Classifications

• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
  • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
  • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
  • G09G3/3611—Control of matrices with row and column drivers
  • G09G3/3685—Details of drivers for data electrodes
  • G09G3/3688—Details of drivers for data electrodes suitable for active matrices only
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2310/00—Command of the display device
  • G09G2310/06—Details of flat display driving waveforms
  • G09G2310/066—Waveforms comprising a gently increasing or decreasing portion, e.g. ramp
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2330/00—Aspects of power supply; Aspects of display protection and defect management
  • G09G2330/02—Details of power systems and of start or stop of display operation
  • G09G2330/021—Power management, e.g. power saving
  • G09G2330/023—Power management, e.g. power saving using energy recovery or conservation

Definitions

• This invention relates to driving capacitive loads and, more particularly, to driving liquid crystal displays ("LCDs"). Description of Related Art
• LCDs are in widespread use today, and their popularity is expected to increase. These devices operate by controlling the amount of light that is passed or reflected by a set of liquid crystal (LC) elements arranged in rows and columns in the display. Each LC element comprises a pair of plates surrounding liquid crystal material. The amount of light that is passed or reflected by an LC element is controlled by the voltage that is delivered to the plates of that element.
• LC liquid crystal
• the voltage across the element must usually be reversed in polarity periodically.
• an AC signal is typically used to drive the element, the magnitude of the signal determining the amount of light that is passed or reflected.
• a typical LCD has hundreds of thousands of LC elements arranged in hundreds of rows and columns. To reduce the amount of circuitry that is needed to drive each LC element, all LC elements in the same row typically communicate through a single row line, while all elements in the same column typically communicate through a single column line. Each LC element is thus uniquely defined by the row and column line that intersect at its location. The voltage across each element is regulated by controlling the amount of charge that is delivered to it through its coordinating row or column line.
• the picture displayed by an LCD is typically painted by sequentially scanning each line of the display, somewhat like the way a picture is painted in a television set.
• the first row line might be activated, followed by the delivery of the desired signal to the first column line, thus establishinu the desired voltaue across the first element in the first row. While the first row line is still activated, the ⁇ esired signal would then be delivered to the second column line, thus establishing the desired voltage across the second element in the first row This process would typically continue until all of the elements in the first row are set to their desired levels Alternatively, the desired voltage across all of the elements in a row can be applied at the same time
• the second row line would then be activated, followed by the sequential or simultaneous charging of each LC element in the second row This process would continue until the voltages across all of the LC elements in the display are set to their desired levels This entire cycle would then repeat itself a short time later, but with the voltages being of opposite polarity, to provide the refreshment needed for each LC element
• One object of the invention is to minimize these as well as other problems in the prior art.
• Another object of the invention is to provide a system and method for driving capacitive loads to controllable voltage levels in a power-efficient manner.
• a still further object of the invention is to provide a system and method for recovering energy that is stored in a capacitive load.
• a still further object of the invention is to recover energy that is stored in capacitances associated with the driving lines of an LCD, other than in the LC elements.
• a still further object of the invention is to reduce the amount of energy that is needed to drive an LCD.
• one of the LC elements is charged by delivering a voltage on the line that is associated with the element. Energy is then recovered from the other capacitances that are associated with the line while the voltage across the charged element is maintained. This process may then be repeated until all of the other elements in the display are driven.
• each LC element is connected to its associated column line through an electronic switch that is controlled by the row line associated with the element.
• adiabatic charging is used to drive the LC elements. This can utilize various signals, including a ramp signal, a staircase signal, or a half-wave sine pulse.
• adiabatic discharging is used to recover the energy from the driving line. This can similarly use a variety of signals, including a ramp signal, a staircase signal or a half-wave sine pulse.
• the invention also includes a circuit for reducing the energy consumed by a display.
• the circuit advantageously includes a voltage connection system connected to the driving line for controllably causing the driving line to connect to a voltage source; a recovery connection system for connecting to a driving line for controllably causing the driving line to connect to a reservoir; and a control system for causing the voltage connection system to connect the driving line to a voltage source during a first time period and for causing the recovery connection system to connect the driving line to the reservoir during a second time period.
• the display is an LCD and voltages on the LC elements are not materially changed during the second time period.
• the source and the reservoir constitute a single supply that generates a signal conducive to adiabatic charging and discharging.
• the voltage connection system includes a first electronic switching system connected between the supply and the driving line.
• the recovery system includes a second electronic switching system connected between the supply and the driving line.
• the control system controls the first and second electronic switching systems.
• the adiabatic charging and discharging may use a variety of signals, including a ramp signal, a staircase signal, or a half-wave sine pulse.
• the first electronic switching system includes a transmission gate connected in series with a MOSFET.
• the second electronic switching system may also advantageously include a MOSFET.
• the second time period begins a predetermined amount of time after the first time period.
• the second time period begins when the voltage of the supply is approximately equal to the voltage of the driving line.
• a comparator circuit may advantageously be connected to the supply and the driving line for determining when the voltage of the supply is substantially equal to the voltage of the driving line.
• the display is an LCD, an electroluminescence display or a field-emission display.
• the circuitry and process is adapted to work in conjunction with a serial video signal, such as the serial video signal delivered at a VGA port
• FlG 2 IS a block diagram of one embodiment of the invention shown connected to the combined capacitance that is imposed on a single line in a display
• FlG 4 IS a schematic of one embodiment of a circuit that can advantageously be used to implement a portion of the invention
• FlG 5 IS a diagram illustrating various signals present during the operation of the circuit shown in FlG 4
• FlG 6 IS a schematic of a circuit that produces a signal useful in adiabatic charging and/or discharging
• FlG 7 is a schematic of a cu cuit that uses a set of capacitoi s to furnish the voltage levels necessary for generating a staircase signal useful in adiabatic charging and/or discharging
• FlG 8 illustrates a half-wave sine pulse that is useful in adiabatic charging and/or discharging
• FlG 9 IS a block diagram of a collection of drivers that mav advantageously be used for an LCD, incorporating concepts of the invention
• FIG 10 IS a schematic of a comparator circuit that genei ates a signal that can be used to activate the energy recovery phase of the system
• FIG 1 1 illustiates portions of a circuit that can advantageously be used to sample the desired input voltage to effectuate pipelining
• FIG 13 IS a schematic of one embodiment of a circuit that can advantageously be used to implement portions of the invention in connection with a display for a serial video signal
• FIG 14 is a diagram illustrating various signals that are present during the operation of the circuit shown in FIG 13
• FIG 1 illustrates a portion of a typical prior art LCD
• the LCD includes a plurality of LC elements arranged in rows and columns, such as LC elements 1, 3, 5 and 7 arranged in rows 9 and 1 1 and columns 13 and 15
• each LC element includes liquid crystal material, such as liquid crystal materials 25, 27, 29 and 31, sandwiched between a set of plates, such as plates 33 and 35, plates 37 and 39 plates 41 and 43, and plates 45 and 47 respectfully
• the amount of light which is permitted to pass through each element is directly related to the voltage that is placed across the plates surrounding each liquid crystal material
• LCDs As is also well known, there are many types of LCDs, including active-matrix, thin-film- transistor (“AMTFT”) panel types and passive-matrix, super-twisted nematic (“PMSTN”) panel types. Some LCDs, moreover, include backlighting, while others do not
• each LC element There are also a broad variety of techniques used to drive each LC element As indicated in the Description of Related Art above, the voltage on each element is usually periodically reversed in order to maintain the same level of light transmittance
• one plate of the element is connected to a constant voltage such as ground, and the other plate is driven both positively and negatively
• one plate of each element is connected to a square-wave signal having the same amplitude as the maximum data line swing and either the frequency of the frame or the line This latter approach reduces the amount of swing needed on the data line, but increases the amount of flicker
• one plate is connected to a voltage that is half of the maximum driving voltage
• Fid 1 illustrates a portion of a typical active-matrix display with one connection of each LC element 1, 3, 5 and 7 goins to "round
• each LC element is connected to a switch
• one connection of LC element 1 is connected to a switch 49
• one connection of LC element 3 is connected to a switch 51
• one connection of LC element 5 is connected to a switch 53
• one connection of LC element 7 is connected to a switch 55
• the control lines of each switch are connected to a row line, such as a control line 57 of switch 49 and a control line 59 of switch 5 1 being connected to a row line 65, and a control line 61 of switch 53 and a control line 63 of switch 55 being connected to a row line 67.
• each switch is typically connected to a column line, such as an input 69 to the switch 49 and an input 71 to the switch 53 to a column line 73 and an input 75 to the switch 51 and an input 77 to the switch 55 to a column line 79.
• Each row line may be actuated sequentially by the delivery of a signal on that row line to its driver, such as a driver 81 for the row line 65 and a driver 83 for the row line 67. While a particular row line is actuated, the voltage that is needed to be placed across each LC element connected to that row line is typically delivered on the column line that coordinates with that LC element. This process may continue sequentially from one column line to the next, until all of the LC elements in a row are driven to their desired states, or simultaneously to all of the LC elements in a row.
• Drivers such as a driver 85 for the column line 73 and a driver 87 for the column line 79, are typically used to facilitate this process. Typically, only one row line is actuated at a time.
• FIG . 1 Only a portion of a typical LCD is illustrated in FIG . 1 .
• An actual LCD would usually have hundreds of rows and hundreds of columns of LC elements with all of the associated lines and components that have been described above being duplicated to match.
• FIG. 2 is a block diagram of one embodiment of the invention shown connected to the combined capacitance that exits on a single line in a display.
• FIG . 3 is a flow diagram of the process employed in the embodiment of the invention shown in FlG. 2. The operation of the embodiment shown in FIG 2 will now be explained in conjunction with the diagram of that process shown in FIG 3 and the prior art LCD illustrated in FIG 1
• the first step is for a particular row to be activated, such as, for example, by activating the row line 65 shown in FIG 1
• switches such as switches 49, 51, 53 and 55, shown in FIG 1, act as control mechanisms for the rows of LC elements that are activated
• the invention is also applicable to displays in which the row lines are directly connected to the LC elements without any intervening switches, such as passive displays
• the other connection to the LC elements might be directly connected to their associated column lines
• references in this application to "'activating" a line are intended to apply to both types of situations, as well as to any other technique that is used to drive an LC element
• the source is then connected to the column line that is associated with the LC element to be driven, such as to the column line 73 that is associated with LC element 1 in FlG 1 This is reflected by a Connect Source to Driving Line block 101 in FlG. 3.
• the necessary voltage is then applied to the LC element in that row through the column line that is associated with that element This step is reflected in a Deliver Voltage to LC Element block 102
• a control system 107 activates a voltage connection system 109 to connect a voltage source 111 to the column line associated with the LC element, such as the line 73 in FlG 1
• a voltage connection system 109 to connect a voltage source 111 to the column line associated with the LC element, such as the line 73 in FlG 1
• the other LC elements in the same row may then be driven sequentially or simultaneously in the same manner
• the control system 107 signals the voltage connection system 109 to disconnect the source 1 1 1 from the column line, as reflected by a Disconnect Source From Driving Line block 103.
• the control system 107 then causes a recovery connection system 1 15 to connect the column line to a reservoir 1 17, as reflected by a Connect Reservoir to Driving Line block 113.
• the energy that is stored in the capacitances associated with the column line (again, shown as the capacitor 105) is then recovered and stored in the reservoir 1 17. This is reflected in a Recover Energy block 1 19 in FlG. 3.
• the reservoir is disconnected from the column line, as reflected by a Disconnect Reservoir from Driving Line block 1 19
• the voltage that was placed on the LC element is not affected during the recovery phase because the circuit to the plates of the LC element is broken during this phase, as explained above, while the energy is being recovered from the other capacitances.
• This driving and recovery cycle can then be repeated in the course of driving the other LC elements in the display, as well as during subsequent frames when the light transmittance on the already driven element is either maintained through the application of an equal but opposite voltage or is changed through the application of a voltage having a different voltage.
• Both the voltage connection system 109 and the recovery connection system 1 15 may include electronic switches, such as transistors (e.g., FETs or MOSFETs) and gates, that are controlled by the control system 107.
• the control system 107 may include electronic circuitry, such as transistors (e.g., FETs or MOSFETs) and gates, that generate the necessary control signals in accordance with well-known control signal techniques
• FlG. 4 is a schematic of one embodiment of a circuit that can advantageously be used to implement a portion of the invention.
• the total capacitance imposed on a particular line 13 1 of an LCD, such as the column line 73 shown in FlG. 1, is modeled in FlG. 4 as a capacitor 133.
• the total capacitance includes the capacitance imposed by the particular LC element that is connected to the line that is currently being driven, as well as the far more substantial capacitance between the particular line and the backplane and the capacitances associated with the other inactive switches that are connected to the same line.
• FlG. 4 illustrates one terminal of this total capacitance 133 as being connected to V ⁇ X - for simplicity, it is to be understood that, in practice, each of the contributing capacitive components may, in fact, be connected to different potentials.
• the line 13 1 is connected to a terminal 135 of a transmission gate 137.
• the transmission gate 137 also has a control input 139, an inverting control input 14 1 , and another terminal 143.
• a transmission gate is a semiconductor device, typically including an N-channel semiconductor device connected in parallel to a P-channel semiconductor device, that electrically connects its two terminals upon receiving a control signal at its control signal input and an inverting control signal at its inverting control signal input, without any appreciable voltage drop
• the terminal 143 is connected to a terminal 145 of an electronic switching device 147, such as a MOSFET
• Another terminal 149 of the switching device 147 is connected to a voltage source V ⁇ through a connection 151
• the switching device 147 also has a control input terminal 153
• the line 131 is also connected to a terminal 163 of another transmission gate 155 which also has a control input 157, an inverting control input 159, and another terminal 161
• the terminal 161 is also connected to the same voltage source V ⁇ through the connection 151 As will soon be seen, the voltage source V ⁇ simultaneously acts as a reservoir
• FIG 5 IS a diagram illustrating various signals present during the operation of the circuit shown in FlG 4
• the operation of the circuit shown in FIG 4, as well as the signals that the circuit processes and generates, are best understood by consideration of FIGS 4 and 5 together
• a signal equivalent to the voltage that is desired to be placed across the LCD element that is being driven (plus the anticipated gate to source threshold voltage drop Vi in the switching device 147) is delivered to the conti ol input terminal 153 of the switch, as shown by a line segment 205 in FlG 5
• tiansmission gate 137 is activated by the delivery of an activation signal to its control input 139 and an inverse activation signal to its inverting control input 141
• the activation signal is shown by a line segment 207 in Flo 5 This causes the transmission gate 137 to connect its terminal 143 to the capacitances represented by capacitor 133
• the desired level of voltage at the control input terminal 153 to the switching device 147 is greater than the output of the switching device 147 at its terminal 145 As a result, the switching device 147 is activated In turn, the voltage source V A at the connection 151 is connected to the line 13 1 and in turn, to the plate of the LC element to be driven
• the voltage source V ⁇ now rises from its initial value, as shown by line segment 213 This causes charge to be gradually delivered to the LC element As the voltage across the LC element builds up, it approaches the voltage V ⁇ n at the control input terminal 153 to the switching device 147, less the gate to source threshold voltage Vi across switch 147, as shown by a line segment 209 As it does, the resistance of the switching device 147 increases until the switching device 147 cuts off This occurs at approximately point 21 1 shown in FlG.
• the switching device 147 acts as a voltage regulator to ensure that the voltage across the LC element is charged to the desired value applied at its control input terminal 153, less the gate to source drop V ⁇ across the switching device 147, without placing a large load on V,un, thus ensuring that its unloaded value is preserved
• the voltage source V ⁇ is preferably a time- varying supply voltage It also preferably does not rapidly rise from zero to its maximum value, such as would happen in the case of a fast-rising square-wave signal Instead, V A , rises more slowly, such as the ramp signal shown in FIG 5 by a segment 213
• a time-varying supply voltage reduces this lost energy by reducing the instantaneous voltage drop across the resistive components of the voltage supply and switching drive system
• the supply voltage rises just slightly faster than the voltage across the capacitive load, thus minimizing the voltage differential at all times
• adiabatic charging is referred to by the inventors as adiabatic charging
• a ramp signal such as the segment 213 in FlG 5, is only one of a variety of wave shapes that can be used to effectuate adiabatic charging
• FlG 6 is a schematic of a circuit that produces another form of a signal useful in adiabatic charging, i e , a staircase signal
• the combined capacitive load is illustrated as a capacitor 23 1
• the ultimate voltage desired across the capacitor is V N
• a se ⁇ es of lower voltage steps are illustrated as V,, V 2 , etc
• a switch 233 is closed, causing the first level of the voltage V, to be applied
• the switch 233 is opened and a switch 235 is closed, causing the next level of voltage V 2 to be applied This process continues until the final voltage level V ⁇ is applied through the closure of a switch 237
• a switch 239 is also provided to discharge the capacitive load 23 1 at the appropriate time
• FIG 7 IS a schematic of a circuit that uses a set of capacitors to furnish the voltage levels necessary for generating a staircase signal used in adiabatic charging
• the combined capacitive load to be charged is illustrated as a capacitor 251 connected to a se ⁇ es of stepping switches 255, 257 and ultimately 259, as well as a discharge switch 261
• the voltages necessary for each step before the desired voltage V ⁇ is reached are supplied by a series of capacitors including capacitors 262 and 263 Using appropriate circuitry and timing, these capacitors are charged to the appropriate step levels and, thereafter, function as the needed voltage sources for their respective steps
• FIG 8 illustrates a half-wave sine pulse Circuitry that may advantageously be used to generate such a half-wave sine pulse is described in U S Patent 5,559,478, the contents of which are also incorporated herein by reference
• the transmission gate 137 is turned off by the removal of the activation signal from its control input 139, as shown by a line segment 281 in FlG 5 (Again, the complementary signal is delivered to the inverting control input 141 .) This disconnects the capacitive load 133 from the connection 151 that goes to the voltage supply.
• the row line that is activating the particular LC element that has just been charged is then deactivated. This disconnects the LC element from the driving line and leaves the voltage across the LC element (and thus the level of light transmittance of the LC element) intact. However, the energy contained in the other large capacitances that are associated with the driving line remains.
• the supply signal V A starts to ramp back down, as shown by a line segment 283 in FlG. 5.
• the transmission gate 155 is closed by the delivery of a control signal at its control input 157, as illustrated by a rising pulse 287 (Although not shown, a complementary segment is delivered to the inverting control input 159.)
• a rising pulse 287 (Although not shown, a complementary segment is delivered to the inverting control input 159.)
• This causes the line containing the large parasitic charge to be connected to the source V A through the connection 151.
• energy stored in the parasitic capacitance is gradually returned to the voltage source V A through the connection 151 during this recovery phase.
• the transmission gate 155 is opened by the removal of an activation signal from its control input 157, as shown by a line segment 291, and by the delivery of a complementary signal to its inverting control input 159. The system is then ready for the entire driving and recovery process to be repeated.
• the voltage source V A does not rapidly fall from its maximum amplitude, such as would occur in the case of a fast-falling square-wave signal.
• a time-varying supply voltage is preferably used during the discharge phase, such as the ramp signal that is shown in FlG. 5 by the line segment 289.
• the use of a time-varying supply voltage during the recovery phase -adiabatic discharging- prevents high voltages from appearing across the resistive devices in the driving system, such as the switches and internal impedance of the voltage source, thereby reducing energy losses during the recovery phase. Without adiabatic discharging, much of the stored energy would be dissipated.
• the shape of the signal used in adiabatic discharging can take a variety of forms, in addition to the ramp signal that is illustrated by the line segment 289 in FIG. 5.
• it could take the same staircase form that may be advantageously produced by the circuitry shown in FlGS. 6 and 7, as well as the circuitry shown in U.S. Patent 5,473,526
• It may also take the form of a half-wave sine pulse, such as the half-wave sine pulse shown in FlG 8
• the key feature is that the voltage supply provide a time-varying signal and, preferably, one that does not fall rapidly, as does a typical square wave signal
• FIG 9 is a block diagram of a collection of drivers that may advantageously be used for an LCD panel, incorporating the concepts of the invention
• a pulsed-power supply 301 generates the charging and discharging signal
• both the charging and discharging signal are preferably of the type that cause adiabatic charging and discharging
• the signal generated by the pulsed-power supply 301 is delivered to drivers for each line, such as line drivers 305, 307, 309 and 3 1 1
• the output of each driver is connected to the line which it drives
• the output of the line driver 305 is connected to a line 315
• the output of the line driver 307 is connected to a line 3 17
• the output of the line driver 309 is connected to a line 319
• the output of line driver 3 1 1 is connected to a line 321
• each driver is connected to the signal that represents the desired voltage to be placed across the LC element that is being driven
• the line driver 305 is connected to the desired signal at an input 325
• the line driver 307 is connected to its desired signal at an input 327
• the line driver 309 is connected to its desired signal at an input 329
• line driver 31 1 is connected to its desired signal at an input 33 1
• the configuration shown in FIG 9 allows for the use of a single power supply to provide the needed voltage for all of the drivers To accomplish this, all of the drivers are configured to deliver their voltage at the same time, thus causing all of the LC elements in a single activated row to be driven at the same time
• each dnver includes an output stage 351 , such as the circuit shown in FlG 4, a digital-to-analog converter 353 for converting a digital signal representing the desired voltage level into its analog equivalent, and a recovery controller 355 for controlling the point in time when the output stage is directed to recover energy from the other capacitances imposed on the line by returning it to the power supply 301
• the recovery controller 355 There are numerous ways to implement the recovery controller 355 One approach is to use an open-loop timing scheme to cause the transmission gate 1 55 (FlG 4) to close at the moment when the supply voltage is expected to be approximately equal to the voltage across the capacitive load
• This open-loop process can key the necessary timing to a wide variety of events, one of which, in the case of the ramp shown in FlG 5, might be the point in time 361 when the downward ramp begins
• the recovery controller would detect the beginning of the declining ramp (or be provided with this information from the voltage source) and would then issue a signal to turn off the transmission gate 155 at a pre-determined time later.
• the pre-determined amount of time would depend upon the slope of the ramp and the level of the voltage on the line
• Another approach is to compare the voltage of the downward ramp with the voltage across the capacitive load and to activate the transmission gate 155 when these voltages are approximately equal.
• FlG. 10 is a schematic of a comparator circuit that generates a signal used to activate the energy recovery phase of the system. As shown in FIG 10, the voltage supply V A is delivered to a switch 401 The voltage V, may be delivered to a control input 403 of the switch 401
• the circuit Before entry into the recovery phase, the circuit is reset by pulsing the pre-charge input PC to a gate 405 high and a complementary input to a gate 407 low This causes the control output 409 of the circuit to be low and, in turn, to turn on a gate 410 After this pre-charge pulse, all switches in the device are off, including switches 41 1 and 413 However, switch 410 is on.
• control output 409 transitions when V A falls below V ⁇ n - V T , not when V A falls below V, parent In other words, the comparator has an offset voltage of V T . This is not a drawback when used with the output stage shown in FIG 4
• Control input 403 can be connected to control input terminal 153
• the control output 409 then transitions when V, n equals V A , as desired
• the desired voltage V,just may change from its original value before discharging commences at point 285 This facilitates pipelining
• the circuit shown in FlG. 10 requires the value of V render, to be known during the recovery phase
• FlG. 1 1 illustrates a circuit that can advantageously be used to sample the desired input voltage to effectuate pipelining
• V, perhaps is connected to the input of electronic switching device 147, exactly as it is shown in FlG 4 Unlike what is shown in FlG 10, however, the input to the switch 401 is connected to a transmission gate 501 and a storage capacitor 503
• the transmission gate 501 is closed (by sending appropriate control signals to its complementary inputs 505 and 507) at some point in time while V ⁇ n is at its desired state, such as at some point in time during the line segment 205 shown in FlG. 5.
• V ⁇ n is at some point in time during the line segment 205 shown in FlG. 5.
• V ⁇ n is at some point before the value of V, rather changes, such as before the line segment 281 in FlG.
• the transmission gate 501 is opened (again, by sending appropriate signals to its complementary inputs 505 and 507), causing the previous value of V,creme to be stored on the storage capacitor 503 and, in turn, to continue to be input to the control input 403 of the comparator circuit shown in FIG 10
• the value of V, chorus is preserved until it is no longer needed
• the invention is also applicable to displays that display video information received in a serial format in the form of a serial video signal, such as the serial video signal typically provided from the VGA port of a personal computer.
• FIG. 12 illustrates a portion of the typical prior art LCD that has been used to display a serial video signal.
• a serial video signal V m is delivered to the display over a line 601.
• the voltage of such a signal varies as a function of time and, more precisely, as a function of the anticipated position of a scanning beam in a cathode ray tube (CRT).
• a typical prior art LC display includes a horizontal shift register 603 that shifts a single bit and is driven by a horizontal clock pulse H CL K over a line 605. This causes the outputs of the horizontal shift register, two of which are shown as outputs 607 and 609, to turn on and off in sequence.
• the outputs of the horizontal shift register are typically used to drive switches, such as switches 61 1 and 613.
• the outputs of these switches drive the respective column lines to which they are attached, such as column lines 615 and 617, respectively.
• the vertical shift register 619 similarly controls the activation of the row lines, such as row lines 621 and 623. This is similarly done by shifting a single bit through the register in response to a clocking signal V CI . K being delivered over a line 625
• the activation of a row line activates a switch that is associated with each LC element in the display, such as a switch 631 that is associated with an LC element 635, a switch 637 that is associated with an LC element 639, a switch 641 that is associated with an LC element 643, and a switch 645 that is associated with an LC element 647.
• a first row line is actuated, such as the row line 621 .
• this readies the LC elements that are associated with that row to receive a voltage from their associated column lines.
• the horizontal shift register 603 actuates the switch 61 1 which, in turn, connects the column line 615 to the serial video signal V, n over the line 601, thus delivering the serial video signal at this point in time to the LC element 635 in the first row and column.
• horizontal shift register 603 deactivates the line 607 which, in turn, turns off the switch 61 1 and thus disconnects the serial video signal V m from the LC element 635. It instead connects the serial video signal V taste, to the next column line through the next switch (neither of which are shown in FlG. 12).
• FIG 14 is a diagram illustrating various signals that are present during the operation of the circuit shown in FlG 13 The operation of the present invention in connection with a display for a serial video signal is best understood by a discussion of FlGS 13 and 14 together
• the serial video signal V, makeup is delivered over a line 701 to the input of a column storage switch for each column line, such as a column storage switch 703 for a column line 705
• the process in connection with the particular LC element 713 begins by the temporary activation of the output from the horizontal shift register HS that corresponds with the particular column that is being actuated This signal is delivered over the line 709 to cause the switch 703 to close and, in turn, to cause the voltage of the serial video signal V, n to be imposed across a storage capacitor 71 1 In a preferred embodiment, nothing further is done at this moment to deliver the signal from the serial video signal V, n to the LC element 713 Instead, a similar process is employed in connection with all of the other switches and their associated storage capacitoi s (not shown in FIG 13) that are associated with the other column lines in the display By the end of this process, the voltage that existed on the serial video signal V, reinforce at the point in time when a particular column storage switch was actuated is now stored on the capacitor associated with that column switch, such as the capacitor 71 1 that is associated with the switch 703.
• a time-varying source voltage V A is delivered to an input 715 of a switch 717 that is configured to function as a voltage regulator. Initially, switch 717 is closed, due to the voltage across the capacitor 71 1. As a consequence, the rising voltage V as shown by a line 721 in FIG 14 is transferred to the column line 705, as shown by a line 723 in FIG. 14.
• a row line 725 may be actuated when the voltage source V ⁇ begins to rise, as reflected by a line segment 727 in FlG 14 Alternatively, the actuation of the row line 725 may be deferred until later, as reflected by a line segment 729 in FlG 14 In either case, the switch 717 will begin to shut off as the voltage V ⁇ approaches the stored voltage on the capacitor 71 1, as reflected by a line 731 in FIG 14. As soon as the voltage across the capacitor 71 1 is reached (less the threshold voltage across the switch 717), the switch 717 will turn off, leaving the desired voltage on the column line 705 and, in turn, across the LC element 713
• a time-varying voltage is preferably used for V ⁇ , thus effectuating adiabatic charging
• a ramp signal has been illustrated, it is of course to be understood that all of the other types of signals discussed above in connected with adiabatic charging may be used instead, such as a half-wave sine pulse or a staircase signal.
• the row line 725 is typically deactivated, thus disconnecting the LC element 713 from the column line 705 through the operation of a transmission gate 732, as reflected in FIG 14 by a line segment 733 (or in the alternative a line segment 735).
• the discharging segment of the voltage source V A is also preferably a time-varying signal, thus effectuating adiabatic discharging, as explained above.
• any other type of time-varying signal could instead be used, such as the staircase signal or half-wave sine pulse discussed above
• the intrinsic capacitance of the switch 717 will often cause some current to flow between the voltage source V ⁇ and the storage capacitor 71 1 , even when the switch 717 is open.
• the level of voltage that is stored on the storage capacitor 71 1 will change, potentially introducing an error
• the value of the storage capacitor 71 1 should be substantial in connection with the intrinsic capacitance of the junction of the switch 717 Alternatively, or m addition, the amount of this error can be calculated and compensated by an offsetting amount being imposed on V ⁇ n
• Such an offsetting amount is capable of being provided, for example, by a table in the video driver card that generates the serial video signal V, makeup and/or by appropriate adjustments in the software driver that serves as an interface between the video driver card and the microprocessor of the personal computer.
• the second plate of each LC element such as the plates 35, 39, 43 and 47 in FlG. 1 are not connected to ground, but are connected to a DC voltage that lies halfway between ground and the maximum voltage that is expected to be applied to the LC element.
• the other plate of the LC element such as the other plates 33, 37, 41 and 45 shown in FlG. 1, are driven between this mid-way value and the maximum value.
• the other plate is driven between zero and the mid-way value
• a seven-step staircase signal generator is used to generate the staircase signal during the odd frames, i e .
• the escalating voltage source is not typically connected to the display until after the seventh step, thus ensuring against an unnecessary interim reversal in polarity across the LC element.
• the invention is of far broader scope and encompasses components, features, methods, and processes other than those that have been described.
• the invention is broadly applicable to driving a broad variety of capacitive loads (e.g., capacitive electrostatic transducers and display devices based on electroluminescence or field-emission) to controllable voltage levels, not simply LCDs.
• capacitive loads e.g., capacitive electrostatic transducers and display devices based on electroluminescence or field-emission
• the charge to each LC element as being delivered through its associated column line, it is, of course, understood that the charge might instead be delivered through its associated row line.
• the invention is limited solely by the following claims.

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• 1999
  • 1999-09-03 WO PCT/US1999/020358 patent/WO2000014708A2/en active IP Right Grant
  • 1999-09-03 EP EP99945512A patent/EP1114410A2/en not_active Ceased
  • 1999-09-03 JP JP2000569373A patent/JP2002524950A/ja active Pending
  • 1999-09-03 AU AU58099/99A patent/AU5809999A/en not_active Abandoned
  • 1999-09-03 KR KR1020017002796A patent/KR100707042B1/ko not_active IP Right Cessation

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