JP5219392B2 - Display device and display device drive circuit - Google Patents

Description

  The present invention relates to a display device and a drive circuit using a capacitive light emitting element such as an organic EL (electroluminescence) element as a display pixel.

  With the widespread use of mobile phones and portable information terminals (PDAs), there is an increasing demand for display panels that have a high-definition image display function and that can be thin and achieve low power consumption. Liquid crystal display panels have been adopted in many products as display panels that satisfy these requirements.

  On the other hand, in recent years, an organic EL element that takes advantage of the characteristic of being a self-luminous element has been put into practical use, and has attracted attention as a next-generation display panel that replaces a conventional liquid crystal display panel. This is also due to the fact that the use of an organic compound that can be expected to have good light-emitting characteristics for the light-emitting layer of the device has led to higher efficiency and longer life that can withstand practical use.

  The organic EL element described above is basically configured by sequentially laminating a transparent electrode made of ITO, a light emitting functional layer, and a metal electrode (cathode) made of aluminum alloy or the like on a transparent substrate such as glass. Yes. In general, the transparent electrode is used as an anode and the metal electrode is used as a cathode to apply a driving voltage.

  The light emitting functional layer is a single light emitting layer made of an organic compound, or a two-layer structure composed of an organic hole transport layer and a light emitting layer, or a three layer structure consisting of an organic hole transport layer, a light emitting layer and an organic electron transport layer, There may be a multilayer structure in which a hole injection layer is inserted between the transparent electrode and the hole transport layer, and an electron injection layer is inserted between the metal electrode and the electron transport layer. Then, the light generated in the light emitting functional layer is led out through the transparent electrode and the transparent substrate.

  The above-described organic EL element can be replaced with a configuration of a light emitting element having an electrically diode characteristic and a parasitic capacitance component coupled in parallel to the light emitting element. The organic EL element is a capacitive light emitting element. I can say that. In the organic EL element, when a light emission driving voltage is applied, first, a charge corresponding to the electric capacity of the element flows into the electrode as a displacement current and is accumulated. Subsequently, when a certain voltage specific to the element (light emission threshold voltage = Vth) is exceeded, a current starts to flow from one electrode (the anode side of the diode component) toward the light emitting functional layer, and light is emitted with an intensity proportional to the current. Then you can think.

  On the other hand, the current / luminance characteristics of organic EL elements are stable against changes in temperature, while the voltage / luminance characteristics are highly dependent on temperature, and the organic EL elements are subject to overcurrent. In general, constant current driving is performed due to the fact that the deterioration is severe and the light emission life is shortened. As a display panel using such an organic EL element, a passive drive display panel in which elements are arranged in a matrix has already been put into practical use.

  FIG. 1 shows an example of a conventional passive matrix display panel and its driving circuit, which shows a form of cathode line scanning / anode line drive. That is, m data lines (hereinafter also referred to as anode lines) A1 to Am are arranged in the vertical direction, and n scanning lines (hereinafter also referred to as cathode lines) K1 to Kn are in the horizontal direction. The display panel 1 is configured by arranging organic EL elements E11 to Emn as display elements arranged in parallel and arranged in parallel with a symbol mark of a diode and a capacitor at each crossed portion (total m × n locations). doing.

  Each EL element E11 to Emn constituting the pixel has one end (in the equivalent diode of the EL element) corresponding to each intersection position of the anode lines A1 to Am along the vertical direction and the cathode lines K1 to Kn along the horizontal direction. The anode terminal is connected to the anode line, and the other end (the cathode terminal in the equivalent diode of the EL element) is connected to the cathode line. Further, each anode line A1 to Am is connected to an anode line driving circuit 2 as a data driver, and each cathode line K1 to Kn is connected to and driven by a cathode line scanning circuit 3 as a scanning driver.

  The anode line driving circuit 2 includes constant current sources I1 to Im and drive switches Sa1 to Sam that operate using a supply voltage from a driving voltage source VH, and the drive switches Sa1 to Sam include the constant current sources I1 to Im. By being connected to the current sources I1 to Im, the current from the constant current sources I1 to Im acts so as to be supplied to the individual EL elements E11 to Emn arranged corresponding to the cathode lines. The drive switches Sa1 to Sam are configured so that the anode line can be connected to the ground side as a reference potential point of the circuit when the currents from the constant current sources I1 to Im are not supplied to the individual EL elements. ing.

  On the other hand, the cathode line scanning circuit 3 that functions as a scanning driver is provided with scanning switches Sk1 to Kn corresponding to the cathode lines K1 to Kn, and a reverse bias voltage from a reverse bias voltage source VM that functions as a non-scanning selection potential. Either the VM or the ground potential GND as a reference potential point that functions as a scanning selection potential can be supplied to the corresponding cathode line.

  The anode line driving circuit 2 and the cathode line scanning circuit 3 are each supplied with a control signal from a light emission control circuit (not shown) including a CPU via a control bus, and based on a video signal to be displayed, The scanning switches Sk1 to Skn and the drive switches Sa1 to Sam are switched.

  Thus, the constant current sources I1 to Im are connected to the desired anode line while setting the cathode line to the ground potential GND at a predetermined cycle based on the video signal, and the EL elements E11 to Emn selectively emit light. Is done. Therefore, it is as if images based on the video signal are continuously displayed on the display panel 1.

  In the state shown in FIG. 1, the first cathode line K1 is set to the ground potential GND to be in the scanning state. At this time, each of the cathode lines K2 to Kn in the non-scanning state is supplied with the reverse bias voltage source VM. The reverse bias voltage VM is applied. Here, when the forward voltage of the EL element in the scanning lighting state is Vf, each potential is set such that [(forward voltage Vf) − (reverse bias voltage VM)] <(light emission threshold voltage Vth). Therefore, each EL element connected to the intersection of the driven anode line and the cathode line not selected for scanning acts to prevent crosstalk light emission.

  By the way, each organic EL element arranged in the display panel 1 has a parasitic capacitance individually as described above, and this is arranged in a matrix at the intersection of the anode line and the cathode line. Taking a case where several tens of EL elements are connected to one anode line as an example, a combined capacity of several hundred times or more of each parasitic capacity as viewed from the anode line is connected to the anode line as a load capacity. It will be. This combined capacity increases significantly as the size of the matrix increases.

  Therefore, at the beginning of the lighting period of the EL element for each scan, the current from the constant current sources I1 to Im via the anode line is consumed to charge the combined load capacitance, and the EL element emits light. There is a time delay in charging the load capacity before the threshold voltage (Vth) is sufficiently exceeded. Therefore, there arises a problem that the rise of light emission of the EL element is delayed (slows down). In particular, when the constant current sources I1 to Im are used as the EL element drive sources as described above, the constant current source is a high-impedance output circuit in terms of operation principle, and therefore the current is limited and the EL element The delay of light emission rises remarkably.

  This reduces the lighting time rate of the EL element, and thus has a problem of reducing the substantial light emission luminance of the EL element. Therefore, in order to eliminate the delay in the rise of light emission of the EL element due to the parasitic capacitance described above, a pre-charge for charging the parasitic capacitance by applying a constant voltage from the anode to the EL element to be lit. The operation and the reset operation for charging the parasitic capacitance of the EL element to be lit using the reverse bias voltage VM are performed.

  FIG. 2 schematically shows the state of current flowing through each element, focusing on the anode line A1, in the lighting driving operation of the EL element including the reset operation described above. That is, FIG. 2 shows an EL element connected to the second cathode line (second scanning line) K2 from the lighting state of the EL element E11 connected to the first cathode line (first scanning line) K1 through the reset operation. The state where E12 is lit is shown.

  As shown in FIG. 2A, when the EL element E11 is lit, the cathode of the EL element E11 is set to the ground potential GND via the first scanning line K1, and the EL element is supplied from the constant current source I1. A drive current is supplied to E11. At this time, the reverse bias voltage VM is applied to the other EL elements (indicated by a capacitor symbol mark) connected to the anode line A1.

  In the next scan, the EL element E12 is turned on. Before the EL element E12 is turned on, the anode line A1 is connected to the ground potential GND via the drive switch Sa1 as shown in FIG. All the cathode lines are also connected to the ground potential GND through SK1 to SKn. As a result, a reset operation is performed to discharge all charges accumulated in the parasitic capacitance of each EL element.

  Next, in order to turn on the EL element E12, the second scanning line K2 is brought into a scanning state. That is, the second scanning line K2 is connected to the ground potential GND, and the reverse bias voltage VM is applied to the other scanning lines. At this time, the drive switch Sa1 is switched to the constant current source I1 side.

  Since the charge of the parasitic capacitance in each element is discharged during the reset operation described above, as shown in (c) at this moment, the parasitic capacitance of the elements other than the element E12 to be lighted next is indicated by an arrow. In the reverse direction, charging is performed in the reverse direction by the reverse bias voltage VM.

  The charging current for these flows into the EL element E12 to be lighted next through the anode line A1, and instantly charges the parasitic capacitance of the EL element E12. At this time, the constant current source I1 connected to the anode line A1 is basically a high impedance circuit as described above, and does not affect the movement of the charging current. Thereafter, the EL element E12 is turned on as shown in (d) by the drive current from the constant current source I1 flowing through the anode line A1.

  FIG. 3 is a timing chart illustrating the lighting driving operation of the EL element including the reset period described above in one scanning period. FIG. 3A shows a scanning synchronization signal, and a reset period and a lighting period (constant current driving period = CC) are set in synchronization with the scanning synchronization signal.

  3B and 3C show potentials applied to the lighting line and the non-lighting line in the anode line connected to the anode line driving circuit 2 in each period. 2D and 2E show potentials applied to the scanning line and the non-scanning line in the cathode line connected to the cathode line scanning circuit 3 in each period.

  In the reset period shown in FIG. 3, the drive switches Sa1 to Sam included in the anode line driving circuit 2 are used as anode lines (lighting lines) corresponding to the EL elements to be turned on, and EL elements not turned on. The corresponding anode line (non-lighting line) is set to the ground potential GND as shown in FIGS. 3B and 3C.

  On the other hand, the cathode line scanning circuit 3 in the reset period displays the cathode lines (scanning target lines) to be scanned and the cathode lines (non-scanning target lines) to be scanned by scanning switches Sk1 to Skn provided therein. 2 (D) and (E) are set to the ground potential GND, respectively.

  As a result, the anodes and cathodes of all EL elements arranged in the display panel 1 are set to the ground potential GND, and the charges accumulated in the parasitic capacitances are reset to zero (GND-GND reset). That is, the state shown in FIG.

  In the subsequent constant current drive period, which is the EL element lighting period, the anode lines (lighting lines) corresponding to the EL elements to be lit by the drive switches Sa1 to Sam are as shown in FIG. A constant current is supplied from the constant current sources I1 to Im. Further, the anode line (non-lighting line) corresponding to the EL element which is not lighted is set to the ground potential GND as shown in FIG.

  On the other hand, the cathode line scanning circuit 3 in the lighting period (constant current driving period) shows the cathode lines (scanning target lines) to be scanned by the scanning switches Sk1 to Kn provided therein as shown in FIG. Is set to the ground potential GND which is the scanning selection potential, and the reverse bias voltage VM which is the non-scanning selection potential is applied to the non-scanning target cathode line (non-scanning target line) as shown in FIG. Control to be applied.

  Thus, immediately after the transition to the lighting period (constant current driving period) of the organic EL element, the EL element to be lit is scanned from the reverse bias voltage source VM as described based on FIG. A current flows transiently through the EL element that is not turned on, and the parasitic capacitance of the EL element to be lit is rapidly charged, so that the light emission of the EL element to be lit can be quickly raised.

  That is, T1 indicated by a chain line in FIG. 3B shows the effect of charging the parasitic capacitance by the reset operation, and the solid line T2 indicates the forward voltage of the EL element when the reset operation is not performed. An example of the rise is shown.

As described above, the passive drive type display device that rapidly charges the EL element that is to be driven to be lit after the reset operation by using the non-scanning selection potential (reverse bias voltage) This is disclosed in Japanese Patent Application Laid-Open No. 2004-133830, which has been filed by the applicant.
Japanese Patent No. 3507239

  By the way, in the constant current driving period shown in FIG. 3 in which the organic EL element is turned on, the EL element to be turned on is connected to the scanning selection potential, for example, the ground potential GND via the cathode line. In the element connected to the anode line close to the scanning circuit and the element connected to the anode line far from the cathode line scanning circuit, the cathode potential is offset by the wiring resistance of the cathode line.

  That is, the cathode potential of the element connected to the anode line far from the cathode line scanning circuit rises with respect to the cathode potential of the element connected to the anode line near the cathode line scanning circuit. Therefore, as described above, the luminance of the element connected to the anode line close to the cathode line scanning circuit is darker than the luminance of the element connected to the anode line far from the cathode line scanning circuit. become.

The luminance gradient in this case occurs because the constant current characteristics of the constant current source connected to the anode line cannot be ensured due to an increase in the cathode potential of the element, and the above-described luminance gradient occurs. In order to solve this problem, Patent Document 2 discloses using a voltage obtained by resistance-dividing the drive voltage of each constant current source connected to the anode line side.
JP 2006-163293 A

  By the way, the invention disclosed in Patent Document 2 pays attention to the luminance gradient generated during the constant current driving period in which the EL element is in the lighting state. On the other hand, the present invention will be described in detail later. As described above, paying attention to the luminance gradient generated in the charge operation to the parasitic capacitance of the element using the reverse bias voltage VM from the cathode and the precharge operation to charge the parasitic capacitance of the element from the anode in association with the reset operation described above. It was made.

  The above-described reset operation is performed by using the reverse bias voltage VM and the parasitic capacitance of the EL element to be turned on via each cathode line that is in the non-scanning state and the EL element that is connected to each cathode line that is not to be scanned. Since the capacitor is charged with charge, a difference occurs in the charge amount of the EL element to be lit due to the influence of the wiring resistance of the cathode line.

  That is, in the charge charging operation with respect to the EL element connected to the anode line A1, for example, close to the cathode line scanning circuit 3 shown in FIG. 1, the influence of the wiring resistance of the cathode line is small, and therefore a sufficient charge charging function can be achieved. it can. On the other hand, in the charge charging operation for an EL element connected to, for example, the anode line Am far from the cathode line scanning circuit 3, the charge charge amount becomes insufficient due to the influence of the wiring resistance of the cathode line.

  Therefore, the brightness of the element connected to the anode line far from the cathode line scanning circuit emits darker than the brightness of the element connected to the anode line close to the cathode line scanning circuit, thereby generating a so-called brightness gradient. It will be.

  On the other hand, in the precharge operation in which a constant voltage is applied from the anode to the EL element to be lit as described above, there is a difference in the precharge amount for each anode due to the influence of the wiring resistance of the cathode. Inclination occurs. That is, for example, when the EL element connected to the anode line A1 close to the cathode line scanning circuit 3 shown in FIG. 1 is charged from the anode with a constant voltage, the influence of the wiring resistance of the cathode line is small, and therefore sufficient. It is possible to perform a charging operation of various charges. On the other hand, when the charging operation by a constant voltage is performed from the anode to the EL element connected to the anode line Am, for example, far from the cathode line scanning circuit 3, the wiring resistance of the cathode line enters in series and the influence of this wiring resistance is affected. Therefore, the charge amount of the charge is insufficient.

  As a result, the luminance of the element connected to the anode line far from the cathode line scanning circuit emits darker than the luminance of the element connected to the anode line near the cathode line scanning circuit, and similarly the luminance gradient occurs. It will be.

  The present invention has been made paying attention to the problem of the above-described luminance gradient, and charges the parasitic capacitance of the EL element to be lit using the reverse bias voltage VM from the cathode accompanied by the reset operation described above. Occurrence of the luminance gradient in each of the operation to be performed and the operation to rapidly charge the parasitic capacitance by applying a constant voltage from the anode side to the EL element to be lit It is an object of the present invention to provide a display device and a driving circuit that can effectively suppress the above.

The display device drive circuit according to the present invention, which has been made to solve the above-described problems, includes a plurality of anode outputs for supplying drive power to the anode input terminals of the display device according to claim 1. A plurality of constant current sources each connected to the anode output terminal and supplying a constant current to the anode output terminal; and a plurality of constant current sources connected to the plurality of anode output terminals. A constant voltage supply means for supplying a voltage; and a cathode line scanning circuit which is connected to each cathode line of the display device and selectively applies a scanning signal to each cathode line, and each anode output is provided by the constant voltage supply means. constant voltage value supplied to the terminal are set to be different for each anode output terminals, the constant voltage supply means includes a resistive element to generate different constant voltage value for each anode output terminals, wherein A plurality of analog switches for selectively supplying different constant voltage values generated by the anti-elements to the anode output terminal are provided, and a reset operation for resetting both-end voltages of the display elements arranged in the display device At the timing, the constant voltages having different values are output to the anode output terminals via the analog switches, and the different constant voltage values applied to the anode output terminals control the brightness of the display image in the display device. It is characterized by being variable according to the dimmer information to be performed.

Further, in the display device according to the present invention made to solve the above-described problems, a capacitive display element is arranged at each intersection of a plurality of anode lines and a plurality of cathode lines as described in claim 4 . A display panel; an anode line driving circuit for selectively supplying a driving current and a constant voltage to each display element via each anode line; and a scanning signal selectively connected to each cathode line and connected to each cathode line. A constant voltage value from constant voltage supply means for supplying constant voltage to the plurality of anode lines is set to be different from each other, and the constant voltage supply means includes: A resistance element that generates a different constant voltage value for each anode line of the display panel, and a plurality of analog switches that selectively supply different constant voltage values generated by the resistance element to the anode line of the display panel. The constant voltage having a different value is output to the anode line of the display panel through the analog switch at the timing of the reset operation for resetting the voltages across the display elements arranged in the display panel; and Each of the different constant voltage values applied to each anode line of the display panel is variable according to dimmer information for controlling the brightness of a display image on the display panel.

  Hereinafter, a display device and a drive circuit according to the present invention will be described based on embodiments shown in the drawings. FIG. 4 shows the first embodiment, which is for a display device in which an operation of applying a precharge voltage to each display element to be scanned is performed every scanning period. It can be suitably employed. In the drawings described below, parts corresponding to the parts shown in FIG. 1 already described are denoted by the same reference numerals. Therefore, the detailed description is abbreviate | omitted.

  Reference numeral 2 shown in FIG. 4 indicates an anode line driving circuit as a driving circuit in this embodiment. The anode line driving circuit 2 includes a plurality of elements for supplying driving power to the display panel 1 as a display device. Anode output terminals t1 to tm are provided. The terminals t1 to tm also function as anode input terminals of the display panel 1. The anode lines A1 to Am arranged on the display panel 1 are connected to the terminals t1 to tm, and the anode line driving circuit 2 is connected. Is supplied to the EL elements E11 to Emn as the display elements.

  The anode line driving circuit 2 includes constant current sources I1 to Im that operate using a supply voltage from a driving voltage source VAH. The constant currents from these constant current sources I1 to Im are supplied to the terminals. It is configured to be supplied to each anode line A1 to Am of the display panel 1 via t1 to tm. The anode line driving circuit 2 including the constant current sources I1 to Im is composed of a semiconductor integrated circuit such as a semiconductor chip, and receives the driving voltage source VAH at power supply terminals arranged on both sides of the chip. Thus, the voltage can be made constant (stabilized). Note that the anode line driving circuit and the cathode line scanning circuit may be composed of TFTs formed on a substrate on which a display element is formed.

  On the other hand, the anode line drive circuit 2 includes a first group of analog switches Q1a to Qma and a second group of analog switches Q1ba to Qmb that perform the same functions as the drive switches described with reference to FIG. Each is provided corresponding to Im.

  The second group of analog switches Q1b to Qmb are composed of n-type MOSFETs, and their drains are connected to the current output terminals of the constant current sources I1 to Im, that is, the anode output terminals t1 to tm. Has been. Each source is connected to the ground potential GND. The potential to which the sources are connected is not limited to the ground potential GND, but may be a voltage value far lower than the voltage value of the voltage source VAH that drives the constant current sources I1 to Im.

  As a result, when the analog switches Q1b to Qmb are turned on, the EL elements arranged on the display panel 1 are turned off. The ground potential GND is also configured so that the voltage can be stabilized (stabilized) by receiving it at the power supply terminals arranged on both sides of the chip.

  The analog switches Q1a to Qma of the first group are constituted by p-type MOSFETs, and their drains are connected to the anode output terminals t1 to tm. Also, constant voltages having different voltage values are supplied to the sources of the analog switches Q1a to Qma.

  That is, the respective divided voltages of the resistance elements R1 to Rm connected in series to the precharge voltage source VAM are applied to the sources of the analog switches Q1a to Qma. When Q1a to Qma are turned on, the constant voltage values output from the anode output terminals t1 to tm are changed stepwise.

  That is, the anode output terminals t1 to tm are arranged in a line corresponding to the anode input terminals of the display panel 1, and are output from the anode output terminals according to the arrangement order of the anode output terminals t1 to tm. The constant voltage value is set to change stepwise.

  Thereby, the said constant voltage value supplied to the anode lines A1-Am in the display panel 1 is according to the line length of the said cathode line from the cathode line scanning circuit 3 to the intersection of each anode line via each cathode line K1-Kn. Is set. That is, the constant voltage value applied to the anode line A1 closest to the cathode line scanning circuit 3 is set to be the lowest, and the constant voltage value applied to the anode line Am farthest from the cathode line scanning circuit 3 is set to be the highest.

  The precharge voltage source VAM constitutes a variable voltage source, which is configured such that its voltage value is variable according to dimmer information for controlling the brightness of a display image on the display panel 1. In this case, when the display image is set to be displayed brightly, the output voltage value of the precharge voltage source VAM is increased, and when the display image is set to be displayed darkly, the precharge voltage source VAM is displayed. The output voltage value of the charge voltage source VAM is set to be low.

  Therefore, the value of the constant voltage supplied to each of the anode lines A1 to Am in the display panel 1 is also varied according to the dimmer information. In the embodiment shown in FIG. 4, the precharge voltage source VAM, the resistance elements R1 to Rm, and the first group of analog switches Q1a to Qma constitute constant voltage supply means.

  FIG. 5 is a timing chart for explaining in particular a precharge operation performed by the circuit configuration shown in FIG. 5A to 5E respectively correspond to (A) to (E) shown in FIG. 3 already described.

  In the reset period shown in FIG. 5, the output from the precharge voltage source VAM is applied to the lighting line shown in (B). In FIG. 5, the voltage value applied at this time is indicated as VAM for convenience, but this is obtained by dividing the output voltage from the precharge voltage source VAM by the series resistors R1 to Rm. The ground potential GND is applied to the non-lighting line shown in (C).

  In this case, among the first group of analog switches Q1a to Qma shown in FIG. 4, the analog switch corresponding to the lighting line is turned on. Further, among the second group of analog switches Q1b to Qmb shown in FIG. 4, the analog switches corresponding to the non-lighting lines are turned on.

  On the other hand, in this reset period, as shown in FIGS. 5D and 5E, the reverse bias voltage VM is applied to the scanning target line and the non-scanning target line. That is, all the scanning switches Sk1 to Skn in the cathode ray scanning circuit 3 are connected to the reverse bias voltage VM side. Therefore, the voltage difference between the VAM and VM is applied across the EL element to be lit.

  In the precharge period following the reset period, as shown in FIGS. 5B and 5C, the voltage applied to the lighting line does not change with VAM, and the potential with respect to the non-lighting line is also changed to the ground potential GND. . That is, the first group of analog switches Q1a to Qma and the second group of analog switches Q1b to Qmb shown in FIG. 4 maintain the same state as the reset period.

  On the other hand, in the precharge period, the scanning target line is set to the ground potential GND as shown in FIG. 5D, and the potential of the non-scanning target line does not change as shown in (E). That is, in the precharge period, only the scanning switch corresponding to the scanning target line selects the ground potential GND. For this reason, a precharge voltage VAM is applied in the forward direction to the EL element to be lit next connected to the lighting line to be scanned, and the parasitic capacitance is rapidly charged (precharged). The

  At this time, the cathode potential of the element connected to the anode line far from the cathode line scanning circuit rises with respect to the cathode potential of the element connected to the anode line close to the cathode line scanning circuit 3 due to the wiring resistance of the cathode line. The constant voltage value applied to the element connected to the anode line far from the circuit is set to a higher voltage by the voltage dividing action of the resistance elements R1 to Rm. As a result, the amount of charge accumulated with respect to the parasitic capacitance of each element during the precharge period becomes substantially equal.

  After the precharge period has elapsed, among the first group of analog switches Q1a to Qma, the analog switch corresponding to the lighting line is turned off, so that the EL elements to be lit are supplied from the constant current circuits I1 to Im. A constant current is supplied, and lighting of the precharged EL element continues in the constant current driving period.

  Then, after the constant current drive period has elapsed, all of the second group of analog switches Q1b to Qmb are turned on, whereby all the EL elements arranged on the display panel 1 are turned off. The Q1b to Qmb may be in an open (high impedance) state.

  According to the configuration shown in FIG. 4, the cathode potential of the element connected to the anode line far from the cathode line scanning circuit is smaller than the cathode potential of the element connected to the anode line close to the cathode line scanning circuit 3 due to the wiring resistance of the cathode line. The constant voltage value applied during the precharge period for the element connected to the anode line far from the cathode line scanning circuit 3 is high, and during the precharge period for the element connected to the anode line close to the cathode line scanning circuit 3 Since the applied constant voltage value is set low, the charge accumulation amount with respect to the parasitic capacitance of each element during the precharge period becomes equal.

  Therefore, it is possible to effectively suppress the occurrence of the luminance gradient due to the difference in the amount of charge charged with respect to the parasitic capacitance of each element in the precharge period due to the influence of the wiring resistance. Further, according to the configuration shown in FIG. 4, since the output voltage value of the precharge voltage source VAM is made variable according to the dimmer information as described above, an optimum voltage value is set in accordance with the dimmer setting change. The brightness gradient can be effectively suppressed even when the dimmer setting is changed.

  Next, FIG. 6 shows a second embodiment of the display device and the drive circuit according to the present invention. This relates to a display device in which an operation of applying a precharge voltage to a display element to be scanned is executed as in the example shown in FIG. 4, and particularly for a display device having a large number of anode lines. It can be suitably employed.

  The basic configuration shown in FIG. 6 is the same as the configuration shown in FIG. 4 already described, and the reference numerals of the respective parts are omitted as appropriate. In the example shown in FIG. 6, in order to reduce the influence of the wiring resistance of the cathode line, the cathode line scanning circuit is arranged at both ends of each cathode line. That is, the cathode ray scanning circuit is indicated by reference numerals 3A and 3B, and both are configured to execute a scanning operation in synchronization with each other.

  In addition to this, the output from the precharge voltage source VAM constituting the constant voltage supply means is supplied at the central portion of the anode line driving circuit 2, and each of the voltage dividing resistors connected in series from the central portion to the left and right respectively. A partial pressure output is obtained from the connecting portion. Therefore, according to the configuration shown in FIG. 6, as the precharge voltage value applied to the anode line arranged in the central portion of the display panel 1 is set higher and approaches the left and right cathode line scanning circuits 3A and 3B, The precharge voltage value applied to the anode line is set so as to decrease sequentially.

  As shown in FIG. 6, according to the configuration in which the cathode scanning circuits 3A and 3B are arranged at both ends of each cathode line, the cathode potential of the EL element during the precharge period due to the wiring resistance of the cathode line is near the center of the panel 1 However, as it approaches the left and right cathode-ray scanning circuits 3A and 3B, the precharge voltage value applied to the anode line arranged at the center of the display panel 1 is set high, as described above. Since the precharge voltage value applied to the anode line is set to be sequentially lower as the cathode line scanning circuits 3A and 3B become closer, the potential difference between both ends of each element becomes substantially equal during the precharge period. There is no difference in the amount of charge to be charged.

  According to the configuration shown in FIG. 6, it is possible to effectively suppress the occurrence of the luminance gradient due to the wiring resistance of the cathode line. Further, the output voltage value of the precharge voltage source VAM constituting the constant voltage supply means is configured to be variable according to the dimmer information as in the example shown in FIG. An optimum voltage value can be set, and the luminance gradient can be effectively suppressed even when the dimmer setting is changed.

  FIG. 7 shows a third embodiment of the display device and the drive circuit according to the present invention, in which a reset operation for resetting the voltages across the EL elements arranged in the display panel is performed. The present invention can be suitably used for a display device that charges a parasitic capacitance of an EL element to be lit using a reverse bias voltage VM.

  Reference numeral 2 shown in FIG. 7 indicates an anode line driving circuit as a driving circuit in this embodiment. The anode line driving circuit 2 includes a plurality of elements for supplying driving power to a display panel 1 as a display device. Anode output terminals t1 to tm are provided. The terminals t1 to tm also function as anode input terminals of the display panel 1. The anode lines A1 to Am arranged on the display panel 1 are connected to the terminals t1 to tm, and the anode line driving circuit 2 is connected. Is supplied to the EL elements E11 to Emn as the display elements.

  The anode line driving circuit 2 includes constant current sources I1 to Im that operate using a supply voltage from a driving voltage source VAH. The constant currents from these constant current sources I1 to Im are supplied to the terminals. It is configured to be supplied to each anode line A1 to Am of the display panel 1 via t1 to tm. The anode line driving circuit 2 including the constant current sources I1 to Im is constituted by a semiconductor integrated circuit such as a semiconductor chip, and receives the driving voltage source VAH at power supply terminals arranged on both sides of the chip. Thus, the voltage can be made constant (stabilized).

  On the other hand, the anode line driving circuit 2 includes analog switches Q1 to Qm corresponding to the constant current sources I1 to Im, respectively. These analog switches Q1 to Qm are composed of n-type MOSFETs, and their drains are connected to the current output terminals of the constant current sources I1 to Im, that is, the anode output terminals t1 to tm. . Further, constant voltages having different voltage values are supplied to the sources of the analog switches Q1 to Qm.

  That is, the respective divided voltages of the resistance elements R1 to Rm connected in series to the reset voltage source VAL are applied to the sources of the analog switches Q1 to Qm, whereby the analog switch Q1. When .about.Qm is turned on, the constant voltage value output from the anode output terminals t1 to tm is set to change stepwise.

  That is, the anode output terminals t1 to tm are arranged in a line corresponding to the anode input terminals of the display panel 1, and are output from the anode output terminals according to the arrangement order of the anode output terminals t1 to tm. The constant voltage value is set to change stepwise.

  Thereby, the said constant voltage value supplied to the anode lines A1-Am in the display panel 1 is according to the line length of the said cathode line from the cathode line scanning circuit 3 to the intersection of each anode line via each cathode line K1-Kn. Is set. That is, the constant voltage value applied to the anode line A1 closest to the cathode line scanning circuit 3 is set to be the lowest, and the constant voltage value applied to the anode line Am farthest from the cathode line scanning circuit 3 is set to be the highest.

  The reset voltage source VAL constitutes a variable voltage source, and the voltage value thereof is varied according to dimmer information for controlling the brightness of the display image on the display panel 1. In this case, when the display image is set to be displayed brightly, the reset voltage source VAL is set so that the output voltage value is increased, and when the display image is set to be displayed darkly, the reset voltage is set. The output voltage value of the source VAL is set to be low.

  Therefore, the value of the constant voltage supplied to each of the anode lines A1 to Am in the display panel 1 is also varied according to the dimmer information. In the embodiment shown in FIG. 7, the reset voltage source VAL, the resistance elements R1 to Rm, and the analog switches Q1 to Qm constitute constant voltage supply means.

  FIG. 8 is a timing chart for explaining particularly the reset operation performed by the circuit configuration shown in FIG. Note that (A) to (E) in FIG. 8 correspond to (A) to (E) shown in FIG. 3 already described, and therefore detailed description of each waveform is omitted.

  In the reset period shown in FIG. 8, all the analog switches Q1 to Qm are turned on. Further, all the scanning switches Sk1 to Skn in the cathode ray scanning circuit 3 are set to the ground potential GND side. Therefore, with respect to the lighting line shown in FIG. 8B, the divided output of each of the resistance elements R1 to Rm constituting the constant voltage supply means is supplied to each anode line. In FIG. 8, the voltage value supplied at this time is indicated as VAL for convenience, but this is obtained by dividing the output voltage from the reset voltage source VAL by the series resistors R1 to Rm.

  In this case, a relatively low constant voltage is applied to the anode line close to the cathode line scanning circuit 3, and a higher value constant voltage is applied to the anode line as the distance from the cathode line scanning circuit 3 increases. That is, during the reset period, the voltage across the EL element close to the cathode line scanning circuit 3 is low in the forward direction, and the voltage across the EL element far from the cathode line scanning circuit 3 is close to the cathode line scanning circuit 3 in the forward direction. A reset operation is performed in which the voltage is higher than the voltage across the EL element. This makes a difference in the reset voltage (the forward voltage value of the element) in the reset operation.

  In the constant current driving period following the reset period, the ground potential GND is set as shown in (D) for the cathode line to be scanned, and the reverse bias is set for the cathode line not to be scanned as shown in (E). A reverse bias voltage VM from the voltage source VM is applied. On the other hand, the analog switches Q1 to Qm corresponding to the anode line to be lit are selectively turned off. Thus, a charging current is supplied to the EL element to be lit through the non-scanning cathode line and the EL element (parasitic capacitance) connected thereto. That is, the state shown in (c) described with reference to FIG.

  At this time, a predetermined reset voltage that varies stepwise according to the distance from the cathode-ray scanning circuit 3 is accumulated in the forward direction in the non-scanning EL element. Therefore, the constant current driving period shown in FIG. In the initial rising period at, charging current flows through the EL element to be lit while the reset voltage is applied to the reverse bias voltage VM. On the other hand, the reset voltage is stored in the EL element to be lit, and thus the EL element to be lit is immediately turned on.

  As the constant current drive period elapses, all of the analog switches Q1 to Qm are turned on, whereby the constant current from the constant current sources I1 to Im is sucked into the analog switches Q1 to Qm, and the display panel All the EL elements arranged in 1 are turned off. In this case, Q1 to Qm may be set in an open (high impedance) state.

  By the way, in the charging operation to the EL element using the reverse bias voltage VM with the reset operation described above, as described above, it is connected to the anode line far from the cathode line scanning circuit 3 due to the influence of the wiring resistance of the cathode line. The charge operation of the EL element becomes insufficient, and this causes a luminance gradient.

  However, according to the configuration and operation shown in FIGS. 7 and 8, as described above, there is a difference in the reset voltage of the device, and the charge charging operation to the EL device connected to the anode line far from the cathode line scanning circuit 3 is achieved. Since it acts so as to be promoted, it is possible to cover the problem of insufficient charging operation due to the wiring resistance of the cathode line. Further, according to the configuration shown in FIG. 7, since the output voltage value of the reset voltage source VAL is made variable according to the dimmer information as described above, an optimum voltage value is set in accordance with the setting change of the dimmer. Thus, even when the dimmer setting is changed, the luminance gradient can be effectively suppressed.

  FIG. 9 shows a fourth embodiment of the display device and the drive circuit according to the present invention. This relates to a display device in which a charging operation to an element using a reverse bias voltage VM accompanied by a reset operation is executed as in the example shown in FIG. 7, and particularly for a display device having a large number of anode lines. It can be suitably employed.

  The basic configuration shown in FIG. 9 is the same as the configuration shown in FIG. 7 already described, and the reference numerals of the respective parts are omitted as appropriate. In the example shown in FIG. 9, in order to reduce the influence of the wiring resistance of the cathode line, the cathode line scanning circuit is arranged at both ends of each cathode line. That is, the cathode ray scanning circuit is indicated by reference numerals 3A and 3B, and both are configured to execute a scanning operation in synchronization with each other.

  In addition to this, the output from the reset voltage source VAL constituting the constant voltage supply means is supplied at the central portion of the anode line driving circuit 2, and each connection of the voltage dividing resistors connected in series from the central portion to the left and right respectively. The partial pressure output is obtained from the part. Therefore, according to the configuration shown in FIG. 9, the reset voltage value applied to the anode line disposed in the center of the display panel 1 is set higher, and the anode voltage becomes closer to the left and right cathode line scanning circuits 3A and 3B. The reset voltage value applied to the line is set so as to decrease sequentially.

  As shown in FIG. 9, according to the configuration in which the cathode line scanning circuits 3A and 3B are arranged at both ends of each cathode line, the charging operation by the reverse bias voltage VM after the reset operation is caused by the wiring resistance of the cathode line. Insufficient proximity occurs, and this causes a luminance gradient that emits light near the center of the panel 1 and brightly emits light on the left and right cathode ray scanning circuit sides.

  According to the configuration shown in FIG. 9, it is possible to effectively suppress the occurrence of the luminance gradient caused by the wiring resistance of the cathode line. Further, the output voltage value of the reset voltage source VAL constituting the constant voltage supply means is configured to be variable according to the dimmer information as in the example shown in FIG. Therefore, even when the dimmer setting is changed, the luminance gradient can be effectively suppressed.

It is the circuit block diagram which showed an example of the conventional display apparatus. It is an equivalent circuit diagram explaining the reset operation | movement performed in the display apparatus shown in FIG. It is a timing chart explaining the lighting drive operation | movement of the conventional display apparatus. BRIEF DESCRIPTION OF THE DRAWINGS It is the circuit block diagram which showed 1st Embodiment of the display apparatus concerning this invention. 6 is a timing chart for explaining a lighting drive operation of the display device shown in FIG. 4. It is the circuit block diagram which showed 2nd Embodiment of the display apparatus concerning this invention. It is the circuit block diagram which showed 3rd Embodiment of the display apparatus concerning this invention. It is a timing chart explaining the lighting drive operation | movement of the display apparatus shown in FIG. It is the circuit block diagram which showed 4th Embodiment of the display apparatus concerning this invention.

Explanation of symbols

1 Display panel 2 Anode line drive circuit (drive circuit)
3 Cathode line scanning circuit A1-Am Anode line E11-Emn Display element (organic EL element)
I1-Im Constant current source K1-Kn Cathode line Q1-Qm Analog switch Q1a-Qma Analog switch (first group)
Q1b to Qmb Analog switch (second group)
R1 to Rm Resistive elements VAH Drive voltage source VAM Precharge voltage source VAL Reset voltage source VM Reverse bias voltage source t1 to tm Anode output terminal

Claims (5)

A plurality of anode output terminals for supplying driving power to the anode input terminals of the display device;
A plurality of constant current sources each connected corresponding to the anode output terminal and supplying a constant current to the anode output terminal;
Constant voltage supply means connected to the plurality of anode output terminals and supplying a constant voltage to each of the anode output terminals ;
A cathode line scanning circuit that is connected to each cathode line of the display device and selectively applies a scanning signal to each cathode line ;
The constant voltage value supplied to each anode output terminal by the constant voltage supply means is set to be different for each anode output terminal ,
The constant voltage supply means includes a resistance element that generates a different constant voltage value for each anode output terminal, and a plurality of analogs that selectively supply different constant voltage values generated by the resistance element to the anode output terminal. A switch is provided,
At the timing of the reset operation that resets the voltage across each display element arranged in the display device, the constant voltage of a different value is output to each anode output terminal via each analog switch,
A display device drive circuit , wherein each constant voltage value applied to each anode output terminal is varied according to dimmer information for controlling brightness of a display image in the display device. The anode output terminals are arranged in a line corresponding to the anode input terminals of the display device, and the constant voltage value output from each anode output terminal is stepwise according to the arrangement order of the anode output terminals. The display device driving circuit according to claim 1 , wherein the display device driving circuit is set to change. The constant voltage having a different value is output to each anode output terminal via each analog switch at the timing of a precharge operation in which a precharge voltage is applied to each display element arranged in the display device. The display device driving circuit according to claim 2 , wherein the driving circuit is a display device driving circuit. A display panel in which capacitive display elements are arranged at intersections of a plurality of anode lines and a plurality of cathode lines, and a driving current and a constant voltage are selectively supplied to the display elements via the anode lines. An anode line driving circuit and a cathode line scanning circuit that is connected to each cathode line and selectively applies a scanning signal to each cathode line;
The constant voltage values from the constant voltage supply means for supplying a constant voltage to the plurality of anode wires are set to be different from each other ,
The constant voltage supply means selectively supplies a resistance element that generates a different constant voltage value for each anode line of the display panel and a different constant voltage value generated by the resistance element to the anode line of the display panel. A plurality of analog switches,
At the timing of the reset operation for resetting the both-end voltage of each display element arranged in the display panel, the constant voltage having a different value is output to the anode line of the display panel via each analog switch.
A different constant voltage value applied to each anode line of the display panel is variable according to dimmer information for controlling the brightness of a display image on the display panel . The constant voltage value to be supplied to the plurality of anode lines, claims, characterized in that from the cathode line scanning circuit are set in accordance with the line length of said cathode lines to the intersection of respective anode lines via said cathode lines Item 5. A display device according to Item 4 .

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