JPS5922954B2 - Drive device for thin film EL display device - Google Patents

Description

[Detailed Description of the Invention] Overview In a thin film EL having a hysteresis memory, writing or erasing is performed by instantaneously applying a voltage equal to or less than the maintenance AC amplitude under maintenance AC drive, and subsequent The present applicant has already filed an application as a prior invention for a technique for maintaining the light-emitting state or light-off state using a maintenance AC voltage.

The present invention relates to a sustain drive circuit, a write circuit, and a clean circuit for a thin film EL matrix panel having an AC hysteresis phenomenon, that is, a memory function.

Prior Art> First, the technology of the prior invention, which is the basis of the present invention, will be briefly explained.

First, the configuration of the EL display device will be explained.

Striped transparent electrodes are arranged in parallel in one direction on a glass substrate. A layer of dielectric material such as Y, O3, etc. is placed on the entire surface.
Furthermore, a phosphor layer such as ZnS doped with Mn is formed on the entire surface, and three layers of dielectric material are further formed on top of this by vapor deposition.
It is deposited to a thickness of 500 to 10,000 layers using a thin film technique such as a sputtering method to form a three-layer structure, and striped electrodes are arranged in parallel thereon in a direction orthogonal to the transparent electrode. With this structure, when an appropriate AC voltage is applied to one of the first electrode group and one of the second electrode group, only the minute area sandwiched between the two electrodes crosses. It will emit light,
This corresponds to one picture element on the screen. An EL display device can be constructed by sandwiching an EL-emitting fluorescent lamp layer between two dielectric layers and forming two more electrodes on it, but as described above, it is possible to construct an EL display device by sandwiching the fluorescent lamp layer that emits EL light between two dielectric layers and forming two more electrodes on it. By forming a grid, a matrix display panel can be formed.
EL with this type of structure has superior characteristics in terms of brightness, lifespan, and stability compared to conventional dispersion type EL elements, but this thin film EL element has a new feature that improves the relationship between brightness and applied voltage. shows the historical phenomenon. When a pulse of voltage amplitude , is first applied, the brightness is at the low brightness level B1. Maintain voltage here,
is 1>Th, where Th is the light emission threshold voltage. When high voltage 2 for writing is applied to this, the brightness changes all at once to high brightness B.
3, and thereafter, even if the voltage value is returned to the maintenance voltage 1 again, the brightness settles to B, which is a higher brightness B2. When a low voltage 3 for erasing is applied to this, the brightness level decreases rapidly, and when it is returned to the light sustaining voltage, the brightness settles to B. This hysteresis phenomenon can take any small loop depending on the amplitude and pulse width (not shown) of the write voltage. That is, it is also possible to display halftones. A major feature of the ELP, which is not found in other display elements, is that once a write voltage is applied, each picture element continues to emit light without losing the gradation given to it by the sustain pulse. The above voltages vary greatly depending on the composition, film thickness, and applied waveform, but in a prototype example, Th-200, 1=
210V, 2=210-280, 3=190.

Problems to be solved by the Invention The circuit shown in FIG. 1 can be considered as a single power source type point sequential drive circuit for a thin film EL matrix panel with memory.

FIG. 1a shows electrodes arranged in a matrix, switches and power supplies connected thereto, and FIG. 1b shows one unit circuit of the switch in FIG. 1a.

The X-direction electrodes Xl, x2, . This electrode has letters,
Since the switching of the switches Sx, sx2, . Electrodes Yl, Y2, in the Y direction
..., Yn are also switches SYl, SY2, ...
・It is switched and connected to the ground side contact and the power supply side contact through , SYn. These electrodes are electrodes Yl and Y2 arranged in the Y direction.
,...Yn sequentially switches SY,,SY2...
・Since SYn is controlled, it is called a scanning electrode. The ground side contact is grounded through line 10, and the power side contact is connected through line 20 to the sustain voltage terminal V8, the write voltage terminal and the erase voltage terminal. , is connected to a switch 30 which switches the connection to the ground terminal E. The above switches Sxl, sx2,...
・, Sxm and SYl, SY2, ..., SYn are the first
As shown in FIG. b, it has a power supply terminal 1, an input terminal 2, and an output terminal 3, and consists of two transistors Trl and Tr2.

The collector of the transistor Trl is connected to the power supply terminal 1, and its emitter is connected to the collector of the transistor Tr2 through the output terminal 3 and the diode D1. A resistor R, is inserted between the collector and base of the transistor Trl, and the base is connected to the collector of the transistor Trl. The base of the transistor Tr2 is connected to the input terminal 2 via a resistor R2, and the emitter is directly grounded.
In the above circuit, switches SX,, SX2,...
, SXm, SYl, SY2, . . . , SYn perform point-sequential scanning by sequentially selecting display pixel points in a fixed direction. The switch then alternately switches between ground potential and the supply voltage at a frequency on the order of 100 HZ to 5 KHz, applying substantially bipolar pulses to the thin film EL panel.
The switch 30 is switched in synchronization with the above scanning to apply a sustain voltage, a write voltage, and an erase voltage to the selected picture element point. By the way, as shown in FIG. 1b, the above circuit has an input terminal 2.
The positive pulse applied to transistors Trl and Tr
2 are controlled to be turned on and off alternately.

Since the on/off control is performed alternately in this manner, the scan electrode and the data electrode cannot be set to an open state, that is, the two transistors Trl and Tr2 cannot both be set to an off state. This disadvantageously disables the readout operation of the thin film EL matrix panel with memory and eliminates one function. Moreover, since one transistor is always on, power consumption is large. In order to solve this problem, the circuit shown in FIG. 2 can be considered.

FIG. 2a has a configuration substantially similar to that of FIG. 1, and corresponding parts are given the same reference numerals and explanations will be omitted. In Fig. 2a, the data side switches SXζ, SX6, ..., SXm' and the scanning side switches SY{, SY6, ..., SY'n are configured as one unit of two on/off switches. .
Switch Sxl, sx2,...Sxm, sYl, sY
2, ..., SYn are power supply terminals 1 as shown in Figure 2b.
, two input terminals 2a, 2b and an output terminal 3, and is composed of three transistors Tr3, Tr4, Tr5.
In this circuit, transistors Tr3, Tr5 and Tr4 are turned on or off according to the signals applied to the two input terminals 2a and 2b, and when a positive pulse is not applied to both input terminals 2a and 2b, the three Transistor Tr3, Tr
4, Tr5 are all off. Therefore, both the scan electrode and the data electrode can be set in an open state, and the problem of the circuit of FIG. 1 is solved. However, the circuit of FIG. 2 requires three transistors for each data electrode and scan electrode.

Currently 2/M7 on 8 inch EL panel! Electrodes are attached at L intervals, and 320 data electrodes and 340 scan electrodes are provided. Therefore, the number of transistors increases in accordance with the number of electrodes. This means that power consumption also increases. The present invention was invented in view of the above problems, and provides a rational new circuit with a small number of transistors. In addition, a new problem arises with the circuit of the present invention, namely, when writing and erasing any selected pixel point, the write pulse and erase pulse are applied to one electrode connected to the selected point, the other is grounded, and all other However, in the case of writing, since the writing voltage is high, an erase effect may appear due to the floating of the half-selected line.

Therefore, it is an object of the present invention to provide a driving method in which a write pulse is applied to an EL panel with the same polarity as the sustain pulse immediately before it, thereby preventing the above-mentioned undesired erasing effect from occurring. The present invention also provides an effective method for applying an erase pulse.

Furthermore, the present invention provides a method for solving the problem of half-selected line processing, which is always a problem when driving a matrix panel, by changing the timing of applying pulses without adding any new circuits.

One Embodiment of the Present Invention> FIG. 3 shows a circuit diagram of the device of the present invention, in which the data electrode
, x2...Xm is an on/off data switch Sxl
, sx2, . . . , Sxm to ground by line 40.

Further, each data electrode is connected to the pulse power switch 30 via the switch SXO by a common line 50 through a diode D2. The scan electrodes are connected to the pulse power switch 30 by a line 60 via on/off scan switches SYl, SY2, .
Grounded via YO. The above data switch Sx,,
One unit of sx2,...,Sxm is 1 as shown in Figure 4a.
The input terminal 21 is connected to the base through the resistor R6, the emitter is grounded, and the collector is connected to the output terminal 22 connected to the data electrode.

Switch SYO is also constructed as shown in FIG. 4a, with output terminal 22 connected to common line 70. Further, one unit of scanning switches SY, SY2, . . . , SYn is constructed as shown in FIG. 4b.

The input terminal 23 is connected to the base of the transistor Tr7 through a resistor R, and its emitter is grounded. The emitter of the transistor Tr8 is connected to the terminal 24 connected to the common line 60, and the collector thereof is connected to the output terminal 25 connected to the scanning electrode. A resistor R8 is inserted between the terminal 24 and the base of the transistor Tr8, and the collector of the transistor Tr and the base of the transistor Tr8 are connected by a resistor. The switch SXO is also constructed as shown in FIG. 4b, and the output terminal 25 is connected to the line 60. Note that the voltages supplied to the sustain voltage source terminal S, the write voltage source terminal w, and the erase voltage source terminal VE of the pulse power switch 30 are all positive voltages here.

The circuit of the present invention is configured as described above, and writing, erasing, and sustain driving are performed as follows.

Electrical writing of a thin film EL element takes several tens to ten times more than a sustain pulse.
This can be done by applying a single write pulse of about 100 volts in one direction.

In addition, complete erasure is achieved by applying many erase pulses in both directions with an erase voltage several tens of volts lower than the sustain voltage, but one pulse can be used to erase a considerable amount with just one pulse. Basically, single-pulse erasing is sufficient for erasing. Incidentally, in one example, the sustain voltage (8) was 200 volts, the write voltage (w) was 270 volts, and the erase voltage (Ve) was 160 volts.

Based on the above considerations, the present invention performs writing and erasing using pulse pulses. First, consider the case of writing to picture element (1,j).

In order to apply a bipolar sustain pulse Ps to the entire surface of the thin film EL panel before writing, the pulse power switch 30 is connected to the sustain voltage source terminal s. Then, at time T, the switch SXO is turned on, and the data switches SX,, SX2,...
・, SXi, SXk, ..., SXm are off, switch SYO is on, and scanning switches SYl, SY2,
..., SYj, SYl, ...SYn are turned off.
As a result, a negative sustain pulse Ps is applied to the thin film EL panel when viewed from the data electrode side. Next, at time T2, switch SXO is turned off, and all data switches SX, ~SXm
, turn on switch SYO, turn on full scan switch SY
, ~SYn is turned off to short-circuit the scan electrode and data electrode of the thin film EL panel. Furthermore, at time T, switch SXO
is turned off, all data switches Sxl to Sxm are turned on, switch SYO is turned off, all scanning switches SYl to SYn are turned on, and a positive sustain pulse Ps is applied to the thin film EL panel. At time T4, each switch is changed in the same manner as at time T, and the voltage applied to the thin film EL panel is set to O voltage. When sustain pulses are applied as described above,
In order to apply a write pulse Pw having a write voltage Vw to the picture element (1, j) point at time Tw, the pulse power switch 30 is connected to the terminal Vw.

and the switch SXi of the data electrode including the write pixel point.
is turned on, and the other data electrode switches SXk (KX
i) is off, the switch SxO is turned off, the switch SYj of the scan electrode including the write pixel point is on, the switch SY2 (l'8.j) of the other scan electrodes is off, and the switch SYO is turned off. Ru. This result picture element (1,j)
A write pulse Pw is applied to and emits light of high brightness B. At this time, switches SXk (KXi), SYI (1
Sj) are both in the off state, so the data electrode
J pixel (1,1) (J,
k) (Hereinafter, these points will be referred to as half-selected pixel points.

) Furthermore, the potential rises at the picture element (11,k) (hereinafter these points will be referred to as non-selected picture element points), and pulses Pl, P2, P substantially appear. Here these pulses Pl
,P,,P,, now the number of electrodes in the x direction is Mly, the number of electrodes in the direction is Nll, the capacitance of the pixel is C
Then, since the capacitance is proportional to the area, each capacitance is as follows: pixel point (1, 2) is C, pixel point (J, k) is (m-1) C1 pixel point (I, l) is ( n-1) C1 picture element point (!, k) is (
m-1)(n-1)C. Therefore, the equivalent circuit when the write pulse Pw (voltage w) is applied can be expressed as shown in FIG. Here, the voltage appearing on the capacitor C is the voltage V1 of the pulse P1, the voltage appearing on the capacitor C2 is the voltage 2 of the pulse P2, and the voltage appearing on the capacitor C3 is the pulse P3.
The voltage is 3. Since M and n are usually 100 or more, c1
=Mclc2=NcSc3=Mnc>>C, so since the capacitance of C3 is extremely large compared to Cl and C2, it is considered to be almost a short circuit, and 3=O. Then voltage 1,
2 becomes.

m:n=4:3, sustain voltage 8=200 write voltage w-2
When it is 80, it becomes.

The optimum erase voltage is approximately 100s-100s, so 160 to 167
Therefore, voltage 2 becomes the optimal erasing voltage, and the picture element (1, 1)
The contents written in will be erased. In other words, writing at a writing point affects some of the other picture elements, which is not desirable. As is clear from equation (1), if n = m, V, - 2 = 100 W, and in this case, Max [,, 2] -, = 2 is the minimum, but it is still possible to erase this. Furthermore, as n=m, Max[1,2] becomes larger and larger. Ma
There is a limit to how low the voltage W can be in order to keep x[,,2] below the erase level, so this is not a fundamental solution. Before solving this problem, let's consider the phenomenon of erasure. FIG. 7c shows that when an erase pulse having an erase voltage E as shown in FIGS. 7A and b is inserted between sustain pulses into a single thin film EL element with memory, the voltage value E is plotted on the horizontal axis. This is a graph plotting the brightness after erasure on the secondary axis.

In FIG. 7c, the upper dotted line indicates writing luminance, and the lower dotted line indicates erasing luminance. Further, as for the positive/negative voltage of the voltage VE, a voltage in the opposite direction to the immediately preceding sustain pulse as shown in FIG. 7a is positive, and a voltage in the same direction as in FIG. 7b is negative. As can be seen from Figure 7c,
It can be seen that the erasing effect occurs when the erasing voltage is positive and the magnitude is slightly lower than the sustaining voltage Vs.
That is, it can be seen that erasing cannot be achieved at all by applying the erasing pulse as shown in FIG. 7b, and that erasing is effective only when it is applied as shown in FIG. 7a. By the way, the reason why there was a concern about erasure with the applied waveform shown in FIG. 5 is that as shown in FIG. 5, a rise occurs in the opposite direction to the immediately preceding sustain pulse. Therefore, if a write pulse is applied in the same direction as the previous sustain pulse, the half-selected line will rise in the same direction.
As can be seen from the discussion of FIG. 7, there is no erasing effect due to lifting. Since the write pulse voltage W is larger than the sustain voltage Vs, the direction of the immediately preceding sustain pulse has almost no relation to the write effect. As mentioned above, when applying the sustain pulse PSl write pulse Pw as shown in FIG. 5, problems arise as discussed above and in FIG.
Based on these problems and ideas, the present invention provides a driving method that completely eliminates the possibility of erasing a semi-selective picture element.

Furthermore, when erasing an arbitrary point in the present invention, what is meaningful as an erasing pulse is the erasing pulse that is issued in the opposite direction to the immediately preceding sustain pulse, as shown in Figure 7a. The best way to do this is to use a pulse like the one shown.
According to the present invention, the sustain pulse Ps write pulse P when performing effective writing and erasing to any selected picture element (1, j)
w. A timing chart of the erase pulse PE is shown in FIG.

In FIG. 8, Tl, T3, and T5 are sustain pulse periods, T2 is a write period, and T4 is an erase period. Sustain pulse period T
,, T3, T5, the respective switches Sxl to Sxm, sx are operated in the same way as explained in conjunction with FIG.
O, SYl to SYn, SYO operate. Writing period T
2, each switch operates in the same manner as in the case of FIG. 5, except that the write pulse Pw is applied immediately after the sustain pulse is applied from the scanning electrode side. Apply a write pulse with the same polarity as the previous sustain pulse. Therefore, the potential of the half-selected picture element rises, and the pulses Pl, P
2 and P3 appear, but since this pulse has the same polarity as the previous sustain pulse and is a negative voltage as explained in FIG. 7c, there is no erasure phenomenon of half-selected picture elements. At time Te of the erase period T4, the pulse power switch 30 is connected to the terminal e, and the switch S of the data electrode containing the erased picture element (1, j) is connected to the terminal e.
Xi is on, other data electrode switches SXk (K
Xi) is turned off, switch SXO is turned off, switch SYj of the scan electrode including the write picture element is turned on, switches SYI (l-j) of the other scan electrodes are turned off, and switch SYO is turned off.

As a result, the erase pulse Pe is applied to the picture element (1,j). The erasing pulse Pe has the opposite polarity to the sustain pulse immediately before it, and erasing is completely performed. Since the erase pulse Pe is applied, it is possible that the potential of the half-selected picture elements (J, k) (I, l) rises, but the sustain voltage s - 200V1 optimal erase voltage E = 160, m:n = 4:3 In the case of equation (1), ,
2, and although there is a slight rise, the voltage is lower at 91V compared to the erase voltage of 160, and the emission threshold voltage Vth
, so the thin film EL panel will not take any action. Effects of the Invention The present invention provides an on-line conductor that is commonly connected to all scanning electrodes and led to ground.
Since it is equipped with an off switch and an on/off switch that is commonly connected to all data electrodes and leads to the power supply line, the on/off switch that is connected to each scan electrode and each data electrode applies a bipolar sustaining pulse to the thin film EL panel. This switch does not have to have the function of opening the scan electrode and the data electrode, so in the embodiment shown in FIGS. 3 and 4,
It can be constructed using 2n+1+m+2=2n+m+3 (pieces) of transistors.

In the case of the circuit considered in Figure 2, this is 3(m+n)(
This means that the number of transistors required is approximately half of that required. In this way, the power consumption decreases by the amount of the decrease in the number of transistors. In addition, the present invention solves the problem of erasing effect that occurs at half-selected pixel points when a write pulse is applied to a selected pixel point by adjusting the application timing of the write pulse by utilizing the properties of a thin film EL panel. No additional circuitry or new configuration is required.

Similarly, since the erasing pulse is effectively applied by selecting the application timing of the erasing pulse using the properties of the thin film EL panel, effective erasing is performed and there is no influence on half-selected picture elements.

[Brief explanation of drawings]

1 and 2 are circuit diagrams of a thin film EL matrix panel considered as a preliminary stage of the present invention, FIG. 3 is a circuit diagram of a drive device for a thin film EL display device according to an embodiment of the present invention, and FIG. 4 A and b are circuit diagrams of switching elements used in the circuit of FIG. 3, FIG. 5 is a time chart explaining the operation of the present invention, and FIG. 6 is a thin film EL when a write pulse is applied to a selected picture element. Equivalent circuit diagram of the display device, Figures 7a and b are time charts when erasing pulses are applied at different timings, and Figure 7c is the erasing pulse voltage and thin film EL.
FIG. 8, which is a relationship diagram with the brightness of the display device, is a time chart explaining the operation of an embodiment according to the present invention. x1~Xm are data electrodes, Y1~Yn are scan electrodes, SX
,~SXm are data side on/off switches, SXO is a switch, SYl~SYn are scanning side on/off switches,
SYO is a switch, Ps is a sustain pulse, Pw is a write pulse, and Pe is an erase pulse.

Claims (1)

[Scope of Claims] 1. One of the two electrodes arranged in a matrix in a thin film EL display device is a scan electrode and the other is a data electrode, and an on/off switch is connected to each of the scan electrodes and connected to a power supply line. , an on/off switch that is commonly connected to all the scanning electrodes and leads to the ground, an on/off switch that is connected to each of the data electrodes and leads to the ground, and an on/off switch that is commonly connected to all the data electrodes and leads to the power line. A driving device for a thin-film EL display device, which consists of a connected on/off switch. 2. The drive device for a thin film EL display device according to claim 1, further comprising a switch connected to the power supply line to selectively supply a sustain voltage, a write voltage, and an erase voltage. 3. When applying a pulse having a write voltage to any selected pixel point, one of the two electrodes arranged in a matrix in a thin film EL display device is used as a scanning electrode and the other as a data electrode, and the polarity is the same as that of the sustain pulse immediately before it. All scan electrodes are connected to a sustain voltage so as to apply a write pulse of , and all data electrodes are connected to ground to apply a sustain pulse to the thin film EL display, and then connected to the scan electrode containing the selected pixel. A switch that is turned on to apply a write voltage, a switch that is connected to each scan electrode that does not include the selected picture element and is turned off, and a switch that is commonly connected to all of the scan electrodes that is turned off. , a switch connected to the data electrode containing the selected picture element and turned on so as to lead to ground, a switch connected to the data electrode not containing the selected picture element and turned off, and all the data electrodes A drive device for a thin film EL display device, comprising: a switch that is commonly connected to a switch that is turned off; 4 When applying a pulse having an erase voltage to a given pixel point by using one of the two electrodes arranged in a matrix in a thin film EL display device as a scanning electrode and the other as a data electrode, a pulse with an opposite polarity to the previous sustain pulse is applied. All scan electrodes are connected to ground so as to apply an erase pulse, and a sustain voltage is connected to all data electrodes to apply a sustain pulse to the thin film EL display device.Then, the scan electrodes containing the selected picture element are connected to erase. A switch that is turned on to apply a voltage, a switch that is connected to each of the scan electrodes that do not include the selected picture element and is turned off, and a switch that is commonly connected to all of the scan electrodes that is turned off. A switch that is connected to the data electrode containing the selected picture element and turned on so as to lead to ground, a switch that is connected to the data electrode that does not contain the selected picture element and turned off, and a switch that is common to all the data electrodes mentioned above. A thin film EL comprising a switch that is connected and turned off.
Display device drive device.