Touch pad

Abstract

A touch pad includes transducers for receiving acoustic signals resulting from touch events, such as the continuous movement of a fingertip across the surface of the touch pad. The acoustic signals are acquired at different transducer locations in the surface. Signals from different transducers are combined, preferably in antiphase, to improve signal characteristics. The transducer signals are supplied to a stereo analogue to digital converter. Phase differences are obtained and compared with phase difference profiles of known location, in order to identify the location of the touch event. An index is used to identify candidate locations to reduce the amount of processing. Interpolation is used to locate the touch event between profile locations.

1 . A touch pad for acquiring acoustic signals resulting from touch events, comprising:
 a surface having an area in which said touch events may be formed;   a plurality of transducers for acquiring said acoustic signals at a plurality of different locations in said surface; and   an output for supplying representations of said acoustic signals to an analogue to digital converter;   wherein said plurality of transducers are arranged to be configured to electrically combine said acoustic signals from a plurality of different locations in said surface for said output.   
     
     
         2 . A touch pad according to  claim 1 , including signal conditioning means arranged to emphasize preferred components of said acoustic signals. 
     
     
         3 . A touch pad according to  claim 1 , wherein a plurality of said transducer means is connected together in antiphase so as to electrically combine preferred components of said acoustic signals. 
     
     
         4 . A touch pad according to  claim 3 , including resistance means connected in parallel with an intrinsic capacitance of one or more of said transducer means to form a high pass filter that emphasizes said preferred components. 
     
     
         5 . A touch pad according to  claim 1 , wherein signals from a plurality of transducers are electrically combined by connecting said plurality of transducers in series. 
     
     
         6 . A touch pad according to  claim 1 , wherein signals from a plurality of transducers are electrically combined by connecting said plurality of transducers in parallel. 
     
     
         7 . A touch pad according to  claim 1 , wherein a pair of said transducer means whose signals are combined are located diagonally. 
     
     
         8 . (canceled) 
     
     
         9 . (canceled) 
     
     
         10 . (canceled) 
     
     
         11 . A method for acquiring and processing acoustic signals arising from an acoustic interaction between an object and a surface, the method comprising the operations of:
 (a) acquiring said acoustic signals at a plurality of locations in said surface;   (b) extracting phase difference information from said acoustic signals; and   (c) locating said acoustic interaction on the basis of comparisons between said phase difference information and interpolating between a plurality of phase difference profiles whose respective locations are known.   
     
     
         12 . A method according to  claim 11 , wherein said operation (c) includes the sub-operations of:
 (c1) processing said phase difference information with an index to identify candidate locations; and   (c2) locating said acoustic interaction by further processing of said phase difference information with phase difference profiles associated with said candidate locations.   
     
     
         13 . (canceled) 
     
     
         14 . A method according to  claim 11 , including updating a cursor location parameter in a graphical user interface in response to an incrementally detected change in the location of said object. 
     
     
         15 . A method according to  claim 11 , wherein said acoustic interaction between an object and a surface is a continuous frictional interaction. 
     
     
         16 . A method according to  claim 11 , including electrically combining acoustic signals from a plurality of respective locations in said surface. 
     
     
         17 . A method according to  claim 16 , wherein said acoustic signals are combined in antiphase. 
     
     
         18 . (canceled) 
     
     
         19 . A method for calibrating an acoustic touch pad by acquiring and processing acoustic signals resulting from sound supplied to said touch pad at selected locations on the surface of said touch pad; the method comprising repeated operations of:
 (a) selecting a location for calibration;   (b) supplying a sound to said surface at said selected location;   (c) acquiring said acoustic signals from a plurality of transducers in said surface;   (d) extracting a location-related profile from said acoustic signals; and   (e) storing said location-related profile in association with said selected location.   
     
     
         20 . A method according to  claim 19 , wherein after said repeated operations (a) to (e), a finalizing operation (f) is performed comprising repeated operations of:
 (f1) classifying locations in terms of the similarity of their respective location-related profiles; and   (f2) generating an index entry from which candidate locations can be identified in response to location-related information.   
     
     
         21 . (canceled) 
     
     
         22 . (canceled) 
     
     
         23 . (canceled) 
     
     
         24 . (canceled) 
     
     
         25 . (canceled) 
     
     
         26 . (canceled)