JP2008257023A - Active matrix driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate an influence of parasitic capacitance on a pixel potential without greatly increasing a circuit. <P>SOLUTION: An active matrix driving circuit is equipped with a selection driver 101 which selects a line to be applied with an image voltage according to a selection signal, a signal driver 102 which applies an image voltage corresponding to an image signal, a control unit 108 which controls generation of the selection signal to be sent to the selection driver and the image signal to be sent to the signal driver according to a data signal supplied from outside, and power supply units 110-1 and 110-2 having a power source determining a voltage for selection and a power source determining a voltage for non-selection, and a power source determining a plus-side voltage of the signal driver and a power source determining a minus-side voltage, and is provided with processing means 105 of processing a source voltage so as to round a leading-edge waveform between the power supply units 110-1 and 110-2 and the selection driver 101 and signal driver 102. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a driving device for driving an organic TFT in an active matrix.

  Active matrix driving is often used to drive display devices such as liquid crystal display devices, organic EL display devices, and electrophoretic display devices. As an example of an active matrix driving method, Japanese Patent Application Laid-Open No. 5-257123 discloses a driving method in which a positive signal and a negative signal of an arbitrary display signal are applied within a selection time of one scanning line. It is written.

  An active matrix driving circuit using the above driving method is shown in FIG. The active matrix driving circuit shown in FIG. 17 includes a control unit 1708, a selection driver 1701, a signal driver 1702, and power supply units 1707-1 and 1707-2.

  The control unit 1708 generates and controls a selection signal 1711 and an image signal 1712 according to a data signal 1710 supplied from the outside, and provides the selection driver 1701 and the signal driver 1702. The selection driver 1701 outputs a selection signal 1713 for selecting a line to which the image signal 1714 is applied in response to the selection signal 1711 from the control unit 1708 to the selection line. The signal driver 1702 applies an image signal 1714 corresponding to the image signal 1712 from the control unit 1708 to the signal line.

  The power supply unit 1707-1 includes a power source (hereinafter referred to as a selected power source) 1703 that determines a voltage at the time of selection, and a power source (hereinafter referred to as an unselected power source) 1704 that determines a voltage at the time of non-selection. Reference numeral 2 denotes a power source (hereinafter referred to as a “+ signal power source”) 1705 for determining a positive voltage of the signal driver and a power source (hereinafter referred to as a “− signal power source”) 1706 for determining a negative side voltage.

  Then, from the selection driver 1701 and the signal driver 1702, the controlled signal group is input to the thin film transistor (TFT) 1716 of the corresponding pixel arranged in a matrix on the display portion 1715 through the selection line group 1713 and the signal line group 1714. Is done. Then, the display of the pixel 1717 is controlled.

  Both the drivers 1701 and 1702 have a plurality of ON-OFF type analog switches, serial-to-parallel convert the serially input signal 1711 or 1712 with a shift register, and input two types of voltages to a plurality of An analog switch is used to output a plurality of output signals by switching according to shift register data.

  In the driving method described above, rectangular waves are used for the selection signal 1711 and the image signal 1712. That is, the selection signal 1711 and the image signal 1712 output from both drivers 1701 and 1702 use rectangular waves as shown in FIGS. In this example, the selection signal 1711 is selected when the voltage is negative, and a positive or negative power source is output as the pixel signal.

An organic thin film transistor (organic TFT) can be used as the TFT of the display portion described above. An example of the organic TFT is shown in FIG. FIG. 16 is a cross-sectional view of a pixel in an electrophoretic display device using organic TFTs. In the structure of the organic TFT shown in FIG. 16, a gate electrode 1601 is formed on a substrate 1606, a source electrode 1603 and a drain electrode 1602 are formed on the gate electrode 1601 with an insulating film 1605 interposed therebetween, and an organic semiconductor is formed thereon. 1607 is provided. A pixel is provided on the organic TFT as shown in FIG. The device shown in FIG. 16 uses an electrophoretic element as an image display element. As shown in this figure, a pixel electrode 1611 is provided on the organic TFT via an interlayer film 1609. The pixel electrode 1611 is connected to the drain of the organic TFT through the through hole 1608. An electrophoretic element 1612 is sealed between the pixel electrode 1611 and the common electrode 1610. The top of the pixel electrode 1611 is a pixel portion, and the display of the electrophoretic element is switched by the potential applied to the pixel electrode 1611 from the active matrix driving circuit.
JP-A-5-257123

  However, when an organic thin film transistor (organic TFT) as shown in FIG. 16 is used as the TFT of the display unit driven by the active matrix drive circuit shown in FIG. 17, the following problems occur.

  In the structure of the organic TFT shown in FIG. 16 described above, parasitic capacitance is generated in the overlap portion 1604 (the hatched portion in the drawing) of the gate electrode 1601 and the drain electrode 1602.

  If the selection signal 1711 of FIG. 17 is input as a rectangular wave there, the parasitic capacitance becomes a part of the gate-drain capacitance Cgd and Cgd = 0 cannot be set. When the polarity of the gate voltage is changed by the Cgd, the potential of the pixel is changed as indicated by reference numeral 703 in FIG. 7 through Cgd according to the ratio of the potential change amount and Cgd to the pixel capacitance Cep1717 shown in FIG. Will change. FIG. 7 shows a rectangular wave when the pixel signal 702 is negatively applied and a change in the pixel voltage 703 at that time. As shown in FIG. 7, the pixel potential is displaced to the + side through Cgd. Therefore, there arises a problem that the display is switched by affecting the pixel potential stored in the pixel by the image signal 1712 of FIG.

  Also, when the image signal 1712 shown in FIG. 17 is given by a rectangular wave, a sudden change in potential occurs between the source 1603 and the drain 1602 in FIG. 16 when switching to a signal having the opposite polarity to the potential charged in the pixel. This causes a problem that a large burden is applied to the TFT. This problem will be described with reference to FIG. FIG. 9 shows a rectangular wave when the pixel signal 902 is applied positively and the change in the pixel voltage 903 at that time. When the pixel signal 902 is applied positively, a surge as indicated by reference numeral 903 in FIG. 9 is generated, which places a burden on the organic TFT.

  On the other hand, even if some means for reducing the load on the organic TFT due to the parasitic capacitance or the rapid change in potential is included, for example, when a VGA (640 × 480 pixels) size matrix is used, the signal output is There are 1120 selection lines and signal lines in total, and 1120 are required for all output signals, which is not practical. That is, if any measure is taken in order to reduce the load on the organic TFT, circuit elements and the like increase by the number of selection lines and signal lines.

  The first object of the present invention is to eliminate the influence of the parasitic capacitance on the pixel potential without significantly increasing the number of circuits. A second object of the present invention is to reduce the load on the organic TFT due to a rapid change in potential.

  According to the present invention, in an active matrix driving circuit for active matrix driving a display panel configured by arranging a plurality of pixels in a matrix, the active matrix driving circuit selects a line to which an image voltage is applied according to a selection signal. A selection driver, a signal driver that applies an image voltage according to an image signal, a control unit that generates and controls a selection signal to be sent to the selection driver and an image signal to be sent to the signal driver according to a data signal supplied from the outside, and a selection A power source that determines a voltage at the time, a power source that determines a voltage at the time of non-selection, a power source that determines a voltage on the positive side of the signal driver, and a power source unit that determines a voltage on the negative side, and the selection driver and the signal driver A rising waveform of the power supply voltage between at least one of the power supply and the power supply unit And providing a processing means for processing.

  The processing means for processing the power supply voltage is composed of an RC integration circuit and a switch, and switches the switch to turn on / off the input power by a synchronization signal synchronized with the output of the selected driver.

  Further, the power source for determining the selection voltage can be turned off during the selection period, and the processing means for processing the power supply voltage can process the power supply voltage to the minimum voltage at which the transistor can be turned on during the selection period.

  Further, the power source for determining the voltage at the time of non-selection is turned off during the selection period, and the processing means for processing the power source voltage can be configured to process the power source voltage to the minimum voltage at which the transistor does not turn on.

  In the present invention, by controlling the power supplied to the driver, the signal of the output line handled by one driver can be processed together by the two power supply voltage processing means of + power supply and -power supply. The number can be greatly reduced.

  Further, by processing the power supply voltage to the minimum voltage that can turn on the transistor (TFT) during the selection period, the selection signal of the next selection line can be raised from the minimum voltage, and the pixel potential is increased with Cgd. Can be reduced.

  Further, the voltage of the non-selection signal can be lowered without turning on the transistor (TFT), the influence on the pixel potential can be suppressed, the display is not switched, and the burden on the transistor (TFT) is reduced. Can be suppressed.

  In addition, the power supply voltage is processed to the minimum voltage at which the transistor (TFT) does not turn on, and the rise time of the image signal is delayed to switch the driver output voltage to a signal having the opposite polarity to the potential charged in the pixel. An abrupt change in potential generated between the source and the drain can be reduced, and the burden on the transistor (TFT) can be reduced.

  Embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated in order to avoid duplication of description.

  In the electrophoretic display device having the above-described structure, the active matrix drive for driving so as to eliminate the influence on the pixel potential due to the parasitic capacitance of the organic TFT and to reduce the load on the organic TFT due to the rapid change of the potential. A circuit is provided.

  FIG. 1 is a block circuit diagram showing an active matrix driving circuit according to an embodiment of the present invention. As shown in FIG. 1, the active matrix driving circuit 1 includes a control unit 108, a selection driver 101, a signal driver 102, and power supply units 110-1 and 1101-2.

  The control unit 108 generates and controls the selection signal 112 and the image signal 113 according to the data signal 111 supplied from the outside, and supplies the selection signal 101 and the signal driver 102 to the selection driver 101 and the signal driver 102. In response to the selection signal 112 from the selection driver 101 and the control unit 108, a selection signal 114 for selecting a line to which the image signal 113 is applied is output to the selection line. The signal driver 102 applies an image signal 115 corresponding to the image signal 113 from the control unit 108 to the signal line.

  The power supply unit 110-1 includes a selection power supply 103 that determines a voltage at the time of selection, and a non-selection power supply 104 that determines a voltage at the time of non-selection. The power source 106 and the negative side voltage are determined.

  Then, the control signal group is input from the selection driver 101 and the signal driver 102 to the organic TFTs of the corresponding pixels arranged in a matrix on the display unit through the selection line group 114 and the image signal line group 115.

  In the present invention, power supply voltage processing means 105-1 and 105-2 are provided between the selected driver 101 and the selected power supply 103 and the non-selected power supply 104 of the power supply unit 110-1. The selected power supply output 116 passes through the power supply voltage processing means 105-1 as shown in FIG. The non-selected power supply output 118 passes through the power supply voltage processing means 105-2 and becomes the non-selected voltage 119. Then, the selection voltage 117 and the non-selection voltage 119 are input to the selection driver 101.

  Also, power voltage processing means 105-3 and 105-4 as shown in FIG. 2 are provided between the signal driver 102 and the + signal power source 105 and the − signal power source 106 of the power source unit 110-2. The + signal power output 120 passes through the power supply voltage processing means 105-3 and becomes the + signal voltage 121. The -signal power output 122 passes through the power supply voltage processing means 105-4 to become a -signal voltage 123. Then, the + signal voltage 121 and the − signal voltage 123 are input to the signal driver 102.

  The control unit 108 generates the synchronization signals 124-1 and 124-2 synchronized with the output of the selection line 114 and the signal line 115 which are output signals of the selection driver 101 and the signal driver 102, and the power supply voltage processing means 105-1. Give to 105-2 respectively.

  Next, the power supply voltage processing means used in the present invention will be described with reference to FIG. FIG. 2 is a circuit diagram showing an embodiment using an RC integration circuit as the power supply voltage processing means. As shown in FIG. 2, the power supply voltage processing means includes an RC integration circuit including a capacitor 201 and a resistor 202 and a switch 204. The switch 204 is switched by a synchronization signal 205 (124-1 and 124-2 in FIG. 1) synchronized with the output of the selection line 114 and the signal line 115 which are output signals of the selection driver 101 and the driver 102 shown in FIG. The The power supply voltage always input by the switch 204 is turned on / off, and when it is turned off, the potential stored in the capacitor 201 is discharged through the resistor 203.

  Next, the operation of the circuit shown in FIGS. 1 and 2 will be further described with reference to the example shown in FIG. In the example shown in FIG. 3, the + signal power output 120 in FIG. 1 is the applied voltage 301 that is turned off in the time section 304 after voltage application in the time section 303 and is input to the RC integration circuit in FIG. A waveform 302 of the voltage 121 is shown. By providing the RC integration circuit as the power supply voltage processing means in FIG. 2, the input voltage of the driver can be smoothed as a waveform 302 shown in FIG. Driver output can be controlled by a signal with a smoothed waveform. Further, the rising waveform can be adjusted by changing the values of the capacitor 201 and the resistor 202 in FIG. 2 and arbitrarily setting the time constant (product of the capacitance of the capacitor and the resistance value).

  Further, each signal will be described below.

  An embodiment of a waveform (hereinafter referred to as a selection waveform) that makes the selection voltage the minimum voltage at which the organic TFT can be turned on during the selection period will be described with reference to FIG. FIG. 4 shows the operation timing for creating the selection waveform 402.

  FIG. 4 shows a waveform obtained by applying the selected power supply voltage 116 of FIG. 1 in the time period 403 within the selection period t (405) and then turning off the applied voltage 401 through the voltage processing means 105-1 in the time period 404. It is. Even if the voltage is around 0 V, the TFT threshold is on the positive side, so the TFT does not turn off completely. However, in the case of the P channel, it is necessary to apply a bias voltage because a larger ON current can be obtained by applying a bias voltage to the negative side. For this reason, if the voltage is set to 0 V during the selection period, the change in potential at the time of non-selection can be reduced by the selection voltage, so that the influence on the pixel potential can be reduced by Cgd.

  Similarly, the non-selected power source may be turned off, and the potential difference may be further reduced by lowering the voltage. However, when the voltage is lowered to 0V, the organic TFT is turned on. Therefore, as shown in a waveform (hereinafter, non-selected waveform) 502 shown in FIG. 5, while the voltage stored in the capacitor of the non-selected voltage 119 is indicated by 504, the voltage does not exceed the threshold voltage even if it is discharged. It is better to set the time constant of the integration circuit to be put in the non-selected power source.

  A non-selected waveform 502 in FIG. 5 is obtained by applying the voltage 501 turned off in the time interval 504 after applying the non-selected power source 104 in FIG. 1 in the time interval 503 to the RC integrating circuit 105-2.

  FIG. 6 shows an output signal of the selection line 114 in FIG. 1 that can be switched by switching between the selection waveform 402 shown in FIG. 4 and the non-selection waveform 502 shown in FIG.

  Next, FIG. 7, FIG. 8, FIG. 9, and FIG. 10 show pixel potentials when a rectangular wave is inserted and when the waveform of FIG. 6 is input, respectively.

  As described above, FIG. 7 shows a change in the pixel voltage 703 when the image signal 702 is negatively applied when the conventional rectangular wave 701 is input to the TFT. When the selection signal 701 is inputted and the pixel voltage is selected, the pixel voltage becomes the same potential as the image signal when the image signal 702 is inputted. However, when the selection signal 701 is not selected, the TFT is not completely turned off. Therefore, the display is switched when it is pulled to the non-selection voltage according to the potential difference between the selection and non-selection and becomes a positive value. As shown in FIG. 8, when the selection signal waveform 801 of FIG. 6 which is the output of the present invention is inserted, the voltage at the time of selection finally becomes 0V, and the voltage at the time of non-selection also drops to the threshold value, so the potential difference Since the influence on the pixel voltage 803 is weakened and does not change to a positive value, the pixel potential is not pulled by the non-selection signal as the display is switched, and the influence on the display can be suppressed.

  FIG. 9 shows the change in the pixel voltage 903 when the image signal 902 is negatively applied when a conventional rectangular wave 901 is input to the TFT. When the selection signal 901 is input and the image signal 902 is input, the pixel potential becomes the same potential as the image signal 902. However, when the selection signal 901 is not selected, the pixel potential depends on the potential difference between selection and non-selection. Surge. At this time, when the selection signal waveform 1001 of FIG. 6 according to the present invention is inserted as shown in FIG. 10, the voltage at the time of selection finally becomes 0V, the voltage at the time of non-selection is lowered to the threshold value, and the potential difference can be reduced. Since the rise of the non-selection voltage is gentle due to the time constant, the surge occurring in the pixel voltage 1003 can be reduced.

  Next, an integration circuit inserted between the signal driver and the power source will be described.

  The + signal power source 106 and the − signal power source 107 in FIG. 1 are synchronized with the selected driver output 114, and the switch 204 in FIG. In addition, the burden on the TFT can be reduced by the sudden drain-source potential change that occurs when the potential and polarity stored in the pixel change.

  It is also possible to change the time constant between rising and falling. If the rise time resistance 202 (R1) is not equal to the fall time resistance 203 (R2), the time constant at the rise time and the fall time can be changed.

  For example, after applying a voltage between 1103 in the diagram of FIG. 11, there may be a case where the applied voltage 1101 that has been turned off between 1104 in the diagram remains in the OFF period as shown by the waveform 1102 that has passed through the RC integrating circuit shown in FIG. In such a case, a load is applied to the TFT when the pixel polarity is switched. Therefore, in the circuit diagram shown in FIG. 2, R1> R2 is set, the time constant at the time of falling is increased, and the charge is discharged quickly. When the polarity of the pixel is switched, the burden on the TFT can be reduced.

  A second embodiment of the present invention will be described.

  In the second embodiment, the RC integration circuit of FIG. 2 shown in the first embodiment is configured using an integration circuit using operational amplifiers 1204 and 1404 shown in FIGS.

  The integration circuit shown in FIG. 12 is an integration circuit that inputs the + signal voltage 121 of FIG. 1 to the signal driver 102 and is switched to a synchronization signal 1206 that rises in synchronization with the output of the selection driver 101. 1205 switches the + signal power source 1207 in FIG. 12 corresponding to the + signal power source 106 in FIG. 1 and the − signal power source 1208 in FIG. 1 corresponding to the − signal power source 108 to output an image voltage.

  FIG. 13 shows the waveform of this integration circuit. Since the output of the operational amplifier is inverted with respect to the input when the synchronization signal 1206 is input to FIG. 12, the voltage 120 of the signal power source 1208 is applied in the time interval 1303, and the ON-OFF-ON shown in FIG. The waveform corresponding to the + signal voltage 121 of FIG. 1 through the integrating circuit of FIG. 12 becomes 1302 after the waveform 1301 of applying the voltage 122 of the + signal power source 1208 in the time interval 1305 is turned off by the switch. Further, without providing an OFF period, a diode may be put in and saturated in parallel with the capacitor 1201 in FIG. 12, or saturation of the operational amplifier 1204 may be used.

  When outputting the minus signal voltage 123 in FIG. 1, the switch 1405 in FIG. 14 may be switched so that the input voltage is the reverse of that in FIG. FIG. 14 shows an integration circuit for inputting the minus signal voltage 123 of FIG. 12 is the same as the integration circuit of FIG. 12, but when the synchronization signal 1406 of FIG.

  By providing the integration circuit of FIG. 12 and FIG. 14, an output voltage having a slope of V (applied voltage value) × t (applied time) ÷ τ (time constant) can be obtained as the driver output.

  In this case as well, a waveform having an arbitrary slope can be created by arbitrarily changing the input voltage and the time constant (= input resistance × feedback capacitance).

  To change the time constant, switch the rising resistor 1202 and the falling resistor 1203 with the switch 1205 that is switched to the synchronization signal 1206 synchronized with the output of the selected driver, and switch between the rising resistor 1202 and the falling resistor 1203. By changing the size, the input resistance can be switched and the inclination can be changed. In this case, since the integrating circuit drifts, it is better to short-circuit both ends of the capacitor at 0V or the like and apply a reset.

  Similar to the embodiment using the RC integration circuit, in the integration circuit using the operational amplifiers 1204 and 1404 shown in FIGS. 12 and 14, the waveform can be controlled by switching the rising and falling slopes.

  Next explained is the third embodiment of the invention.

  Instead of the integration circuit shown in FIGS. 2 and 12, the DA converter circuit shown in FIG. 15 may be inserted into the power supply voltage processing means 105 shown in the first and second embodiments.

  The DA converter in FIG. 15 will be described. Driven by a DC power supply 1501, a waveform generated by a DC converter 1503 by an input signal of a control signal 1502 is output to a driver 1505 by an input of a synchronization signal 1504.

  Since the DA converter can arbitrarily output a waveform by a control signal, the waveform as shown in the first embodiment can be created.

  In the embodiment described above, the power supply voltage processing means is provided between the selection driver and the signal driver and the power supply unit. However, if the withstand voltage of the TFT is sufficient, the power supply voltage processing means between the signal driver and the signal driver. May be omitted.

  Further, although an electrophoretic element is exemplified as an image display element, the present invention can also be applied to other display elements, for example, an image display element using a liquid crystal display element.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiment but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 is a block diagram showing an active matrix driving circuit provided with an integrating circuit according to an embodiment of the present invention. FIG. It is a circuit diagram which shows the RC integration circuit used for the power supply voltage processing means as 1st Embodiment of this invention. It is a voltage waveform diagram through the RC integration circuit diagram of this invention. It is a selection voltage waveform diagram through the RC integration circuit diagram of this invention. It is a non-selection voltage waveform diagram through the RC integration circuit diagram of this invention. It is a selection signal waveform diagram by this invention. It is a wave form diagram which shows the influence (at the time of signal-application) of the selection line input by the conventional rectangular wave. It is a wave form diagram which shows (at the time of signal-application) by this invention. It is a wave form diagram which shows the influence (at the time of signal + application) of the selection line input by the conventional rectangular wave. It is a wave form diagram which shows the effect (at the time of signal + application) by this invention. It is a signal voltage waveform diagram through the RC integration circuit diagram of this invention. It is the integration circuit figure by the side of + signal voltage used for the power supply voltage processing means as 2nd Embodiment of this invention. It is a voltage waveform diagram through an integration circuit diagram. FIG. 6 is an integration circuit diagram on the −signal voltage side used for power supply voltage processing means as a second embodiment of the present invention. DA converter circuit used for power supply voltage processing means as the third embodiment of the present invention It is a schematic structure figure of an image display element using organic TFT. It is a block diagram which shows the active matrix drive circuit of a prior art example.

Explanation of symbols

  108 control unit, 101 selection driver, 102 signal driver, 110-1, 1101-2 power supply unit, 105-1, 105-2 power supply voltage processing means.

Claims (4)

  In an active matrix driving circuit for active matrix driving a display panel configured by arranging a plurality of pixels in a matrix, the active matrix driving circuit selects a line for applying an image voltage in accordance with a selection signal; A signal driver that applies an image voltage according to an image signal, a selection signal that is sent to a selection driver according to a data signal supplied from the outside, a control unit that generates and controls an image signal that is sent to the signal driver, and a voltage at the time of selection A power source for determining, a power source for determining a voltage at the time of non-selection, a power source for determining a positive side voltage of the signal driver and a power source for determining a negative side voltage, and at least one of the selection driver and the signal driver Processing to smooth the rising waveform of the power supply voltage between the power supply unit Active matrix driving apparatus characterized by providing means.   The processing means for processing the power supply voltage includes an RC integration circuit and a switch, and the switch is switched by a synchronization signal synchronized with the output of the selected driver to turn on / off the input power. 2. The active matrix drive device according to 1.   The power source for determining the selection voltage is turned off during the selection period, and the processing means for processing the power supply voltage processes the power supply voltage to the minimum voltage at which the transistor can be turned on during the selection period. The active matrix driving device according to claim 1 or 2.   The power source that determines the voltage at the time of non-selection is turned off during a selection period, and the processing means for processing the power supply voltage processes the power supply voltage to the minimum voltage at which the transistor does not turn on. The active matrix drive device according to any one of claims 1 to 3.

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