such that the smaller the Hamming distance is between a bit string, with which the value of a certain symbol is associated, and a bit string, with which the value of another symbol is associated, the smaller the difference is between the shift quantity for the value of the certain symbol and the shift quantity for the value of the other symbol. The reason why a shift quantity is determined based on the Hamming distances between the bit strings as depicted in Table 1, rather than simply increasing a shift quantity as the value of a symbol increases, will be described later.

The transmitter60(the spread processor63that has acquired the chip string CN2) may not use chip strings CN2acquired as depicted in Table 1 as a transmission signal, but may perform a process (secondary modulation process) for generating a transmission signal by modulating a carrier signal with chip strings CN2. Although the secondary modulation process is not necessarily required, the secondary modulation process may include a process for Manchester-encoding chip strings CN2.

FIGS. 3A through 3Care diagrams depicting examples of signals generated by the spread processor63. These examples will be described below.

FIG. 3Adepicts an example in which the spread processor63does not perform the secondary modulation process. In this example, a chip string CN2generated by primary modulation directly becomes a transmission signal generated by the spread processor63.

FIG. 3Bdepicts an example in which the spread processor63performs only Manchester encoding as the secondary modulation process. In this example, the spread processor63assigns rising (positive-going) edges to chips “1” and falling (negative-going) edges to chips “0” of a plurality of chips included in a chip string CN2, thereby acquiring a Manchester-encoded chip string CN2. Alternatively, the spread processor63may Manchester-encode a chip string CN2by assigning falling edges to chips “1” and rising edges to chips “0.” In the example depicted inFIG. 3B, the Manchester-encoded chip string CN2becomes a transmission signal generated by the spread processor63.

FIG. 3Cdepicts an example in which the spread processor63performs Manchester encoding and digital modulation as the secondary modulation process. In this example, the spread processor63modulates a predetermined carrier signal with the Manchester-encoded chip string CN2, generating a transmission signal depicted inFIG. 3C. Although a transmission signal generated according to BPSK (Binary Phase Shift Keying) is illustrated inFIG. 3C, another digital modulating technique may be used. InFIG. 3C, a sine-wave signal is used as the carrier signal. However, another type of carrier signal such as a rectangular-wave signal may be used.

With Manchester encoding included in the secondary modulation process carried out by the spread processor63, the same value does not continue over a period more than a period corresponding to one chip, as can be understood fromFIG. 3B. By thus performing secondary modulation on a transmission signal whose spectrum is spread by the spread code PN, the transmission signal can be sent using a desired frequency band in order to avoid low-frequency components, for example.

Referring back toFIG. 2, the transmission signal (the first control signal US_c1and the second control signal US_c2) generated by the spread processor63is supplied to the transmission guard section65. The transmission guard section65has a function to insert a guard period, which is a period in which neither transmission nor reception is carried out in order to switch between a transmitting operation and a receiving operation, between a transmission period for the first control signal US_c1and the second control signal US_c2and a reception period RDS, according to a control signal ctrl_t4supplied from the logic unit70.

The selecting section40is a switch for switching between the transmission period in which the sensor30sends signals and the reception period in which the sensor30receives signals, under the control of the logic unit70. Specifically, the selecting section40includes switches44xand44yand conductor selecting circuits41xand41y. Based on a control signal sTRx supplied from the logic unit70, the switch44xoperates to connect the output terminal of the transmitter60to the input terminal of the conductor selecting circuit41xduring the transmission period and to connect the output terminal of the conductor selecting circuit41xto the input terminal of the receiver50during the reception period. Based on a control signal sTRy supplied from the logic unit70, the switch44yoperates to connect the output terminal of the transmitter60to the input terminal of the conductor selecting circuit41yduring the transmission period and to connect the output terminal of the conductor selecting circuit41yto the input terminal of the receiver50during the reception period. Based on a control signal selX supplied from the logic unit70, the conductor selecting circuit41xoperates to select one of the line-shaped electrodes30X and to connect the selected line-shaped electrode30X to the switch44x. Based on a control signal selY supplied from the logic unit70, the conductor selecting circuit41yoperates to select one of the line-shaped electrodes30Y and to connect the selected line-shaped electrode30Y to the switch44y.

The receiver50is a circuit for detecting or receiving the position signal DS_pos and the data signal DS_res sent by the stylus2based on a control signal ctrl_r from the logic unit70. Specifically, the receiver50includes an amplifying circuit51, a detecting circuit52, and an analog-to-digital (AD) converter53.

The amplifying circuit51amplifies and outputs the position signal DS_pos and the data signal DS_res supplied from the selecting section40. The detecting circuit52is a circuit for generating a voltage commensurate with the level of an output signal from the amplifying circuit51. The AD converter53is a circuit for generating a digital signal by sampling the voltage output from the detecting circuit52at predetermined time intervals. The digital data output by the AD converter53are supplied to the MCU80.

The logic unit70and the MCU80serve as a controller for controlling the transmitter60and the receiver50, etc. Specifically, the MCU80includes a microprocessor that has a ROM and a RAM therein and operates according to predetermined programs. The logic unit70is configured to output control signals described above under the control of the MCU80. The MCU80is configured to derive coordinate data x, y indicating the position of the stylus2based on digital data supplied from the AD converter53and to output the derived coordinate data x, y to the host processor32.

FIG. 4is a block diagram depicting functional blocks of the stylus2. As depicted inFIG. 4, the stylus2includes a switching section SW, a receiver26, a transmitter27, and a controller28.

The switching section SW is a switch for switching between reception R and transmission T based on a control signal SWC from the controller28. The switching section SW connects the electrode21to the receiver26during the reception R and connects the electrode21to the transmitter27during the transmission T. The switching section SW is set to the reception R in an initial state, i.e., during a pre-detection period BD (seeFIG. 5) before the stylus2detects the first control signal US_c1.

The receiver26is a circuit for receiving a signal (a signal arriving at the electrode21) supplied from the switching section SW and obtaining the values of symbols from the transmission signal depicted in Table 1. The receiver26includes a demodulating circuit26aand a correlating circuit26b. In order to reduce electric power consumption, the receiver26is disabled in its operation except for shortened reception periods SRP, during the pre-detection period BD before the stylus2detects the sensor controller31.

Operation of the receiver26will be described also with reference toFIG. 5. The receiver26performs a receiving operation in predetermined period WPa (e.g., 2.5 msec.) to receive a first control signal US_c1in the shortened reception periods SRP (periods shorter than the periods WPa, e.g., 60 μsec.), and determines whether a detection pattern c1that is a pattern of the values of symbols, such as “PM” or “MP,” not associated with a bit string having a predetermined length is included in the first control signal US_c1. The stylus2thus tries to detect the sensor controller31. After having detected the sensor controller31, the receiver26continues the receiving operation to detect a delimiter pattern STP. The receiver26receives a signal, which is detected after the delimiter pattern STP, as a second control signal US_c2, and performs a process of extracting control information c2made up of values D associated with a bit string having a predetermined length.

According to the present embodiment, as described above, two successive identical symbol values “PP” make up the delimiter pattern STP. The delimiter pattern STP is thus configured because the stylus2may receive a signal from the position detector3via its housing, not the electrode21, as an antenna. In such a situation, since the circuit unit24of the stylus2is supplied with signals whose positive and negative signs are inverted, the stylus2is unable to receive control information c2properly. Accordingly, for detecting the delimiter pattern STP, the stylus2monitors not only the symbol values “PP,” but also symbol values “MM” made up of a chip string which is produced by inverting the chip string representing the symbol values “PP.” If the stylus2detects the symbol values “PP,” then the stylus2tries to receive control information c2by detecting a subsequent chip string as usual. On the other hand, if the stylus2detects the symbol values “MM,” the stylus2tries to receive control information c2by inverting a subsequent chip string in its entirety after having detected the same. In this manner, for determining whether the symbol values are inverted or non-inverted, the stylus2uses the first chip string, inverted or non-inverted, as a reference, thereby allowing itself to acquire data of the control information c2without making errors about deciding on polarity inversion or non-inversion, even if a signal comes from the position detector3via the housing of the stylus2, not the electrode21, and the polarity of a signal obtained through the electrode21is inverted.

The demodulating circuit26ais a receiving circuit for generating a series of chips by receiving a signal sent by the position detector3. Specifically, if the position detector3performs Manchester encoding and digital modulation as the secondary modulation process, then the demodulating circuit26aperforms a process of successively acquiring a series of chips by demodulating a signal induced on the electrode21according to the modulating technique that the spread processor63of the position detector63has used to modulate the carrier signal, and successively decoding the series of chips according to an inverted process of Manchester encoding. The demodulating circuit26ais configured to supply the decoded series of chips, chip by chip, to the correlating circuit26b. If the spread processor36performs neither Manchester encoding nor digital modulation, then the demodulating circuit26adirectly supplies a series of chips that are successively received, chip by chip, to the correlating circuit26b.

The correlating circuit26bhas a function to detect a detection pattern c1, a delimiter pattern STP, or control information c2included in the series of chips supplied from the demodulating circuit26aby performing a correlating process between the series of chips and a plurality of known code strings. This detecting function will be described in detail later with reference toFIG. 11. If the correlating circuit26bdetects a detection pattern c1, then the correlating circuit26bissues an activation signal EN to the controller28. If the correlating circuit26bdetects a delimiter pattern STP, then the correlating circuit26boutputs detected time t2to the controller28. If the correlating circuit26bdetects control information c2, then the correlating circuit26boutputs the detected control information c2to the controller28.

The controller28includes a microprocessor (MCU), and is activated when it is supplied with the activation signal EN from the receiver26(i.e., when the receiver26detects the detection pattern c1), and performs various processes. Specifically, based on the detected signal t2supplied from the receiver26, the controller28generates a transmission and reception schedule for various signals (the control information c2, the position signal DS_pos, and the data signal DS_res). The controller28performs a process of generating control signals SWC based on the generated transmission and reception schedule and supplying the generated control signals SWC to the switching section SW, and a process of controlling a method of sending the data signal DS_res based on control information c2supplied from the receiver26.

The process of controlling the method of sending the data signal DS_res will be described in detail below. If the contents of information to be sent (pen ID, a pen pressure value, and the state in which a side switch is pressed, etc.) are specified by the control information c2, then the controller28controls the contents of information to be sent to the position detector3according to the specified contents. Specifically, the controller28generates transmission data Res including the information to be sent and supplies the generated transmission data Res to the transmitter27. If the transmission timing to send the data signal DS_res (e.g., a time slot used to send the data signal DS_res) is specified by the control information c2, then the controller28controls the timing to supply the transmission data Res to the transmitter27so that the data signal DS_res will be sent at the transmission timing. Furthermore, if the frequency used to send the data signal DS_res is specified by the control information c2, then the controller28controls a modulation circuit27ato be described later in order to generate a carrier signal having the specified frequency.

If the receiver26has not detected the detection pattern c1, i.e., if the receiver26has completed the above processes in response to the previous activation signal EN supplied thereto, but has not yet been supplied with a next activation signal EN, then the controller28may disable the above processes (i.e., the controller28does not perform its processes). In this fashion, the electric power consumption of the controller28can be reduced.

The transmitter27is a circuit for sending the position signal DS_pos and the data signal DS_res, and includes a modulation circuit27aand a voltage boosting circuit27b.

The modulation circuit27ais a circuit for generating a carrier signal (e.g., a rectangular-wave signal) having a predetermined frequency or a frequency controlled by the controller28, and outputting the carrier signal as it is or after modulating it under the control of the controller28. When the position signal DS_pos is to be sent, the modulation circuit27adoes not modulate the carrier signal and outputs the carrier signal as it is. When the data signal DS_res is to be sent, the modulation circuit27amodulates the carrier signal with transmission data Res supplied from the controller28, and outputs the modulated signal obtained as a result. A digital modulating technique such as PSK (Phase Shift Keying) may be described as a specific modulating technique for modulating the carrier signal.

The voltage boosting circuit27bis a circuit for boosting the voltage of output signals from the modulation circuit27ato a certain amplitude thereby to generate the position signal DS_pos and the data signal DS_res. The position signal DS_pos and the data signal DS_res that have been generated by the voltage boosting circuit27bare supplied via the switching section SW to the electrode21, from which they are transmitted into space. The voltage boosting circuit27band the modulation circuit27amay be realized as a single processor.

FIG. 5is a timing chart illustrative of a chronological sequence of operation of the stylus2and the sensor controller31. InFIG. 5, a time axis indicated at an upper section Ts represents transmission Tx and reception Rx of the stylus2, and a time axis indicated at a lower section Tt represents transmission Tx and reception Rx of the sensor controller31.

A period up to time t0is a period in which the stylus2is outside a detecting range of the sensor controller31. In order to reduce electric power consumption, the stylus2operates the receiver26intermittently a plurality of times in periods WPa shorter than the successive transmission period TCP. Specifically, in each of the periods WPa, the stylus2operates the receiver26only during the shortened reception period SRP, and disables the receiver26for the rest of the time in WPa. The time length of the reception period SRP is set to a value that is necessary and sufficient to receive the detection pattern c1once.

The sensor controller31is configured to repeat the transmission of the first control signal US_c1and the second control signal US_c2in a period WP.

Specifically, as the period WP starts, the sensor controller31repeats the transmission of a chip string representing the detection pattern c1over the successive transmission period TCP that is longer than the period WPa.

As described above, the detection pattern c1according to the present embodiment is “PMPMPMP . . . .” The position detector3converts each of the values P and the values M that make up the detection pattern c1into a chip string CN2that is 12 chips long according to the chip string acquiring function of the spread processor63depicted inFIG. 2. Details will be described later.

The sensor controller31is configured to send a delimiter pattern STP indicating the end of the transmission of the detection pattern c1(or the start of the second control signal US_c2) by sending a chip string that represents the same symbol value P successively twice immediately after the end of the successive transmission period TCP. Each value P is converted into a chip string CN2which is 12 bits long according to the chip string acquiring function of the spread processor63depicted inFIG. 2. The transmission of the first control signal US_c1is completed at this point.

Having completed the transmission of the first control signal US_c1, the sensor controller31then sends a chip string representing control information c2(i.e., the second control signal US_c2). The control information c2, which is sent subsequently to the delimiter pattern STP, as described above, includes information including an arbitrary bit string representing a command. “D1,” “D2,” “D3,” . . . , and “Dn” depicted inFIG. 4each represent a value D that is an arbitrary 4-bit bit string (“0000,” “0001,” or the like), and is converted into a chip string CN2which is 12 chips long according to the chip string acquiring function of the spread processor63depicted inFIG. 2.

The sensor controller31that has completed the transmission of the second control signal US_c2provides a reception period RDS for receiving a signal from the stylus2. In case the stylus2has received the first control signal US_c1sent as described above, the stylus2sends the position signal DS_pos in the reception period RDS. During the reception period RDS, the sensor controller31waits for the reception of the position signal DS_pos thus sent.

Upon movement of the stylus2into the detecting range of the sensor30at time t0(stylus-down), the stylus2detects the detection pattern c1sent by the sensor controller31at the timing of time t1immediately after the reception period SRP positioned in the subsequently arriving successive transmission period TCP.

When the stylus2detects the detection pattern c1, the stylus2generates the activation signal EN described above and subsequently continues the receiving operation beyond the reception period SRP. If the sensor controller31sends the delimiter pattern STP while the stylus2is performing the receiving operation, the stylus2detects the delimiter pattern STP. In case the stylus2detects the delimiter pattern STP, it refers to time t2at which it detects the delimiter element STP, and generates a transmission and reception schedule for the second control signal US_c2, the position signal DS_pos, and the data signal DS_res. Specifically, as depicted inFIG. 5, the stylus2waits for the reception of the second control signal US_c2at the timing based on time t2, then sends the position signal DS_pos, and finally sends the data signal DS_res.

As described above, the sensor controller31provides the reception period RDS after having sent the second control signal US_c2and waits for the reception of the position signal DS_pos. Having received the position signal DS_pos, the sensor controller31calculates the position (coordinate data x, y) of the stylus2based on how the position signal DS_pos is received by the line-shaped electrodes30X,30Y depicted inFIG. 2, outputs the calculated position to the host processor32depicted inFIG. 1, provides the reception period RDS again, and waits for the reception of the data signal DS_res. Having received the data signal DS_res, the sensor controller31extracts the transmission data Res from the received data signal DS_res and outputs the extracted transmission data Res to the host processor32.

Even after having received the position signal DS_pos and the data signal DS_res from the stylus2, the sensor controller31still repeats the transmission of the first control signal US_c1and the second control signal US_c2in the same manner as before. The stylus2also repeats the above operation. The sensor controller31receives the position signal DS_pos and the data signal DS_res from the stylus2each time the stylus2repeats the above operation, thereby calculating the position of the stylus2and acquiring the transmission data Res sent by the stylus2.

The outline of the position detecting system1has been described above. The chip string acquiring function of the spread processor63depicted inFIG. 2and the detecting function of the correlating circuit26bdepicted inFIG. 3will be described successively in detail below. In particular, specific contents of the spread code PN in addition to an example of a specific configuration of the chip string acquiring function of the spread processor63that obtains a transmission signal from the values of symbols depicted in Table 1 will also be described in detail below.

FIG. 6is a block diagram depicting functional blocks of the spread processor63depicted inFIG. 2. As depicted inFIG. 6, the spread processor63has a control circuit63a, a code inversion/non-inversion switching circuit63b(code string generator), a cyclic shifter63c(cyclically shifting unit), a shift register63d(chip string generator), and a modulating circuit63e.

The code inversion/non-inversion switching circuit63bhas a function to generate a code string PNa (first code string) which is 11 chips long and which has autocorrelation characteristics, based on the spread code PN (second code string) which is 11 chips long and which is stored in the code string hold section64. Specifically, the code inversion/non-inversion switching circuit63bselects either the spread code PN or the inverted code from the spread code PN according to inversion information II supplied from the control circuit63a, and generates a code string PNa according to the selected code string.

The spread code PN will be described in detail below. As described above, the spread code PN is a code string having autocorrelation characteristics. When correlation values between the spread code PN and a code string produced by cyclically shifting the spread code PN or its inverted signal by an arbitrary shift quantity are calculated, a peak correlation value appears only at a shift quantity 0. The fact that the spread code PN has autocorrelation characteristics will be described below with reference toFIG. 9. It is assumed below that the spread code PN is “00010010111.”

FIG. 9Adepicts a broken-line curve that represents correlation values between the spread code PN “00010010111” and a code string produced by cyclically shifting the spread code PN by an arbitrary shift quantity. According to the broken-line curve, the correlation values at a shift quantity “+1” are correlation values between the spread code PN “00010010111” and a code string “10001001011” produced by cyclically shifting the chips of the spread code PN to the right by 1. Furthermore, the correlation values at a shift quantity “−2” are correlation values between the spread code PN “00010010111” and a code string “01001011100” produced by cyclically shifting the chips of the spread code PN to the left by 2. It should be noted that “0” is treated as “−1” in computing the correlation value.

FIG. 9Bdepicts a broken-line curve that represents correlation values between the spread code PN “00010010111” and a code string produced by cyclically shifting an inverted code “11101101000” by an arbitrary shift quantity. According to the broken-line curve, the correlation values at a shift quantity “+1” are correlation values between the spread code PN “00010010111” and a code string “01110110100” produced by cyclically shifting the chips of the inverted code to the right by 1. Furthermore, the correlation values at a shift quantity “−2” are correlation values between the spread code PN “00010010111” and a code string “10110100011” produced by cyclically shifting the chips of the inverted code to the left by 2.

In either one ofFIGS. 9A and 9B, a correlation value peak represented by the broken-line curve appears only at a shift quantity “0.” Therefore, when correlation values are calculated between the spread code PN and a code string produced by cyclically shifting the spread code PN or an inverted signal by an arbitrary shift quantity, since a correlation value peak appears only at a shift quantity “0,” it can be said that the spread code PN has autocorrelation characteristics.

Referring back toFIG. 6, the code inversion/non-inversion switching circuit63bhas a function to be supplied with a fixed code NR from the control circuit63a, and invert or not invert the fixed code NR according to the inversion information II supplied from the control circuit63a, thereby generating a fixed chip NRa. The fixed code NR is a code that is 1 chip long, and is represented by “1” in the example depicted inFIG. 6. The fixed code NR is used in order to make the floor value (correlation values other than the peak) of the correlation values of the chip string CN2output from the shift register63dequal to “0.” This point will be described separately in detail later.

The cyclic shifter63cis a functional block for cyclically shifting the code string PNa generated by the code inversion/non-inversion switching circuit63bby a shift quantity SA supplied from the control circuit63a, thereby generating a chip string CN1(first chip string). The shift register63dis a functional block for receiving the chip string CN1generated by the cyclic shifter63cand the fixed chip NRa generated by the code inversion/non-inversion switching circuit63bas parallel data, adding the received fixed chip NRa to the received chip string CN1to thereby generate a chip string CN2(second chip string), and outputting the generated chip string CN2as serial data.

FIG. 8is a diagram illustrative of the chip string CN2output from the shift register63d. A code string C1-0depicted inFIG. 8represents the chip string CN2output from the shift register63dif the code inversion/non-inversion switching circuit63bdoes not perform its inverting process and the cyclic shifter63cdoes not cyclically shift the supplied code string (when the shift quantity SA is “0”), and includes the spread code PN “00010010111” with the fixed code NR “1” added to the beginning thereof. A code string C1-nis a code string produced by cyclically shifting the chip string CN1part of the code string C1-0by a shift quantity n, and represents the chip string CN2output from the shift register63dif the code inversion/non-inversion switching circuit63bdoes not perform its inverting process and the cyclic shifter63ccyclically shifts the supplied code string by the shift quantity n.

A code string C2-0depicted inFIG. 8represents the chip string CN2output from the shift register63dif the code inversion/non-inversion switching circuit63bperforms its inverting process and the cyclic shifter63cdoes not cyclically shift the supplied code string (when the shift quantity SA is “0”), and includes an inverted code from the code string C1-0. A code string C2-nis a code string produced by cyclically shifting the chip string CN1part of the code string C2-0by a shift quantity n, and represents the chip string CN2output from the shift register63dif the code inversion/non-inversion switching circuit63bperforms its inverting process and the cyclic shifter63ccyclically shifts the supplied code string by the shift quantity n.

Referring toFIGS. 9A and 9Bagain,FIG. 9Adepicts a solid-line curve that represents correlation values between the code string C1-0depicted inFIG. 8and a code string produced by cyclically shifting a portion, except the fixed chip NRa, of the code string C1-0by an arbitrary shift quantity. In addition,FIG. 9Bdepicts a solid-line curve that represents correlation values between the code string C1-0depicted inFIG. 8and a code string produced by cyclically shifting a portion, except the fixed chip NRa, of an inverted code (e.g., the code string C2-0depicted inFIG. 8) by an arbitrary shift quantity. In either one ofFIGS. 9A and 9B, a correlation value peak represented by the solid-line curve appears only at a shift quantity “0,” as with the broken-line curve. This holds true for all the code strings C1-n, C2-nthough not illustrated. Consequently, the stylus2that receives the code strings C1-n, C2-ncan store the code strings C1-n, C2-nin advance and detect code strings C1-n, C2-nincluded in received chip strings by calculating correlation values between the stored code strings C1-n, C2-nand the received chip strings. The position detecting system1according to the present embodiment sends and receives the first control signal US_c1and the second control signal US_c2, using such properties. Details of a detecting operation of the stylus2to detect the code strings C1-n, C2-nwill be described later.

As depicted inFIG. 9A, the floor value of the correlation values (broken-line curve) calculated with respect to the spread code PN is “−1,” whereas the floor value of the correlation values (solid-line curve) calculated with respect to the code string C1-0is “0.” Furthermore, as depicted inFIG. 9B, the floor value of the correlation values (broken-line curve) calculated with respect to the inverted code from the spread code PN is “+1,” whereas the floor value of the correlation values (solid-line curve) calculated with respect to the inverted code from the code string C1-0is “0.” The floor value of the correlation values is “0” because the fixed chip NRa is placed at the beginning of the chip string CN2, making the number of positive chips and the number of negative chips equal to each other. Conversely, placing the fixed chip NRa at the beginning of the chip string CN2makes the floor value of the correlation values equal to “0.”

If the fixed chip NRa is not added to the spread code PN, then the distance between the floor value “−1” of the correlation values and the maximum value “+11” thereof is 10. If the fixed chip NRa is added to the spread code PN, then the distance between the floor value “0” of the correlation values and the maximum value “+12” thereof is 12. Consequently, it can be said that decision errors on the reception side can be reduced by adding the fixed chip NRa to the spread code PN, making the floor value equal to “0.” The position detector3according to the present embodiment makes it possible, from this standpoint, to reduce decision errors on the stylus2side.

Referring back toFIG. 6, the modulating circuit63ecarries out the secondary modulation process for generating a transmission signal including the first control signal US_c1and the second control signal US_c2based on the chip string CN2generated by the shift register63d. The secondary modulation process has been described in detail above. The transmission signal generated by the modulating circuit63eaccording to the secondary modulation process reaches the sensor30via the transmission guard section65and the selecting section40depicted inFIG. 2, and is sent through the touch surface3a(seeFIG. 1) to the stylus2by the sensor30.

The control circuit63ais a functional block for controlling various parts of the spread processor63. The functions performed by the control circuit63ainclude a function to generate the fixed code NR and the inversion information II and supply them to the code inversion/non-inversion switching circuit63b, and a function to generate the shift quantity SA and supply it to the cyclic shifter63c.

FIG. 7is a block diagram depicting functional blocks of the control circuit63afor generating the fixed code NR and the inversion information II. As depicted inFIG. 7, the control circuit63afunctionally has an input acceptor100, an inversion information determining section101, a shift quantity determining section102, a shift quantity/inversion information storage unit103, and an output selecting section104.

The input acceptor100is a functional block for accepting the values P, M, D that make up the detection pattern c1, the delimiter pattern STP, and the control information c2input from the switch62depicted inFIG. 2. If the input acceptor100accepts the value P or the value M input which is not associated with a particular bit string, then it supplies the accepted value to the output selecting section104. If the input acceptor100accepts the value D (which is 4 bits long here) representing a bit string, it supplies the most significant bit thereof as an inversion information indicator bit IIIB (a second bit string which is 1 bit long that is to be sent to the stylus2) to the inversion information determining section101, and supplies the rest (three bits) as a shift quantity indicator bit string SAIB (a first bit string which has a predetermined bit length of 2 bits or more that is to be sent to the stylus2) to the shift quantity determining section102.

The inversion information determining section101is a functional block for determining first inversion information II1based on the inversion information indicator bit IIIB supplied from the input acceptor100. Specifically, the inversion information determining section101stores therein an inversion allocation table101adepicted in Table 2 below, and determines first inversion information II1according to the inversion allocation table101a. The first inversion information II1thus determined is supplied to the output selecting section104.

The shift quantity determining section102is a functional block for determining a first shift quantity SA1based on the shift quantity indicator bit string SAIB supplied from the input acceptor100. Specifically, the shift quantity determining section102stores therein a shift quantity allocation table102adepicted in Table 3 below, and determines a first shift quantity SA1according to the shift quantity allocation table102a. The first shift quantity SA1thus determined is supplied to the output selecting section104.

As can be understood from Table 3, the shift quantity determining section102according to the present embodiment first determines a value “2” as the first shift quantity SA1for a bit string “000” (predetermined reference bit string). The value represented by “2” is a value produced by adding a predetermined value (=2) to a second shift quantity SA2(=0) to be described later. With respect to each of a plurality of bit strings produced by successively incrementing the bit string “000” according to a predetermined criterion, values obtained by adding the number of incrementing to the first shift quantity SA1(=2) determined for the bit string “000” are determined as the first shift quantity SA1. The predetermined criterion is given as the fact that the Hamming distance between a bit string to be incremented and a bit string that has been incremented is 1. The significance of why the above criterion is employed will be described later.

For example, a bit string that is obtained by incrementing the bit string “000” three times according to the above criterion is “010,” and a first shift quantity SA1to be allocated to the bit string “010” is “5” (=2+3) obtained by adding the number (=3) of incrementing to the first shift quantity SA1(=2) determined for the bit string “000.”

The shift quantity/inversion information storage unit103stores therein respective values of second inversion information112, a second shift quantity SA2, third inversion information113, and a third shift quantity SA3. Specifically, the shift quantity/inversion information storage unit103stores therein “not to be inverted” as the second inversion information112, “0” as the second shift quantity SA2, “to be inverted” as the third inversion information113, and “0” as the third shift quantity SA3.

In response to the value P supplied from the input acceptor100, the output selecting section104supplies the second inversion information112and the second shift quantity SA2stored in the shift quantity/inversion information storage unit103respectively as the inversion information II and the shift quantity SA to the code inversion/non-inversion switching circuit63band the cyclic shifter63c, respectively, depicted inFIG. 6. The shift register63ddepicted inFIG. 6now outputs the code string C1-0depicted inFIG. 8as the chip string CN2. Moreover, in response to the value M supplied from the input acceptor100, the output selecting section104supplies the third inversion information113and the third shift quantity SA3stored in the shift quantity/inversion information storage unit103respectively as the inversion information II and the shift quantity SA to the code inversion/non-inversion switching circuit63band the cyclic shifter63c, respectively, depicted inFIG. 6. The shift register63ddepicted inFIG. 6now outputs the code string C2-0depicted inFIG. 8as the chip string CN2.

In response to neither of the values P, M supplied from the input acceptor100(i.e., in response to the value D input from the input acceptor100), the output selecting section104supplies the first inversion information II1determined by the inversion information determining section101as the inversion information II to the code inversion/non-inversion switching circuit63bdepicted inFIG. 6, and also supplies the first shift quantity SA1determined by the shift quantity determining section102as the shift quantity SA to the cyclic shifter63cdepicted inFIG. 6. The shift register63ddepicted inFIG. 6now outputs either one of the code strings C1-2through C1-9and C2-2through C2-9depicted inFIG. 8as the chip string CN2. More specifically, if the inversion information II represents “not to be inverted,” then the shift register63doutputs a code string C1-SA, and if the inversion information II represents “to be inverted,” then the shift register63doutputs a code string C2-SA.FIG. 8also illustrates an associated relationship between the bit string that is 4 bits long which is accepted by the input acceptor100and the chip string CN2output by the shift register63d. For example, if the bit string accepted by the input acceptor100is “0010,” then the chip string CN2output by the shift register63dis the code string C1-5, i.e., “110111000100.” Furthermore, if the bit string accepted by the input acceptor100is “1010,” then the chip string CN2output by the shift register63dis the code string C2-5, i.e., “001000111011.”

In this manner, the transmitter60can generate a transmission signal including a chip string CN2that is obtained by cyclically shifting the spread code PN having autocorrelation characteristics by the shift quantity based on the value of a symbol to be sent, and inverting (or non-inverting) the cyclically shifted spread code PN, if necessary, as depicted in Table 1 above. As long as a chip string CN2can be obtained, the order of the cyclically shifting process and the inverting or non-inverting process carried out by the transmitter60does not matter. Alternatively, the transmitter60may store the association between the values of symbols and chip strings CN2or transmission signals including them as depicted in Table 1 in a memory, and may read and send a chip string CN2stored in the memory each time the value of a symbol is input thereto.

FIG. 10is a diagram depicting an example of the second control signal US_c2that the position detector3sends to the stylus2. In the example depicted inFIG. 10, the position detector3sends the value P successively twice to form the delimiter pattern STP as a preamble, and thereafter sends three values D1“0” (0b0000), D2“8” (0b1000), D3“6” (0b0110) as the control information c2. For sending the value P, the shift register63doutputs the code string C1-0, i.e., “100010010111,” depicted inFIG. 8as the chip string CN2. For sending the control information c2, the shift register63dgenerates a chip string CN2for each of the 4-bit values D1, D2, D3. For the first 4-bit value D1, since the corresponding bit string is “0000,” the shift register63dgenerates the code string C1-2, i.e., “111000100101,” depicted inFIG. 8as the chip string CN2. For the next 4-bit bit string D2, since its content is “1000,” the shift register63dgenerates the code string C2-2, i.e., “000111011010,” depicted inFIG. 8as the chip string CN2. For the last 4-bit bit string D3, since its content is “0110,” the shift register63dgenerates the code string C1-6, i.e., “101011100010,” depicted inFIG. 8as the chip string CN2.

Part or all of the bit string D3that is the last one value (4-bit value) of the control information c2, for example, may include an error-correcting code calculated based on the bit strings D1and D2, which precede the bit string D3. In this manner, the stylus2on the reception side is able to detect or correct a bit error generated in the bit strings D1and D2using the error-correcting code.

The criterion “that the Hamming distance between a bit string to be incremented and a bit string that has been incremented is 1” used as the predetermined criterion for determining the first shift quantity SA1will be described below. When the stylus2receives a chip string CN2, it may receive a chip string CN2with the shift quantity shifted by 1. For example, such a case happens when although the position detector3has sent the code string C1-6depicted inFIG. 8, the stylus2determines that it has received the code string C1-7. In order to correct the erroneous decision with the above error-correcting code, it is desirable that the difference between the bit string represented by the code string C1-6and the bit string represented by the code string C1-7should be as small as possible. According to the present embodiment, inasmuch as the above predetermined criterion is employed, the bit string represented by the code string C1-6is “0110” and the bit string represented by the code string C1-7is “0111,” and the difference between them is only one bit. Even if an erroneous decision is made, it is only one bit different, and the error can be corrected by an error-correcting code capable of correcting one bit which is sent with the transmission of the command. By thus employing the criterion “that the Hamming distance between a bit string to be incremented and a bit string that has been incremented is 1” and adding the error-correcting code, therefore, signals can be sent which are robust against erroneous decisions about shift quantities.

FIG. 11is a block diagram depicting functional blocks of the correlating circuit26bdepicted inFIG. 4. As depicted inFIG. 11, the correlating circuit26bhas a shift register110, a code string storage unit111, a detection pattern detector112, a delimiter pattern detector113(preamble detector), a bit string detector114, and a command restorer115.

The shift register110includes a first-in, first-out register for accepting a series of chips acquired by the demodulating circuit26a, bit by bit, and is configured to be able to accumulate 12 chips. When more than 12 chips are input to the shift register110, older ones are successively deleted from the shift register110.

The code string storage unit111stores a plurality of code strings that are obtained by cyclically shifting a predetermined code string having autocorrelation characteristics by arbitrary shift quantities. Specifically, code strings that need to be stored in the code string storage unit111are all code strings that can possibly be sent by the position detector3. Therefore, the code string storage unit111according to the present embodiment may store the code strings C1-0, C1-2through C1-9, C2-0, and C2-2through C2-9depicted inFIG. 8.

The detection pattern detector112, which has an internal timer (not depicted), is a functional block for performing a detecting operation to detect the detection pattern c1included in a series of chips output from the demodulating circuit26ain case the timer indicates that the present time is within a reception period SRP depicted inFIG. 5. In the detecting operation, specifically, each time a new chip is input to the shift register110, the detection pattern detector112calculates correlation values between the chip string temporarily accumulated in the shift register110and those code strings which correspond to the values P, M of the detection pattern c1, among the code strings stored in the code string storage unit111, specifically, the code string C1-0and the code string C2-0. Then, when the correlation value with the code string C1-0represents a peak value, the detection pattern detector112determines that it has detected the value P, and when the correlation value with the code string C2-0represents a peak value, the detection pattern detector112determines that it has detected the value M. In response to alternately detecting the value P and the value M successively a predetermined number of times, the detection pattern detector112determines that it has detected the detection pattern c1, and issues the activation signal EN described above to the controller28.

The delimiter pattern detector113is a functional block for starting a detecting operation to detect the delimiter pattern STP (preamble) included in a series of chips output from the demodulating circuit26ain response to the detection of the detection pattern c1by the detection pattern detector112. In the detecting operation, specifically, each time a new chip is input to the shift register110, the delimiter pattern detector113calculates a correlation value between the chip string temporarily accumulated in the shift register110and the code string which corresponds to the value P of the delimiter pattern STP, among the code strings stored in the code string storage unit111, specifically, the code string C1-0. Then, when the calculated correlation value represents a peak value, the delimiter pattern detector113determines that it has detected the value P. In response to detecting the value P successively twice, the delimiter pattern detector113determines that it has detected the delimiter pattern STP, stops the detecting operation, and outputs detected time t2described above to the controller28.

The bit string detector114is a functional block for performing a detecting operation to detect the value D (a bit string that is 4 bits long) included in a series of chips output from the demodulating circuit26aat a timing when the transmission and reception schedule generated by the controller28indicates that the present time is within the reception period of the control information c2. In the detecting operation, specifically, each time a new chip is input to the shift register110, the bit string detector114calculates correlation values between the chip string temporarily accumulated in the shift register110and those code strings which correspond to the value D, among the code strings stored in the code string storage unit111, specifically, the code string C1-2through C1-9, C2-2through C2-9. When any of the calculated values represents a peak value, the bit string detector144determines that it has detected the value D (a bit string that is 4 bits long) corresponding to the code string that indicates the peak value. The bit string detector144outputs the bit string which is the detected value D to the command restorer115each time.

The command restorer115is a functional block for joining bit strings successively supplied from the bit string detector114to restore the control information c2sent by the position detector3. The command restorer115is configured to output the restored control information c2to the controller28. The command set by the position detector3is thus supplied to the controller28.

As described above, since the position detector3and the stylus2according to the present embodiment uses the cyclic shifting of code strings in generating a chip string CN2to be sent by the position detector3, it is possible to express 2 bits or more with one code string. Accordingly, it is possible to obtain a high bit rate at the same chip rate, compared with the background art where only 1 bit can be expressed by one code string.

Furthermore, because the chip string CN1with the fixed chip NRa added thereto is used as the chip string CN2, detection errors on the reception side are reduced, reducing the possibility that a reception error will occur on the stylus2side.

For each of a plurality of bit strings produced by successively incrementing a predetermined reference bit string according to a predetermined criterion, a value obtained by adding the number of incrementing to a first shift quantity SA1determined for the reference bit string is determined as a first shift quantity SA1, and the criterion “that the Hamming distance between a bit string to be incremented and a bit string that has been incremented is 1” is employed as the above predetermined criterion. Consequently, even if a chip string CN2is received with the shift quantity shifted by 1, error correction due to erroneous decisions about a shift quantity can be kept to a 1-bit error, and hence can be realized by a shorter error-correcting code.

Although the preferred embodiment of the present disclosure has been described above, the present disclosure is not limited to the embodiment, but can be reduced to practice in various forms without departing from the scope thereof.

For example, in the above embodiment, 11-bit “00010010111” is used as the spread code PN. However, any code string can be used as the spread code PN insofar as it has autocorrelation characteristics. Though one spread code PN is used to send the value of one symbol, a plurality of (e.g., five) identical chip strings CN2may be included with respect to the value of one symbol. Such a case is equivalent to the transmission of the value of the same symbol a plurality of times (i.e., five times), and erroneous decisions about a shift quantity can further be reduced by selecting a most probable shift quantity from a plurality of shift quantities.

Table 4, Table 5, andFIGS. 12 and 13are illustrative of chip strings CN2output from the shift register63ddepicted inFIG. 6according to a first modification of the above embodiment.

According to the present modification, a bit string “0000100100011011011110001010111” that is 31 bits long is used as the spread code PN. This spread code PN has autocorrelation characteristics as with the 11-bit spread code PN used in the above embodiment.

According to the present modification, a shift quantity allocation table102ais configured as depicted in Table 6 below. Table 6 is different from the shift quantity allocation table102adepicted in Table 3 in that the first shift quantity SA1determined for the reference bit string “000” is “5” (a value produced by adding 5 to the second shift quantity SA2(=0)) rather than “2” and the number added to the first shift quantity SA1(=5) is not the number of incrementing itself, but a number corresponding to the number of incrementing (specifically, “the number of incrementing” times 3). The values of the second inversion information112and the second shift quantity SA2that are stored in the inversion allocation table101aand the shift quantity/inversion information storage unit103are the same as those indicated in the above embodiment.

According to the present modification, a code string C3-0depicted inFIG. 12corresponds to the value P, a code string C4-0depicted inFIG. 13corresponds to the value M, and code strings C3-5, C3-8, C3-11, C3-14, C3-17, C3-20, C3-23, and C3-26depicted inFIG. 12and code strings C4-5, C4-8, C4-11, C4-14, C4-17, C4-20, C4-23, and C4-26depicted inFIG. 13correspond to bit strings that are 4 bits long. The code string C3-0includes the spread code PN “0000100100011011011110001010111” with a fixed code NR“1” added to the beginning thereof. A code string C3-nis a code string produced by cyclically shifting only part corresponding to the chip string CN1of the code string C3-0by a shift quantity n, a code string C4-0is an inverted code from the code string C3-0, and a code string C4-nis a code string produced by cyclically shifting only part corresponding to the chip string CN1of the code string C4-0by a shift quantity n.

Even though the longer spread code PN is used, it is thus possible to express multiple values of 2 bits or more with one transmission signal as is the case with the above embodiment. Though the bit rate is lower to the extent that the spread code PN is now longer, since the difference between shift quantities for adjacent code strings is larger, it is possible to reduce the possibility that the stylus2will erroneously determine and detect a shift quantity (the value of a corresponding symbol). For example, even if a shift quantity is detected as +6 to the right, robust decoding can be carried out for the shift quantity error by determining the shift quantity as a value “0” which is originally +5 to the right. With a shift quantity being set to an odd number of 3 or more in the modification, a margin of the same discrete variant can preferably be provided in determining shift quantities, for example, by determining a shift quantity as a value “1” which is originally +8 to the right if the shift quantity is detected as +7 to the right and by determining a shift quantity as a value “0” which is originally +5 to the right if the shift quantity is detected as +5 to the right.

In the above modification, the difference between the closest shift quantities among the shift quantities for the bit train associated values 0 through 7 used in a command is 3. On the other hand, the difference between a shift quantity (i.e., 0) for the symbol value “P” used in the delimiter pattern STP such as a preamble or the like and the closest shift quantity (5 to the right) for the value “0” or the closest shift quantity (5 to the left) for the value “4” among the bit train associated values 0 through 7 used in a command is 5, which is large compared with 3 that represents the difference between the shift quantities for bit train associated values 0 through 7. Since the smallest difference (5) among the differences between the shift quantities based on the symbol values “P” and “M” used in the delimiter pattern STP such as a preamble or the like and the shift quantities based on the values that make up a command is thus larger than the smallest difference (3) among the differences between the shift quantity based on one value of a command and the shift quantity based on another value of the command, the probability that the delimiter pattern such as a preamble or the like will be determined in error as a predetermined value corresponding to a command is reduced.

In the above embodiment, the demodulating circuit26aof the stylus2performs an inverted process of Manchester encoding. However, even though the spread processor63of the position detector3carries out Manchester encoding, the demodulating circuit26aneed not perform an inverted process of Manchester encoding. A processing operation of the stylus2in such a modification will be described below with reference toFIG. 14.

FIG. 14is a block diagram depicting functional blocks of a correlating circuit26baccording to a second modification of the above embodiment. As depicted inFIG. 14, the correlating circuit26baccording to the present modification has a shift register120, a Manchester encoder121, a detection pattern detector122, a delimiter pattern detector123(preamble detector), and a bit string detector124, in place of the shift register110, the detection pattern detector112, the delimiter pattern detector113(preamble detector), and the bit string detector114depicted inFIG. 11.

The shift register120is different from the shift register110according to the above embodiment, which is able to store only 12 chips, in that the shift register120is configured to be able to store 24 chips. This is because the number of chips that are input to the shift register120for one chip string CN2increases to 24 as the demodulating circuit26adoes not perform an inverted process of Manchester encoding.

The Manchester encoder121is a functional block for Manchester-encoding a code string stored in the code string storage unit111when the code string is supplied to the detection pattern detector122, the delimiter pattern detector123, and the bit string detector124. Therefore, the detection pattern detector122, the delimiter pattern detector123, and the bit string detector124are supplied with the Manchester-encoded code string.

The detection pattern detector122, the delimiter pattern detector123, and the bit string detector124are different respectively from the detection pattern detector112, the delimiter pattern detector113, and the bit string detector114in that they are configured to calculate correlation values between a chip string that is 24 chips long which is temporarily accumulated in the shift register120and the code string that is 24 chips long which has been Manchester-encoded. The other details of the detection pattern detector122, the delimiter pattern detector123, and the bit string detector124are the same as those of the detection pattern detector112, the delimiter pattern detector113, and the bit string detector114.

A Manchester-encoded code string usually does not exhibit the clean autocorrelation characteristics (autocorrelation characteristics whose floor values are the same) depicted inFIGS. 9A and 9B. However, since its peak value can be detected, the detection pattern detector122, the delimiter pattern detector123, and the bit string detector124are able to detect a detection pattern c1, a delimiter pattern STP, and a bit string that is 4 bit long, respectively, according to the above process.

In the above embodiment, it has been described that the position detector3sends the second control signal US_c2following the first control signal US_c1, as depicted inFIG. 5. However, after having sent the first control signal US_c1(specifically, a chip string CN2corresponding to the delimiter pattern STP), the position detector3may send the second control signal US_c2(specifically, a chip string CN2corresponding to the control information c2) after the elapse of a predetermined time period longer than 0.

FIG. 15is a timing chart illustrative of a chronological sequence of operation of a stylus2and a sensor controller31according to a third modification of the above embodiment. A position detector3depicted inFIG. 15is different from the position detector3according to the above embodiment in that it does not send the second control signal US_c2following the first control signal US_c1, but provides a reception period RDS having a predetermined time length WT after having sent the first control signal US_c1, and sends the second control signal US_c2only if the position signal DS_pos is received during the reception period RDS. Even though the gap is provided between the first control signal US_c1and the second control signal US_c2, as long as the time length of the gap is determined in advance, the stylus2can determine a transmission and reception schedule while taking the gap into account, and hence can receive the second control signal US_c2without any problems.

In the above embodiment, one chip string CN2is assigned to 4 bits. However, the number of bits that can be assigned to one chip string CN2is not limited to 4. Particularly, if long code strings as depicted inFIGS. 12 and 13are used, one code string may represent more bits.

In the above embodiment, the detection pattern c1and the delimiter pattern STP are represented by the dedicated code strings C1-0, C2-0. However, they may be represented by code strings which are the same as code strings for bit strings. If the code strings C1-0, C2-0are dedicated to the detection pattern c1and the delimiter pattern STP, then as depicted inFIG. 8, detection errors are reduced in detecting the detection pattern c1and the delimiter pattern STP by making the differences (2 inFIG. 8) between the shift quantities for the code string C1-0(or the code string C2-0) and the adjacent code strings C1-1, C1-9(or the code strings C2-1, C2-9) larger than the differences (1 inFIG. 8) between the shift quantities for the code strings C1-n(or the code strings C2-n) (n≠1), although code strings that can be used for sending bit strings are reduced. However, using code strings which are the same as code strings for bit strings as the delimiter pattern STP, as described above, is advantageous in that code strings that can be used for sending bit strings are increased.

In the above embodiment, a chip string CN1with a fixed chip NRa added thereto is used as a chip string CN2. However, if no problem arises from noise caused by the fact that the floor value of correlation values is not “0,” then a chip string CN1may be used directly as a chip string CN2.

In the above embodiment, a chip string CN1with a fixed chip NRa added to the beginning thereof is used as a chip string CN2. However, a chip string CN2may be made up of a chip string CN1and a fixed chip NRa added to the tail end of the chip string CN1.

In the above embodiment, an example in which the detection pattern c1is sent before the delimiter pattern STP has been described. However, if the stylus2may perform its receiving operation continuously rather than intermittently, then the transmission of the detection pattern c1may be omitted. In such a case, the stylus2detects the position detector3by detecting the delimiter pattern STP.

In the above embodiment, the present disclosure is applied to signals that the position detector3sends to the stylus2. However, the present disclosure is also applicable to signals that the stylus2sends to the position detector3.

In the above embodiment, the spread processor63includes the code inversion/non-inversion switching circuit63band the cyclic shifter63c, so that code strings are inverted and cyclically shifted in the spread processor63. However, the spread processor63may be configured such that it stores the values of symbols that may possibly be input to the control circuit63aand chip strings CN2to be output in an associated relationship in a storage area, and generates a chip string CN2corresponding to the value of an input symbol by reading it from the storage area.

DESCRIPTION OF REFERENCE SYMBOLS