JP2000132133A - Display element driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise the circuit area efficiency as the driving circuit of a display element so as to be conformable to standardization. SOLUTION: All display elements 11a, 11b,..., and 11n are mutually connected in parallel to constitute a parallel circuit, and a constant current Isum is supplied from a constant current control circuit 12 to the parallel circuit to equally apply an applied voltage to all the display elements 11a, 11b,..., and 11n. A control part 13, which is a programmable arithmetic control circuit, is used to make the constant current Isum easily applicable to the drive of every display element only by the change of software program.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display element driving apparatus for driving a plurality of fixed segment type display elements.

[0002]

2. Description of the Related Art FIG. 7 shows the relationship between current density and luminance in an organic EL device. The coordinates of the current density and the brightness are indicated by logarithms. In general,
The organic EL light-emitting element is a current-driven light-emitting element.
As described above, the light emission luminance is determined according to the current value per light emission unit area, that is, the current density. For this reason, it is generally driven using a constant current reference source.

FIG. 8 shows a dot matrix type organic E.
FIG. 3 is a circuit block diagram illustrating an example of an L light emitting element. This FIG.
In the case where the area of each pixel is constant, such as the dot matrix type, one constant current reference source 1 and a plurality of constant current drivers (sink type columns) are selected while the display operation is selected by the source type row driver 4. Drivers) 2a, 2b, 2c, ...
.., 2n can drive all pixels. still,
Reference numeral 3 in FIG. 8 indicates each organic EL light emitting element.

[0004]

Here, in addition to the above-described dot matrix type display device, a fixed segment type display device is generally known. Although the display device of the fixed segment type has a limitation that the display pattern is fixed, the display of the edge portion such as the curve is more beautiful than that of the dot matrix type, and the number of steps in the manufacture of the EL element itself is small. This is advantageous in that it is easy to use, and is effectively used in a field where display quality is required with relatively low-cost equipment.

In this fixed segment type display device, the area of each image (segment) is different from the dot matrix type display device.
Therefore, the drive current value differs for each segment, and a plurality of constant current reference sources are required to emit light with the same luminance.

FIG. 9 is a circuit block diagram showing a conventional fixed segment type display device. Here, a constant current is applied to the constant current drivers 6a, 6b, 6c,..., 6n from a plurality of constant current reference sources 5a, 5b, 5c,.
7b, 7c,..., 7n.

As described above, in the fixed segment type display device, the display pattern differs for each segment, and the number of segments and the area of each segment vary depending on the equipment to which the display pattern is applied. Therefore, considering the standardization of the display device, the constant current reference sources 5a,
, 5n and current drivers 6a, 6
, 6n include constant current reference sources 5a, 5b, 5c,.
It is not preferable to fix the set value of n, and as a result,
There is a disadvantage that a drive device must be individually designed for each display device. In addition, the use of the plurality of constant current reference sources 5a, 5b, 5c,..., 5n itself has been a cause of efficiency hindrance in terms of circuit area efficiency.

It is also possible to use a constant voltage circuit instead of the drive circuit shown in FIG. 9 and drive all the organic EL light emitting elements by connecting them in parallel. In this case, a separate constant current reference source is not required, and the efficiency of the circuit area can be improved.

However, in general, the voltage-current characteristics of the organic EL light emitting element are as shown in FIG. 10, and the change in current increases exponentially with the change in voltage. For this reason, in the case of driving using the constant voltage circuit, the luminance change due to the aging of the element resistance and the current value change due to the individual difference in the manufacturing process becomes excessive, and the constant current reference sources 5a, 5b, 5c, 5c
... There is a disadvantage that the durability is lower than when 5n is used.

Accordingly, an object of the present invention is to increase the circuit area efficiency as a drive circuit for a display element and to withstand standardization.
Moreover, it is an object of the present invention to provide a display element driving device which has a small change in light emission luminance of the element and has excellent durability.

[0011]

Means for Solving the Problems In order to solve the above problems,
The invention according to claim 1 is a display element driving device for driving a fixed segment type EL display element having a plurality of segments having different areas, wherein the parallel circuit is formed by connecting all the segments in parallel with each other. A single constant current control circuit that supplies a constant current corresponding to a predetermined applied voltage, and a control unit that selectively switches on and off each of the segments and controls a voltage applied to the constant current control circuit. The control unit calculates the constant current to be given to the parallel circuit as a sum of drive currents corresponding to the respective areas of the segments selectively switched to the on state,
Setting the applied voltage according to the constant current and applying the voltage to the constant current control circuit.

According to a second aspect of the present invention, the control unit includes:
A software program that uses a programmable arithmetic and control circuit and is a reference for calculating the constant current and setting the applied voltage according to the constant current in response to changes in the area of each segment and the number of segments installed. Is provided.

According to a third aspect of the present invention, there is provided a plurality of switching circuits for switching whether or not to shunt a constant current from the constant current control circuit for each of the segments connected in parallel in the parallel circuit. And the control unit controls on / off of each of the switching circuits based on a predetermined screen display instruction signal externally supplied to selectively turn on / off each of the segments.

According to a fourth aspect of the present invention, there is provided a display element driving apparatus for driving a fixed segment type EL display element having a plurality of segments having different areas, wherein all the segments are connected in parallel with each other. A single voltage control element for applying a constant voltage according to a predetermined control signal to the parallel circuit, a reference EL display element connected in parallel to the parallel circuits of all the segments, and a reference EL display element. A driving state detecting means for detecting a driving state and changing an output signal according to the driving state; and a driving state of the reference EL display element being fixed based on an output signal from the driving state detecting means. And a voltage control circuit that supplies a control signal to the voltage control element to control the constant voltage.

According to a fifth aspect of the present invention, the driving state detecting means detects a driving current flowing through the reference EL display element as the driving state of the reference EL display element, and responds to the value of the driving current. And the voltage control circuit outputs an output from the voltage control element such that the drive current of the reference EL display element becomes constant based on the output signal from the drive state detection means. The constant voltage is controlled.

According to a sixth aspect of the present invention, the driving state detecting means is disposed near the reference EL display element, receives light from the reference EL display element, and is substantially proportional to the emission luminance thereof. A photoelectric conversion circuit that outputs an output signal, wherein the voltage control circuit is configured to output the output signal from the voltage control element such that the emission luminance of the reference EL display element is constant based on the output signal from the drive state detection unit. The output constant voltage is controlled.

The invention according to claim 7, wherein a plurality of switching circuits for switching whether or not to apply a constant voltage from the voltage control element to each of the display elements connected in parallel in the parallel circuit. Is further provided.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a circuit diagram showing a display element driving device according to a first embodiment of the present invention, and FIG. 2 is driven by the display element driving device. FIG. 7 is a diagram showing a display screen to be displayed. This display element driving device is for driving a plurality of fixed segment type organic EL display elements (segments) 11a, 11b,..., 11n each having a different shape and area as shown in FIG. In particular, each organic EL display element 11a,
11b, a single constant current control circuit 12 having a sum (Isum) of current values required for driving
The organic EL display elements 11a, 11b,..., 11n are connected in parallel to the output side of the constant current control circuit 12 so as to correspond to the area of each of the organic EL display elements 11a, 11b,. The current is divided into currents Ia, Ib,..., In, and each of the organic EL display elements 11a, 11b,.
A control unit 13 for controlling the on / off switching of 11n and the voltage Vref applied to the constant current control circuit 12 is provided.

Each of the organic EL display elements 11a, 11b,.
, 11n are for displaying various information to a viewer by being turned on and off as segments having individually defined shapes, as shown in FIG. Are formed and arranged on the same glass substrate within a predetermined display area.

Each of the organic EL display elements 11a, 11b,.
, 11n are switching circuits 15a, 15
, 15n are connected to the constant current control circuit 12 and the control unit 13 controls the switching circuits 15a, 1
The drive switching is performed by performing on / off switching of 5b,..., 15n. Each switching circuit 15
, 15n, the currents Ia, Ib,..., In given from the constant current control
.., 11n, and a PNP transistor Q6 for supplying the L display elements 11a, 11b,.
An NPN transistor Q5 for switching on and off of the NPN transistor Q6. The base of the PNP transistor Q6 and the collector of the NPN transistor Q5 are connected via a resistor R5, and the base of the NPN transistor Q5 is connected to a resistor R5.
4 to the control unit 13. Also, NPN
The emitter of the transistor Q5 is grounded.

The constant current control circuit 12 receives the voltage Vref from the first current mirror circuit 21 and the control unit 13 and controls the current of the first current mirror circuit 21.
And a current mirror circuit 22.

The first current mirror circuit 21 has a first PNP transistor Q1 having an emitter connected to a battery power supply (+ B) via a first resistor R1, and a battery having an emitter connected via a second resistor R2. The second PNP transistor Q2 connected to the power supply (+ B) forms a pair and the bases are connected to each other. Also, the second
Of the PNP transistor Q2 is connected to the collector. When the current Iref flows through the second PNP transistor Q2, the current Isum output from the collector of the first PNP transistor Q1 is a value given by the following equation due to the difference between the values of the resistors R1 and R2. It is established.

Isum (R2 / R1) × Iref (1) Further, this current Isum is calculated for each organic EL display element 11
a, 11b,..., 11n
.., In, the following equation holds.

Isum = Ia + Ib +... + In (2) In the equation (2), each of the organic EL display elements 11a, 1
When 1b,..., 11n are selected, each current I
The values of a, Ib,..., In are positive and significant, while they are zero when not selected.

The second current mirror circuit 22 has a collector connected to the second resistor R2 and the second PNP transistor Q2.
A first NPN transistor Q3 connected to a battery power supply (+ B) via an emitter and having an emitter grounded;
The collector and the base are connected to the control unit 1 via the third resistor R3.
3 and a second N connected with an emitter.
PN transistor Q4 is paired with each other and the bases are connected to each other.
3, Q4 always have substantially the same current (Iref). Here, the voltage applied to the resistor R3 from the control unit 13 described later is “Vref”, and the forward voltage of the NPN transistor Q4 is “VQ4 (= about 0.65)”.
, The relationship between Iref and Vref is as follows.

Iref = (Vref−VQ4) / R3 = (Vref−0.65) / R3 (3) The control unit 13 is a programmable arithmetic control circuit,
A general microcomputer chip including a CPU, a ROM, a RAM, and the like is used, and its arithmetic operation is performed by a ROM.
Each of the switching circuits 15 is a functional element that is executed by a software program stored in advance in the switching circuit 15.
, 15n, NPN transistors Q
5 is output to the base of the organic EL display elements 11a, 11b,.
11n, and all organic EL display elements 11a, 11b,... According to the selection result.
· Total current value Isum given to the parallel circuit composed of 11n
Is calculated, and based on the calculation result, the constant current control circuit 12
And a total current value calculation function for changing the voltage Vref applied to the power supply.

In the segment selection function, a segment to be driven to emit light is selected based on a predetermined screen display instruction signal Si externally provided through a serial data communication port, and current is supplied to the selected segment. Each of the switching circuits 15a, 15b,.
A digital signal is output to the base of each of the 15n NPN transistors Q5.

In the total current value calculation function, the organic EL display elements 11a, 11 selected in the segment selection function are used.
1b,..., 11n (current Isu
m) is calculated based on the above equation (2), and the voltage Vr applied to the constant current control circuit 12 is obtained from the equations (1) and (3).
ef is set, and after D / A conversion, the constant current control circuit 12
Output to Specifically, the voltage Vref is obtained by the following equation (4) obtained from equations (1) to (3).

Vref R3 × (R1 / R2) (Ia + Ib +... + In) +0.65 (4) Then, the control unit 13 controls the flash ROM or the EEPROM.
A rewritable non-volatile memory (storage unit: not shown) such as M is provided, and a software program for defining the segment selection function and the total current value calculation function can be arbitrarily rewritten and updated in this storage unit. .

The operation of the display element driving device having the above configuration will be described.

FIG. 3 is a block diagram schematically showing the display element driving device. Reference numeral 15 in FIG. 3 denotes a plurality of switching circuits 15a, 15b,.
Are shown. As shown in FIG. 3, first, the control unit 13 selects a segment based on a predetermined screen display instruction signal Si externally given through a serial data communication port, and selects the selected one of the switching circuits 15a, 15b,. A high signal as a digital signal is output to the base of each of the 15n (15) NPN transistors Q5. As a result, only the NPN transistor Q5 of the selected switching circuit 15a, 15b,..., 15n is turned on, and the base of the corresponding PNP transistor Q6 is turned low and turned on.

As shown in FIG. 3, the control unit 13 controls the organic EL display elements 11a, 11b,.
.., 11n (Ia + Ib +... +
In = Isum), a voltage Vref to be applied to the constant current control circuit 12 is set by the above equation (4), and this is applied to the constant current control circuit 12.

In the constant current control circuit 12, the resistor R3 and the second NP of the second current mirror circuit 22, as shown in FIG.
The voltage Vref from the constant current control circuit 12 is applied to the series circuit including the N transistor Q4, and the current Iref flows through the series circuit. At this time, the first current mirror operation of the second current mirror circuit 22 causes the first
A current Iref equivalent to NPN transistor Q3 flows. This current Iref is supplied to the first current mirror circuit 21 connected in series to the first NPN transistor Q3.
Flows through the second PNP transistor Q2 and the resistor R2, the current Isum shown by the above equation (1) flows through the first PNP transistor Q1 by the current mirror operation of the first current mirror circuit 21. The current Isum is applied to all the organic EL display elements 11a, 11a.
, 11n are supplied to the parallel connection point.

Here, each of the organic EL display elements 11a, 11
In b,..., 11n, if the current density per unit area at the time of luminance Lo is Io, the applied voltage is Vo, and the resistance per unit area at this time is Ro, Io, Vo, and Ro have the following relationship. Having.

Io × Ro = Vo (5) Each segment (organic EL display elements 11a, 11b,...) Of areas Sa, Sb,..., Sn (hereinafter, typically referred to as “Sm”). , 11n) to emit light with Lo brightness, the following values are required for the currents Ia, Ib,..., In (hereinafter, typically referred to as “Im”).

Im = Sm × Io (6) On the other hand, each organic EL display element 11a, 11b,.
Since the resistance values Ra, Rb,..., Rn of 1n (hereinafter, typically referred to as “Rm”) are values obtained by dividing the resistance value Ro per unit area by the area Sm, Rm = Ro × (1 / Sm) (7) Therefore, if the applied voltage is Vm, this Vm (= I
m × Rm) is given by the following equations (6) and (7): Vm = Im × Rm = (Sm × Io) × {Ro × (1 / Sm)} = Sm × Io × Ro × (1 / Sm) = Io × Ro = Vo (8) It can be seen that, when the light is emitted with the same luminance even if the areas are different, the applied voltage becomes equal. Conversely, if the applied voltages Vm are all equal (Vm = Vo),
The brightness will be the same. That is, when the segments (organic EL display elements 11a, 11b,..., 11n) are connected in parallel, if all the applied voltages Vm are equal to Vo, the segments are inversely proportional to the resistance Rm of each segment. The current Im (Ia, Ib,..., In) shunts. Therefore, here, the current Isum is simply given to the parallel connection point of all the organic EL display elements 11a, 11b,..., 11n, and the respective organic EL display elements 11a, 11b,. 11n automatically adjusts the current by itself.

With the above operation, each segment (the organic EL display elements 11a, 11b,..., 11) can be provided without the need for a plurality of constant current reference sources and drivers as in the prior art.
It is possible to easily perform current driving while making the luminance of n) uniform.

The segment (organic EL display element 11)
a, 11b,..., 11n), the number of segments and the area of each segment may be changed. In the software program to be stored in the control unit 13, the above equation (4) is used. By simply changing the data of the drive current value (Ia, Ib,..., In) of each of the segments, it is possible to easily respond to such a design change
It is possible to provide a display element driving device which can easily cope with a change in specifications such as a display area of the display element itself and emission luminance (efficiency).
Therefore, various circuit changes can be handled only by changing the software program without changing the circuit design at all. Further, the display element driving device according to this embodiment includes:
Although it is configured to drive a plurality of segments uniformly, this same display element driving device has only a single segment by changing a software program while keeping the hardware configuration unchanged. It is also possible to drive this by connecting to a display element that is not present.

{Second Embodiment} FIG. 4 is a block diagram showing a display element driving device according to a second embodiment of the present invention, and FIG. 5 is a diagram showing the circuit configuration thereof. In addition,
In FIGS. 4 and 5, elements having the same functions as in the first embodiment are denoted by the same reference numerals.

The display element driving device of this embodiment is similar to that of FIG.
And a plurality of fixed segment type organic Es as shown in FIG.
By driving the L display elements 11a, 11b,..., 11n at a constant voltage, a plurality of conventional drive reference sources (current sources) required depending on the area are omitted.
In addition, the luminance of each segment is made equal.

In addition to the above-mentioned organic EL display elements 11a, 11b,..., 11n, one specific organic EL display element is provided in order to cope with characteristic variations and aging when a constant voltage is applied. (Hereinafter referred to as “reference organic EL display element”
Current detecting means 31 (driving state detecting means) for detecting a current value flowing through 11z (reference light emitting display element) and outputting a current value signal which varies according to the current value; A voltage control circuit 32 for converting a current value signal into a voltage control signal, and a voltage control for converting a voltage Vin from an unstable battery power supply (+ B) into a constant stabilized voltage Vout by a control signal from the voltage control circuit 32 An element 33 is provided.

The reference organic EL display element 11z is connected to the current detecting means 31 so that a current is supplied from the current detecting means 31. On the other hand, the other organic EL display elements 11b,..., 11n are similar to the switching circuits 15a, 15b,.
An electric current is supplied through this. Incidentally, these switching circuits 15a, 15b,.
Are connected in parallel with each other so that a common stabilizing voltage Vout is applied.
.., 15n are switched by a control unit (not shown) (see reference numeral 13 in FIG. 1). Each of the switching circuits 15a, 15b,.
The on / off switching of n is performed by a selection signal from the control unit 13 as shown in FIG. Since the internal configuration of each of the switching circuits 15a, 15b,..., 15n is as described in the first embodiment, a detailed description will be omitted here.

The current detecting means 31 includes one reference organic EL.
This is for detecting a drive state of the reference organic EL display element 11z by detecting a current value flowing through the display element 11z, and is interposed between the reference organic EL display element 11z and the voltage control element 33. One current detection resistor Rref
, One operational amplifier A-2, and four resistors Rf1, Rf
f2, Rf3, and Rs.

The inverting input terminal of the operational amplifier A-2 is connected so that the output of the operational amplifier A-2 is negatively fed back through the resistor Rf1, and the resistor Rf2 is connected to the connection point between the resistor Rref and the reference organic EL display element 11z. Connected via The non-inverting input terminal of the operational amplifier A-2 is connected to a connection point between the current detection resistor Rref and the voltage control element 33 via the resistor Rs, and the resistor Rf3
Grounded. With this circuit configuration, the operational amplifier A-2 functions as a differential amplifier that converts the voltage across the current detection resistor Rref into the current value signal V.

The pair of resistors Rf3 and Rs connected to the non-inverting input terminal of the operational amplifier A-2 are connected to the stabilized voltage Vou.
It is a voltage dividing resistance for t (= Rref × Iref). Therefore, in the current value signal V, the current flowing through the current detection resistor Rref is defined as Iref, and the rate of voltage division by the voltage dividing resistors Rf3 and Rs is represented by α (= Rf3 / R
f2), it can be expressed by the following equation.

V = (Rf3 / Rf2) × Rref × Iref = α × Rref × Iref (9) When Rf2 and Rs are equal, α = Rf3 / Rs.

The current detection resistor Rref is connected to each segment (organic EL display elements 11z, 11a, 11b,...).
., 11n) own resistances Rz, Ra, Rb,.
n (Rm) is set to a sufficiently small value, and Iref · Rr
ef is the switching circuits 15a, 15b,.
n, the forward voltage V when the PNP transistor Q6 is turned on.
By making it approximately equal to ce, the reference organic EL
The voltage applied to the display element 11z and the voltage applied to each of the other segments (organic EL display elements 11a,..., 11n) can be made substantially equal.

The voltage control circuit 32 includes one operational amplifier A
-1, one resistor R11, and one Zener diode ZD1 as a constant voltage element. The non-inverting input terminal of the operational amplifier A-1 is connected to the cathode of the Zener diode ZD1, and is grounded via the Zener diode ZD1. The inverting input terminal of the operational amplifier A-1 is connected to the current detecting means 31. The operational amplifier A-1 is connected to the voltage V (= α · Rref · Ir) applied to the inverting input terminal from the current detecting means 31.
ef) is controlled to be substantially equal to the reverse voltage Vz provided and connected to the Zener diode ZD1. In addition, Zener diode Z
The cathode of D1 is connected to a battery power supply (+ B) via a resistor R11. Note that the output from the operational amplifier A-1 always has a positive power value such that the transistor Q11 can output the output Vout.

The voltage control element 33 is specifically composed of one N
A PN transistor Q11 based on a base potential supplied from the voltage control circuit 32;
B) is converted into a stabilized voltage Vout as an emitter potential,
, 15n and the current detection resistor Rref of the current detection means 31.

The operation of the display element driving device having the above configuration will be described.

First, the voltage V from the battery power source (+ B)
When in is applied to the cathode of the Zener diode ZD1 as a constant voltage element through the resistor R11, the non-inverting input terminal of the operational amplifier A-1 of the voltage control circuit 32 is fixed to the constant voltage Vz by the Zener diode ZD1. At this time, the operational amplifier A-1 applies the voltage V (= α · Rref · Ir) applied to the inverting input terminal from the current detecting means 31.
ef) is output substantially equal to the constant voltage Vz.

The voltage control element 33 (Q11) controls the unstable power supply voltage Vin by the control signal from the voltage control circuit 32.
Is converted to a constant stabilized voltage Vout and output.

At this time, each of the organic EL display elements 11z, 1
In the case of 1a, 11b,..., 11n, when the stabilization voltage Vout is applied to these parallel connection points, all segments (organic EL display) are used for the same reason as described in the first embodiment. The elements 11z, 11a, 11b,.
.., 11n) as well as the applied voltage (stabilized voltage Vou)
t) is applied, the resistance value R of each segment is
The current Im (Iz, Ia, Ib,...,
In) is automatically adjusted according to the area of each segment. Therefore, the light emission luminance of all the segments (organic EL display elements 11z, 11a, 11b,..., 11n) becomes uniform.

By the way, the element resistance changes over time and the current value changes due to individual differences in the manufacturing process, and the voltage Vin of the battery power supply (+ B) and each segment (organic EL display elements 11z, 11a, 11b,. , 11n) may be out of balance. In this manner, when the voltage fluctuates, as shown in FIG. 10, the change in the current increases exponentially with respect to the change in the voltage, which is not preferable.

However, even in such a case, the operational amplifier A-2 of the current detecting means 31 is connected to the current detecting resistor Rr.
ef functions as a differential amplifier that converts the voltage at both ends into a current value signal V, and outputs the current value signal V based on the above equation (9).
To the voltage control circuit 32. Then, as described above, the voltage V applied to the inverting input terminal from the current detecting means 31 is output by the operational amplifier A-1 of the voltage control circuit 32.
(= Α · Rref · Iref) is output substantially equal to the constant voltage Vz. In the voltage control element 33 (Q11),
Based on the output of the voltage control circuit 32, the unstable power supply voltage Vin is converted into a constant stabilized voltage Vout and output. That is, the resistance (Rz) of the reference organic EL display element 11z.
Decrease, Vout also decreases. When the resistance (Rz) of the reference organic EL display element 11z increases, Vout also increases. Further, the resistance of the reference organic EL display element 11z (R
Even if z) does not change, V changes with respect to Vin.
The constant voltage control at which out is constant is also performed.

As described above, the stabilization voltage depends on the reference organic EL.
Even if the resistance (Rz) of the display element 11z changes, the voltage Vout applied to each of the switching circuits 15a, 15b,..., 15n and the current detection resistance Rref is always stabilized, and therefore, each organic EL display element 11a , 11b, ...
.., 11n can be stabilized and the luminance thereof can be kept constant.

Here, the voltage-current characteristics and their changes with time are not affected by all of the organic EL display elements 11z, 11a, 11
, 11n, the internal resistances (Rz, Ra, R
b,..., Rn) change, the drive currents Iz, Iz
Since Vout is controlled so that a, Ib,..., and In become constant, the change in luminance is small as compared with a simple constant voltage drive. Further, the difference in luminance between segments can be reduced.

In this embodiment, the current detecting means 3
In No. 1, the current value flowing through one reference organic EL display element 11z is detected, and a current value signal that changes according to the current value is output. By specifying two or more current values and changing the current value signal based on the sum of these current values, the voltage control circuit 3
2 may be output.

Third Embodiment FIG. 6 is a diagram showing a display element driving device according to a third embodiment of the present invention. In FIG. 6, elements having the same functions as those in the second embodiment are denoted by the same reference numerals.

The display element driving device according to this embodiment has a second
Instead of the current detection means 31 in the embodiment, the segment luminance of the reference organic EL display element 11z is detected, and this is used as reference information of the driving state of the entire segment, and an applied voltage value based on the reference information is set as a voltage. Control circuit 32
Is provided with a driving state detecting means 34 provided to the motor.

The driving state detecting means 34 is provided with a reference organic E
A light receiving element 35 as a phototransistor arranged near the L display element 11z and directly measuring the emission luminance thereof
And a negative feedback operational amplifier 36 to which an output from the light receiving element 35 is provided. A change in the output value photoelectrically converted by the light receiving element 35 is amplified by the negative feedback operational amplifier 36, and the voltage control circuit 32 Is to be given.

Here, the voltage Vin from the battery power supply (+ B) is applied to the collector of the light receiving element 35.
The emitter of the light receiving element 35 is grounded via the resistor R31. The non-inverting input terminal of the negative feedback operational amplifier 36 is connected to the emitter of the light receiving element 35 via a resistor R32. The inverting input terminal of the negative feedback operational amplifier 36 is grounded via a resistor R33.
Negative feedback is input through.

The voltage control circuit 32 and the voltage control element 3
The configuration of No. 3 is the same as that of the second embodiment. In this embodiment, the current I is supplied to the reference organic EL display element 11z.
Unlike the second embodiment in which the ref is supplied and the measurement is performed, all the organic EL display elements 11a, 11b,.
., Switching circuits 15a, 1 equivalent to 11n
5a, 15b,..., 15n through Ia, Ib,.
.., In are supplied (see FIG. 1).

In the display element driving device having such a configuration,
When the emission luminance of each of the organic EL display elements 11a, 11b,..., 11n decreases, the output voltage from the light receiving element 35 decreases, and the output from the negative feedback operational amplifier 36 decreases accordingly. In the voltage control circuit 32, the output from the negative feedback operational amplifier 36 is input through the inverting input terminal, and is output substantially equal to a constant voltage (see the reference Vz in FIG. 5). The voltage control element 33 converts the unstable power supply voltage Vin into a constant stabilized voltage Vout based on the output of the voltage control element 33 and outputs the converted voltage. As a result, the stabilization voltage is increased for each of the organic EL display elements 11z, 11a, 11
, 11n, the voltage applied to each of the switching circuits 15a, 15b,..., 15n is always stabilized at a constant value. Similarly, each of the organic EL display elements 11z, 11a, 11
, 11n (reference numerals Iz,
Ia, Ib,..., In) can be stabilized.

In each of the above embodiments, a segment type organic EL display element has been described as an example of a display element, but any type of segment type display element having a different shape and area can be used. It may be applied, of course, for example, to an inorganic EL display element or the like.

[0066]

According to the first aspect of the present invention, a parallel circuit is formed by connecting all display elements in parallel with each other.
Since the constant current is supplied from the constant current control circuit to the parallel circuit, the applied voltage is applied equally to all the display elements, and at the same time, the individual drive is performed in inverse proportion to the resistance value of each display element. By automatically adjusting the current according to each area, the drive current shunted to each display element is stabilized. In this case, it is only necessary to provide a single constant current control circuit, so that the area efficiency of the circuit can be improved as compared with the conventional example using a plurality of constant current sources.

In the control section, each display element is selectively switched on and off, and a constant current to be given to the parallel circuit as a sum of drive currents corresponding to respective areas of the display elements selectively switched on is set. The constant current supplied from the constant current control circuit can be constantly changed according to the display contents because the calculation is performed, the applied voltage corresponding to the constant current is set and applied to the constant current control circuit. Therefore, it is possible to always stabilize the display of each display element uniformly.

According to the second aspect of the present invention, a programmable arithmetic and control circuit is used as a control unit, and the area of each fixed segment type display element and the number of display elements to be installed are changed. The software program, which is the standard for calculating the constant current and setting the applied voltage according to the constant current, can be rewritten and updated, so that it can be easily applied to driving any display element only by changing the software program, and standardization A display element driving circuit capable of withstanding the above can be provided.

According to the third aspect of the present invention, when the control unit calculates the constant current to be given to the parallel circuit as the sum of the drive currents corresponding to each area of the display element which is selectively turned on. In addition, since each switching circuit is controlled to be turned on / off by the same control unit, there is an advantage that it is extremely convenient for the control unit to know the on / off state of each switching circuit.

According to the present invention, all display elements are connected in parallel to each other to form a parallel circuit, and a constant voltage is output from the voltage control element to this parallel circuit. As a result, a constant voltage is applied equally to all display elements, and at the same time, the individual drive current is automatically adjusted in inverse proportion to the resistance value of each display element in accordance with each area, so that individual And the drive current shunted to the display element is stabilized. In this case, since only a constant voltage needs to be applied from a single voltage control element, the area efficiency of the circuit can be improved as compared with the conventional example using a plurality of constant current sources.

The driving state of one or more reference light emitting display elements of the plurality of light emitting display elements is detected by driving state detecting means, and a voltage control circuit is provided based on an output signal from the driving state detecting means. Since the constant voltage from the voltage control element is controlled so that the driving state of the reference light emitting display element becomes constant, the element resistance changes over time, and the current value changes due to individual differences in the manufacturing process. Also,
In response to this, a constant voltage from the voltage control element can be controlled by the voltage control circuit so that the driving state of the reference light emitting display element is constant, and a display element driving device with extremely excellent durability and little change in light emission luminance is provided. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a display element driving device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a display screen of a general segment type organic EL display device.

FIG. 3 is a block diagram schematically showing a display element driving device according to the first embodiment of the present invention.

FIG. 4 is a block diagram schematically showing a display element driving device according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing a display element driving device according to a second embodiment of the present invention.

FIG. 6 is a circuit diagram showing a part of a display element driving device according to a third embodiment of the present invention.

FIG. 7 is a diagram showing a relationship between current density and light emission luminance of each organic EL display element.

FIG. 8 is a diagram showing a general dot matrix type organic EL display element.

FIG. 9 is a circuit block diagram showing a conventional fixed segment type display device.

FIG. 10 is a diagram showing general voltage-current characteristics.

[Explanation of symbols]

 , 11n Organic EL display element 12 Constant current control circuit 13 Control unit 15a, 15b, ..., 15n Switching circuit 21 First current mirror circuit 22 Second current mirror circuit 31 Current detection means 32 voltage control circuit 33 voltage control element 34 driving state detecting means

Continued on the front page (72) Inventor Takayuki Tomita 1-7-10 Kikuzumi, Minami-ku, Nagoya City, Aichi Prefecture Inside Harness Research Institute, Inc. (72) Inventor Hiroshi Yamagishi 1-7-10 Kikuzumi, Minami-ku, Nagoya City, Aichi Prefecture No. Harness Research Institute, Inc. (72) Inventor Junichi Ono 1-7-10 Kikuzumi, Minami-ku, Nagoya-shi, Aichi F-term in Harness Research Institute, Inc. (reference) 5C080 AA06 BB04 DD03 EE28 FF01 FF03 FF09 GG02 JJ01 JJ02 JJ03 JJ05 5C094 AA03 AA07 AA15 AA22 AA37 AA43 AA44 AA51 AA55 BA23 BA28 CA02 CA14 CA19 DB02 DB10 GA10

Claims (7)

[Claims] 1. A display element driving apparatus for driving a fixed segment type EL display element having a plurality of segments having different areas, wherein a predetermined circuit is connected to a parallel circuit formed by connecting all the segments in parallel with each other. A single constant current control circuit that supplies a constant current according to the applied voltage; and a control unit that selectively switches on and off each of the segments and controls a voltage applied to the constant current control circuit. The unit calculates the constant current to be given to the parallel circuit as a sum of drive currents according to each area of the segment selectively switched to the on state, sets the applied voltage according to the constant current, and sets the applied voltage. A display element driving device for applying a voltage to a constant current control circuit. 2. The display element driving device according to claim 1, wherein the control unit uses a programmable arithmetic and control circuit, and responds to changes in the area of each segment and the number of the segments to be installed. And a storage unit for rewriting and updating a software program serving as a reference for calculating the constant current and setting the applied voltage according to the constant current. 3. The display element driving device according to claim 1, wherein each of the segments connected in parallel to each other in the parallel circuit is controlled by the constant current control circuit. The control unit further includes a plurality of switching circuits for switching whether current is shunted, and the control unit selectively controls each of the segments by on / off controlling each of the switching circuits based on a predetermined screen display instruction signal externally provided. A display element driving device which switches on and off. 4. A display element driving device for driving a fixed segment type EL display element having a plurality of segments having different areas, wherein a predetermined circuit is connected to a parallel circuit in which all the segments are connected to each other in parallel. A single voltage control element for applying a constant voltage according to the control signal, a reference EL display element connected in parallel to the parallel circuits of all the segments, and a driving state of the reference EL display element, Driving state detecting means for changing an output signal in accordance with a driving state; and controlling the voltage control element based on an output signal from the driving state detecting means so that a driving state of the reference EL display element becomes constant. And a voltage control circuit for controlling the constant voltage by giving a signal. 5. The display element driving device according to claim 4, wherein the driving state detecting means detects a driving current flowing through the reference EL display element as the driving state of the reference EL display element, The output signal is changed according to the value of the drive current, and the voltage control circuit controls the drive current of the reference EL display element to be constant based on the output signal from the drive state detection unit. Wherein the constant voltage output from the voltage control element is controlled. 6. The display element driving device according to claim 4, wherein the driving state detecting means is arranged near the reference EL display element, receives light from the reference EL display element, and receives the light from the reference EL display element. A photoelectric conversion circuit that outputs the output signal substantially in proportion to light emission luminance, wherein the voltage control circuit makes the light emission luminance of the reference EL display element constant based on the output signal from the drive state detection means The constant voltage output from the voltage control element is controlled as described above. 7. The display element driving device according to claim 4, wherein the voltage control element is provided for each of the display elements connected in parallel with each other in the parallel circuit. A display element driving device further comprising a plurality of switching circuits for switching whether or not to apply a constant voltage from the display device.