JPH0656544B2 - Driving circuit for thin film EL display device - Google Patents

Abstract

PURPOSE:To realize a light controlling function extending over a wide range without deteriorating the quality of a display screen by applying a write voltage, and thereafter, applying a light controlling pulse voltage whose polarity is opposite to that of said write voltage to a scanning side electrode. CONSTITUTION:By varying a variable voltage from a variable voltage generating means 7, a third DC voltage VW+VM and a modulation voltage VM are varied, a voltage applied to an EL layer is varied and a light control is executed. Also, a write voltage is applied by a write voltage applying means 5, and thereafter, a light controlling pulse voltage whose polarity is opposite to that of the write voltage is applied by a light controlling pulse applying means 6. The light controlling pulse voltage is a first DC voltage VW or a second DC voltage 1/2 VW, therefore, even if the variable voltage is varied in order to execute a light control, the light controlling pulse voltage is not varied. In such a way, a light controlling level can be varied without deteriorating the quality of a display screen of the EL layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an AC drive type capacitive flat matrix display panel having a dimming function, that is, a thin film E.
The present invention relates to a drive circuit of an L display device.

[Prior Art] For example, a double-insulation (or three-layer structure) thin film EL display device is configured as follows.

As shown in FIG.
A band-shaped transparent electrode 102 made of n ₂ O ₃ is provided in parallel. Then, on this, for example, Y ₂ O ₃ , Si ₃ N ₄ ,
A dielectric material layer 103 such as TiO ₂ or Al ₂ O ₃ , an EL layer 104 made of ZnS doped with an activator such as Mn, Y ₂ O ₃ , Si ₃ N ₄ , TiO ₂ , or Al ₂ O ₃ as described above.
A dielectric material layer 103a such as the above is sequentially laminated with a film thickness of 500 to 10000Å using a thin film technique such as a vapor deposition method and a sputtering method to form a three-layer structure. Further, a strip-shaped back electrode 105 made of Al is provided in parallel on the transparent electrode 102 in a direction orthogonal to the transparent electrode 102.

The thin film EL display device has an EL layer 10 sandwiched between the electrodes 102 and 105 with dielectric materials 103 and 103a.
4 is interposed, it can be regarded as a capacitive element in terms of an equivalent circuit. Further, the thin film EL display device has a voltage-luminance characteristic shown in FIG.
It is driven by applying a relatively high voltage of about 00V.

This thin film EL display device is characterized in that it emits light with high brightness due to an AC electric field and has a long life.

The applicant of the present invention has proposed the drive circuit shown in FIG. 2 in order to reduce the modulation power consumption, cost reduction and thinness and compactness of such a thin film EL display device.

In FIG. 2, the thin film EL display device 10 has a light emission threshold voltage V _TH (V _W <V _TH <V _W + V _M ), and includes a plurality of X-direction electrodes and a plurality of Y-direction electrodes. The X-direction electrodes become the data-side electrodes X _{1 to} X _i , and the Y-direction electrodes become the scanning-side electrodes Y _{1 to} Y _i . The odd-numbered lines of the scanning electrodes Y _{1 to} Y _i are the high withstand voltage push-pull type driver IC on the scanning side.
(Hereinafter referred to as the scan side driver IC) 20 is connected,
The even lines of the scanning electrodes Y _{1 to} Y _i are similarly connected to the scanning driver IC 30. Scan side driver IC2
0 is a plurality of high voltage push-pull type drivers SDr
And a logic circuit 21 such as a shift register. Similarly, the scanning side driver IC 30 includes a plurality of high breakdown voltage push-pull type drivers SDr and a logic circuit 31 such as a shift register. Each driver SDr is shown in FIG.
FIG. 3 (b) shows a specific circuit configuration of the driver of FIG. 3 (a). In FIG. 3 (b), the high voltage H
A pull-up Pch high withstand voltage MOSFET 501 is connected between a high voltage side terminal to which V _CC is applied and an output terminal, and a pulldown Nch high withstand voltage is provided between a low voltage side terminal to which a low voltage V _DD is applied and an output terminal. MOSFET 502
Are connected. Also, pull-up MOSFET 5
01 and the pull-down MOSFET 502 in parallel,
Diodes 503 and 50 for passing current in the opposite direction
4 are connected to each other. MOSFE for pull-up
The T501 and pull-down MOSFET 502 are turned on and off by a circuit 505 such as a level shifter according to input data. This high breakdown voltage push-pull type driver may have another configuration as long as it is composed of a switching element having a pull-up function and a switching element having a pull-down function.

As shown in FIG. 2, the scanning side driver ICs 20 and 3
The low voltage side terminal of each driver SDr of 0 is commonly connected to the scan side pull-down common line SD, and the high voltage side terminal is commonly connected to the scan side pull-up common line SU.
On the other hand, the logic circuits 21 and 31 are controlled by the control signal Scan da
By using ta, PUP, PDW, etc., pull-up MOSFET 5 of driver SDr corresponding to Scan data
01 or the pull-down MOSFET 502 is turned on, and the pull-up MOSFET 501 or the pull-down MOSFET 502 of all the drivers SDr is turned on regardless of the Scan data.

Further, the data side electrodes X _{1 to} X _i are connected to a data side high breakdown voltage push-pull type driver IC (hereinafter, referred to as data side driver IC) 40. The data side driver IC 40, like the scanning side driver ICs 20 and 30,
It comprises a plurality of high breakdown voltage push-pull type drivers DDr and a logic circuit 41 such as a shift register. The high voltage side terminal of each driver DDr of the data side driver IC is commonly connected to the data side pull-up common line DU, and the low voltage side terminal is grounded.

The scan side pull-down common line SD is connected to the scan side pull-down potential switching circuit 100, and the scan side pull-up common line S is connected.
A scanning-side pull-up potential switching circuit 200 is connected to U. The scan-side pull-down potential switching circuit 100 is composed of switches SW1, SW2, SW3 and SW3 '. These switches SW1, SW2 and SW3 are control signals NVC, NGC and NM2 in response to negative writing voltage _-V W, 0V and a modulation voltage 1/2 · _{V M}
To the pull-down common line SD. The switch SW3 'causes a current to flow in the opposite direction to the switch SW3 in response to the control signal NM2R. The scan-side pull-up potential switching circuit 200 includes switches SW4 and SW5. Switches SW4 and SW5 respond to control signals PVC and PM2, respectively, to write voltage V _W + V _{M of} positive polarity and modulation voltage 1
/ Give the 2 · _{V M} to the pull-up common line SU.

A data side pull-up potential switching circuit 300 is connected to the data side pull-up common line DU. The data side pull-up potential switching circuit 300 includes switches SW6 and SW.
It consists of 6 '. The switch SW6 is to whether or pullup common line DU provide modulation voltage 1/2 · V _M to the pull-up common lines DU responds to a floating state to the control signal M1. The switch SW6 'causes a current to flow in the opposite direction to the switch SW6 in response to the control signal M1R.

Modulated voltage supply circuit 400 is for supplying a modulation voltage 1/2 · _{V M} to the switch SW3, the switch SW5 and the switch SW6, the switch SW7, the switch SW
8, consisting of a diode and a capacitor C _M. The control signal M is applied to each of the switches SW7 and SW8.
UP and MDW are given. Control signal MDW by the switch SW8 is when it is turned on is charged modulated voltage 1/4 · _{V M} is the capacitor _{C M,} the modulation voltage 1/4 · _{V M} to the switch SW3, SW5 and SW6 are supplied. After that, when the switch SW8 is turned off and the switch SW7 is turned on by the control signal MUP, the switches SW3 and SW
Modulation voltage 1/2 · _{V M} is applied to the 5 and SW6.

On the other hand, the switch SW3 'of the scan-side pull-down potential switching circuit 100 and the data-side pull-up potential switching circuit 300.
When the switch SW6 'is turned on by the control signals NM2R and M1R and the switch SW8 of the modulation voltage supply circuit 400 is turned on by the control signal MDW,
Part of the energy stored in the thin film EL display device 10 is stored in the capacitor C _M.

The display data signal D is sent to the logic circuit 41 of the data side driver IC 40 via the data inversion control circuit 500.
ATA or its inverted data signal is applied.

Next, the operation of the drive circuit in FIG. 2 will be described using the time chart in FIG.

Here, it is assumed that the scanning side electrode Y ₁ including the picture element A and the scanning side electrode Y ₂ including the picture element B are selected by the line sequential driving. In addition, in this drive circuit, the polarity of the write voltage applied to the picture element is inverted for each line and driven. Scanning-side driver is connected to the scanning electrode _Y 1 to Y _i IC 2
The drive timing of one line for turning on the pull-down MOSFETs 502 of 0 and 30 and applying the negative write pulse to the picture elements on the electrode lines is called N drive timing, and the pull-up MOSFET 501 is turned on and its electrode line The drive timing of one line for applying a positive write pulse to the upper picture element will be referred to as P drive timing. In addition, N drive is executed for the odd line on the scanning side,
A field (screen) that executes P drive for even lines is called an NP field, and the opposite field is P field.
Let's call it N field.

(A) NP field 1. First modulation voltage charging period (T _N1 ) in N drive Turning on the pull-down MOSFETs 502 of all the drivers SDr _{1 to} SDr _i on the scanning side and the control signal NG
By turning on the switch SW2 by C, keeping all the scanning electrode _Y 1 to Y _i to 0V. At the same time, the switch SW6 is turned on by the control signal M1. At this time, the drivers DDr _{1 to} DDr _i on the data side are pulled up by the MOS for pull-up in the case of light emission according to the display data signal DATA.
The FET 501 is turned on, and in the case of no light emission, the pull-down MOSFET 502 is turned on. Here, when the display data signal DATA is “H” to emit light and “L” to not emit light, it is necessary to input the input display data signal DATA as it is to the data side driver IC 40, and thus the data inversion control circuit 500. The signal RVC applied to the pull-up MOSFET 501 is set to "L" when the input signal is "H" in the driver IC.
Is on and the pull-down MOSFET 502 is off, and the input signal is "L", the pull-up MOSFET is
It is assumed that 501 is turned off and the pull-down MOSFET 502 is turned on. Further, since the line-sequential driving is performed, the display data signal DATA is transferred at the time of driving the previous line and is held by the latch. Here, the switch SW8 is turned on by the control signal MDW to charge the capacitor C _M with the modulation voltage of 1/4 · V _M. Next, after turning off the switch SW8 by the control signal MDW, control signals MUP by turns on the switch SW7 applying a modulation voltage of 1/2 · _{V M} to the data side electrodes of the light emitting picture elements. In this way, only the data-side electrodes of the light emitting picture element is charged to the first modulation voltage 1/2 · V _M stepwise data-side electrodes of the non-light-emitting pixel is maintained at 0V without being charged. When charging is completed, the switches SW6 and SW7 are turned off.

2. Second modulation voltage charging and writing period (T _N2 ) in N driving Only the pull-down MOSFET 502 of the driver SDr connected to the selected scan-side electrode is turned on, and the pull-up MOSF for the other scan-side driver SDr.
Turn on the ET501. Simultaneously scanning side pull-up common lines SU, the control signal turns on the switch SW5 by PM2, applying a modulation voltage of 1/4 · _{V M,} then
By turning on the switch SW7 by the control signal MUP applying a modulation voltage of 1/2 · _{V M.} Further, the switch SW1 is turned on by the control signal NVC and the negative write voltage −V _W is applied to the scan-side pull-down common line SD. On the other hand, the data-side driver IC40 continues the driving of the first modulation voltage charging period in the N drive _{(T N1).}

As a result, in the light emitting picture element,
During the modulation voltage charging period ( _TN1 ), the data side electrode is 1/2
Since the modulation voltage of V _M is charged, the potential V _M becomes the data side electrodes, the scanning electrode selected negative writing voltage -V _W is applied. Therefore, the light emitting picture elements _{V M - (- V W)} = V W + V M is to emit light is applied. Further, in the non-emission picture element, the potential of the data side electrode is 0 V, and the negative write voltage −V _W is applied to the selected scanning side electrode. Therefore, 0 V-(-V _W ) = V _W is applied to the non-emission picture element, but it does not emit light because it is the light emission threshold voltage V _TH or less.

3. Write voltage discharge in N drive and second modulation voltage recovery period ( _TN3 ) Switch SW by control signals NVC, PM2, MUP
1, SW5, SW7 after turning off the, all the scanning-side driver _SDr 1 _~SDr pull-down MOSFET of
Turn on 502. Thus, the written voltage is discharged, all of the scanning electrode becomes 1/2 · V _M.

Accordingly, then the control signal NM2R, switch SW3 by MDW ', When on SW8, accumulation portion of the accumulated charge to the scanning electrode as a positive in the second modulation voltage charging period _{(T N2)} are in the capacitor _{C M} To be done. Then, the potential of all of the scanning electrode becomes 1/4 · _{V M.} On the other hand, the potential of the data side electrode connected to the light emitting pixel is 3/4 V _M
become.

4. N second modulation voltage discharge and first modulation voltage recovery period in driving _{(T N4)} control signal NM2R, switching 3 by MDW ', S
After turning off W8, switch S by the control signal NGC.
When W2 is turned off, the potential of the scanning side electrode becomes 0V. In addition, the potential of the data side electrode connected to the light emitting pixel is 1/2
· Become _{V M.} Here, the switch SW6 ', When on SW8, part of charges accumulated data side electrodes as the plus first modulation voltage period _{(T N1)} is accumulated in the capacitor _{C M} by the control signal M1R, MDW . Then, the potential of the data-side electrode becomes 1/4 · _{V M.}

5. First modulation voltage charging period (T _P1 ) in P drive Turning on the pull-down MOSFETs 502 of all the drivers SDr _{1 to} SDr _i on the scanning side and the control signal NG
By turning on the switch SW2 by C, keeping the potential of all of the scanning electrodes _Y 1 to Y _i to 0V. At the same time, the switch SW6 is turned on by the control signal M1.
At this time, the drivers DDr _{1 to} DDr _i on the data side turn on the pull-down MOSFET 502 in the case of light emission and turn on the pull-up MOSFET 501 in the case of non-light emission according to the inverted signal of the display data signal DTAT. Here, since it is necessary to input the inverted signal of the input display data signal DATA to the data side driver IC 40, the signal RVC supplied to the data inversion control circuit 500 is set to "H". Further, the switch SW8 is turned on by the control signal MDW to charge the capacitor C _M with the modulation voltage of 1/4 · V _M. Next, after the switch SW8 is turned off by the control signal MDW, the switch SW7 is turned on by the control signal MUP to set 1 to the data side electrode of the non-emission pixel.
A modulation voltage of / 2 · V _M is applied. As a result, only the first modulation voltage 1/2 is gradually applied to only the data side electrode of the non-emission pixel.
_-VM is charged. At this time, the data side electrode of the light emitting pixel is not charged and becomes 0V. When charging is completed, the switches SW6 and SW7 are turned off.

6. Second modulation voltage charging and writing period (T _P2 ) in P drive Only the pull-up MOSFET 501 of the driver SDr connected to the selected scan-side electrode is turned on, and the pull-down MOSF for the other scan-side driver SDr.
Turn on the ET502. At the same time, the switch SW4 is turned on by the control signal PVC to the scan-side pull-up common line SU, and the positive write voltage V _W + V _M is applied. The control signal NM2 is applied to the scan-side pull-down common line SD.
Turn on the switch SW3 by, 1/4 · _{V M} a modulation voltage is applied to, then, stepwise 1/2 · _{V M} by turning on the switch SW7 by the control signal MUP
The modulation voltage of is applied. On the other hand, the data side driver IC4
0 is the first modulation voltage charging period (T _P1 ) in P drive
Continue to drive.

Accordingly, in the light emitting picture elements, scanning electrode the potential of the data side electrodes is 0 is charged to the second modulation voltage of stepwise 1/2 · V _M. At the same time, since the positive write voltage V _W + V _M is applied to the selected scanning-side electrode, (V _W + V _M ) −0 V = V _W + V _M is applied to the light-emitting pixel to emit light. To do. In the case of non-emissive picture elements, P
Since the modulation voltage of the first modulation voltage charging period (V _P1) 1/2 · V _M to the data side electrode is charged in the driving, the potential of the data-side electrode V _M becomes, the scanning electrode which is selected Is applied with a positive write voltage V _W + V _M.
Therefore, the non-emission picture element has (V _W + V _M ) −V _M = V _W
Is applied, but it does not emit light because it is less than the light emission threshold voltage V _TH .

7. Write voltage discharge in P drive and second modulation voltage recovery period (T _P3 ) Switch SW by control signals NM2, PVC, MUP
3, SW4, SW7 after turning off a pull-down of all drivers _SDr 1 _{~SDr i} of the scanning MOSFE
Turn on T502. Thus, the written voltage is discharged, all of the scanning electrode becomes 1/2 · V _M. Therefore, the switch SW is next driven by the control signals NM2R and MDW.
When 3 ′ and SW8 are turned on, a part of the electric charges accumulated in the second modulation voltage charging period (T _P2 ) with the scanning side electrode being positive is accumulated in the capacitor C _M. Then, the potential of all of the scanning electrode becomes 1/4 · _{V M.} On the other hand, the potential of the data side electrode connected to the non-emission pixel is 3/4 · V _M
become.

8. Second modulation voltage discharge in P drive and first modulation voltage recovery period (T _P4 ). Control signals NM2R, MDW are used to switch SW3 ', S
After turning off W8, switch S by the control signal NGC.
When W2 is turned on, the potential of the scanning side electrode becomes 0V. Further, the potential of the data side electrode connected to the non-emission pixel is 1 /
Become 2 · _{V M.} Here, when the switches SW6 'and SW8 are turned on by the control signals M1R and MDW, a part of the charges accumulated with the data side electrode being positive in the first modulation voltage charging period (T _P1 ) is accumulated in the capacitor C _M. It
Then, the potential of the data-side electrode becomes 1/4 · _{V M.}

(B) PN field 1. First modulation voltage charging period (T _P5 ) in P driving The same driving as in the first modulation voltage charging period (T _P1 ) in NP field P driving is performed.

2. Second modulation voltage charging and writing period (T _P6 ) in P driving The same driving as in the second modulation voltage charging and writing period (T _P2 ) in NP field P driving is performed.

3. Write voltage discharge in P drive and second modulation voltage recovery period (T _P7 ) Write voltage discharge in P drive and second modulation voltage recovery period (T _P7 )
The same driving as in the modulation voltage recovery period (T _P3 ) is performed.

4. Second modulation voltage discharge and first modulation voltage recovery period (T _P8 ) in P drive The same drive as the second modulation voltage discharge and first modulation voltage recovery period (T _P4 ) in NP field P drive is performed.

5. First modulation voltage charging period (T _N5 ) in N driving The same driving as in the first modulation voltage charging period (T _N1 ) in NP field N driving is performed.

6. Second modulation voltage charging and writing period (T _N6 ) in N driving The same driving as in the second modulation voltage charging and writing period (T _N2 ) in NP field N driving is performed.

7. Write voltage discharge in N driving and second modulation voltage recovery period ( _TN7 ) Write voltage discharge in N driving N field and second
The same driving as in the modulation voltage recovery period ( _TN3 ) is performed.

8. , Second modulation voltage discharge in N drive and first modulation voltage recovery period (T _N8 ) The same drive as in second modulation voltage discharge and first modulation voltage recovery period (T _N4 ) in NP field N drive is performed.

As described above, this drive circuit is composed of the drive timings of the NP field and the PN field,
In the NP field, N drive is performed on the odd-numbered selection lines on the scanning side, and P is performed on the even-numbered selection lines.
The driving is performed, and the opposite driving is performed in the PN field, thereby applying an AC pulse required for light emission to all the picture elements of the thin film EL display device. FIG. 4 shows the voltage waveforms applied to the picture elements A and B as a typical example.

Further, the present applicant has proposed a step drive system in which the write voltage is raised stepwise by the multi-output voltage supply circuit shown in FIG.

This voltage supply circuit includes a multi-output transformer 11, a transistor 12, a control IC 13, a variable resistor 14, a rectifying unit 15, and a smoothing unit 16. Rectifier 15 is a rectifier diode D
11 to D14, and the smoothing unit 16 includes smoothing capacitors C11 to C14. The current on the secondary side of the transformer 11 is rectified and smoothed by the rectification unit 15 and the smoothing unit 16, and constant DC voltages V _W + V _M , (V _W + V _M ) / 2, −1 / are output from the output terminals o11 to o14, respectively. 2 · V _W and −V _W are output. These voltages are control IC13
Stabilized by. Output terminal o1 of this voltage supply circuit
1 and o12 are connected to a switch SW4 of the scanning side pull-up potential switching circuit 200 of FIG. 2 via a switch circuit (not shown). Also, output terminals o13 and o
14 is connected to the switch SW1 of the scan-side pull-down potential switching circuit 100 via a switch circuit (not shown).

Using this voltage supply circuit, the positive writing voltage applied to the scanning side electrode in FIG. 2 is gradually increased to (V _W + V _M ) / 2, V _W + V _M, and the negative writing voltage applied to the scanning side electrode. Built-in voltage -1
The power consumption can be reduced by gradually lowering the value by 2 · V _W and −V _W.

On the other hand, the applicant of the present invention has proposed a driving method for realizing the dimming function in the thin film EL display device 10. In this driving method, dimming of 0 to 100% is performed by changing the voltage applied to each picture element, and as shown in FIG. A dimming pulse having a constant polarity voltage is applied.
Thereby, the applied voltage-luminance characteristic can be stabilized. That is, the applied voltage-luminance characteristic when no dimming pulse is applied has a steep gradient up to a certain voltage as shown by the line 14 in FIG. 7, but the luminance is saturated at a voltage higher than that. On the other hand, when the dimming pulse is applied, a stable gradient can be obtained as shown by the line l5, and even if the thin film EL display device 10 is changed with time, the same gradient as shown by the line l6 is obtained. The characteristics are obtained. Therefore, even if the voltage of the write pulse is changed, the amount of change in luminance due to the change with time of the applied voltage-luminance characteristic is kept small in any region. As a result, even if the voltage of the write pulse is changed to realize the dimming function, the luminance of the picture element operating in the light emitting state and the picture element operating in the non-light emitting state with time The difference can be made sufficiently small and a desired dimming function can be realized.

In this way, by applying the dimming pulse, a wide range of dimming can be realized without deteriorating the quality of the screen obtained by the thin film EL display device.

[Problems to be Solved by the Invention] In the above driving method, dimming is performed by changing the writing voltage while keeping the voltage of the dimming pulse constant. In the voltage supply circuit shown in FIG. 8, the voltage of each output terminal o11 to o14 cannot be controlled individually, so that the voltage of the dimming pulse is kept constant and only the write voltage is changed. The function cannot be realized.

Therefore, the voltage supply circuit shown in FIG. 9 has been devised. In this voltage supply circuit, the transformer 21, the transistor 22, the control IC 23, the variable resistor 24, the rectifying diode D
21 and the smoothing capacitor C21 to connect the node N1
A stabilized DC voltage of 1/2 · V _W can be obtained. On the other hand, the modulation voltage generation circuit 25 generates the modulation voltage V _M which is a variable voltage. The first voltage generating circuit 20a generates a voltage 1/2 from the DC voltage 1/2 · V _W obtained at the node N1 and the modulation voltage V _M obtained from the modulation voltage generating circuit 25.
Deriving V _W , V _W and V _W + V _M to the output terminal o21. The second voltage generating circuit 20b outputs the voltage −1 to the output terminal o22 from the DC voltage 1/2 · V _W obtained at the node N1.
Derive 2 · V _W and −V _W.

In the first voltage generation circuit 20a, the switching elements SW21 and SW22 are turned off, and the switching element S
When W23 is turned on, the positive terminals of the capacitors C23 and C22 are charged to a voltage of 1 / 2.V _W through the diodes D24 and D23, and the voltage of 1 / V is output from the output terminal o21.
2 · V _W is output. And the switching element SW
When the switching element SW22 is turned off and the switching element SW22 is turned on, the negative terminal side of the capacitor 23 is charged to the voltage ½ · V _W via the diode D23. Accordingly, the voltage of the positive terminal side of the capacitor C23 is raised to _{V W,} the voltage _{V W} is outputted from the output terminal o21. Further, the switching element SW21 is turned on, the negative terminal side of the capacitor C22 is charged to the voltage _{V M.} Thus, the positive terminal of the capacitor C23 is pulled up to the voltage _V W + _{V M,} the voltage _V W + _{V M} is output from the output terminal o21.

On the other hand, in the second voltage generating circuit 20b, when the switching element SW24 is turned on and the switching elements 25 and SW26 are turned off, the capacitors C24 and C25.
The positive terminal side of is charged to a voltage of 1/2 · V _W. And
When switching element SW24 turns off and switching element SW26 turns on, capacitors C24 and C25
The negative terminal side of is pulled down to a voltage of −1 / 2 · V _W. As a result, the voltage from the output terminal o22 is -1/2.
V _W is output. Next, when the switching element SW25 is turned on, the positive terminal side of the capacitor C24 has a voltage of −1 /
It is pulled down to 2 · _{V W.} Thus, the negative terminal of the capacitor C24 is lowered to the voltage -V _W, the voltage -V _W is output from the output terminal o22.

According to the voltage supply circuit, by changing only the magnitude of the modulation voltage V _M by the modulation voltage generation circuit 25, it is possible to vary the magnitude of the voltage V _{W +} V _M while the voltage V _W constant. Therefore, a dimming function is realized in which the voltage of the dimming pulse is kept constant or only the voltage of the writing pulse is changed.

However, the voltage supply circuit shown in FIG. 9 has a problem that the number of parts is large and the cost is high.

An object of the present invention is to solve the above problems and provide a drive circuit that realizes a dimming function at low cost and low power consumption.

[Means for Solving the Problems] A driving circuit of a thin film EL display device according to the present invention includes a plurality of scanning electrodes arranged in one direction and a plurality of data sides arranged in a direction intersecting the scanning electrodes. A driving circuit for a thin film EL display device comprising an electrode and an EL layer interposed between a scanning side electrode and a data side electrode, the direct current voltage generating means, the variable voltage generating means, the voltage synthesizing means, and the writing. It is provided with a voltage applying means, a modulation voltage applying means, and a dimming pulse applying means. The DC voltage generating means generates a first DC voltage having a first polarity and a second DC voltage having a second polarity. The variable voltage generating means generates a variable voltage whose magnitude can be changed according to the dimming degree. The voltage synthesizing means generates a third DC voltage by adding the first DC voltage generated by the DC voltage generating means to the variable voltage generated by the variable voltage generating means. The writing voltage applying means sequentially applies the second DC voltage or the third DC voltage as a writing voltage to the plurality of scanning electrodes. The modulation voltage applying means applies a variable voltage as a modulation voltage to any of the plurality of data side electrodes based on the display data.
The dimming pulse applying means applies the writing voltage by the writing voltage applying means to the scanning-side electrode and has a first polarity opposite to the writing voltage.
The DC voltage or the second DC voltage is applied as a dimming pulse voltage.

[Operation] In the drive circuit according to the present invention, positive and negative write voltages are sequentially applied to the plurality of scanning electrodes. This write voltage is the second DC voltage or the third DC voltage. On the other hand, a modulation voltage is applied to the plurality of data electrodes based on the display data. This modulation voltage is a variable voltage. As a result, E at each intersection of the scanning side electrode and the data side electrode
A voltage which is the difference between the write voltage and the modulation voltage is applied to the L layer. Then, when the applied voltage exceeds a predetermined threshold value, the EL layer at the intersection emits light.

The third DC voltage and the modulation voltage are changed by changing the variable voltage from the variable voltage generating means. As a result, the voltage applied to the EL layer changes and light control is performed.

After the write voltage is applied by the write voltage applying means, the dimming pulse voltage having the opposite polarity to the write voltage is applied by the dimming pulse applying means. Since the dimming pulse voltage is the first DC voltage or the second DC voltage, the dimming pulse voltage does not change even if the variable voltage is changed to perform dimming. By applying this dimming pulse voltage, the dimming level can be changed without degrading the quality of the display screen of the EL layer.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a voltage supply circuit included in a drive circuit according to an embodiment of the present invention.

In FIG. 1, the power supply voltage V is applied to one terminal T1 on the primary side of the multi-output transformer 1, and the other terminal T2 is connected to the ground terminal via the collector and emitter of the transistor 2. The base of the transistor 2 is the control IC 3
And a variable terminal of the variable resistor 4. One terminal of the variable resistor 4 is connected to the first output terminal o1 on the secondary side, and the other terminal is connected to the ground terminal. Secondary side first terminal T3, second terminal T of the multi-output transformer 1
The fourth terminal 4, the fourth terminal T6, and the fifth terminal T7 are connected to the output terminals o1, o2, o3, and o4 via rectifying diodes D1, D2, D3, and D4, respectively. The third terminal T5 is connected to the ground terminal. The rectifying diodes D1 to D4 form a rectifying unit. Smoothing capacitors C1, C2 are provided between the output terminal o1 and the ground terminal, between the output terminal o4 and the ground terminal, between the output terminal o2 and the ground terminal, and between the output terminal o3 and the ground terminal, respectively. C3
C4 is connected. These smoothing capacitors C1
C4 form the smoothing part 6.

On the other hand, the output terminal o1 is connected to the node N2 via the switching element SW1, and the switching element SW2 is connected between the node N2 and the ground terminal. For example, switching transistors are used as the switching elements SW1 and SW2. Further, the node N2 is connected to the output terminal o5 via the boosting capacitor C5.

Further, the input terminal I1 is connected to the output terminal o5 via the modulation voltage backflow prevention diode D5. Modulation voltage generation circuit 7 sizes from Adjustable modulation voltage V _M is applied to the input terminal I1.

Next, the operation of the voltage supply circuit of FIG. 1 will be described.

The voltage appearing at each terminal T3 to T7 on the secondary side of the multi-output transformer 1 is rectified and smoothed by the rectifying unit 5 and the smoothing unit 6, and a positive voltage V _W at the output terminals o1 to o4, half the voltage 1 / 2 · V _W , a negative voltage −V _W , and a half voltage −½ · V _W are output. These voltages are
It is stabilized by the control IC3.

The voltage V _W + V _M is output from the output terminal o5 as follows. First, the switching element SW1 is in the off state,
The switching element SW2 is in an ON state, the modulation voltage V _M is charged in the capacitor C5 via a diode D5 from a modulation voltage generating circuit 7. Next, the switching element SW2
Is turned off and the switching element SW1 is turned on,
The cathode side of the capacitor C5 is the voltage V _{W of the} output terminal o1.
Boosted to. As a result, the anode side of the capacitor C5 is boosted to the voltage V _W + V _M. Therefore, the voltage V _W + V _M is obtained from the output terminal o5. By changing the magnitude of the modulation voltage V _M obtained by the modulation voltage generation circuit 7, the voltage V _W + V _M changes.

As described above, the voltage supply circuit 60 described above has a simpler circuit configuration than the conventional voltage supply circuit, so that the number of partial points can be reduced and the cost can be reduced.

The structure of the portion other than the voltage supply circuit 60 in the drive circuit of this embodiment is the same as that of the circuit shown in FIG. Switch SW of the scanning-side pull-down potential switching circuit 100 in FIG.
1 is supplied with the voltage −V _W of the output terminal o4 of the voltage supply circuit or the voltage −½ · V _W of the output terminal o3 via a switch circuit (not shown). Further, the switch SW4 of the scanning-side pull-up potential switching circuit 200 has a voltage V _{W at} the output terminal o1 of the voltage supply circuit 60, a voltage ½ · V _{W at the} output terminal o2, or a voltage V _W + V _{M at the} output terminal o5.
Are provided via a switch circuit (not shown).

The operation of the drive circuit shown in FIG. 2 is similar to the operation described with reference to FIGS. 4 and 5. That is, the scan side driver ICs 20 and 30 sequentially apply the write voltage to the scan side electrodes Y _{1 to} Y _i . At this time, the data side electrodes X _{1 to} X
The _i applies a modulation voltage _{V M} or 0V according to the display data signal TATA by the data-side driver IC 40.
In this case, in the NP feed, the scanning side electrodes Y ₁ to
N drive is applied to the odd lines of Y _i to apply a negative write voltage V _W, and P drive is applied to the even lines of the scan side electrodes Y _{1 to} Y _i to apply a positive write voltage V _W + V _M. To do. NP
In the field, the opposite drive is performed. At this time, perform dimming by changing the magnitude of the voltage V _M by the modulation voltage generation circuit 7 of FIG. 1. Then, as shown in FIG. 5, in each field, after applying a write pulse to each of the scanning side electrodes Y _{1 to} Y _i , a dimming pulse having a polarity opposite to that of the writing pulse is applied to the scanning side electrode. To do.
That is, after applying a negative write pulse voltage -V _W by N drive applies a dimming pulse of constant voltage V _W by P driving, a positive write pulse voltage V _{W +} V _M by P drive After the application, a dimming pulse having a constant voltage −V _W is applied by N driving. When the dimming pulse is applied, the voltage V _W of the output terminal o1 of the voltage supply circuit 60 is applied to the switch SW4 of the scanning side pull-up potential switching circuit 200.

Thus, the voltage applied to each pixel by changing the voltage V _M varies, dimming function is realized. Then, by applying a dimming pulse having a constant voltage −V _W , V _W , deterioration of the quality of the display screen is prevented.

When the step driving method is used in order to reduce the power consumption when the write pulse and the dimming pulse are applied, the following is performed. That is, when a negative write pulse is applied, the switch SW1 of the scan-side pull-down potential switching circuit 100 is first supplied with the voltage −1 / 2 · V _W of the output terminal o3 of the voltage supply circuit 60 and then the voltage of the output terminal o4. -V _W
give. When a positive write pulse is applied, the switch SW4 of the scan-side pull-up potential switching circuit 200 first sets the voltage −1 / 2 · V _W of the output terminal o2 of the voltage supply circuit 60.
Then, the voltage V _W + V _M of the output terminal o5 is applied.
Then, when the negative dimming pulse is applied, the voltage −1 / 2 · V _W of the output terminal o3 of the voltage supply circuit 60 is first applied to the switch SW1 of the scanning side pull-down potential switching circuit 100,
Next, the voltage −V _W of the output terminal o4 is applied. When a positive dimming pulse is applied, the scanning side pull-up potential switching circuit 1
00 switch SW4 is first applied with the voltage ½ · V _W of output terminal o2 of voltage supply circuit 60, and then output terminal o1
Of the voltage V _W.

As described above, according to the drive circuit of this embodiment, it is possible to realize the dimming function with low power consumption without deteriorating the quality of the display screen.

[Effects of the Invention] As described above, according to the present invention, a drive circuit of a thin film EL display device that realizes a wide range of dimming function without deteriorating the quality of a display screen and consumes less power is provided. It is provided at low cost due to the small number of parts.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a voltage supply circuit included in a drive circuit of a thin film EL display device according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing a drive circuit of a thin film EL display device, and FIG. 3 (a).
Shows a driver included in the drive circuit of FIG. 2, FIG.
FIG. 4B is a diagram showing a detailed circuit configuration of the driver of FIG. 3A, and FIG. 4 is a timing chart for explaining the operation of the drive circuit of FIG. 2 and voltage waveforms applied to picture elements. FIG. 5 is a voltage waveform diagram showing a method of applying a dimming pulse, FIG. 6 is a partially cutaway perspective view of a thin film EL display device, and FIG. FIG. 8 is a circuit diagram showing an example of a voltage supply circuit included in the drive circuit of the conventional thin film EL display device, and FIG. 9 is included in the drive circuit of the conventional thin film EL display device. FIG. 7 is a circuit diagram showing another example of a voltage supply circuit that is used. In the figure, 1 is a multi-output transformer, 2 is a transistor,
3 is a control IC, 4 is a variable resistor, 5 is a rectifying unit, 6 is a smoothing unit, 7 is a modulation voltage generating circuit, D1 to D5 are diodes,
C1 to C5 are capacitors, SW1 and SW2 are switching elements, 10 is a thin film EL display device, 20 and 30 are scanning side high breakdown voltage push-pull type driver ICs, 40 is a data side high breakdown voltage push pull type driver IC, and 100 is a scanning side. A pull-down potential switching circuit, 200 is a scanning side pull-up potential switching circuit, 300 is a data side pull-up potential switching circuit, 400 is a modulation voltage supply circuit, and 50 is a data inversion control circuit.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Hiroshi Kishishita 22-22 Nagaike-cho, Abeno-ku, Osaka, Osaka Within Sharp Corporation

Claims (1)

[Claims] 1. A plurality of scanning electrodes arranged in one direction,
A driving circuit for a thin-film EL display device comprising a plurality of data-side electrodes arranged in a direction intersecting with the scanning-side electrode and an EL layer interposed between the scanning-side electrode and the data-side electrode. And a DC voltage generating means for generating a first DC voltage of a first polarity and a second DC voltage of a second polarity, and a variable voltage whose magnitude can be changed according to the dimming degree. Variable voltage generating means, voltage synthesizing means for generating a third DC voltage by adding the variable voltage generated by the variable voltage generating means to the first DC voltage generated by the DC voltage generating means, Write voltage applying means for sequentially applying the second direct current voltage or the third direct current voltage as a write voltage to a plurality of scanning side electrodes, and to one of the plurality of data side electrodes based on display data. Yes A modulation voltage applying unit that applies a voltage as a modulation voltage, and the first DC voltage having the opposite polarity to the writing voltage or the second DC voltage to the scanning-side electrode after the writing voltage is applied by the writing voltage applying unit. A drive circuit for a thin-film EL display device, comprising a dimming pulse applying means for applying the DC voltage as a dimming pulse voltage.