Abstract:
We describe a projected capacitance touch screen sensing system comprising: a plurality of touch sensing circuit modules each configured to interpolate between sensed touching of a plurality of adjacent electrodes simultaneously and to output corresponding interpolated touch sense data at a resolution greater than that of a spacing between said electrodes; wherein each of said row and column electrodes has a break to divide the electrode into portions, one of said portions having an electrical connection at one side of the display screen, the other of said portions having an electrical connection at an opposite side of the screen; the sensing system comprising a controller coupled to touch sense data outputs of first to fourth touch sensing circuit modules, said controller configured to select interpolated touch sense data from one of first and second modules to provide row interpolated touch sense data, wherein selection of said first and second modules is responsive to interpolated touch sense data from said third and fourth modules, and wherein said controller is configured to select interpolated touch sense data from one of said third and fourth modules to provide column interpolated touch sense data, wherein selection of said interpolated touch sense data from one of said third and fourth modules is responsive to said interpolated touch sense data from said first and second modules.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to (is a US National Stage Filing of) PCT Application No. PCT/GB2010/051601 filed Sep. 24, 2010. The aforementioned PCT application claims priority to British Patent Application No. GB0916806.3 filed Sep. 24, 2009. The entirety of each of the three aforementioned references is incorporated herein by reference for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present inventions relate to improved techniques for implementing touch screen displays, in particular projected capacitance touch screen sensing for large electrophoretic display screens, and to electronic document readers implementing these techniques. 
         [0003]    Background prior art relating to electronic document reading devices can be found in U.S. Pat. No. 6,124,851, US2004/0201633, US2006/0133664, US2006/0125802, US2006/0139308, US2006/0077190, US2005/0260551, U.S. Pat. No. 6,124,851, U.S. Pat. No. 6,021,306, US2005/0151742, and US2006/0119615. Examples of electronic document reading devices are the Iliad Ilex®, the Amazon Kindle® and the Sony® Reader. Background prior art relating to power saving can be found in: US2007/0028086, US2007/0115258, and U.S. Pat. No. 7,058,829. 
         [0004]    We have previously described electronic document reading devices using an electrophoretic display with a flexible or flex-tolerant backplane based on plastic (solution-deposited) electronics, for example in our earlier applications PCT/GB2006/050235, PCT/GB2008/050980, PCT/GB2008/050977, PCT/GB2008/050985, PCT/GB2008/050985, and PCT/GB2008/050985, hereby incorporated by reference. 
         [0005]    As a skilled person will appreciate, there is a range of touch screen technologies. We have described an electronic document reading device with a touch sensitive display using resistive touch screen technology in WO2007/012899. However a particularly advantageous touch screen technology is capacitive-based sensing, in particular projected capacitance touch sensing. This typically employs an XY array of thin conducting electrodes mechanically located behind the front surface of the display screen, projecting an electric field beyond the display screen. Touching the screen results in capacitance between a user&#39;s finger and the sensing electrodes, changing the capacity of coupling between the wires at the touched X-Y position this change in mutual capacitance is detected to detect the touch position. The term projected capacitance arises because of the electrostatic field lines projected by the sensing electrodes. An alternative capacitive sensing technology, sometimes called surface or absolute capacitance sensing, relies on the user&#39;s finger approximating a ground connection, detecting the change in absolute capacitance (to ground) to identify a touched location. 
         [0006]    Projected capacitance touch sensing is commonly used on mobile phones, personal media players and the like, using transparent ITO (Indium Tin Oxide) electrodes deposited on an interior surface in front of the displayed information. There is, however, a problem with achieving fine sensing resolution because of the large number of electrode connections needed to be routed back to a single touch sensing integrated circuit, and because fine (thin) ITO tracks are relatively resistive. It will be appreciated that these problems are exacerbated as display size increases. 
         [0007]    One solution to these problems is to employ interpolation between sensor electrodes to increase the effective sensing resolution. Touch sensing integrated circuits for projected capacitance touch screens which employ such interpolation are available for example, from Cypress Semiconductor Corp., in particular in their PSOC (Programmable System—On-Chip®) devices which implement so-called “sliders” which perform linear interpolation for increased sensing accuracy. There is, however, a need for improved techniques, in particular for larger display screens. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The present inventions relate to improved techniques for implementing touch screen displays, in particular projected capacitance touch screen sensing for large electrophoretic display screens, and to electronic document readers implementing these techniques. 
         [0009]    According to a first aspect of the invention there is therefore provided a projected capacitance touch screen sensing system, the system comprising: an electronic display screen, said display screen incorporating a plurality of substantially transparent row and column electrodes to provide projected capacitance touch sensing; and a plurality of touch sensing circuit modules coupled to said row and column electrodes to sense touching of said display screen, wherein each said touch sensing circuit module has a plurality of sensor connections for connecting to a plurality of said electrodes and a touch sense data output, and wherein each said touch sense circuit module is configured to interpolate between sensed touching of a plurality of adjacent said electrodes simultaneously and to output corresponding interpolated touch sense data at a resolution greater than that of a spacing between said electrodes; and a sensing system data output to provide row and column interpolated touch sense data; wherein each of said row electrodes and each of said column electrodes column electrodes has a break to divide the electrode into first and second portions, one of said first and second portions having a first electrical connection at one side of the display screen, the other of said first and second portions having a second electrical connection at an opposite side of the display screen; wherein a first of said touch sensing circuit modules has said plurality sensor connections connected to said first electrical connections of said row electrodes, wherein a second of said touch sensing circuit modules has said plurality of sensor connections connected to said second electrical connections of said row electrodes, wherein a third of said touch sensing circuit modules has said plurality of sensor connections coupled to said first electrical connections of said column electrodes, and wherein a fourth of said touch sensing circuit modules has said plurality of sensor connections coupled to said second electrical connections of said column electrodes; and wherein the sensing system further comprises a controller coupled to said touch sense data outputs of said first, second, third and fourth touch sensing circuit modules, and wherein said controller is configured to select said interpolated touch sense data from one of said first and second touch sensing circuit modules to provide said row interpolated touch sense data from said sensing system data output, wherein said selection of said first and second touch sensing circuit modules is responsive to said interpolated touch sense data from said third and fourth touch sensing circuit modules, and wherein said controller is configured to select said interpolated touch sense data from one of said third and fourth touch sensing circuit modules to provide said column interpolated touch sense data from said sensing system data output, wherein said selection of said interpolated touch sense data from one of said third and fourth touch sensing circuit modules is responsive to said interpolated touch sense data from said first and second touch sensing circuit modules. 
         [0010]    In embodiments of the sensing system one touch sensing circuit module is provided for the connections to each end of a broken row and column line and, in embodiments, substantially all of the electrical connections to each of the two ends of the row electrode lines and of the column electrode lines go to a single touch sensing circuit module which performs interpolation across the electrode lines. 
         [0011]    Breaking the row and column electrode lines, in particular approximately half way across the display screen, effectively halves the length of ITO electrode employed for the touch sensing. In theory it would be possible to segment the display screen into quadrants and to apply one touch sensing circuit module or integrated circuit to form touch sensing for each quadrant, but this would create problems at the boundaries of the quadrants, in particular when interpolating touch sensed position between electrode lines. Since interpolation uses the “raw” sensor data (that is, data defining degree of mutual capacitance in between row and column electrodes) to interpolate across quadrant boundaries would seem to require one touch sensing circuit module to pass the raw X- and Y-sensing data to the adjacent touch sensing circuit modules on the X- and Y-sides respectively, to enable the combined data to be processed to interpolate position across quadrant boundaries. However this is a relatively inefficient both in terms of data connections and power requirements. 
         [0012]    In preferred embodiments, therefore, the display screen is segmented so that as well as the row and column electrodes only going approximately half way across the display screen from either side, all the ends of the electrodes at each side of the display screen go into respective first, second, third and fourth touch sensing circuit modules (or integrated circuits). Then the pair of (interpolating) Y-position (row) sensing modules can be employed to determine which column sensing module is to be employed to determine the X-(column) position, by identifying whether the touch row is towards one or the other end of a column, and hence toward one or the other of the X-(column) sensing modules. In a corresponding way the (interpolating) output from the column sensing modules can be used to determine which of the row sensing modules to employ when sensing (interpolator) Y-position. Further, in preferred embodiments employing one touch sensing integrating circuits to perform the function of each touch sensing circuit module enables these integrated circuits (ICs) each to be located physically adjacent one side (or edge) of the display screen, close to the connections to the relevant ends of the row and column electrode lines, thus reducing the distance over which interconnects need travel and minimising external noise. In preferred embodiments each of these touch sensing circuit modules or ICs has a serial data output, for example a SPI (Serial Peripheral Interface) bus or I2C (Inter-Integrated circuit) bus. 
         [0013]    In preferred implementations the controller is implemented in a separate microprocessor or microcontroller, for example an AVR (registered trademark) microprocessor from Atmel Corp. In embodiments the touch sensing circuit modules perform interpolation of sensed position between the electrodes and the controller microprocessor selects the interpolated data for output. Depending on the configuration of the touch sensing, multi-touch detection may be performed or the controller may be configured to perform multi-touch rejection based on the outputs from the touch sensing circuit modules. It will be appreciated that a single physical integrated circuit could incorporate two touch sensing circuit modules, and that therefore a single physical device could provide two separate slider channels. 
         [0014]    In preferred embodiments the controller microprocessor also identifies gestures and/or geometrical objects such as lines or circles which are primitives for gestures and outputs corresponding object and/or gesture data in preferred embodiments the controller microprocessor also outputs the row and column interpolated position data as well as the higher level data in order to enable corresponding image data to be written back to the display either as an indication on the display of where the display was touched or in the form of an icon or other response to an interpreted gesture, or both. This approach facilitates, for example, a combination of gesture recognition and user annotation of a document on an electronic document reader since having the row and column interpolated position data available in addition to gesture recognition data enables such annotation as well as reducing overall data flow and facilitating division of different types of processing task between the controller and a higher level, main processor. 
         [0015]    Embodiments of the above described touch screen sensing system are particularly useful when applied to a large electrophoretic display screen, for example a display screen having an active or rewriteable-display area with a diagonal dimension of at least 20 cm, especially a flexible or flex-tolerant electrophoretic display screen, since these present particular problems for projected capacitance touch sensing. In preferred embodiments of the electronic document reading device the active display area is at least sufficient to display a page of text at A4 or US Letter size at at least 0.7:1 scale. 
         [0016]    In preferred embodiments of such an electronic document reading device the controller of the projected capacitance touch screen sensing system also performs power management. Thus such a document reading device may also comprise a main processor to control display of information on the display screen, a (rechargeable) battery and a controllable power switch between the main processor and the battery to entirely switch off power to the main processor. In a document reader with an electrophoretic display, the display is non-volatile, that is the image remains even when the power is removed, and it is therefore possible to operate in a mode in which the document reading device is in the main switched off. Only being powered up when some action need be performed, more particularly to change or update the displayed information. In such a system it is desirable to switch power off entirely from the main processor since even a few microamps of stand by current can decrease the battery life from potentially, a few months down to potentially, a few days. However in order to operate in a mode in which power to the main processor is entirely removed the touch sensing circuit modules and controller may be powered in order that a wake-up gesture may be recognised and power applied to the main processor to perform the desired action (the wake-up gesture need not be a gesture dedicated to waking the device up but may comprise, for example, a page turn gesture). Thus sensing of touch of the display screen and interpretation of an applied gesture can be performed by low power circuitry and, when a gesture is recognised, the main processor can be powered up in response to perform the desired action. To further reduce power it is desirable that rather than the touch sensing circuit modules be continually powered, these may be polled at intervals and power maintained only when a touch is sensed. For this reason it is desirable that the touch sensing circuit modules (for example PsoCs®) power up in a short time interval, for example less than 1 ms. 
         [0017]    In embodiments the main processor performs a cold boot in response to the power supply to the main processor being turned on, prior to performing the desired action. For this reason in embodiments only a selected portion of the operating system of the main processor is loaded, that needed to perform the desired action, in order that the processor starts up quickly to enhance the user experience. 
         [0018]    In a related aspect the invention provides a method of sensing user touch of an electronic display screen having four sides comprising first pair of opposite sides and a second pair of opposite sides orthogonal to the first, and having a plurality of substantially transparent row and column electrode lines in front of information displayed by said display screen, the method comprising splitting each said electrode line into two portions, one connecting substantially all of the electrode lines at each said side to a single touch sensing circuit module; using touch sensed by the modules on one said pair of opposite sides to determine which of the modules connected to the orthogonal pair of opposite sides to use for detecting position along a direction parallel to said orthogonal pair of opposite sides; and using a said determined module on each of the two orthogonal sides of said display screen to determine an X-Y position of touch of said display screen sensed by said determined modules. 
         [0019]    In preferred embodiments of the method, as previously described, preferably a touch sensing module is connected to substantially all the electrode lines at a side or edge of the display screen, to enable interpolation between touch sensed by these electrode lines without communication between a adjacent touch sensing modules. 
         [0020]    The invention also provides a carrier such as a disc or non-volatile memory storing processor control code for implementing the functions of the controller in the above described systems/methods. 
         [0021]    This summary provides only a general outline of some embodiments of the invention. Many other objects, features, advantages and other embodiments of the invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    A further understanding of the various embodiments of the present invention may be realized by reference to the figures which are described in remaining portions of the specification. In the figures, like reference numerals are used throughout several figures to refer to similar components. In some instances, a sub-label consisting of a lower case letter is associated with a reference numeral to denote one of multiple similar components. When reference is made to a reference numeral without specification to an existing sub-label, it is intended to refer to all such multiple similar components. 
           [0023]      FIGS. 1   a  to  1   c  show, respectively, a front, display face view, a rear view, and a vertical cross-section view of an electronic document reading device; 
           [0024]      FIG. 2  shows a detailed vertical cross-section through a display portion of the device of  FIG. 1 ; 
           [0025]      FIGS. 3   a  and  3   b  show, respectively, a block diagram of a power management system for electronic document reading device according to an embodiment of the invention, and a flow diagram of a cold boot procedure employed by the power management system of  FIG. 3   a ; and 
           [0026]      FIG. 4  shows a projected capacitance touch screen sensing system according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    The present inventions relate to improved techniques for implementing touch screen displays, in particular projected capacitance touch screen sensing for large electrophoretic display screens, and to electronic document readers implementing these techniques. 
         [0028]    We first describe an example of an electronic document reading device, to illustrate the context in which embodiments of the invention may be employed. Embodiments of the invention can be especially useful for large screen devices, in particular devices with large, flexible electrophoretic display screens as described further below. However applications of embodiments of the invention are not limited to such devices and also include, for example, a device with an LCD display screen on a glass substrate. 
         [0029]    Referring to  FIGS. 1   a  to  1   c , these schematically illustrate an electronic document reading device  10  having a front display face  12  and a rear face  14 . As can be seen from  FIG. 1   c , in preferred embodiments the display surface  12  is substantially flat to the edges of the device. However in embodiments described later it will be seen that the electronic (electrophoretic) display does not extend right to the edges of the display surface  12 , and rigid control electronics are incorporated around the edges of the electronic display, this approach reducing the overall thickness of the device and thus facilitating flex-tolerance, at the expense of making the overall area of the device slightly larger. 
         [0030]    Referring now to  FIG. 2 , this illustrates a vertical cross-section through a display region of the device between the frame members  16 . The drawing is not to scale. 
         [0031]    As can be seen, in preferred embodiments the device has a substantially transparent front panel  100 , for example made of Perspex®, which acts as a structural member. The active matrix pixel driver circuitry layer  106  may comprise an array of organic or inorganic thin film transistors as disclosed, for example, in WO01/47045. However such a front panel is not necessary—sufficient physical stiffness could be provided, for example, by the substrate  108  optionally in combination with one or both of the moisture barriers  102 ,  110 . 
         [0032]    The illustrated example of the structure comprises a substrate  108 , typically of plastic such as PET (polyethylene terephthalate) on which is fabricated a thin layer  106  of organic active matrix pixel driver circuitry. Attached over this, for example by adhesive, is an electrophoretic display  104 , although alternative display media such as an organic LED display medium or liquid-crystal display medium may also be used. A moisture barrier  102  is provided over the electronic display  104 , for example of polyethylene and/or Aclar™, a fluoropolymer (polychlorotrifluoroethylene-PCTFE). A moisture barrier  110  is also preferably provided under substrate  108 ; since this moisture barrier does not need to be transparent preferably moisture barrier  110  incorporates a metallic moisture barrier such as a layer of aluminium foil. This allows the moisture barrier to be thinner, hence enhancing overall flexibility. 
         [0033]    In preferred embodiments the display medium is a reflective display medium, in particular an electrophoretic display medium and the backplane comprises a flexible substrate such as PET or PEN (polyethylene naphthalene). Preferably the backplane is fabricated using solution-based transistors preferably patterned by techniques such as direct-write printing, laser ablation or photolithography. Further details can be found in the applicant&#39;s earlier patent applications, including, in particular, WO 01/47045, WO 2004/070466, WO 01/47043, WO 2006/059162, WO 2006/056808, WO 2006/061658, WO 2006/106365 and PCT/GB2006/050265, all hereby incorporated by reference in their entirety. 
         [0034]    Approximate example thicknesses for the layers are as follows: 100 μm for moisture barrier  110 , 200 μm for substrate  108 , 5-6 μm for active layer  106 , 190 μm for display  104 , and 200 μm for moisture barrier  102 . The set of layers  102 - 110  form an encapsulated electronic display  112 ; preferably this is bonded, for example by adhesive, to a touch sensor as described, and a transparent display panel  100 . The front panel  100  may have a thickness in the range 0.1-2 mm, for example approximately 1 mm or approximately 0.2 mm. 
         [0035]    As illustrated, conductive electrode lines  101 , such as ITO, for touch sensing are located behind the front panel of the device, although in alternative implementations they may be located elsewhere. A set of transparent touch screen electrodes may be laminated onto the display medium and display backplane (using a pressure sensitive adhesive). 
         [0036]    An electrode layer may be a conductive polymer or a metallic layer such as copper, nickel, gold or silver or printable metal. The layer may be deposited using techniques such as vacuum deposition, electroplating and printing techniques, such as screen printing. An intermediate insulating layer may be deposited by techniques such spray or blade coating or printing techniques. Connections to the electrode layers may be formed, for example, mechanically, say with the aid of an adhesive, or through a welding or soldering process. 
         [0037]    Embodiments of the device thus incorporate a capacitive touch sensitive electrophoretic display, preferably a projected capacitance touch sensitive electrophoretic display using a touch sensing system as described in more detail later. This may be used to identify gestures for selecting documents and/or pages, turning pages forward and back and the like. In embodiments the touch sense processing may be such that gestures are location/orientation agnostic, so that a user may perform the same gesture at any location to produce the same result and, in embodiments, independent of orientation (portrait or landscape) of the device. In such embodiments, documents may also be electronically “marked-up”, with mark-up data being written to or being associated with the electronic document being displayed. Additional user controls, optionally also touch sensitive, may be provided in the border around the active display region. 
         [0038]    In embodiments, the electronic document reader has connectors located along an edge of the device to enable the device to be connected to other electronic devices, such as a laptop or desktop computer, a PDA (Personal Digital Assistant), a mobile phone or ‘smart’ phone, or other such devices. A USB (universal serial bus) and one or more wireless interfaces (for example a infrared and/or Bluetooth™ interface) may also be provided to enable documents to be transferred to and from the electronic document reader. 
       Power Management 
       [0039]    Referring now to  FIG. 3   a , this shows preferred power management architecture  500  for an electronic document reading device incorporating an electrophoretic display  32 . 
         [0040]    The electronic document reading device includes a touch sensitive display  400 , as previously described. This enables the user to control the device through touch and/or gesture; in embodiments no power on/off switch or control is needed. In preferred embodiments data from the touch sensing electrodes is processed by a set of dedicated processors  502   a - d , one per side of the display, in embodiments PSoC (Registered Trade Mark) microcontroller devices available for example from Cypress Semiconductor Corporation. Each of these provides an input to a further, control processor  504  via a serial I2C bus, in embodiments an AVRmega48 device from Atmel (Registered Trade Mark) Corp, which includes on-chip Flash, RAM, and EEPROM. Processor  504  processes data from the touch sensing processors to integrate this data and make touch decisions (as described in more detail below), as well as to identify gesture primitives and/or gestures, and provides processed touch sensed information to a main CPU (Central Processing Unit)  512  of the electronic document reading device via a bi-directional serial bus  522 , for example an SPI bus. Processor  504  also provides a number of power control functions, described below. 
         [0041]    The touch sensitive display  400  can respond to a conductive stylus as well as to a finger. In this case XY location data from the processors  502   a - d  can be passed to the main processor  512  in addition to recognised gesture or gesture primitive data, to enable a user to write on the display with a stylus and the CPU  512  to processes this data and provides it to the display controlled  514  for display, for annotation of a document. 
         [0042]    Power for the electronic document reading device is provided from a rechargeable battery  508 , for example a 3 volt lithium battery, via a main switch  506  which switches power on and off to the entire device. The switch  506  has at least one control input for controlling the switch on and off and in embodiments comprises a low-on-resistance CMOS switch, more generally a solid state switch such as a MOS-FET switch. A first power supply bus  507  provides the switched power from the main switch a secondary, CPU power switch  510 , again comprising a controllable CMOS switch, which in turn provides power to a second, switched power bus  511 . 
         [0043]    The electronic document reading device includes a main CPU  512 , for example an ARM (Registered Trade Mark) device having a bus  512   a  coupling the device to NAND Flash  524 , SD RAM  526 , a Bluetooth interface  528 , and a USB interface  530  as well as, optionally, to other peripheral devices. bus  512   a  also couples the main CPU  512  to a display controller at  514 , for example implemented as an FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit), which in turn drives display  32 . In embodiments the CPU and display controller are implemented on a single chip for example using a customisable microcontroller such as an Atmel CAP 9 series, the display controller being implemented using an on-chip programmable block. 
         [0044]    The display  32  has a dedicated display power supply unit  518  to provide the relatively high voltages used to drive the electrophoretic display from the battery  508 ; these may be of order tens of volts. In the illustrated embodiment the display controller  514  is coupled to dynamic RAM  516  comprising blocks of memory at least one of which has its own, separate power supply. The DRAM  516  stores data for display controller  514  and has a portion for storing data representing a current state of the electrophoretic display which has a separately switchable power supply; memory  516  may physically comprise either a single memory device or multiple separate memory devices. 
         [0045]    In  FIG. 3   a  power supply rails are shown with triangular arrow heads and signal/control lines are shown using arrow heads with a slightly indented rear. Thus it can be seen that power bus  511 , as well as providing a power to the main CPU  512 , also provides a power supply to memory elements  524 ,  526 , peripheral devices  528 ,  530 , to the display controller  514  and display power supply  518 , and to a first part of the display memory  516 . The main power supply bus  507  provides power to a second part of the display memory, to processors  502   a - d  and to processor  504  (which provide touch-sense and power management functions). This power supply bus also provides a second power supply to Bluetooth interface  528 . A charger  532  has a wired or wireless external power input and operates to charge battery  508 , as well as providing a battery status sense function and a low battery output signal to the main CPU  512  (in other embodiments such a battery status sense function may be provided in different ways). The charger  523  also provides a recharge detect signal, as illustrated to main switch  506 , but in other embodiments this may be configured differently, for example to provide a signal to process  504 . 
         [0046]    Broadly speaking, in operation processor  504  controls the CPU power switch  510  to switch on and off power to the main CPU, the CPU memory and peripherals, the display RAM, display controller and display power supply only when it is needed for example in response to a user request for a page term. To provide a long battery life, preferably of order months, since even the leakage current through the CPU is unacceptably high rather than put the main CPU  512  into a standby state, the power supply is entirely removed from the CPU and from as many of its associated elements as possible. However preferably a power supply is maintained to the second part of DRAM  516 , which stores data representing a current state of the electrophoretic display. As power to the entire CPU is turned off, when the power is re-applied the main CPU by definition performs a cold boot which is potentially a slow process. It is therefore preferable to minimise the delay between re-applying power to the CPU and performing the desired user action, and storing a current state of the electrophoretic display helps to achieve this. When the desired user action has been performed, because the processor performs a cold boot in response to the user action, if desired the power to the CPU can simply be removed without prior notification to the CPU—that is a handshaking process requesting power down and having the CPU acknowledged that a power down can take place is not necessary. 
         [0047]    In the illustrated embodiment, elements of the system which are not powered down by the CPU power switch  510  are the secondary processor  504  and the touch/gesture processors  502 , so that the document reading device remains sensitive to a user touch/gesture when the main CPU is switched off. Alternatively, however, processor  504  may have one or more inputs from buttons or switches on the device to enable the main CPU to be restarted. 
         [0048]    When the CPU power switch  510  is off preferably power is still applied to the Bluetooth® interface  528  so that, in embodiments, the Bluetooth® system has two power supplies, one to power the main Bluetooth system and a second, derived from bus  507 , to provide a minimal amount of power to the Bluetooth system to provide a Bluetooth ‘sniffing’ function powering on a receiver at intervals to check whether a Bluetooth-compatible signal is locally present. The Bluetooth system  528  provides a signal to processor  504  when a Bluetooth compatible RF signal is detected and processor  504  can then control switch  510  to switch the main CPU on. In this way the device can be configured to automatically power up and connect to a Bluetooth network when one is present, (for example to perform automatic synchronisation when the device is brought into proximity with a Bluetooth-enabled host computer system. 
         [0049]    Preferred embodiments of the electronic document reading device also include a main switch  506  configured to switch power on and off to the entire document reading device, for example in response to detection that the battery  508  is low. There are many different possible signal routes which could be employed. As illustrated charger  532  senses a condition of the battery and provides a signal to the main CPU  512  which either directly, or via processor  504 , controls the main switch  506  off. However in other arrangements a charger  532  could directly control the main switch  506  off, or this control could be performed via a loop including processor  504  but not main CPU  512 . The main switch  506  may be switched on, for example, by detection of recharging of the electronic document reading device and/or by a USB power detect function provided by USB interface  530  which detects when power is available from the connected USB socket. In embodiments this power source may additionally or alternatively be employed to recharge battery  508 . 
         [0050]    Referring now to  FIG. 3   b , this shows a flow diagram of a cold boot procedure employed by the power management architecture of  FIG. 3   a . The procedure begins with no power at all applied to the CPU but with power applied to the second part of the display memory and preferably at least part of the working memory which stores the operating system and/or parameters for the operating system. 
         [0051]    At step S 550  power is applied to CPU  512  and the cold boot process begins, the CPU initialising the system clock (not shown in  FIG. 3   a  for clarity), the SDRAM  526 , the memory management and other elements of the system. The CPU  512  then reads boot control data from the working memory or Flash to determine whether booting is in response to a particular user action and hence whether there is a previously saved state of the system or whether the system is performing an ab initio start up of a type employed when main switch  506  is switched on (step S 554 ). If the system is performing an ab initio cold boot then, at step S 556  the system performs an ab initio start up including a self test, initialising the status of any stored documents, checking for software updates and the like. The procedure then continues to step S 566 , to await a user command. In preferred embodiments the ab initio boot procedure is used only when the device is first ever powered on or after an exception procedure, in particular when the battery has become discharged, reserving power entirely from the device, or in response to user operation of a (hidden) reset control. 
         [0052]    At step S 557 , in embodiments where power is maintained to the working memory (SDRAM), then the state of the device at previous shut-down may be resumed by trading device state data from the working memory. This device state data may comprise one or more of register settings, operating system parameters and the operating system itself. Where power is not maintained to the working memory, this data may be retrieved from the Flash memory. 
         [0053]    If the CPU  512  is performing a second type of cold boot, that is in response to a user action (which may include a connection to a USB interface or Bluetooth network) then at step S 558  main CPU  512  selects a cold boot procedure dependent on the user action and determines whether the desired action can be performed with only a limited portion of the operating system, which is desirable, if possible, for speed of response. A preferred operating system is Windows CE®. If the main CPU  512  was switched on in response to a page turn or similar page manipulation gesture then, at step  560 , the main CPU loads the relevant page data from flash memory  524  and provides this to display controller  514  for display on electrophoretic display  32 . In preferred embodiments this page data is stored in flash memory  524  in the form of image data which can be written to the display via the display controller without substantial further processing. 
         [0054]    In general a page manipulation function may be performed by loading (only) a specific application to perform the desired function. In general in embodiments of the systems different functions of the device are performed by different applications which may be selectively loaded as required (by the user command causing the device to start up). In this way the effect of latency of a cold boot start prior to performing a user-specified action may be reduced. A similar procedure is performed at step S 564  in response to other user actions, for example connecting power to the device after which it may simply wait for further user input. 
         [0055]    If the cold boot of main CPU  512  was performed in response to a USB or Bluetooth wake signal then, step S 562 , in embodiments a USB or Bluetooth communications module is loaded and a data transfer procedure is started, typically to retrieve one or more documents or portions of documents from another computing device, for example a desktop or laptop computer system, PDA, mobile phone or any other type of processor-driven device. Optionally the synchronisation may include sending data back to the other computing device, for example annotation data for a displayed page captured by stylus sensor  520 . 
         [0056]    Once the main CPU has been turned on it preferably waits for a period in an idle state for any further user input/commands (S 566 ). This helps to improve the user experience by reducing the number of cold boot start-ups where, for example, a user is performing a sequence of actions. If no further user input is received then, at step S 568 , the CPU  512  instructs processor  504  to turn off power to the CPU  512 , to shut the document reader down. Prior to powering off the CPU the system writes the aforementioned device state data to the working memory (if power to this is being maintained) and/or to the Flash memory, thus performing a controlled shut-down. As previously mentioned, the electronic document reading device may be used for writing as well as reading, for example to annotate a page which is being read. A displayed document may include, for example, pictures, music and in general any material which may be printed to a page. 
       Touch Sensing 
       [0057]    Referring now to  FIG. 4  this shows an embodiment of a projected capacitance touch screen sensing system according to the invention, in which like elements to those of  FIG. 3   a  are indicated by like reference numerals. The touch sensor portion  400  of the display  32  comprises a plurality of transparent ITO row electrodes  600  and column electrodes  610 . In one implementation a sensor array  400  comprising 30 columns by 38 rows was employed, with 5 mm (pitch) sense elements. Each of the row electrodes is divided in the middle by a break in electrical conductivity into two portions  600   a ,  600   b , and the column electrodes are likewise divided into two portions  610   a ,  610   b . The “half electrode lines” on each side of the sensor array  400   a - d  are connected to a respective touch sensing circuit module  502   a - d , in embodiments each implemented by an individual PSoC. In this way the sensing is split across 4 PsoCs. One advantage to segmenting the sensor array in this way is that a thinner ITO layer can be employed since the architecture can cope with an increased ITO resistance, thus improving optical clarity. 
         [0058]    Each of the touch sensing circuit modules  502  is connected via a I2C serial bus  612  to a control processor  504 . The control processor  504  also provides individual poll and acknowledge lines  613   a - d ,  614   a - d . The controller  504  reports X and Y position data, strokes and gestures, in embodiments at a 50 Hz rate, to the main processor  512 , which processes the gesture information using typically a tablet mouse or stylus input device driver of an operating system such as WinCE™. In embodiments an SPI bus connects controller  504  with main processor  512 . 
         [0059]    In operation the controller  504  is in control of the touch sensing system and polls the touch sense circuit modules  502  to start a scan. The circuit modules  502  are either sleeping or scanning and the controller  504  is in control of the power profile: the sleep power for a PSoC is of order 10 μW and the wake up time is less than 100 ms. Once activated the scan time is of order 20 ms and a return bit map of the active lines is provided via the I2C bus  612 . In one implementation the touch sense circuit modules  502  each comprised a CY8C24x94 device, using the Cypress™ slider library to provide sub-sensor resolution. The controller  504  handles merging of the X and Y coordinates and performs stroke and gesture recognition as well as, optionally, accommodating one or more “home” buttons. In more detail, the Y result determines which X result to use, and the X result determines which Y result to use. In more detail, referring to  FIG. 4  and to, say, the row (Y) position, either touch sense module  502   a  or touch sense module  502   c  could be used to provide his position, and modules  502   b, d  are employed to select which of modules  502   a, c  are employed, using module  502   a , the Y o  value, if the X position is less than half way across the screen and using the  502   c  module, Y 1  value, if the sensed touch position is more than half way across the screen. In a similar way the Y o /Y 1  modules determine which row touch sensing module  502   b, d  (X o  or X 1 ) to employ. 
         [0060]    In principle this approach could be extended to, say, subdivide the rows vertically and/or the columns horizontally, for example using two row modules  502   aa ,  502   ab  to replace module  502   a  and so forth. Then modules  502   b,d  would select which pair of row touch sense modules (the left pair or the right pair) was employed, and optionally vice versa. It will be appreciated that this could be extended to 3 or more touch sense circuit modules along each side of the sensor array  400 . However such an arrangement would employ communication between the touch sense circuit modules along each side of the sensor array, if interpolation across the electrodes at the boundaries between the modules were desired. 
         [0061]    The above described architecture is further advantageous because the controller  504  is able to provide a single view of multi-touch rejection and in an arrangement of the type shown in  FIG. 4  complexity is reduced because there is no need for communications between touch sensing circuit modules  502 . 
         [0062]    In preferred implementations the controller  504  is also configured to identify linear strokes as primitives for gestures. This can be done by determining changes in detected X,Y touch position over a sequence of scans using either, for example, a simple moving average filter or more sophisticated Kalman filtering to improve detection. Preferred implementations restrict to 8 45° vectors, and once a stroke has been identified gesture by identification is straightforward. For example a curve may be mapped to a sequence of linear segments and/or stroke directions. Some examples of how letters may be defined are as follows:
       Z is {W→E, NE→SW, W→*E}   N is {+90°, −45°, +90°}   V is {−45°, +45°}.
 
Stroke identification and gesture recognition can be implemented, for example, either using a state machine or by employing a sliding window and pattern matching; in either case the code is small and fast.
       
 
         [0066]    In one implementation recognised gestures are reported to the main processor running windows CE via a keyboard handler interface, and XY coordinates are reported to windows CE via a tablet interface. The controller  504  also in embodiments, wakes up the main processor  512  and controls power management, as previously described. In preferred implementations the XY coordinates reported to the main processor are used to enable annotation of a displayed document. 
         [0067]    Preferred implementations of the touch sensing system have been described with specific reference to a projected capacitance touch screen sensing system, but the skilled person will appreciate that the segmented sensor design and sensing module control and selection architecture may be employed in the context of other types of capacitive sensing and, in principle, with non-capacitive touch sensors. 
         [0068]    No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto 
         [0069]    In conclusion, the invention provides novel systems, devices, methods and arrangements. While detailed descriptions of one or more embodiments of the invention have been given above, various alternatives, modifications, and equivalents will be apparent to those skilled in the art without varying from the spirit of the invention. Therefore, the above description should not be taken as limiting the scope of the invention, which is defined by the appended claims.