Patent Publication Number: US-8542211-B2

Title: Projection scan multi-touch sensor array

Description:
FIELD OF THE INVENTION 
     This invention relates to touch sensor panels, and more particularly, to multi-touch sensor panels whose elements can be applied to a single surface of a substrate. 
     BACKGROUND OF THE INVENTION 
     Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, touch panels, joysticks, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch panel, which can be a clear panel with a touch-sensitive surface. The touch panel can be positioned in front of a display screen so that the touch-sensitive surface covers the viewable area of the display screen. Touch screens can allow a user to make selections and move a cursor by simply touching the display screen via a finger or stylus. In general, the touch screen can recognize the touch and position of the touch on the display screen, and the computing system can interpret the touch and thereafter perform an action based on the touch event. 
     Touch panels can include an array of touch sensors capable of detecting touch events (the touching of fingers upon a touch-sensitive surface). Some current touch panels are able to detect multiple touches (the touching of fingers upon a touch-sensitive surface at distinct locations at about the same time) and near touches (fingers within the near-field detection capabilities of their touch sensors), and identify and track their locations. Examples of multi-touch sensor panels are described in Applicant&#39;s co-pending U.S. application Ser. No. 10/842,862 entitled “Multipoint Touchscreen,” filed on May 6, 2004 and published as U.S. Published Application No. 2006/0097991 on May 11, 2006, the contents of which are incorporated by reference herein. 
     Capacitive touch sensor panels can be formed as an array of rows and columns of sensors on opposing sides of a touch substrate. For example, the rows can form drive electrodes on one surface of the touch substrate and the columns can form sense electrodes on the opposing surface. To scan a sensor panel, a stimulus can be applied to one row with all other rows held at DC voltage levels. When a row is stimulated, a modulated output signal can appear on the columns of the sensor panel. The columns can be connected to analog channels (also referred to herein as event detection and demodulation circuits). For every row that is stimulated, each analog channel connected to a column generates an output value representative of an amount of change in the modulated output signal due to a touch event occurring at the sensor located at the intersection of the stimulated row and the connected column. After analog channel output values are obtained for every column in the sensor panel, a new row is stimulated (with all other rows once again held at DC voltage levels), and additional analog channel output values are obtained. When all rows have been stimulated and analog channel output values have been obtained, the sensor panel is said to have been “scanned,” and a complete “image” of touch can be obtained over the entire sensor panel. This image of touch can include an analog channel output value for every pixel (row and column) in the panel, each output value representative of the amount of touch that was detected at that particular location. 
     The manufacturing cost of a two-surface sensor panel as described above is generally higher than if only one surface of the substrate was needed for sensor circuitry. In addition, when the touch substrate overlays a display device (e.g., an LCD), circuitry on the second surface typically increases light loss as compared to a single surface system. Therefore, it is desirable for cost and performance reasons to realize a multi-touch sensor that only needs one surface of the touch substrate for sensor circuitry. 
     SUMMARY OF THE INVENTION 
     A multi-touch sensor panel can be constructed on a single surface of a touch substrate to reduce manufacturing costs and minimize light loss in transparent embodiments. The panel can be formed as a plurality of distributed RC lines arranged in an array of rows and columns. Each distributed RC line can include alternating connected transistors and metal pads formed on a single surface of a sensor panel substrate, with the drain and source terminals of the transistors connected to adjacent metal pads. 
     During operation, the rows and columns are enabled at different times, and the pulse travel times for each row and column in both directions are measured. Equalized travel times for each row and column are then computed as the sum of the pulse travel times in both directions. The equalized pulse travel times can be compared to an equalized no-touch pulse travel time to determine which rows and columns, if any, have a finger touching it. The equalized pulse travel times represent a map, albeit an ambiguous one, of all points touched by fingers. However, before an unambiguous map of finger contacts can be generated, more information needs to be applied. The reason for this is that the equalized pulse travel times, which provide high selectivity in determining whether a finger(s) is touching over a row or a column, only provide projection scan-like data that, by itself, cannot resolve rotational ambiguity of multiple finger contacts. 
     However, once the rows and columns containing finger contacts are known, the un-equalized left-to-right, right-to-left, top-to-bottom and bottom-to-top pulse travel time data can be used to determine the relative positions of the fingers within the rows and columns and un-ambiguously determine the positions of all the finger contacts. In particular, for each row indicating a possible contact, the pulse travel times for right-to-left and left-to-right are compared against other rows for which there were possible contacts, one by one, to establish the relative positions of the contacts across the rows. After all rows have been processed, the same process is then repeated for each column showing a possible contact. For each column indicating a possible contact, the pulse travel times for top-to-bottom and bottom-to-top are compared against other columns for which there were possible contacts, one by one, to establish the relative positions of the contacts across the columns. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary distributed resistor-capacitor (RC) line according to one embodiment of this invention. 
         FIG. 2  illustrates how an exemplary distributed RC line can serve as a touch sensor according to one embodiment of this invention. 
         FIG. 3  illustrates an exemplary metal pad and thin film transistor (TFT), which are examples of the basic circuit elements needed to construct a distributed RC line according to one embodiment of this invention. 
         FIG. 4  illustrates an exemplary distributed RC line constructed from discrete resistors, capacitors, and metal pads that can represent one row of multi-touch sensors according to one embodiment of this invention. 
         FIG. 5  illustrates an exemplary distributed RC line constructed using metal pads and field effect TFTs according to one embodiment of this invention. 
         FIG. 6  illustrates an exemplary circuit capable of measuring pulse travel times to allow for equalization of the spatial dependency of the pulse travel times according to one embodiment of this invention. 
         FIG. 7  is a plot of exemplary pulse travel times for a finger touching a distributed RC line at various points along the line according to one embodiment of this invention. 
         FIG. 8  is an exemplary plot showing the sensitivity of the pulse travel time as a function of the ratio of finger capacitance to the compartmental (background) capacitance, C i , of the distributed RC line according to one embodiment of this invention. 
         FIG. 9  illustrates an exemplary four row and four column multi-touch sensor panel constructed with an array of one-dimensional distributed RC lines according to one embodiment of this invention. 
         FIG. 10  illustrates two exemplary cases where the projection scan-like data requires disambiguation according to one embodiment of the invention. 
         FIG. 11  is a flowchart of a process for disambiguating the initial contact map according to one embodiment of this invention. 
         FIG. 12  illustrates an exemplary block diagram of a projection scan multi-touch sensor panel and related components according to one embodiment of this invention. 
         FIG. 13   a  illustrates an exemplary mobile telephone that can include a single-surface multi-touch sensor panel according to one embodiment of this invention. 
         FIG. 13   b  illustrates an exemplary digital audio/video player that can include a single-surface multi-touch sensor panel according to one embodiment of this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following description of preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which it is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the preferred embodiments of the present invention. 
     A multi-touch sensor panel can be constructed on a single surface of a touch substrate to reduce manufacturing costs and minimize light loss in transparent embodiments. The panel can be formed as a plurality of distributed RC lines arranged in an array of rows and columns. Each distributed RC line can include alternating connected transistors and metal pads formed on a single surface of a sensor panel substrate, with the drain and source terminals of the transistors connected to adjacent metal pads. The substrate can constructed from a variety of different materials including, but not limited to, metal, plastic, and glass. Because the single-surface elements of the sensor panel can be manufactured using a printing process (e.g., roll-to-roll or offset), manufacturing costs can be lower as compared to systems produced via a batch process. Transparent multi-touch substrates may also be suitable as an overlay on a display device such as an LCD display, and the presence of elements on only a single side of the substrate can result in less light loss. 
       FIG. 1  illustrates an exemplary distributed resistor-capacitor (RC) line  100 . A distributed RC line  100  as shown in  FIG. 1  delays the propagation of an electrical pulse by an amount that depends on the magnitude of the product RC, where R is the total resistance of all resistive elements and C is the total capacitance of all capacitive elements making up the distributed RC line. The magnitude of RC can be found by measuring the time it takes a pulse that enters the left (or the right side) to appear on the opposite side. Any change in the value of R or C (and thus the product of R and C), either globally or locally, alters the time it takes a pulse to travel from one end to the other of distributed RC line  100 . Because a finger has an inherent capacitance that can change the overall capacitance of distributed RC line  100 , such distributed RC lines can be the basis for a capacitive touch sensor. 
       FIG. 2  illustrates how an exemplary distributed RC line  200  can serve as a touch sensor. It should first be understood that with reasonably constant values for R and C, the pulse travel time from one end of the line to the other is relatively constant. However, when a conducting object such as finger  202  approaches distributed RC line  200 , the capacitance of the line near the finger changes. This causes the pulse travel time to change. While the location of finger  202  along distributed RC line  200  can be inferred by comparing the pulse travel time to a known pulse travel time profile, this methodology is impractical to implement because it would be difficult to create a pulse travel time profile for all possible values of finger capacitance. Furthermore, such a methodology could not identify the presence of a second finger along distributed RC line  200 . 
       FIG. 3  illustrates an exemplary metal pad  300  and thin film transistor (TFT)  302 , which are examples of the basic circuit elements sufficient to construct a distributed RC line according to embodiments of this invention. Metal pad  300  can be square and of sufficient size to provide good spatial resolution for determining the position of a touching finger overlaying an array of closely spaced metal pads, but shapes other than squares also be used. Metal pad  300  can be transparent or opaque. TFT  302  can be a low mobility device such as an organic transistor. 
       FIG. 4  illustrates an exemplary distributed RC line  400  constructed from discrete resistors  402 , capacitors  404 , and metal pads  406  that can represent one row of multi-touch sensors. However, because the use of discrete resistors  402  would not enable the construction of a two-dimensional multi-touch sensor array as required for a multi-touch sensor panel, low mobility transistors can be used instead of discrete resistors  402 . 
       FIG. 5  illustrates an exemplary distributed RC line  500  constructed using metal pads  502  and field effect TFTs  504  according to some embodiments of the invention. In the usual applications where TFTs are employed (e.g., LCDs), they are designed to operate as switches with a low on-state resistance. In other words, when the enable line ENB is asserted, TFTs  504  conduct and metal pads  502  are essentially connected to each other, and when ENB is de-asserted, the TFTs are not conducting and the metal pads are essentially isolated from each other. However, TFTs  504  utilized with embodiments of this invention may have a high on-state resistance and act as resistors. The TFTs also provide an intrinsic capacitance. 
     Note that organic TFTs (used in display devices and plastic rollable/foldable products) typically have very low mobility μ (i.e., high on-state resistance) compared to silicon-based TFTs, and are therefore usually considered “poor” transistors. However, low mobility is a preferred characteristic for embodiments of this invention. Because organic TFTs have low mobility and are easy to manufacture (they can be printed, painted or rolled on surfaces without stringent clean room requirements), the TFTs used with some embodiments of this invention can be organic TFTs. However, in other embodiments, silicon-based TFTs or other transistors fabricated with sufficiently low mobility can also be used. 
     As shown in  FIG. 5 , the gate terminals G of TFTs  504  are connected together and driven by ENB. TFTs  504  turn on when a DC voltage is applied to ENB. A voltage pulse Vstim entering either the right or left side of the row causes TFTs  504  to conduct. As each TFT  504  transitions from an off-state to an on-state it passes through a saturation region where it has very high resistance. As each TFT  504  enters a linear region its resistance decreases and can be approximated using the Shockley model, which expresses the drain current as
 
 I   d =(μ CW/L )( V   gs   −V   th ) V   ds −(½) V   ds   2 ,
 
where μ is the mobility, C is the gate unit capacitance, W is the transistor width, L is the transistor length, V gs  is the gate source voltage, V th  is the threshold voltage, and V ds  is the drain source voltage. Because there is only a capacitive load along the distributed RC line, V ds  can be assumed to be small. Therefore, the effective resistance can be written as
 
     
       
         
           
             
               R 
               eff 
             
             = 
             
               
                 L 
                 
                   
                     ( 
                     
                       μ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       CW 
                     
                     ) 
                   
                   ⁢ 
                   
                     ( 
                     
                       
                         V 
                         gs 
                       
                       - 
                       
                         V 
                         th 
                       
                     
                     ) 
                   
                 
               
               . 
             
           
         
       
     
     When ENB is asserted, TFTs  504  are in their on state and present a high resistance R between metal pads  502 . Each metal pad  502  is capacitively coupled to the AC ground provided by the ENB voltage source through the TFT&#39;s source-gate capacitance. The capacitance C can also be made up of stray components to other grounds. The magnitude of C should preferably be less than the capacitance introduced by a touching finger in order for distributed RC line  500  to have sufficient resolution to be an effective touch sensor. The large TFT resistance R coupled with a small pad capacitance C produces a sufficiently large pulse travel time that can be measured with a low-cost microcontroller. 
     As mentioned above, the pulse travel time depends on the product RC. A finger touching or in close proximity to distributed RC line  500  alters the product RC and thus its presence will increase the pulse travel time. However, because distributed RC line  500  has a distributed resistance and capacitance, the pulse travel time will also depend on where the finger is located along the distributed RC line. For example, a finger touching near one end of distributed RC line  500  will result in a different pulse travel time than the same finger touching the center of the distributed RC line. For multi-touch sensing according to embodiments of this invention, this effect should be equalized so that no matter where the finger is located along distributed RC line  500 , the pulse travel time will be approximately the same. In order to equalize this spatial dependency, two measurements can be taken. For the first measurement, a Vstim pulse is injected into the right side of the line and the pulse travel time is recorded. For the second measurement, a Vstim pulse is injected into the left side and the travel time is once again recorded. Summing the two measurements equalizes the spatial dependency. 
       FIG. 6  illustrates an exemplary circuit capable of measuring pulse travel times to allow for equalization of the spatial dependency of the pulse travel times according to embodiments of this invention.  FIG. 6  includes distributed RC line  600  with the TFTs symbolically replaced with resistors R and capacitors C. In  FIG. 6 , left side driver  602  is enabled while right side driver  604  is disabled. The enabled left-side driver  602  injects a pulse Vstim into the left side of distributed RC line  600 , and the time at which the pulse was injected is recorded. When the amplitude of the exiting pulse  606  on the right side reaches a threshold voltage Vth, the right side voltage comparator  608  changes state. The arrival time of the pulse as indicated by the comparator&#39;s state change can be recorded by a conventional digital timer circuit (not shown). Note that in other embodiments, circuits other than comparators can be used to detect the arrival of the pulse. The difference between the pulse injection time and the arrival time is the pulse travel time going left to right. This process is repeated but with right side driver  604  now enabled and left side driver  602  disabled, which produces a pulse exiting from comparator  610  and a pulse travel time going right to left. The sum of these two measurements is the equalized pulse travel time. 
       FIG. 7  is a plot of exemplary pulse travel times for a finger touching a distributed RC line at various points along the line according to embodiments of the invention. Trace  704  represents pulse travel times for the pulse going left to right while trace  702  is for the pulse going right to left. Note that the pulse travel time changes significantly as a function of finger position, and thus the location of a finger touching a single sensor can be determined from comparing the left-to-right and right-to-left pulse travel times. The equalized travel time is shown as trace  706 , which is substantially independent of finger position. Its profile (general shape) is also independent of the actual capacitance added by the finger. Therefore, if two or more fingers were touching the distributed RC line, the magnitude of the travel times would change (increase) but the profile would remain relatively flat. Trace  708  represents the equalized travel time for the case when no finger is touching the distributed RC line. Therefore, any measured pulse travel times in excess of trace  708  indicates that one or more fingers are touching the distributed RC line. 
       FIG. 8  is an exemplary plot showing the sensitivity of the pulse travel time as a function of the ratio of finger capacitance to the compartmental (background) capacitance, C i , of the distributed RC line. The plot shows that the difference in travel times for the touched versus the untouched cases depends on the ratio of finger capacitance to compartmental (baseline) capacitance. Larger capacitance ratios provide better differentiation between the touched and the untouched cases. If the ratio becomes too small then the temporal resolution of the pulse travel time measurement will have to increase. 
       FIG. 9  illustrates an exemplary four row and four column multi-touch sensor panel  900  constructed with an array of one-dimensional distributed RC lines according to embodiments of this invention. During operation, the rows and columns are enabled at different times, and the left-to-right and right-to-left pulse travel times and equalized travel times for each row and column are measured or computed. For example, to measure the row left-to-right pulse travel times, the left side terminals (LR 0 - 3 ) can be connected to one or more pulse drivers while the right side terminals (RR 0 - 3 ) can be connected to individual time capture circuits through individual comparators. The ENB_ROWS signal can be asserted and the ENB_COLS signal is negated. A pulse is the injected into each left side terminal and the pulse travel time for each row is recorded. Note that these row travel time measurements may be performed simultaneously for two or more rows. This process can then be repeated to capture right-to-left pulse travel times. When the equalized pulse travel times for the rows have been computed, they can be compared to the equalized no-touch travel time to determine which rows, if any, have a finger touching it. 
     The above-described process can be repeated for the columns. The ENB_COLS signal can be asserted and the ENB_ROWS signal is negated. Pulses are injected into the top terminals (TC 0 - 3 ) (in some embodiments a single pulse for each column), and the pulse travel times for top to bottom pulse injection are recorded. This is repeated for bottom to top pulse injection. The resulting equalized pulse travel times for the array of columns provides an indication as to which columns have a finger touching it. The combined row and column data is a map, albeit an ambiguous one, of all points touched by fingers. However, before an unambiguous map of finger contacts can be generated, more information needs to be applied. 
     Using just the equalized pulse travel times does not allow for an unambiguous construction of a map of finger contacts. The reason for this is that the equalized pulse travel times, which provide high selectivity in determining whether a finger(s) is touching over a row or a column, only provide projection scan-like data that, by itself, cannot resolve rotational ambiguities of multiple finger contacts. However, once the rows and columns containing finger contacts are known, the un-equalized left-to-right, right-to-left, top-to-bottom and bottom-to-top pulse travel time data can be used to determine the relative positions of the fingers within the rows and columns and un-ambiguously determine the positions of all the finger contacts. 
     It should be understood that although the single-surface multi-touch sensor panel shown in  FIG. 9  is formed in rows and columns perpendicular to each other, in other embodiments other non-orthogonal orientations are possible. For example, in a polar coordinate system, the “rows” can be concentric circles and the “columns” can be radially extending lines (or vice versa). It should be understood, therefore, that the terms “row” and “column,” “first dimension” and “second dimension,” or “first axis” and “second axis” as may be used herein are intended to encompass not only orthogonal grids, but the intersecting traces of other geometric configurations having first and second dimensions (e.g. the concentric and radial lines of a polar-coordinate arrangement). 
     As mentioned above, the pulse travel time depends on the position of the finger along the distributed RC line. Therefore, the four measurements of pulse travel times for each row and for each column can be compared to each other to resolve rotational ambiguities. For example,  FIG. 10  illustrates two exemplary cases where the projection scan-like data requires disambiguation according to embodiments of the invention. In the exemplary 8×8 array of  FIG. 10 , two finger contacts are shown. In the array on the left, the fingers are located at (1, 5) and (2, 6). In the array on the right the fingers are located at (2, 5) and (1, 6). 
     The equalized pulse travel time data for both cases shown in  FIG. 10  is basically identical. Therefore, the equalized pulse travel time data alone is not sufficient to distinguish the touching pattern shown on the left frame from the touching pattern shown on the right. In other words, the equalized pulse travel time data can be used to determine that contacts were detected in rows 1 and 2 and columns 5 and 6, but either contact pattern in  FIG. 10  could have caused that result. For example, suppose in  FIG. 10  that the actual touching pattern is identical to that shown in the left frame of  FIG. 10 . Nevertheless, the equalized pulse travel times suggest that there are four possible contacts as shown in the following table. These possible contacts represent the initial contact map, which is made up of real and non-existent contacts. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Possible contacts 
                 (1, 5) 
                 (1, 6) 
                 (2, 6) 
                 (2, 5) 
               
               
                   
                 Actual contacts 
                 (1, 5) 
                   
                 (2, 6) 
               
               
                   
                   
               
            
           
         
       
     
     In embodiments of the invention, the raw pulse travel time data can be used to eliminate the nonexistent contacts.  FIG. 11  is a flowchart of a process for disambiguating the initial contact map according to embodiments of this invention. Step  1100  indicates the start of the processing of the rows in the sensor panel. For each row indicating a possible contact, the pulse travel times for right-to-left and left-to-right are compared against other rows for which there were possible contacts, one by one, to establish the relative positions of the contacts across the rows. Thus, in step  1102 , the right-to-left pulse travel time for row “i” is compared to the right-to-left pulse travel time for row “j”. If the right-to-left pulse travel time for row “i” is larger than the right-to-left pulse travel time for row “j”, then it is possible that the row “i” contact is left of the row “j” contact (see step  1104 ). If not, then it is possible that the row “j” contact is left of the row “i” contact (see step  1106 ). Next, in step  1108 , the left-to-right pulse travel time for row “i” is compared to the left-to-right pulse travel time for row “j”. If the left-to-right pulse travel time for row “i” is larger than the left-to-right pulse travel time for row “j”, then it is possible that the row “i” contact is right of the row “j” contact (see step  1110 ). If not, then it is possible that the row “j” contact is left of the row “i” contact (see step  1112 ). The results of steps  1102  and  1108  can be interpreted as shown in the table below. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Step 1108-Yes 
                 Step 1108-No 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Step 1102-Yes 
                 Undefined 
                 Contact in row “i” in 
               
               
                   
                   
                   
                 a column to the left 
               
               
                   
                   
                   
                 of contact in “row 
               
               
                   
                   
                   
                 “j” 
               
               
                   
                 Step 1102-No 
                 Contact in row “i” in 
                 Contact in row “i” in 
               
               
                   
                   
                 a column to the right 
                 same column as 
               
               
                   
                   
                 of contact in row “i” 
                 contact in row “j” 
               
               
                   
                   
               
            
           
         
       
     
     After all rows have been processed (see step  1114 ), the same process is then repeated for each column showing a possible contact (see step  1116 ). For each column indicating a possible contact, the pulse travel times for top-to-bottom and bottom-to-top are compared against other columns for which there were possible contacts, one by one, to establish the relative positions of the contacts across the columns. Thus, in step  1118 , the top-to-bottom pulse travel time for column “k” is compared to the top-to-bottom pulse travel time for column “m”. If the top-to-bottom pulse travel time for column “k” is larger than the top-to-bottom pulse travel time for column “m”, then it is possible that the column “k” contact is below the column “m” contact (see step  1120 ). If not, then it is possible that the column “m” contact is below the column “k” contact (see step  1122 ). Next, in step  1124 , the bottom-to-top pulse travel time for column “k” is compared to the bottom-to-top pulse travel time for column “m”. If the bottom-to-top pulse travel time for column “k” is larger than the bottom-to-top pulse travel time for column “m”, then it is possible that the column “k” contact is above the column “m” contact (see step  1126 ). If not, then it is possible that the column “m” contact is above the column “k” contact (see step  1128 ). The results of steps  1118  and  1124  can be interpreted as shown in the table below. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Step 1124-Yes 
                 Step 1124-No 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Step 1118-Yes 
                 Undefined 
                 Contact in column 
               
               
                   
                   
                   
                 “k” in a row below 
               
               
                   
                   
                   
                 contact in “column 
               
               
                   
                   
                   
                 “m” 
               
               
                   
                 Step 1118-No 
                 Contact in column 
                 Contact in column 
               
               
                   
                   
                 “k” in a row above 
                 “k” in same row as 
               
               
                   
                   
                 contact in column 
                 contact in column 
               
               
                   
                   
                 “m” 
                 “m” 
               
               
                   
                   
               
            
           
         
       
     
     Thus, after disambiguating all rows and columns using the algorithm defined in  FIG. 11 , the actual contact locations can be determined. 
       FIG. 12  illustrates an exemplary block diagram  1200  of projection scan multi-touch sensor panel  1202  and associated components according to one embodiment of this invention. Panel  1202  can be driven with Vstim through left-to-right drivers  1204  selectable by an ENB_LR enable signal, right-to-left drivers  1206  selectable by an ENB_RL enable signal, top-to-bottom drivers  1208  selectable by an ENB_TB enable signal, and bottom-to-top drivers  1210  selectable by an ENB_BT enable signal. The enable rows signal ENB_ROWS can be generated by gating ENB_RL and ENB_LR through OR gate  1212 , while the enable columns signal ENB_COLS can be generated by gating ENB_TB and ENB_BT through OR gate  1214 . Microprocessor  1216  can generate ENB_RL, ENB_LR, ENB_TB, ENB_BT, Vstim, and a multiplex select signal Sel_Mux. When the rows or columns are enabled and a pulse on Vstim is sent through panel  1202 , multiplexer  1218  selects one group of outputs (RL, LR, TB and BT) from panel  1202  in accordance with Sel_Mux, detects the pulse using comparator  1220  and threshold Vth, where it is captured back in microprocessor  1216 , which can then compute the total delay time for that pulse. 
     Microprocessor  1216  can also be communicatively coupled to a host processor (not shown) for performing actions based on the outputs of panel  1202  that can include, but are not limited to, moving an object such as a cursor or pointer, scrolling or panning, adjusting control settings, opening a file or document, viewing a menu, making a selection, executing instructions, operating a peripheral device connected to the host device, answering a telephone call, placing a telephone call, terminating a telephone call, changing the volume or audio settings, storing information related to telephone communications such as addresses, frequently dialed numbers, received calls, missed calls, logging onto a computer or a computer network, permitting authorized individuals access to restricted areas of the computer or computer network, loading a user profile associated with a user&#39;s preferred arrangement of the computer desktop, permitting access to web content, launching a particular program, encrypting or decoding a message, and/or the like. The host processor can also perform additional functions that may not be related to panel processing, and can be coupled to program storage and a display device such as a liquid crystal display (LCD) for providing a UI to a user of the device. 
       FIG. 13   a  illustrates an exemplary mobile telephone  1336  that can include single-surface multi-touch sensor panel  1324  according to embodiments of this invention.  FIG. 13   b  illustrates an exemplary digital audio/video player  1338  that can include single-surface multi-touch sensor panel  1324  according to embodiments of this invention. The mobile telephone and digital audio/video player of  FIGS. 13   a  and  13   b  can advantageously benefit from single-surface multi-touch sensor panel  1324  because only a single surface of circuitry is needed to realize a multi-touch sensor, reducing manufacturing costs and making the sensor panel very thin and flexible. Manufacturing costs may be reduced because no assembly steps are needed on the second side of the substrate, and because the components on the first side can be applied using low cost processes such as printing or rolling. Furthermore, the TFTs can be formed using inexpensive low mobility organic TFTs. The single-surface multi-touch sensor panel is also lower in power consumption, and its projection scanning principles results in fast frame rates, a reduction in the memory needed to hold surface data, and simpler data processing. 
     Although the present invention has been fully described in connection with embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the present invention as defined by the appended claims.