Patent Publication Number: US-7719522-B2

Title: Raw data track pad device and system

Description:
BACKGROUND 
     The invention relates generally to computer input devices and more particularly to a track pad input device that generates and transmits measured (raw) sensor data to a host computer system. Software executing on the host computer system analyzes the raw sensor data to determine the user&#39;s action. 
     A track pad is a touch-sensing planar digitizer input device used instead of, or in conjunction with, a mouse or trackball. During use, an operator places a finger on the track pad and moves the finger along the touch-sensing planar surface. The track pad detects the movement of the finger and in response provides location and/or motion signals to a computer. There are two common types of track pad sensor devices: resistive and capacitive. A resistive track pad sensor is a mechanical sensor that uses two layers of material that are typically separated by air. Pressure from a finger pushes the top layer (generally a thin, clear polyester film) so that it touches the bottom layer (generally glass). The voltage at the contact point is measured and the finger&#39;s location and/or motion is computed and transmitted to a host computer system. After the finger is removed, the top layer “bounces back” to its original configuration. A capacitive track or touch pad sensor, in contrast, is a solid-state sensor made using printed circuit board (“PCB”) or flex circuit technology. A finger on, or in close proximity to, a top grid of conductive traces changes the capacitive coupling between adjacent traces or the self-capacitance of each trace. This change in capacitance is measured and the finger&#39;s location and/or motion is computed and transmitted to a host computer system. 
     Referring to  FIG. 1 , prior art computer system  100  includes track pad device  105  coupled to host computer module  110  via communication path  115 . Track pad device  105  comprises sensor  120 , data acquisition circuit  125 , processor  130 , memory  135  and transmit circuit  140 . In the case of a capacitive track pad device, as a user&#39;s finger(s) is (are) moved over the surface of sensor  120 , data acquisition circuit  125  measures changes in the capacitive coupling between adjacent sensor elements (or the self-capacitance of a given sensor element). Processor  130 , in conjunction with memory  135 , processes the acquired capacitance signals to compute a signal indicating the user&#39;s finger position on sensor  120  (e.g., a Δx and Δy signal). In some prior art track pad devices, processor  130  may also determine if multiple fingers are activating sensor  120  and whether certain predetermined finger motions (often referred to as “gestures”) are being made—e.g., “select,” “drag,” “file open” and “file close” operations. At specified intervals (e.g., 50 times per second), the user&#39;s finger location and/or motion as determined by processor  130  is transmitted to host computer module  110  via communication path  115 . At host computer module  110 , receive circuit  145  receives the transmitted track pad signal and passes it&#39;s information to driver application  150 . Driver application  150 , in turn, makes the computed sensor information available to other applications such as, for example, window display subsystem application  155 . Thus, prior art system  100  utilizes a dedicated processor for measuring and analyzing raw track pad sensor data to generate a signal that indicates a user&#39;s action. 
     One of ordinary skill in the art will recognize that processor  130  may be embodied in a general purpose processor (e.g., a microprocessor), a microcontroller or a special purpose or custom designed processor or state machine (e.g., an application specific integrated circuit or a custom designed gate array device). Further, memory  135  is typically used to provide permanent storage for instructions (i.e., firmware) to drive processor  130  and may, optionally, include random access memory and/or register storage. A benefit of the architecture of  FIG. 1  is that host computer module  110  does not need to know about or understand the type of data generated by sensor  120 . A corollary of this feature is that host computer module  110  does not process track pad sensor data. 
     It will also be recognized by one of ordinary skill that a drawback to the architecture of  FIG. 1  is that the feature set (i.e., what motions are detectable) provided by track pad device  105  is essentially fixed by its dedicated hardware—processor  130  and associated firmware (memory  135 ). Another drawback to the architecture of  FIG. 1  is that each manufactured device  105  includes the cost of processor  130  and associated firmware memory  135 . Thus, it would be beneficial to provide a track pad device that overcomes these inherent drawbacks. 
     SUMMARY 
     In one embodiment the invention provides a track pad input device that includes a track pad sensor element that generates output signals representing a track pad sensor characteristic (i.e., capacitance or resistance), a data acquisition circuit that measures a (digital) value encoding the track pad sensor&#39;s characteristic and a communication circuit that transmits the measured track pad sensor values to a general purpose processor for analysis, the general purpose processor is also responsible for executing user and other system level tasks or applications. In one specific embodiment, the track pad sensor is a capacitive track pad sensor so that measured values comprise raw track pad sensor values and the general purpose processor corresponds to a host computer system&#39;s central processing unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows, in block diagram form, a track pad-computer system architecture in accordance with the prior art. 
         FIG. 2  shows, in block diagram form, a track pad-computer system architecture in accordance with one embodiment of the invention. 
         FIG. 3  shows, in block diagram form, a track pad device and host computer system in accordance with one embodiment of the invention. 
         FIG. 4  shows, in block diagram form, a track pad sensor data acquisition system in accordance with one embodiment of the invention. 
         FIG. 5  shows, in flowchart form, a data acquisition method in accordance with one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring first to  FIG. 2 , the general architecture of a system incorporating a track pad device in accordance with the invention is illustrated. As shown, system  200  includes track pad device  205  coupled to host module  210  through communication path  215 . Track pad device  205  comprises track pad sensor  220  that generates signals based on user manipulation thereof, data acquisition circuit  225  for capturing or measuring the sensor&#39;s and transmit circuit  230  for aggregating and periodically transmitting the measured sensor data values to host module  210  via communication path  215 . At host module  210 , receive circuit  235  receives the measured sensor data and passes them to driver application  240 . Driver application  240 , in turn, processes or analyzes the measured data to determine the user&#39;s conduct (e.g., a “single click,” “double click,” “scroll” or “drag” operation), passing the calculated location and/or movement information to other applications such as, for example, window display subsystem application  245 . In accordance with the invention, driver application  240  is executed by host processor  250  which, as shown, is also responsible for executing (at least in part) one or more user applications or processes  255 . It is significant to note that track pad device  205  has no capability to process or analyze data signals (values) acquired from sensor  220 . In accordance with the invention, sensor data is analyzed by a host computer system&#39;s general purpose processor or central processing unit (“CPU”). 
     The architecture of  FIG. 2  recognizes and takes unique advantage of the processing power of modern CPUs incorporated in host computer systems (e.g., notebook or other personal computers, workstations and servers). This recognition and the architecture of  FIG. 2  permits a computer system  200  that is both lower in cost to manufacture and more flexible than the systems provided by the prior art. Lower costs may be realized by eliminating the prior art&#39;s dedicated hardware for processing track pad sensor data (i.e., a processor and associated firmware memory—see components  130  and  135  in  FIG. 1 ). Increased flexibility may be realized by providing feature set functionality via software that executes on the host computer&#39;s CPU—that is, processing/analyzing measured track pad sensor data on one or more of the host computer&#39;s CPUs. In this architecture, track pad functionality may be modified, updated and enhanced through conventional software upgrade procedures. 
     The following description is presented to enable any person skilled in the art to make and use the invention as claimed and is provided in the context of the particular examples discussed below, variations of which will be readily apparent to those skilled in the art. Accordingly, the claims appended hereto are not intended to be limited by the disclosed embodiments, but are to be accorded their widest scope consistent with the principles and features disclosed herein. 
     Referring to  FIG. 3 , track pad device  300  in accordance with one embodiment of the invention comprises m-row by n-column capacitive sensor array  305 , data acquisition circuit  310  (itself comprising multiplexer (“MUX”) circuit  315 , storage capacitor  320  and scan circuit  325 ) and Universal Serial Bus (“USB”) transmit circuit  330 . During operation, MUX circuit  315  is responsible for coupling and stimulating successive sensor array elements (e.g., rows, columns, or individual pixels—that is, an element at the intersection of a row and column) to storage capacitor  320  in a controlled/sequenced manner and indicating that a measurement cycle has begun to scan circuit  325 . When the charge on storage capacitor  320  reaches a specified value or threshold, scan circuit  325  records the time required to charge storage capacitor  320  to the specified threshold. Accordingly, scan circuit  325  provides a digital value that is a direct indication of the selected sensor array element&#39;s capacitance. USB transmit circuit  330  is responsible for aggregating the measured capacitance values into packets and transmitting them in accordance with the USB protocol to host module  335  via USB bus  340 . One of ordinary skill in the art will understand that depending upon the version of USB used and the bandwidth of bus  340 , USB transmit circuit  330  may transfer each frame of data to host module  335  in more than one, one or more than one packet. When the host module&#39;s USB receive circuit  345  receives the measured sensor data from track pad device  300  via USB bus  340 , it unpacks and passes the measured capacitance data to driver application  350 . Driver application  350 , in turn, accepts and processes the raw (measured) capacitance data to provide meaningful cursor movement input to operating system application  355 . (One of ordinary skill in the art will recognize that scan circuit  325  measures capacitance values from sensor array  305  in a predetermined order or sequence and that this sequence must be known by driver application  350  a priori or conveyed to driver application  350  along with the measured sensor data.) In one embodiment, driver application  350  implements track pad algorithms traditionally provided by a dedicated track pad processor such as, for example, processor  130  and firmware memory  135  of  FIG. 1 . 
     Referring to  FIG. 4 , a more detailed view of MUX circuit  315  as it can be implemented for a row and column addressable capacitive sensor array is illustrated. As shown, each row in sensor array  400  is electrically coupled to voltage source Vcc  405  through MUX- 1   410  and to storage capacitor  415  through MUX- 2   420 . (While not shown in detail, each column of sensor array  400  is similarly coupled to Vcc  405  and to storage capacitor  415  through other MUX circuits—block  425 .) 
     Referring now to  FIG. 5 , in operation MUX- 1   410  couples a first sensor array row to Vcc  405  for a specified period of time (block  500 ) and then isolates or disconnects that row from Vcc  405  (block  505 ). Next, MUX- 2   420  couples the same row to storage capacitor  415  for a specified period of time, or until the voltage on storage capacitor  415  reaches a specified threshold (block  510 ). If, during the time MUX- 2   420  couples the selected sensor row to storage capacitor  415  the storage capacitor&#39;s voltage reaches a specified threshold (the “Yes” prong of block  515 ), the digital value corresponding to the time it took to charge storage capacitor  415  to the threshold is recorded by scan circuit  325  (block  520 ). If, during the time MUX- 2   420  couples the selected sensor row to storage capacitor  415  the storage capacitor&#39;s voltage does not reach the specified threshold (the “No” prong of block  515 ), the acts of block  500 - 510  are repeated. Once a digital value corresponding to the capacitance of the selected row has been obtained (block  520 ), a check is made to see if there are additional rows in sensor array  400  that need to be sampled. If all the rows in sensor array  400  have been sampled in accordance with blocks  500 - 520  (the “Yes” prong of block  525 ), the same process is used to acquire a capacitance value for each column of sensor elements in sensor array  400  (block  535 ). Once all rows and all columns have been processed in accordance with blocks  500 - 535 , the entire process is repeated (block  540 ). If, on the other hand, there are rows in sensor array  400  that have not been sampled in accordance with blocks  500 - 520  (the “No” prong of block  525 ), the next row is selected (block  530 ) and the acts of blocks  500 - 525  are performed. 
     In one illustrative embodiment: sensor array  400  comprises a 16×32 capacitive grid, providing 48 output channels; Vcc is 3.3 volts; storage capacitor  415  is approximately 10,000 picofarads, an average row capacitance value is approximately 12 picofarads; an average column capacitance value is approximately 9 picofarads; the average change in capacitance of a row or column electrode due to a user&#39;s finger touching sensor array  400  is approximately 0.2 picofarads; the threshold value at which a digital capacitance value is obtained is 1.6 volts; and the rate at which MUX circuits  410 ,  420  and  425  are switched is 6 megahertz. It has been found, for these values, that its takes approximately 580-600 sample cycles to charge storage capacitor  415  to the threshold voltage. In one embodiment, the digital capacitance value is, in fact, a count of the number of sampling cycles required to charge storage capacitor  415  to the threshold value. One of ordinary skill in the art will recognize that this value is directly related to the sensor element&#39;s (e.g., row or column) capacitance value. In this embodiment, scan circuit  325  (in conjunction with MUX circuits  410 ,  420  and  425  and storage capacitor  415 ) measures each of the 48 sensor array outputs 125 times each second, with each measurement comprising a 10-bit value (unsigned integer). Referring to the 48 measurements acquired by scan circuit  325  from sensor array  400  in each of the 125 epochs as a frame, the illustrative track pad sensor device generates: 
     
       
         
           
             
               
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     As noted with respect to  FIG. 2  and as further shown in  FIG. 3 , driver application  350  is executed general purpose processing unit  360  that is also responsible for executing user applications and tasks, e.g.,  365 . That is, in accordance with the invention raw track pad sensor data is analyzed by one, or more, general purpose processing units associated with the host computer system and not by a dedicated processor or processing circuit(s) associated with track pad device  300 . A direct consequence of the architecture of  FIGS. 2 and 3  is that the processing resources (e.g., CPUS) tasked with analyzing track pad sensor data must be shared with other computer system processing needs such as other system level and user level applications. 
     Various changes in the materials, components and circuit elements of the described embodiments are possible without departing from the scope of the following claims. Consider, for example, the system of  FIG. 3 . Other embodiments could include a smaller (e.g., 10×16) or larger (e.g., 32×32) sensor array  305 . Further, frame rates other than 125 Hertz (“Hz”) and sample resolutions other than 10 bits are possible. It will also be understood that the host computer system may comprise more than one general purpose processing unit (e.g., processor  250 ). In addition, some of the circuitry identified in  FIGS. 2 and 3  as being integral to track pad device  205  or  300  may be embodied in circuitry also used for other functions. For example, transmit circuits  230  and  330  may be shared by other USB input devices such as, for example, a keyboard. In addition, one of ordinary skill in the art will recognize that the invention is also applicable to track pad sensor devices that are pixilated rather that row-column addressable. It will be further recognized that the operational procedure outlined in  FIG. 5  may be modified. For instance, sensor column values may be obtained before sensor row values. Alternatively, sensor row and sensor column data may be interlaced and/or measured at the same time. In any event, it will be recognized that scan circuit  325  measures sensor pad characteristic values (e.g., capacitance or resistance) in a set order and that this order must be known or communicated to driver application  350 . In yet another embodiment, scan circuit  325  may measure sensor characteristic values in any convenient manner and reorder them into a sequence known or expected by driver application  350  prior to transmission by transmit circuit  330 .