Patent Publication Number: US-2019187828-A1

Title: Location detection for a touch system

Description:
TECHNICAL FIELD 
     This relates generally to integrated circuits, and more particularly to estimating a touch location in a touch system. 
     BACKGROUND 
     A touch system includes interfaces such as touch screens that can include an input device and output device layered on top of an electronic visual display of an information processing system. For example, a user can provide input or control the information processing system through simple or multi-touch gestures by touching the screen with a special stylus and/or one or more fingers. Touch screens are common in devices, such as game consoles, personal computers, tablet computers, electronic voting machines, and smart phones. These interfaces can also be attached to computers or, as terminals, to networks. 
     To detect user gestures such as touching via the touch system interface, common technologies include resistive touch screens and capacitive touch screens can be employed. An example capacitive touch screen panel consists of an insulator such as glass, coated with a transparent conductor such as indium tin oxide. As the human body is also an electrical conductor, touching the surface of the screen results in a distortion of the screen&#39;s electrostatic field, measurable as a change in capacitance. Different technologies may be used to determine the location of the touch. In some touch systems, mutual or self capacitance can be measured by transmitting a signal on a row/column of the touch screen interface and receiving the signal on a respective column/row. When the touch occurs close to a row/column intersection, the received change in signal strength and/or signal phase changes. This change isolates the touch location. 
     SUMMARY 
     In an example, a system includes a receiver to receive output signals from a touch system to detect a user&#39;s touch. The output signals are received in response to excitation signals that are generated out of phase with respect to each other and applied to at least two rows or columns of the touch system. A touch location analyzer compares an amplitude of the output signals received from the rows or columns of the touch system, where a ratio of the output signal amplitudes from the rows or columns of the touch system is utilized to determine the location of the user&#39;s touch relative to the rows or columns of the touch system. 
     In another example, a receiver receives output signals from a touch system to detect a user&#39;s touch. The output signals are received in response to at least two out of phase excitation signals applied to at least two rows or columns of the touch system. A touch location analyzer compares the phase of the output signals received from different rows or columns of the touch system. A difference in phase of the output signal amplitudes from the rows or columns of the touch system is utilized to determine the location of the user&#39;s touch relative to the rows or columns of the touch system. 
     In yet another example, a method includes transmitting excitation signals that are out of phase with respect to each other to a touch system. At least one of the excitation signals is transmitted to at least one row or column of the touch system and at least one other of the excitation signals is concurrently transmitted to at least one other row or column of the touch system. The method includes receiving output signals from the touch system in response to the excitation signals. The output signal includes a combined response from two or more rows or columns of the touch system excited by the excitation signals. The method includes comparing the amplitude or phase of the output signals received from different rows or columns of the touch system to determine a difference in the amplitude or phase of the output signal from the different rows or columns of the touch system to determine the location of the user&#39;s touch relative to the rows or columns of the touch system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic block diagram of an example system to determine touch location of a touch system. 
         FIG. 2  is a circuit diagram of a receiver and transmitter for an example touch system that uses multiphase signaling and processing. 
         FIG. 3  is a circuit diagram of an example touch system that can be excited and analyzed via multiphase signaling to determine touch location. 
         FIG. 4  is a circuit diagram of an example transmitter and receiver circuit that uses multiphase signaling and processing to determine touch location. 
         FIG. 5  is a flow diagram of an example method to determine touch location of a touch system. 
     
    
    
     DETAILED DESCRIPTION 
     In example embodiments, received signals from a touch system are analyzed with respect to signal amplitude and/or phase to determine a location of a user&#39;s touch relative to the rows or columns of the touch system. A receiver receives output signals (or signal) from the touch system to detect the user&#39;s touch. The output signals are received in response to excitation signals that are generated out of phase with respect to each other and applied to at least two rows or columns of the touch system. In some examples, out of phase excitation signals can be applied concurrently to the rows or columns of the touch system to decrease the amount of scan time it takes to receive a response to the excitation signals. Also, by concurrently analyzing multiple touch locations in response to the out of phase excitation signals, receiving hardware to determine the user&#39;s touch can be simplified. A touch location analyzer compares an amplitude of the output signals received from different rows or columns of the touch system. A ratio of the output signal amplitudes from the different rows or columns of the touch system is utilized to determine the location of the user&#39;s touch relative to the rows or columns of the touch system. In another example, received signal phases from different rows or columns of the touch system are analyzed to determine the location of the user&#39;s touch. 
     By analyzing the respective amplitudes and/or phases received in response to a user&#39;s touch of the touch system, precise location of the touch can be determined which includes determining touch locations between rows and/or columns of the touch system. For example, if a stylus (or finger) is placed at a touch location that is directly over a row/column detection point, a maximum signal amplitude may be received for that point. If the stylus is offset to touch/affect more than one row or column detection point of the touch system, a combination of signal amplitudes or phases can be analyzed to detect locations between rows or columns. Thus, if one row yields a signal at 70% of maximum, and another row provides a signal that is 30% of maximum, it can be determined that the stylus is offset from the center of one row in the direction toward about 30% of the other row. 
     The touch system can be excited by a transmitter that transmits excitation signals that are out of phase with respect to each other (e.g., a sine wave generated as one excitation signal and a cosine wave generated as another excitation signal). At least one of the of excitation signals is transmitted to at least one row or column of a touch system and at least one other of the excitation signals is concurrently transmitted to at least one other row or column of the touch system. An output signal having a combination of signals from each of the excitation signals is received by a receiver in response to the excitation signals transmitted to the touch system. Receiver circuits extrapolate the row or column information from the output signal based on the phase of the excitation signals. For example, in a two phase excitation system, at least two receiver circuits include a summing junction to extrapolate signal phases from the output signal to determine which of at least two rows or columns was touched. 
       FIG. 1  illustrates an example system  100  to touch location of a touch system. The system  100  includes a transmitter  110  to transmit excitation signals  114 . At least one of the excitation signals  114  can be transmitted to at least one row or column of a touch system  120  and at least one other of the excitation signals can be concurrently transmitted to at least one other row or column of the touch system. In some examples, individual excitation can be provided where one row or column is excited and in a subsequent scanning sequence another row or column of the touch system  120 . The transmitter  110  generates at least one of the excitation signals  114  at a given phase to one row or column of the touch system  120  and generates the other of the excitation signals at a different phase from the given phase to the other row or column of the touch system. For example, one excitation signal  114  may be generated as a sin wave and another excitation signal generated as a cosine wave. As described hereinbelow, other phase relationships are possible. 
     The transmitter  110  includes at least one alternating current (AC) source  130  to generate the excitation signals  114  to the touch system  120  where each of the excitation signals in one example are transmitted out of phase with respect to each other excitation signal. At least two of the excitation signals  114  can be generated at the same frequency or at different frequencies with respect to each other via the AC source  130 . Different frequencies can be employed for the excitation signals  114  so long as they remain in their given phase relationship (e.g., orthogonal) over the integration time which includes both the time it takes to transmit and receive signals in response to the excitation signals  114 . 
     In one example, at least two of the excitation signals  114  can be transmitted to at least two rows or columns of the touch system  120  where the excitation signals are at least 90 degrees out of phase with respect to each other when transmitted to the respective rows or columns. In other examples, more than two excitation signals  114  can be transmitted to the touch system to further reduce scan time of the touch system. As used herein, the term “scan time” refers to the amount of time it takes to excite each respective row or column of the touch system  120 . In single phase excitation systems, each row or column had to be excited individually to detect the presence of a touch shown as user input  134 . In the multiphase system described herein, multiple rows or columns can be analyzed concurrently to reduce the scan time in half in a two phase excitation system (or reduced more if more than two excitation signals utilized). 
     The touch system  120  can be a mutual capacitance touch system (see e.g.,  FIG. 3 ) having at least two rows and columns that receive the excitation signals  114  from the transmitter  110  where the touch system generates an output signal  140  (or signals) based on the excitation signals. A receiver  150  receives the output signal  140  from the touch system  120 . The receiver  150  includes at least two receiver circuits  160  to process the output signal  140  from the touch system  120  and to determine if or where a user has touched the touch system. As used herein, the term “circuit” can include a collection of active and/or passive elements that perform a circuit function, such as an analog circuit or control circuit. Additionally or alternatively, for example, the term “circuit” can include an integrated circuit (IC) where all and/or some of the circuit elements are fabricated on a common substrate (e.g., semiconductor substrate). 
     Each of the receiver circuits  160  can include a summing junction (see e.g.,  FIG. 4 ) to extrapolate signal phases  170  from the output signal  140  to determine which of the rows or columns was touched from the touch system  120 . At one of the summing junctions of the receiver circuits  160 , the output signal  140  is summed with the excitation signal at the given phase to extrapolate the row or column excited in response to the given phase. At the other of the summing junctions of the receiver circuits  160 , the output signal  140  is summed with the excitation signal at the different phase to extrapolate the row or column excited in response to the different phase. The output of each of the summing junctions can be filtered via a low pass filter to facilitate extrapolating the row or column that was touched from the output of each of the summing junctions in the receiver circuit  160 . 
     By providing multiphase signaling and analysis as described herein to reduce scan time of the touch system, a portion of the touch system  120  can be excited by the transmitter  110  during one scanning sequence and analyzed by the receiver  150  based on the scanning of the portion. At least one other portion of the touch system  120  can be excited by the transmitter  110  during another scanning sequence and analyzed by the receiver based on the scanning of the at least one other portion. In this manner of multiphase signaling and processing, hardware complexity can be reduced because multiple rows or columns can be scanned using fewer connection nodes to the touch system  120  to determine a touch to the system (e.g., in a two phase excitation system, half of the row or column connections from conventional systems can be reduced). 
     A touch location analyzer  180  compares an amplitude of the output signals received from different rows or columns of the touch system. A ratio of the output signal amplitudes from the different rows or columns of the touch system is utilized to determine the location of the user&#39;s touch relative to the rows or columns of the touch system. For example, if the amplitude received from one row was at 20% peak and the amplitude received from another row was at 80% peak, touch location can be calculated base on the ratio of 20/80, such that 80 percent of the users touch force is affecting one row and 20% of the user&#39;s touch force is affecting the other row. As used herein, peak signal amplitude refers to the maximum signal received when no touch force is applied. If it is known that 10 millimeters separate the rows for example, the touch location is approximately 8 millimeters away from one row (the 20% peak row) and about two millimeters away from the other row (e.g., 80% peak row). 
     In another example, received signal phases from different rows or columns of the touch system are analyzed to determine the location of the user&#39;s touch. For example, in a no-touch force situation, received output signals may be 90 degrees out of phase with respect to one another. When a user touches the touch system  120 , the signal phases of the output signal  140  can change such that it can be determined where in between rows or columns the touch has occurred. A calibration table, described below, can be provided where signal amplitudes and phases are analyzed between maximum touch force and minimum touch force to determine the change in location. The table can include a range of amplitude or phase differences corresponding to how close or near a touch has occurred to a given row or column. By analyzing the respective amplitudes and/or phases received in response to a user&#39;s touch of the touch system, precise location of the touch can be determined which includes determining touch locations between rows and/or columns of the touch system. For example, if a stylus (or finger) is placed at a touch location that is directly over a row/column detection point, a maximum signal amplitude may be received for that point. If the stylus is offset to touch/affect more than one row or column detection point of the touch system, a combination of signal amplitudes or phases can be analyzed to detect locations between rows or columns. 
     In a signal amplitude example, if one row yields a signal amplitude at 50% of maximum, and another row provides a signal that is 50% of maximum, it can be determined from this ratio that the stylus is offset approximately half way between the two rows. A similar analysis can be conducted by the touch location analyzer  180  by comparing signal amplitudes received from respective columns to determine touch locations between columns. In a signal phase example for determining touch location, if a touch location is directly over a row/or column detection point, a given phase may be determined between the respective row or column. If the stylus (or finger) is moved between rows or columns a different phase relationship can be determined. A calibration table in the touch location analyzer  180  can be used to determine a range of amplitudes or phases to be encountered at differing distances between rows or columns of the touch system  120 . For example, if a stylus is 100% over a given row of the touch system  120 , a phase of 90 degrees may be detected between the two rows. If the stylus is between rows or columns, a phase other than 90 degrees may be detected where this difference in phase from 90 degrees determines the distance between rows or columns. 
       FIG. 2  illustrates an example circuit  200  of a receiver  210  and a transmitter  220  for a touch system where multiphase excitation and processing is employed. The transmitter  220  provides multiple out of phase excitation signals  234  to a touch panel  240 . The transmitter  220  can provide row or column excitation to the touch panel  240  to detect a user&#39;s touch where more than one row or column are excited concurrently via the excitation signals  234 . In this example, a capacitance touch panel  240  is illustrated. In a touch system, mutual or self capacitance can be measured by transmitting the excitation signals  234  to selected rows/columns of the panel  240 . The receiver  210  receives a signal  244  in response to the excitation signals  234  applied on the columns/rows of the touch panel  240 . When a touch occurs close to a row/column intersection, the received change in signal strength and/or phase change can be detected by the receiver  210 . This change isolates the touch location on the touch panel  240 . 
     The transmitter  220  can include at least one numerically controlled oscillator (NCO)  250  which drives a digital to analog converter (DAC)  254 , which in turn drives an output amplifier  258  to provide the signals  234 . The receiver  210  can include an analog front end  259  that includes an input stage or amplifier  260  which drives an analog to digital converter (ADC)  262 . Output from the ADC  262  and NCO  264  can be multiplied at  266  which is then summed at  268 . As described hereinbelow with reference to  FIG. 4 , the receiver  210  can include summing junctions and filters (e.g., before or after the sense amplifier  260 ) to extrapolate row/column information from the signal  244  as described herein. 
       FIG. 3  illustrates an example of a touch system  300  that can be excited and analyzed via multiphase signaling. In the touch system  300 , a known signal is transmitted via sources which is coupled through a touch panel  320  and then received by the receiver via sense inputs  330 . The change in the gain/phase of the received signal from one or more of the sense inputs  330  indicates the presence or absence of a touch. In conventional touch systems, each transmitter (row/drive line) is stimulated, usually with a sinusoidal signal at a known frequency for a certain period of time. The received signal is concurrently measured by a number of receive channels via inputs  330 . The change in capacitance on any receive channel indicates the presence of a touch close to the intersection of the transmit channel (row) and that receive channel (column). In such systems, the transmit channels are then scanned row by row to obtain the touch image. 
     To reduce the area of the touch controller circuit in conventional single excitation systems, one can reduce the number of receive and/or transmit channels. However this increases the scan time. The scan time increases by the same factor as the hardware reduction. For example, if the hardware is reduced by a factor of 2, the scan time increases by a factor 2 to obtain the same performance level. However, an increase in scan time decreases the responsiveness of the touch screen controller. In the system and methods described herein, multiphase signaling is provided where two or more rows/columns of the touch panel  320  are excited concurrently effectively reducing the scan time. When the scan time is reduced, hardware complexity can thereby also be reduced. As shown, a location analyzer  334  can be provided to detect a location for a user&#39;s touch via stylus or fingering. The location analyzer  334  can include an amplitude comparator  340  to compare signal amplitudes between rows or columns to determine a signal amplitude ratio which determines touch distances between rows and/or columns. A phase comparator  350  can also be provided to determine touch distances between rows and/or columns based on differences in detected signal phases received. 
       FIG. 4  illustrates a circuit diagram of an example transmitter  410  and receiver circuit  420  that uses multiphase signaling and processing. In this example, a SIN signal sin(ωn) is transmitted on row  1  via source  424  and a COS signal cos(ωn) on row  2  transmitted concurrently via source  426 . Both the SIN and COS can be at the same or different frequencies. When choosing different frequencies, the multiphase signals should remain orthogonal (e.g., in substantially the same phase relationship) over the integration time (transmit and receive time). 
     At the receiver circuit  420 , the received signal represented as 2Asin(ωn+φ)+2Bcos(ωn+θ) in this example, can be received via analog front end (AFE)  428  and can be match filtered with the transmitted SIN and COS signal in the digital domain via summing junctions  430  and  434 , respectively. For example, output from the summing junction  430  can be represented as −Acos(2ωn+φ)+Acos(φ)+Bsin(2ωn+θ)-Bsin(θ), and output from the other summing junction can be represented as Asin(2ωn)+Asin(φ)+Bcos(2ωn+θ)+Bcos(θ). These signals can be filtered via low pas filters  440  and  444 , respectively to produce output signals Acos(φ)−Bsin(θ) and Bcos(θ)+Asin(φ), respectively. Output from the filters  450  can be analyzed for amplitude and/or phase differences by a location analyzer  450  to determine touch locations between rows or columns of the touch system. 
     Because the signals can be maintained in a given phase relationship with respect to each other (e.g., orthogonal), changes in the signal strength of the SIN indicates a touch on row  1  and the corresponding receiver while any change in COS will give the touch information on row 2  and the receiver of interest. Thus, information about two touch electrodes can be obtained concurrently. This implies that by scanning in pairs, the touch image can be obtained in half the time. As described hereinabove, more than two rows can be concurrently scanned and analyzed. One half the number of receivers can be employed in an example to facilitate scanning the panel twice (e.g., getting half the entire panel information from the first scan and one half from the second scan). Thus, the total scan time using multiphase stimulation remains substantially the same while the hardware complexity is reduced. In some example, the receive channel can be built with a higher dynamic range to account for interference. Therefore, sending multiphase signals does not impact the individual receiver design. Thus, a factor of two hardware improvement can be easily obtained using two excitation signals. This can also be easily extended to larger number of concurrent excitations. 
     In view of the structural and functional features described hereinabove, an example method is described with reference to  FIG. 5 . For clarity, the method is shown and described as executing serially, but parts of the method could occur in different orders and/or concurrently from that shown and described herein. Such method can be executed by various components, such as components configured in an integrated circuit, a processor or a controller. 
       FIG. 5  illustrates an example method  500  to determine touch location of a touch system. At  510 , the method  500  includes transmitting excitation signals that are out of phase with respect to each other to a touch system (e.g., via transmitter  110  of  FIG. 1 ). At least one of the excitation signals is transmitted to at least one row or column of the touch system and at least one other of the signals is concurrently transmitted to at least one other row or column of the touch system. At  520 , the method  500  includes receiving an output signal from the touch system in response to the excitation signals (e.g., via receiver  150  of  FIG. 1 ). The output signal includes a combined response from two or more rows or columns of the touch system excited by the excitation signals. At  530 , the method  500  includes comparing the amplitude or phase of the output signals received from different rows or columns of the touch system to determine a difference in the amplitude or phase of the output signal from the different rows or columns of the touch system to determine the location of the user&#39;s touch relative to the rows or columns of the touch system (e.g., via touch location analyzer  180  of  FIG. 1 ). The method  500  can also include transmitting the excitation signals 90 degrees out of phase with respect to each other and/or at different frequencies with respect to each other. 
     Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.