JPH11338561A - Constant current driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a constant current driving device which can drive many current driving elements under nearly the same conditions. SOLUTION: A current detecting resistor Rd detects a current as a voltage signal. Switching circuits S11 to S1n of current supply circuits 21 to 2n are connected selectively to the current detecting resistor Rd or current driving elements Z1 to Zn. The switch circuits S21 to S22 turn on when the switching circuits S11 to S1n are switched to the current detecting resistor Rd and off when switched to the current driving elements Z1 to Zn. Storage means SH1 to SHn store the voltage signal supplied from a current detecting circuit 1 when the switch circuits S21 to S2n turn on. Constant-current circuits D1 to Dn supply constant currents which are supplied from the storage means SH1 to SHn and correspond to the stored voltage signals to the current driving elements Z1 to Zn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant current driving device suitable for driving a current driving element such as an organic electroluminescence element (hereinafter referred to as an organic EL element) or a light emitting diode (hereinafter referred to as an LED). In the present invention, a current driving element refers to an element whose operation depends on a supplied current.

[0002]

2. Description of the Related Art An image display apparatus using a current driving element such as an organic EL element or an LED, when driven at a constant voltage, is affected by the electrode resistance, and the light emission luminance varies depending on the pixel position. Causes defects. Such a problem does not occur when driven with a constant current. Therefore, organic E
In an image display device using an L element, it is ideal to employ current driving instead of constant voltage driving.

When a current driving element is driven with a constant current, the light emission luminance naturally changes depending on the value of the current flowing through the current driving element. Therefore, it is necessary to provide a constant current drive circuit to suppress the variation in the light emission luminance of the elements.

In the case of a display device having a constant luminance, the output of one constant current driving circuit can be switched by a switch, and in the case of a display device having a small number of current driving elements, the output of each constant current driving circuit can be changed. It is relatively easy to adjust the output to be constant.

However, a difficult problem is encountered when trying to realize an image display device using (500 × 500) organic EL elements or current driving elements such as LEDs. First, in order to realize an image display device using the above-described number of current driving elements, 500 constant current driving circuits are required. Such a large number of constant current drive circuits are
If it is not integrated, it will not be practical.

Next, in the image display device, for example, (500
× 500) current driving elements must be driven under the same conditions. For that purpose, for example, 500
It is necessary to provide an adjusting means for driving the current driving elements under the same conditions for each of the constant current driving circuits also provided, and the circuit becomes extremely complicated and impractical.

If the adjusting means is omitted, the fluctuation of the output current among a plurality of low current driving circuits becomes large,
It is extremely difficult to make the luminance variation of an image represented by the current driving element 5% or less that is visually permissible.

[0008] The difficulty in making a large number of constant current driving circuits uniform is that although a great number of types of constant voltage driving devices are commercially available, almost no constant current driving devices are commercially available. Prove.

Technically speaking, voltage can be easily measured by comparison with a reference voltage device, but current measurement is generally difficult because reference current devices are rarely available on the market. Therefore, in measuring the current value, the voltage generated at the resistor inserted in the current path is measured, and converted into a current value according to Ohm's law. Here, if there is a variation in the resistance value of the current detection resistor as the basis of the conversion, the measured current value will also vary. That is, the current value cannot normally be measured beyond the resistance accuracy of the current detection resistor.

When a constant current device is constructed, a method of observing an output current value and controlling the observed value to be constant is generally used. However, the resistance used for observing the current cannot be made without variation. However, when a large number of constant current devices are manufactured, the current value varies. Assuming a case where the constant current drive circuit is formed into an IC, the ratio of the resistance in the element can be quite accurately, but the absolute value of the resistance generally fluctuates greatly in the IC technology. Therefore, in order to produce a constant current device with less variation, it is necessary to trim the resistor. However, the introduction of trimming is IC
Significantly increase the manufacturing costs of

In the end, in order to manufacture an IC-type constant current device with little variation, a current observation resistor must be externally provided, and such a device is practically used where high-density mounting is required, such as a drive circuit of a display device. Not a target. In other words, it can be seen that configuring a plurality of current supply circuits with little variation, enabling IC integration, and suppressing an increase in mounting area cannot be solved by mere application of the conventional technology.

Although it is not intended for a driving device of a display device, as a conventional example for obtaining a plurality of current supply circuits with small variations, a hammer driving circuit (Japanese Patent Application Laid-Open No. 53-82) is known.
133) and a constant current circuit example for a D / A converter (Japanese Patent Laid-Open No. 59-83417), but cannot be applied to a drive device of a display device.

Conventionally, when an organic EL image display device is driven at a constant voltage, there is a serious defect that the luminance of light emission varies depending on the position of a pixel due to the influence of electrode resistance, which is disadvantageous in image quality. Nevertheless, a constant voltage drive circuit that can be easily integrated into an IC has been used.

[0014]

An object of the present invention is to provide an IC
It is an object of the present invention to provide a constant current driving device that can be realized.

Another object of the present invention is to provide a constant current driving device which has a small number of parts and can simplify a circuit configuration.

Still another object of the present invention is to provide a constant current driving device capable of driving a large number of current driving elements under substantially the same conditions.

Still another object of the present invention is to provide a constant current driving device suitable for realizing a matrix device in which a large number of current driving elements are arranged in a matrix.

Still another object of the present invention is to provide an organic EL device.
An object of the present invention is to provide a constant current driving device suitable for realizing an image display device using an element or an LED.

[0019]

In order to solve the above-mentioned problems, a constant current driving device according to the present invention includes a current detecting circuit and a plurality of current supply circuits, and drives a plurality of current driving elements.

The current detection circuit includes a current detection resistor, and detects the current as a voltage signal by the current detection resistor.

The current supply circuits are provided in a number corresponding to the number of the current driving elements. Each of the current supply circuits individually includes a switching circuit, a switch circuit, a storage unit, and a constant current circuit.

The switching circuit is switched between the current detecting resistor and the current driving element, and is selectively connected to one of the switching circuits. The switch circuit is turned on when the switching circuit is switched to the current detection resistor, and is turned off when the switching circuit is switched to the current driving element. The storage means is supplied with the voltage signal from the current detection circuit through the switch circuit when the switch circuit is turned on, and stores the supplied voltage signal.

When the switching circuit is connected to the current detection resistor, the constant current circuit constitutes a negative feedback circuit loop together with the current detection resistor, and the switching circuit is connected to the current drive element. Then, a circuit for driving the current driving element is formed, and a constant current corresponding to a storage voltage signal supplied from the storage unit is supplied to the current driving element.

In the above-described constant current driving device according to the present invention, when the switching circuit is switched to the current detecting resistor,
The constant current circuit forms a negative feedback circuit loop together with the current detection resistor. At this time, a current controlled by the constant current circuit flows through the current detection resistor, causing a voltage drop. The current detection circuit detects a voltage drop caused by a current flowing through the current detection resistor as a voltage signal and outputs the voltage signal. Since the constant current circuit forms a negative feedback circuit loop including a current detection resistor, the constant current circuit is driven so that the voltage drop of the current detection resistor is constant.

When the switching circuit is switched to the current detecting resistor, the switching circuit is turned on in synchronization with the switching.
When the switch circuit is turned on, through the switch circuit,
A voltage signal is supplied from the current detection circuit to the storage means.
The storage means stores this voltage signal.

Next, when the switching circuit is switched to the current driving element, the constant current circuit forms a current supply circuit for the current driving element. Then, a constant current corresponding to the storage voltage signal supplied from the storage unit is supplied to the current driving element.
This constant current value is equal to when the switching circuit is connected to the current detection resistor.

When the switching circuit is switched to the current driving element, the switching circuit is turned off in synchronization with the switching. When the switch circuit is turned off, the supply of the voltage signal from the current detection circuit to the storage unit stops, but the storage unit stores the voltage signal. Therefore, even if the switch circuit is turned off, the constant current circuit can continue to supply a constant current to the current drive element based on the storage voltage signal supplied from the storage means. As a result, the current driver is driven.

In the present invention, each of the plurality of current supply circuits individually includes a switching circuit, a switch circuit, a storage means, and a constant current circuit. This is performed for each current supply circuit. Also,
Since the current supply circuits are provided in a number corresponding to the number of the current drive elements, the corresponding current drive elements can be individually driven according to the individual operations of the current supply circuits.

Further, in each of the plurality of current supply circuits, the constant current circuit performs a negative feedback operation sharing one current detection resistor, thereby suppressing the characteristic difference between the plurality of constant current circuits. For this reason, even when there is a characteristic difference between a plurality of constant current circuits, each of the current driving elements can be driven with a substantially constant current.

In addition, only one current detection resistor is required to constitute the current detection circuit with respect to the plurality of current supply circuits, so that the number of components is reduced and the circuit configuration is simplified.

Further, it is possible to avoid the inevitable variation in the detection resistance value and the accompanying variation in the driving conditions of the current driving element, which are inevitable when a plurality of current detection resistors are used.
Therefore, a large number of current driving elements can be driven under substantially the same conditions.

The plurality of current supply circuits have the same configuration. Moreover, the current detection circuit used for current adjustment is outside the current supply circuit and is shared between the current supply circuits. Therefore, it is extremely easy to make an IC. The number of parts is reduced, and the circuit configuration is simplified.

According to the constant current driving device of the present invention described above, the above-described advantages can be obtained even when a matrix device in which a large number of current driving elements are arranged in a matrix is realized. In particular, it is suitable for realizing an image display device using an organic EL element or an LED.

The current detection circuit, the storage means, and the constant current circuit are provided with a negative voltage such that the voltage signal generated in the current detection resistor included in the current detection circuit, that is, the current flowing through the constant current circuit and the current detection resistor becomes constant. Construct a feedback control system. The storage circuit stores this state.

Preferably, the current detection circuit is configured to compare a voltage signal generated in the current detection resistor with a reference voltage signal, invert and amplify the voltage signal, and output an error voltage signal. Then, the current output from the constant current circuit is controlled by the negative feedback loop so that the error voltage is minimized. Thereby, the current output from the constant current circuit is made constant.

The switching operation of the switching circuit and the switching operation of the switch circuit can be executed by well-known time division control.

Other objects, configurations and advantages of the present invention will be described in more detail with reference to the accompanying drawings. The drawing is
It is merely an example.

[0038]

FIG. 1 is a block diagram of a constant current driving device according to the present invention. As shown, the constant current drive device according to the present invention includes a current detection circuit 1 and a plurality of n current supply circuits 21 to 2n, and a plurality of current drive elements Z1 to Zn.
Drive Zn. The current driving elements Z1 to Zn include organic electroluminescent elements or light emitting diodes.
The constant current driving device shown in the embodiment includes a control circuit 3, and the control circuit 3 controls the entire operation.

The current detection circuit 1 includes a current detection resistor Rd, and detects a current as a voltage signal by the current detection resistor Rd. One end of the current detection resistor Rd is connected to the power input terminal P. The current detection circuit 1 shown in the embodiment includes a differential amplifier A1 and an error amplifier A2. The voltage generated at the detection resistor Rd is compared with the reference voltage Vref by the differential amplifier A1, and is inverted and amplified by the error amplifier A2. Then, the inverted and amplified error voltage signal passes through the switch circuits S21 to S2n.
Sample hold circuits SH1 to SHn as storage means
Supplied to The reference voltage Vref may be a constant value or may be variable. When the reference voltage Vref is variable, it can be used as a control signal input to provide a signal-controlled current supply circuit.

The current supply circuits 21 to 2n are provided in a number n corresponding to the number of the current driving elements Z1 to Zn. Each of the current supply circuits 21 to 2n individually includes a switching circuit S11 to S1n, a switch circuit S21 to S2n,
It includes storage means SH1 to SHn and constant current circuits D1 to Dn.

The switching circuits S11 to S1n are switched between the current detection resistor Rd and the current driving elements Z1 to Zn, and are selectively connected to one of them. Switch circuit S
21 to S2n are turned on when the switching circuits S11 to S1n are switched to the current detection resistors Rd, and are turned off when the switching circuits S11 to S1n are switched to the current driving elements Z1 to Zn. The switching operation of the switching circuits S11 to S1n and the switching operation of the switch circuits S21 to S2n can be executed by well-known time division control. Switching operation of switching circuits S11 to S1n and switching circuit S2
Although the switch operations of 1 to S2n need to be synchronized, they need not be completely overlapped in time, and may have a time lag.

The switching circuits S11 to S1n and the switching circuits S21 to S2n are driven by the driving circuit 4. In the figure, a drive signal is supplied from the drive circuit 4 to one of the switching circuits S11 to S1n and one of the switch circuits S21 to S2n with the same wiring. It is only a display to show the synchronous drive of. Arbitrary wiring can be taken.

When the switch circuits S21 to S2n are turned on, the storage means SH1 to SHn store the switch circuit S2.
An error voltage signal is supplied from the current detection circuit 1 through 1 to S2n, and the supplied error voltage signal is stored.
The storage means SH1 to SHn may be, for example, an analog storage circuit such as a sample-and-hold circuit or a digital circuit. In the case where the storage means SH1 to SHn are configured by digital circuits, it may also include storing variation information of the current supply circuits in a memory, and correcting the current supply circuits based on the stored values.

The constant current circuits D1 to Dn include a switching circuit S11
When .about.S1n is connected to the current detection resistor Rd, it forms a negative feedback circuit loop together with the current detection resistor Rd. Since this circuit loop is a negative feedback loop, it controls the constant current circuits D1 to Dn so that the error voltage signal output from the error amplifier A2 is minimized. With this control operation, the voltage drop of the current detection resistor Rd becomes equal to the reference voltage Vref in each of the constant current circuits D1 to Dn.

The constant current circuits D1 to Dn are connected to a switching circuit S11.
To S1n are connected to the current driving elements Z1 to Zn,
A circuit for driving the current driving elements Z1 to Zn is configured to supply a constant current corresponding to the storage voltage signal supplied from the storage means SH1 to SHn to the current driving elements Z1 to Zn.

In the above-described constant current driving device according to the present invention, when the switching circuits S11 to S1n are switched to the current detection resistors Rd, the constant current circuits D1 to Dn form a negative feedback circuit loop together with the current detection resistors Rd. I do. Therefore, the current controlled by the constant current circuits D1 to Dn flows through the current detection resistor Rd, and a voltage drop occurs. The current detection circuit 1 detects a voltage drop caused by a current flowing through the current detection resistor Rd as a voltage signal and outputs the signal. ,
The voltage generated in the current detection resistor Rd is compared with the reference voltage Vref by the differential amplifier A1, and the error voltage signal is inverted and amplified by the error amplifier A2. In this case, the error voltage signal output from the error amplifier A2 is controlled by the negative feedback control action so as to be minimized by the negative feedback control action described above.

Next, when the switching circuits S11 to S1n are switched to the current driving elements Z1 to Zn, the constant current circuits D1 to D1
Dn forms an open circuit loop including the current driving elements Z1 to Zn. Then, a constant current corresponding to the storage voltage signal supplied from the storage means SH1 to SHn is supplied to the current driving elements Z1 to Zn.

When the switching circuits S11 to S1n are switched to the current driving elements Z1 to Zn, the switching circuits S21 to S2n are turned off in synchronization with the switching. When the switch circuits S21 to S2n are turned off, the supply of the voltage signal from the current detection circuit 1 to the storage means SH1 to SHn is stopped, but the storage means SH1 to SHn store the previously applied voltage signal. Therefore, the switch circuits S21 to S2n
Is turned off, the constant current circuits D1 to Dn are based on the storage voltage signals supplied from the storage means SH1 to SHn.
A constant current can be continuously supplied to the current driving elements Z1 to Zn. As a result, the current driving elements Z1 to Zn are driven.

In the present invention, each of the plurality of current supply circuits 21 to 2n is individually connected to the switching circuit S1.
1 to S1n, switch circuits S21 to S2n, storage means SH1 to SHn, and constant current circuits D1 to Dn.
n. Moreover, the current supply circuit 21
To 2n are provided in a number corresponding to the number of the current driving elements Z1 to Zn, so that the corresponding current driving elements Z1 to Zn are provided in accordance with the individual operations of the current supply circuits 21 to 2n.
n can be driven individually.

Moreover, a plurality of current supply circuits 21 are provided.
For 2 to 2n, only one current detection circuit 1 and one current detection resistor Rd are required, so that the number of components is reduced and the circuit configuration is simplified.

Further, it is possible to avoid the inevitable variation in the resistance value, which is inevitable when a plurality of current detection resistors are used, and the accompanying fluctuation in the driving conditions of the current driving elements Z1 to Zn. Therefore, a large number of current driving elements Z1 to Z
n can be driven under substantially the same conditions.

A plurality of current supply circuits 21 to 21 are provided.
2n have the same configuration. Moreover, the current detection circuit 1
Are outside the current supply circuits 21 to 2n and are shared by the current supply circuits 21 to 2n. Therefore, it is extremely easy to make an IC.

FIG. 2 is a block diagram showing another embodiment of the constant current driving device according to the present invention. In the figure, for the same components as those of the embodiment shown in FIG.
The same reference numerals are given. This embodiment is characterized in that the current driving elements Z1 to Zn are provided with switching circuits S11 to S1n,
That is, it is connected between the power supply input terminal P and a wiring led from the power input terminal P. An operating power supply VB1 is supplied to the power input terminal P. It is clear that this embodiment produces the same operation and effect as the embodiment of FIG.

FIG. 3 is a block diagram showing another embodiment of the constant current driving device according to the present invention. In the figure, the same components as those of the embodiment shown in FIGS. 1 and 2 are denoted by the same reference numerals. This embodiment is characterized in that the current driving elements Z1 to Zn are connected to the switching circuits S11 to S11.
1n and a power input terminal P2 different from the power input terminal P1.
And that it is connected between. According to this circuit configuration, the operation power supply VB1 for the current detection resistor Rd is different from the operation power supply VB2 for the current driving elements Z1 to Zn.

Also in this case, since the output currents of the constant current circuits D1 to Dn are determined by the voltage signal determined by the voltage drop of the current detection resistor Rd, the current drive elements Z1 to Dn
The same current as in FIGS. 1 and 2 can be supplied to Zn. Therefore, in the case of the embodiment, it is apparent that the same effects as those of the embodiment of FIGS. Further, in the case of the embodiment shown in FIG.
This has the advantage that the voltage to be applied to n can be selected appropriately.

FIG. 4 is a block diagram of a matrix device using the constant current driving device according to the present invention. In the figure, the same components as those of the embodiment shown in FIGS. 1 to 3 are denoted by the same reference numerals. FIG. 4 shows a matrix device applied to a display device using a current drive element such as an organic EL element. In FIG. 4, current driving elements Z11 to Znn such as organic EL elements have n rows ×
They are arranged as an n-column matrix. In the rows R1 to Rn, row drivers RD1 to RDn according to a conventional technique are arranged, and in the columns C1 to Cn, the constant current driver 21 according to the present invention is provided.
To 2n are connected. Rows R1 to Rn and columns C1 to Cn
Are connected to light emitting elements Z11 to Znn.
The constant current driving devices 21 to 2n forming the column driver are sequentially selected by the switching circuits S11 to S1n, and
It is connected to a current detection resistor Rd connected to another operating power supply VB1 different from Rn.

One of the switching circuits S11 to S1n which is not on the current detection resistor Rd side is connected to columns C1 to Cn of the matrix. The voltage across the current detection resistor Rd is the differential amplifier A
1. Compared with the reference voltage Vref by the error amplifier A2, inverted and amplified, and fed back to the input side of the constant current drive circuits 21 to 2n constituting the column driver.

The constant current operation in this matrix device is obvious from the above description. Even if each light emitting element has a variation in the element's own impedance, threshold value, or line impedance in a row or a column, the current is not changed. A high quality image can be displayed by precise constant current driving by the detection circuit 1 and the constant current driving devices 21 to 2n.

In this embodiment, the current driving elements Z11 to Z11
The nn operating power supply VB2 and the operating power supply VB1 for the current detection resistor Rd are separate. This simplifies the configuration of the matrix device because it is not necessary to provide the current detection resistors Rd in each of the rows R1 to Rn of the matrix device.

FIG. 5 shows a storage means S which can be used in the constant current driving device shown in FIGS. 1 to 3 and the matrix device shown in FIG.
2 shows specific circuits of H1 to SHn and constant current circuits D1 to Dn.

First, the storage means SH1 to SHn are constituted by sample and hold circuits. Hereinafter, in this embodiment, the storage means SH1 to SHn will be described as sample hold circuits. Sample hold circuits SH1 to SH
n stores the output voltage of the error amplifier A2 supplied when the switch circuits S21 to S2n are closed.

The gate G of the transistor Q1 provided in the constant current circuits D1 to Dn is connected to the sample hold circuit SH1.
To SHn. The sample and hold circuits SH1 to SHn include a capacitor C1 and an impedance converter A3. When the input impedances of the constant current circuits D1 to Dn are sufficiently high, the impedance converter A3 can be omitted.

When the switch circuits S21 to S2n are turned off, the sample and hold circuits SH1 to SHn output the switch circuits S21 to S2n from the error amplifier A2.
The constant current circuits D1 to Dn keep flowing the constant currents according to the hold values of the sample and hold circuits SH1 to SHn to the current driving elements Z1 to Zn.

It is easy to make the accuracy of the sample-and-hold circuits SH1 to SHn about 0.5%.
Variations in the ON resistances 11 to S1n do not affect the constant current operation. Therefore, according to this embodiment, even if a considerably large number of constant current circuits D1 to Dn are configured, the variation in the current value can be suppressed to within 1%.

Next, the constant current circuits D1 to Dn are configured by connecting the resistor Rs1 to the source electrode of the transistor Q1. Since the current values of the constant current circuits D1 to Dn are corrected by the error voltage, the resistor Rs1 may be a resistor having a large resistance value variation that can be configured in the IC. The drain D of the transistor Q is connected to the power supply voltage VB1 through the current driving elements Z1 to Zn.
Connected to. The source S is grounded through the resistor Rs1.

Assuming that a constant voltage Vg is applied to the gate G, if the gate potential Vg is constant, the potential of the source S is constant. Therefore, as long as the transistor Q1 is in the active region, the current driving elements Z1 to Zn Even if it fluctuates, a constant current flows through the current driving elements Z1 to Zn. The transistor Q1 may be an FET or a bipolar type.

FIG. 6 shows a storage means S which can be used in the constant current driving device shown in FIGS. 1 to 3 and the matrix device shown in FIG.
9 shows still another specific circuit of H1 to SHn and constant current circuits D1 to Dn. In the figure, the same components as those in the embodiment of FIG. 5 are denoted by the same reference numerals. The feature of this embodiment is that a transistor Q2 serving as variable impedance means is connected in series to the drain side of the transistor Q1 forming the constant current circuits D1 to Dn. According to this embodiment, the gate G of the transistor Q2
2 can be supplied with a control signal to adjust the driving conditions of the current driving element.

FIG. 7 shows a storage means S which can be used in the constant current driving device shown in FIGS. 1 to 3 and the matrix device shown in FIG.
9 shows still another specific circuit of H1 to SHn and constant current circuits D1 to Dn. In the figure, the same components as those in the embodiment of FIG. 5 are denoted by the same reference numerals. The feature of this embodiment is that the constant current circuits D1 to Dn are constituted by current mirror circuits. The transistors Q11 and Q12 have the same characteristics. In fact, transistors configured on the same chip have almost the same characteristics.

Here, assuming that the current i flows through the base of the transistor Q11, the current i also flows through the base of the transistor Q12 since the transistor Q12 has the same characteristics as the transistor Q11. Transistors Q11, Q1
2, the same current (β × i) flows through the collector of the transistor Q11 and the collector of the transistor Q12. Therefore, the current flowing from the terminal B is (2 + β) × i, and the current driving element The current flowing through Z1 to Zn is (β × i).

Here, if β≫2, (2 + β) ≒ β, and the current flowing from the terminal B is (β × i). If the input current flowing from the terminal B is constant, the current flowing through the current driving elements Z1 to Zn is constant regardless of the current driving elements Z1 to Zn.

In the embodiment, the voltage Vb applied to the terminal B through the base resistor R1 is an error voltage signal controlled so that the voltage generated at the current detection resistor group Rd becomes constant. Therefore, the variation in the base resistance R1 is corrected by the error voltage signal Vb, and the current driving element Z1
A constant current flows through Zn.

FIG. 8 shows a storage means S which can be used in the constant current driving device shown in FIGS. 1 to 3 and the matrix device shown in FIG.
9 shows still another specific circuit of H1 to SHn and constant current circuits D1 to Dn. In the drawings, the same components as those in the embodiment of FIGS. 5 to 7 are denoted by the same reference numerals. A feature of this embodiment is that the storage means SH1 to SHn include a digital memory. An A / D converter AD1 is provided on the input side of the memory M, and the D / A converter is provided on the output side.
The converter DA1 is connected. According to this circuit, digital processing is possible. Although not shown, other known constant current circuits can of course be employed.

[0073]

As described above, according to the present invention, the following effects can be obtained. (A) It is possible to provide a constant current driving device that can be integrated into an IC. (B) It is possible to provide a constant current driving device that has a small number of components and can simplify a circuit configuration. (C) It is possible to provide a constant current driving device capable of driving a large number of current driving elements under substantially the same conditions. (D) It is possible to provide a constant current driving device suitable for realizing a matrix device in which a large number of current driving elements are arranged in a matrix. (E) It is possible to provide a constant current driving device suitable for realizing an image display device using an organic EL element or an LED.

[Brief description of the drawings]

FIG. 1 is a block diagram of a constant current driving device according to the present invention.

FIG. 2 is a block diagram showing another embodiment of the constant current driving device according to the present invention.

FIG. 3 is a block diagram showing another embodiment of the constant current driving device according to the present invention.

FIG. 4 is a block diagram of a matrix device using the constant current driving device according to the present invention.

5 is a specific circuit diagram of a storage means and a constant current circuit that can be used in the constant current driving device shown in FIGS. 1 to 3 and the matrix device shown in FIG.

FIG. 6 is still another specific circuit diagram of the storage means and the constant current circuit that can be used in the constant current driving device shown in FIGS. 1 to 3 and the matrix device shown in FIG.

FIG. 7 is still another specific circuit diagram of the storage means and the constant current circuit that can be used in the constant current driving device shown in FIGS. 1 to 3 and the matrix device shown in FIG.

8 is still another specific circuit diagram of a storage means and a constant current circuit that can be used in the constant current driving device shown in FIGS. 1 to 3 and the matrix device shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Current detection circuit 21-2n Current supply circuit S11-S1n Switching circuit S21-S2n Switch circuit D1-Dn Constant current circuit Z1-Zn Current drive element

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[Procedure amendment]

[Submission date] June 19, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

If the adjusting means is omitted, the fluctuation of the output current among a plurality of constant current driving circuits becomes large,
It is extremely difficult to make the luminance variation of an image represented by the current driving element 5% or less that is visually permissible.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0039

[Correction method] Change

[Correction contents]

The current detection circuit 1 includes a current detection resistor Rd, and detects a current as a voltage signal by the current detection resistor Rd. One end of the current detection resistor Rd is connected to the power input terminal P. The current detection circuit 1 shown in the embodiment includes a differential amplifier A1 and an error amplifier A2. The voltage generated at the detection resistor Rd is applied to the differential amplifier A1 and the differential amplifier A1.
And compared with the reference voltage Vref by the error amplifier A2.
And is inverted and amplified. Then, the inverted and amplified error voltage signal is supplied to the sample and hold circuits SH1 to SHn as storage means through the switch circuits S21 to S2n. The reference voltage Vref may be a constant value or may be variable. When the reference voltage Vref is variable, it can be used as a control signal input to provide a signal-controlled current supply circuit.

Claims (8)

[Claims] 1. A constant current driving device including a current detection circuit and a plurality of current supply circuits and driving a plurality of current driving elements, wherein the current detection circuit includes a current detection resistor, and A current is detected as a voltage signal by a detection resistor, and the current supply circuits are provided in a number corresponding to the number of the current driving elements, each of which is individually provided with a switching circuit,
A switch circuit, storage means, and a constant current circuit, wherein the switching circuit is switched between the current detection resistor and the current driving element, and wherein the switching circuit is configured so that the switching circuit detects the current. It is turned on when switched to a resistor, turned off when the switching circuit is switched to the current drive element, and the storage means detects the current through the switch circuit when the switch circuit is turned on. The voltage signal is supplied from a circuit, and the supplied voltage signal is stored.The constant current circuit is configured to perform negative feedback together with the current detection resistor when the switching circuit is switched to the current detection resistor. Forming a circuit loop, wherein when the switching circuit is switched to the current driving element, a circuit for driving the current driving element is formed, and A constant current driving device for supplying a constant current according to a storage voltage signal supplied from a stage to the current driving element. 2. The constant current driving device according to claim 1, wherein the current detection circuit compares a voltage signal generated in the current detection resistor with a reference voltage signal to generate a difference voltage signal. A constant current drive to output. 3. The constant current driving device according to claim 2, wherein the reference voltage signal is constant. 4. The constant current driving device according to claim 2, wherein the reference voltage signal is variable. 5. The constant current driving device according to claim 1, wherein the current detection resistor and the current driving element share a power supply. 6. The constant current driving device according to claim 1, wherein the current detection resistor and the current driving element use different power sources. 7. A matrix device including a constant current driving device and a plurality of current driving devices, wherein the plurality of current driving devices are arranged in a matrix on a plane, and the constant current driving device is Claims 1 to 6
A matrix device for driving the current driving element. 8. The matrix device according to claim 7, wherein the current drive element includes one of an organic electroluminescence element and a light emitting diode.