JP2006071858A - Driving method for light emitting element and matrix type display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving method for a light emitting element and a matrix type display apparatus capable of performing high precision gray scale display by high speed pre-charging. <P>SOLUTION: Scanning signals SS from a first row to a n-th row are grounded for every scanning selection interval Ts on time T1, T4, T7,... by a scanning line driving circuit. Pre-charging of a parasitic capacitance C is started on time T0 which is ΔT ahead of the time T1, when a row to be light emitted is changed by the scanning signal SS, and a constant voltage Vpc is applied to a data line and the parasitic capacitance of an organic EL element 10 is pre-charged. The row to be light emitted is changed during from a (j-1)th row to a j-th row by the scanning signal SS on the time T1. Thereafter, light emitting of the organic EL element is started by a PWM data signal Ipwm on time T2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a matrix display device, and more particularly to a driving technique for a passive matrix display device.

  In recent years, a display used for a liquid crystal television, a mobile phone, a PDA (Personal Digital Assistance) and the like is mostly a matrix type display device in which light emitting elements are arranged in a matrix type. Such a matrix display device has scanning lines corresponding to the rows of the matrix and data lines corresponding to the columns. Light emitting elements are arranged at the intersection of the two signal lines so as to be sandwiched between the two signal lines, and light emission is controlled by applying a data signal and a scanning signal for controlling light emission of each light emitting element to the data line and the scanning line. The

  Here, when a device whose luminance is controlled by a current, such as an LED (Light Emitting Diode) or an EL (Electro Luminescence), is used as the light emitting element, a current source or a voltage source is connected to the data line to each light emitting element. The luminance is controlled by supplying a current based on the light emission gradation.

  Here, there is a parasitic capacitance formed by two types of signal lines at the intersection of the data line and the scanning line where each light emitting element is arranged. Therefore, for example, when a constant current source is connected to the data line and a light emission control signal having a constant current modulated with a pulse width is supplied to the light emitting element to emit light, a potential difference between the data line and the scanning line is Since the constant current light emission control signal supplied from the constant current source is consumed for charging the parasitic capacitance during a period lower than the light emission threshold voltage, the period required for this charging is a non-light emission period. As described above, when the luminance is controlled by the pulse width modulated data signal, there is a problem that it is difficult to emit light at a desired gradation due to the presence of the parasitic capacitance.

  In order to solve such a problem, a precharge method as described in Patent Document 1 has been proposed. In the precharge method, immediately after selection of a row by a scanning signal, a light source is charged by connecting a constant voltage source to a data line prior to supply of a data signal, that is, a precharge, and then a desired light emission control signal is used. The light emitting element is caused to emit light at the gradation.

Japanese Patent Application Laid-Open No. 11-31970

  However, according to the technique described in the above-mentioned patent document, after the row is selected by the scanning signal, a constant voltage is supplied to the data signal to perform precharging, and the light emitting elements in the row selected by the scanning signal are precharged. The light emission is controlled after waiting for completion. For this reason, even after selection by the scanning signal, a non-light emission period during which light emission cannot be controlled may occur for a long time until the precharge is completed.

  The present invention has been made in view of these problems, and an object of the present invention is to provide a driving method and a matrix display device that can perform high-speed precharge and perform high-precision gradation expression.

  One embodiment of the present invention relates to a method for driving a light emitting element. This light emitting element driving method is a driving method for light emitting elements arranged in a matrix type, and is a row that emits light by supplying scanning signals to a plurality of scanning lines provided for each row of the matrix at a constant period. Are switched sequentially, while a plurality of data lines provided for each column of the matrix are supplied with a constant current signal that is pulse-width modulated in accordance with the light emission gradation, and at the time when the row to be lit by the scanning signal is switched. A precharge signal for charging the light emitting element to a predetermined voltage is supplied for a predetermined period from a predetermined time in advance regardless of the light emission gradation.

“Light-emitting element” is a concept including a parasitic capacitance at the intersection of a scanning line and a data line in which the light-emitting element is arranged in addition to a light-emitting element that actually emits light. “Charging a light-emitting element” It means charging this parasitic capacitance.
According to this aspect, since the precharge is started before the row that emits light is selected by the scanning line, the potential of the data line rises to a predetermined voltage in a short time after the row is selected, and the light emitting element is turned on. Light can be emitted immediately, and the non-light emission period can be shortened to perform highly accurate gradation expression.

The predetermined period during which the precharge signal is supplied to the plurality of data lines may be set shorter than the pulse width corresponding to the minimum gradation of the pulse current modulated constant current signal.
In this case, even when the light emitting element is not caused to emit light, that is, when a pulse current modulated constant current signal having a duty ratio of 0 is supplied as a data signal, the light emission caused by the precharge signal is extremely short and is given to gradation expression. The influence can be reduced.

  The precharge signal may be a constant current signal having a larger current value than a constant current signal that is pulse width modulated in accordance with the light emission gradation. Since the light-emitting element can be charged in a short period by charging the light-emitting element with a large constant current, the predetermined period for performing the precharge can be set short, and high-accuracy gradation expression can be realized.

  The precharge signal may be a constant voltage signal. By supplying a constant voltage from a constant voltage source, the voltage of the light emitting element rises in accordance with a CR time constant determined by the parasitic capacitance and the resistance value of the data line and the scanning line. Therefore, by adjusting the constant voltage value of the precharge signal The battery can be charged to a desired voltage in a short time.

  Another embodiment of the present invention is a matrix display device. The matrix display device includes a light emitting element arranged in a matrix type, a scanning line driving circuit for driving a plurality of scanning lines provided for each row of the matrix, and a plurality of elements provided for each column of the matrix. And a data line driving circuit for driving the data lines. The scanning line driving circuit sequentially switches rows to emit light by supplying scanning signals to a plurality of scanning lines at a constant period. On the other hand, the data line driving circuit supplies a plurality of data lines with a constant current signal that is pulse-width modulated in accordance with the light emission gradation, and over a predetermined period from a predetermined time prior to the switching time of the light emitting row. A precharge signal for charging the light emitting element to a predetermined voltage is supplied regardless of the light emission gradation.

  According to this aspect, since the precharge is started before the row that emits light is selected by the scanning line, the potential of the data line rises to a predetermined voltage in a short time after the row is selected, and the light emitting element is turned on. Light can be emitted immediately, and the non-light emission period can be shortened to perform highly accurate gradation expression.

  The data line driving circuit includes a pulse width modulation current source (hereinafter referred to as a PWM current source) that generates a constant current signal that is pulse width modulated in accordance with the gradation, and a precharge for charging the light emitting element to a predetermined voltage. To switch the signal supplied to the data line and the precharge current source that generates a signal as a constant current set larger than the current value generated by the PWM current source to either the PWM current source or the precharge current source The switch may be included. The switch is synchronized with the scanning signal, and the switch is turned on to the precharge current source side for a predetermined period from a predetermined time prior to the time when the row to emit light is switched. Good.

  A data line driving circuit includes a constant current source that generates a constant current signal that is pulse-width modulated in accordance with a gray level, and a constant voltage source that generates a precharge signal for charging a light emitting element to a predetermined voltage as a constant voltage. And a switch for switching a signal supplied to the data line to either a constant current source or a constant voltage source. The switch is synchronized with the scanning signal, and it is turned on to the precharge voltage source side for a predetermined period from a predetermined time prior to the time when the row to emit light is switched, and it may be turned on to the PWM current source side for other periods. Good.

The matrix display device may include a control terminal for controlling a predetermined time and a predetermined period.
By providing a control terminal, it is possible to adjust these parameters for determining the precharge period and timing from the outside according to the environment such as the connected light emitting element and temperature, and more preferably the light emission of the matrix display device Can be controlled.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  With the matrix display device and the driving method according to the present invention, it is possible to precharge the light emitting elements in a short time after switching the rows by the scanning signal, and to perform high-accuracy gradation expression by shortening the non-light emitting period. Become.

FIG. 1 shows a configuration of a matrix type display device 100 according to the first embodiment of the present invention.
The matrix display device 100 includes an organic EL element 10, a scanning line driving circuit 20, a data line driving circuit 30, a control circuit 40, scanning lines S1 to Sn, and data lines D1 to Dm. Here, the subscripts m and n are natural numbers representing the number of rows and columns of the light emitting elements, respectively. In the subsequent drawings, the same components are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

  N scanning lines S1 to Sn (hereinafter collectively referred to as scanning lines S) and m data lines D1 to Dm (hereinafter collectively referred to as data lines D) are arranged in a grid pattern. Yes. At each intersection of the data line Di and the scanning line Sj, an organic EL element 10ji is formed as a light emitting element sandwiched between both signal lines, and the light emitting elements are arranged in a matrix of m rows × n rows.

  In the organic EL element 10ji which is the light emitting element in the j-th row and the i-th column, when the potential of the data line Di is set to the high level and the potential of the scanning line Sj is set to the low level, current flows and light is emitted, and this current flows. The light emission gradation is controlled corresponding to the period. In this embodiment, the low-level potential of the scanning line Sj is set to 0 V of the ground potential.

  A scanning line driving circuit 20 is connected to the scanning lines S1 to Sn. The scanning line driving circuit 20 receives the scanning control signal Scnt from the control circuit 40, and the scanning line driving circuit 20 corresponds to a row to emit light among the first to n-th scanning lines S. The potential of the scanning line is set to a low level 0 V for a predetermined scanning selection period Ts, and a row to emit light is selected. During this period, the potentials of the scanning lines in the rows that do not emit light are all set to the high level. The scanning line driving circuit 20 repeatedly sets the potential of the scanning line S from the first row to the n-th row to the low level 0 V in order, and causes the organic EL elements 10 arranged in each row to emit light.

  A data line driving circuit 30 is connected to the data lines D1 to Dm. The data line driving circuit 30 generates a pulse width modulated data signal to be supplied to each of the data lines D1 to Dm based on the data control signal Dcnt from the control circuit 40. Each of the data lines D1 to Dm is supplied with a pulse width modulated data signal Ipwm (hereinafter referred to as a PWM data signal) whose high-level period changes corresponding to each light emission gradation, and this PWM data signal Ipwm The light emission gradation of the organic EL element 10 is controlled. For example, when the potential of the scanning line S in the j-th row becomes low level, the organic EL element in the j-th row and i-th column emits light with a gradation corresponding to the high level period of the PWM data signal Ipwmi. .

  In this manner, the light-emitting elements from the first row to the n-th row are selected in order by the scanning signal, and the data signal is supplied to each column, whereby the display of the entire matrix display device 100 is controlled.

  The control circuit 40 outputs the scanning control signal Scnt to the scanning line driving circuit 20 and the data control signal Dcnt to the data line driving circuit 30. In the matrix display device 100, the light emitting rows are sequentially switched in synchronization with the scanning control signal Scnt. Further, the data control signal Dcnt is synchronized with the scanning control signal Scnt, and is a signal including light emission gradation data of the organic EL elements 10 in all of the first to m columns.

  FIG. 2 is a circuit diagram showing in more detail the configuration of the data line driving circuit 30 of the matrix type display device 100 of FIG. In FIG. 2, the organic EL element 10 includes a light emitting device EL and a parasitic capacitance C, and the parasitic capacitance C generated between the electrodes of the data line D and the scanning line S exists in parallel with the light emitting device EL. Has been.

  The data line driving circuit 30 includes a PWM current source 34, switches SW1 to SWm, a precharge voltage source 36, and a pulse control circuit 32 provided for each column from the data lines D1 to Dm.

  The pulse control circuit 32 generates PWM control signals Spwm <b> 1 to Spwmm subjected to pulse width modulation for controlling the PWM current source 34 based on the data control signal Dcnt output from the control circuit 40. Further, the pulse control circuit 32 generates a switching signal Ssw for controlling the switches SW1 to SWm.

  The PWM current source 34 generates PWM data signals Ipwm1 to Ipwmm, which are constant current signals pulse-modulated based on the PWM control signal Spwm, and supplies them to the data lines D1 to Dm.

The precharge voltage source 36 is a voltage source for supplying a precharge voltage Vpc for charging the parasitic capacitance C of the organic EL element 10 to each data line as a constant voltage signal. When the precharge voltage Vpc is applied to the parasitic capacitance C, the potential rises according to the CR time constant τ = CR determined by the wiring resistance R of the data line and the scanning line.
In FIG. 2, the precharge voltage source 36 is provided for each data line for explanation. However, in an actual circuit, the precharge voltage Vpc may be the same voltage value for all the data lines D. It is not necessary to provide each column as in FIG. 2, and it may be configured to be connected to each switch SW1 to SWm by wiring from one constant voltage source.

  The switches SW1 to SWm switch the signal supplied to the data lines D1 to Dm to either the PWM data signal Ipwm generated by the PWM current source 34 or the precharge signal supplied from the precharge voltage source 36. It is a switch. Here, a state in which the switch SW is turned on to the PWM current source 34 side is a first state, and a state in which the switch SW is turned on to the precharge voltage source 36 side is a second state. The state of the switch SW is controlled by a switching signal Ssw synchronized with the scanning signal SS, and the first state and the second state are switched at a predetermined timing.

  In the matrix display device 100, the parasitic capacitance C is precharged during the period in which the switch SW is in the second state. Therefore, the value of the precharge voltage Vpc is determined so as to raise the potential of the data line applied to the organic EL element 10 to a desired voltage value during the precharge period Tpc in which the switch SW is set to the second state. That's fine. This may be determined by calculating the time constant τ = CR of the CR circuit formed by the parasitic capacitance C and the wiring resistance R, or may be determined experimentally.

The operation of the matrix display device 100 configured as described above will be described. FIG. 3 shows a time chart of voltage and current waveforms of each signal of the matrix display device 100. Here, attention is paid to the organic EL elements in the j−1, j, and j + 1 rows in the i-th column. In the time charts of FIG. 3 and FIG. 6 to be described later, the time axis and the current / voltage axis are both enlarged and reduced as appropriate for easy viewing.
In FIG. 3, each time waveform is shown in order from top to bottom (j−1) -th scanning signal SSj−1, j-th scanning signal SSj, j + 1-th scanning signal SSj + 1, switching signal Ssw, and i-th column. The PWM data signal Ipwmi supplied to the data line and the potential VDi of the data line in the i-th column are shown.

  The scanning signal SS from the first row to the n-th row is set to the low level, that is, the ground potential 0 V by the time T1, T4, T7,... And the scanning selection period Ts. To go. The organic EL elements 10 in each row are controlled to emit light by the data signal SD during the scanning selection period Ts in which the scanning signal SS is 0V.

  The switch SW switching signal Ssw is generated by the pulse control circuit 32 in synchronization with the switching of the scanning signal SS between the low level and the high level. In FIG. 3, the switching signal Ssw indicates a first state when it is at a high level and a second state when it is at a low level. The switch SW is turned on to the precharge voltage source 36 side at a predetermined time T0, the constant voltage Vpc is applied to the data line Di, and charging of the parasitic capacitance C of the organic EL element 10 is started. After that, the row to emit light is switched from the (j−1) th row to the jth row by the scanning signal SS at time T1. That is, the precharge of the parasitic capacitance C is started prior to the time T1 when the row to be emitted is switched by the scanning signal SS by the period ΔT.

From time T0, the voltage VDi of the data line starts to increase due to the precharge voltage Vpc, and reaches the predetermined reference voltage Vc immediately after time T1. Thereafter, at time T2 when a predetermined precharge period Tpc has elapsed from time T0, the switch SW is turned on in the first state, that is, the PWM current source 34 side, and the PWM data signal Ipwmi having a pulse width Te corresponding to the light emission gradation is The light emission from the organic EL element 10 is started.
When the light emission control by the PWM data signal Ipwmi ends, the data line potential VDi drops to the ground potential. Thereafter, at time T3 prior to selection of the (j + 1) th row of the scanning signal SS, the switch SW enters the second state, precharge is started, and the potential VDi of the data line rises to a predetermined voltage Vc.

  In the present embodiment, the PWM data signal Ipwm has a maximum light emission period Tmax corresponding to the maximum light emission gradation during the period from time T2 to time T3. Therefore, for example, when controlling light emission with 8-bit gradation, the light emission gradation is controlled with 8 bits by controlling the high-level period of the PWM data signal Ipwm with the pulse width (T3-T2) / 256 as the minimum unit. can do.

In the present embodiment, the switch SW switching signal Ssw is always set to the second state during the predetermined precharge period Tpc from the time prior to the time when the scanning signal is switched, regardless of the light emission gradation. Do.
FIG. 4 is a time waveform showing the state of the potential transition of the scanning line and the data line by such regular precharge, and the light emission gradation is minimum (non-light emission state = off) or maximum (light emission state). =) Is shown. FIG. 4 shows the j-th column scanning signal SSj and the j + 1-th column scanning signal SSj + 1 in order from the top two stages. The lower four stages represent the potential VD of the data line, showing the transition from on to off, transition from on to on, transition from off to on, and transition from off to off in order from the top. .

As described above, the precharge voltage Vpc from the precharge voltage source 36 is applied to the data line at the time T0 before the scanning signal SS is switched at the time T1 regardless of the light emission gradation.
As indicated by VDon → off, when the organic EL element in the j + 1 row transitions from the light emitting state to the non-light emitting state in the j + 1 row, after the precharge is performed, the data line Since no constant current is supplied, the precharged electric charge is discharged, and its potential quickly decreases to 0V. In this case, the light is emitted slightly from time T0 until the potential of the data line becomes equal to or lower than the predetermined light emission threshold voltage, but it is very short time and the organic EL element Since the flowing current is also small, the influence on the accuracy of the light emission gradation can be ignored.

  In addition, when the transition from the state where the organic EL element in the j-th row emits light to the state where the organic EL element in the (j + 1) -th row emits light as indicated by VDon → on, the data line is pre-charged for precharging. When connected to the charge voltage source 36, a predetermined voltage Vc is maintained as the potential VD of the data line. As a result, the light emitting elements in the (j + 1) th row quickly emit light with a desired gradation by the PWM data signal Ipwm.

  As indicated by VDoff → on, when the organic EL element in the j-th row transitions from the non-light-emitting state to the state in which the organic EL element in the j + 1-th row emits light, the potential VD of the data line is from the state of 0V. The precharge increases instantaneously to a predetermined voltage Vc, and then light emission is controlled by the PWM current source 34. In this case, since the precharge is started before the j + 1th row is selected at time T1, the precharge is completed soon after the j + 1th row is selected at time T1, and the potential VD of the data line is set to a predetermined value. Since the voltage rises to the voltage Vc, light emission control by the PWM data signal Ipwm can be performed from time T2.

  As indicated by VDoff → off, when the organic EL element in the j-th row transitions from the non-light-emitting state to the non-light-emitting state in the j + 1-th row, the potential VD of the data line is pre-charged from 0V. By charging, the voltage instantaneously rises to a predetermined voltage Vc. After that, when the precharge voltage source 36 is disconnected, the voltage drops to 0 V by discharging. In this case, a predetermined voltage Vc is applied to the light emitting element between times T0 and T2, and the light is emitted slightly. However, setting the precharge period Tpc sufficiently short affects the gradation expression. Can be reduced.

  Preferably, the precharge period Tpc is set shorter than the pulse width corresponding to the minimum gradation, so that even when a predetermined voltage Vc is instantaneously applied to the organic EL element 10 at the time T1, the visual recognition is performed. Therefore, the influence on the gradation expression can be reduced.

  For example, the precharge period Tpc may be determined as follows. From the scan selection period Ts and the time Tpc required for precharging, the maximum light emission period Tmax capable of effectively controlling the light emitting element is given by Tmax = Ts−Tpc. Next, the minimum pulse width is determined according to the resolution of the desired light emission gradation. For example, when controlling with 8-bit 256 gradation, the minimum pulse width Tmin can be Tmin = (Ts−Tpc) / 256. At this time, by setting the precharge period Tpc <Tmin, unnecessary light emission due to precharge can be reduced. The parameter ΔT for determining the precharge start time may be determined according to the precharge speed so that the precharge is completed immediately after the scanning signal SS is switched.

  As described above, according to the matrix display device 100 according to the present embodiment, the precharge is started prior to the switching of the scanning signal SS, so that the light emitting element is used immediately after the row is selected by the scanning signal SS. Light emission of a certain organic EL element 10 can be controlled, and high-accuracy gradation expression can be performed by shortening the non-light emission period. In addition, the apparatus can be simplified by performing precharge at a predetermined timing for a predetermined period regardless of whether or not the organic EL element 10 emits light and the light emission gradation.

FIG. 5 shows a modification of the data line driving circuit of the matrix display device 100. The data line driving circuit 30 ′ includes a PWM current source 34, switches SW1 to SWm, a precharge current source 38, and a pulse control circuit 32 provided for each column from the data lines D1 to Dm.
FIG. 6 shows a time chart of voltage and current waveforms of each signal of the matrix type display device 100 when the data line driving circuit 30 is used.

  The precharge current source 38 is a current source for supplying a precharge current Ipc for charging the parasitic capacitance C of the organic EL element 10 to the data line D as a constant current signal. The parasitic capacitance C is charged by the precharge current Ipc.

  The switches SW1 to SWm send a signal supplied to each of the data lines D1 to Dm to any one of three among the PWM data signal Ipwm from the PWM current source 34, the precharge current Ipc from the precharge current source 38, and the ground potential. It is a switch for switching. A state in which the data line is connected to the PWM current source 34 is a first state, a state in which the data line is connected to the precharge current source 38 is a second state, and a state in which the data line is grounded is a third state. The switches SW1 to SWm are controlled by a switching signal Ssw synchronized with the scanning signal SS, and the first, second, and third states are switched at a predetermined timing.

  In the data line driving circuit 30 ', the parasitic capacitance C is precharged during the precharge period Tpc in which the switch SW is in the second state. Therefore, the value of the precharge current Ipc may be determined so as to increase the potential VD of the data line to the desired voltage value Vc during the precharge period Tpc. Although the value of the precharge current Ipc depends on the parasitic capacitance C, precharge can be appropriately performed in a short period of time by setting the current value to be several times the PWM data signal Ipwm.

  The operation of the matrix display device 100 to which the data line driving circuit 30 ′ configured as described above is applied will be described. Here, attention is focused on the organic EL elements in the i-th column, j−1 to j + 1 rows. FIG. 6 shows a time chart of voltage and current waveforms of each signal of the matrix type display device 100. In FIG. 6, the first state is represented when the switching signal Ssw is at a mid level, the second state is represented when it is at a high level, and the third state is represented when it is at a low level.

  Since the basic waveform is the same as the waveform diagram shown in FIG. 4, the differences will be mainly described. Prior to precharging, the switch SW is set to the third state, and all the data lines D are grounded. As a result, the potential VD of the data line is lowered to 0 V regardless of the light emitting state of the light emitting element before that. Thereafter, the switch SW3 is set to the second state at time T1, and precharging is started. The parasitic capacitance C of the organic EL element 10 is charged by the precharge current Ipc supplied from the precharge current source 38, and immediately after the scanning signal SS is switched at time T2, the potential VD of the data line reaches the predetermined voltage Vc. To do. Thereafter, light emission control is started by the PWM data signal Ipwm supplied from the PWM current source 34 from time T3, and a constant current is supplied during the light emission period Te, so that the organic EL element 10 emits light.

  When a constant current source is used as a precharge signal in this way, the voltage is once lowered to 0 V by grounding the data line before supplying the precharge signal to the data line, and then the precharge is performed. Yes. As a result, the voltage of the light emitting element after precharging can always be set to the predetermined voltage Vc without depending on the state of the light emitting gradation of the light emitting element immediately before precharging.

  Those skilled in the art will understand that the above-described embodiment is an exemplification, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  In this embodiment mode, an organic EL element is described as an example of a light-emitting element. However, the present invention is not limited to this, and precharge is necessary due to parasitic capacitance between data lines and scanning lines such as other EL elements and LEDs. The present invention can be applied to all light emitting elements.

  In this embodiment, the case where the precharge period Tpc for determining the precharge characteristic by the data line driving circuit 30 and ΔT for determining the precharge timing are fixed is described, but the present invention is not limited to this. For example, the data line driving circuit 30 may be provided with a control terminal so that the precharge periods Tpc and ΔT can be changed from the outside. Based on the control signal input to the control terminal, the pulse control circuit 32 changes the switching timing of the state of the switching signal Ssw to determine the optimum precharge condition in the trial production stage, When it is desired to determine the precharge period and timing from the outside according to the environment such as temperature, these parameters can be adjusted, and light emission of the matrix display device can be controlled more suitably.

  In the present embodiment, the scanning lines and the data lines have been described so as to correspond to the rows and columns of the matrix, respectively, but this is also convenient and the rows and columns may be interchanged.

1 is a diagram showing a configuration of a matrix display device according to a first embodiment of the present invention. FIG. 2 is a circuit diagram showing in more detail the configuration of a data line driving circuit of the matrix type display device of FIG. 1. FIG. 2 is a diagram illustrating a time chart of voltage and current waveforms of signals of the matrix display device of FIG. 1. 2 is a time waveform showing transition of potentials of scanning lines and data lines of the matrix type display device of FIG. It is a figure which shows the modification of the data line drive circuit of a matrix type display apparatus. It is a figure which shows the time chart of the voltage of each signal of a matrix type display apparatus at the time of using the data line drive circuit shown in FIG. 5, and a current waveform.

Explanation of symbols

  10 organic EL elements, 20 scanning line drive circuit, 30 data line drive circuit, 32 pulse control circuit, 34 PWM current source, 36 precharge voltage source, 38 precharge current source, 40 control circuit, 100 matrix type display device, SW Switch, D data line, S scan line, Ipwm PWM data signal, Spwm PWM control signal, Ssw switching signal.

Claims (8)

A driving method of light emitting elements arranged in a matrix type,
A plurality of scanning lines provided for each row of the matrix are sequentially switched to emit light lines by supplying a scanning signal at a constant cycle, while a plurality of data lines provided for each column of the matrix have light emission gradations. And supplying a constant current signal that is pulse-width modulated in accordance with the voltage, and charging the light emitting element to a predetermined voltage for a predetermined period from a predetermined time prior to the time when the row to emit light is switched, regardless of the light emission gradation. A driving method of a light emitting element, characterized by supplying a precharge signal for the same.   The predetermined period during which the precharge signal is supplied to the plurality of data lines is set shorter than a pulse width corresponding to a minimum gray level of the pulse current modulated constant current signal. Item 4. A method for driving a light emitting element according to Item 1.   2. The light emitting element driving method according to claim 1, wherein the precharge signal is a constant current signal having a larger current value than a constant current signal pulse-width modulated in accordance with the light emission gradation.   The method according to claim 1, wherein the precharge signal is a constant voltage signal. Light emitting elements arranged in a matrix type;
A scanning line driving circuit for driving a plurality of scanning lines provided for each row of the matrix;
A data line driving circuit for driving a plurality of data lines provided for each column of the matrix;
The scanning line driving circuit sequentially switches rows to emit light by supplying scanning signals to the plurality of scanning lines at a constant period, while the data line driving circuit emits light emission gradations to the plurality of data lines. And supplying a constant current signal that is pulse-width modulated in accordance with the above, and charging the light-emitting element to a predetermined voltage regardless of the light emission gradation for a predetermined period from a predetermined time prior to the switching time of the row to emit light. A matrix display device, characterized by supplying a precharge signal for the purpose. The data line driving circuit includes:
A pulse width modulated current source that generates a constant current signal that is pulse width modulated according to the gradation;
A precharge current source for generating a precharge signal for charging the light emitting element to a predetermined voltage as a constant current signal set larger than a current value generated by the pulse width modulation current source;
A switch for switching a signal supplied to the data line to either the pulse width modulation current source or the precharge current source;
The switch is synchronized with the scanning signal, and is turned on to the precharge current source side for a predetermined period from a predetermined time prior to the time when the row to be emitted is switched, and the pulse width modulation is performed for other periods 6. The matrix type display device according to claim 5, wherein the matrix type display device is turned on to a current source side. The data line driving circuit includes:
A pulse width modulated current source that generates a constant current signal that is pulse width modulated according to the gradation;
A precharge voltage source for generating, as a constant voltage, a precharge signal for charging the light emitting element to a predetermined voltage;
A switch for switching a signal supplied to the data line to either the PMW current source or the precharge voltage source;
And the switch is synchronized with the scanning signal, and is turned on to the precharge voltage source for a predetermined period from a predetermined time prior to the time when the row to be emitted is switched, and the pulse width for the other period 6. The matrix type display device according to claim 5, wherein the matrix type display device is turned on to the modulation current source side.   6. The matrix type display device according to claim 5, further comprising a control terminal for controlling the predetermined time and the predetermined period.

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