JPS63179336A - Electrochromic display device - Google Patents

Abstract

PURPOSE:To maintain the current value to a display part at a constant current value and to stabilize the same as against a temp. change so that the deterioration of a titled device is prevented by setting the bias voltage to be impressed to the gate and source of an FET constituting a constant current means to a value at which a temp. coefft. is zero. CONSTITUTION:The voltage above pinch off is impressed between the source and drain of the FET 20 of a constant current circuit 19 and said FET acts as the constant current element in a saturation region when electric current flows from a counter electrode 4 to display electrodes 4 at the time of coloration. The voltage between the source and gate is adjusted by a variable resistor 21 in which the drain current flows to set the voltage value at which the temp. coefft. of the FET 20 is nearly zero. Then, the constant current circuit 19 maintains the set current value regardless of a temp. change and absorbs the change in the output voltage from the driving part 2 and the cause for the current fluctuation of the display part 1. The constant current driving of the display part 1 is thus stably executed. The p-n junction part between the drain and gate acts as a forward diode and the constant voltage driving is executed if the FET 20 is of a junction type at the time of decoration.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to electrochromic display devices, and in particular to improvements in display element drive circuits.

[Prior Art] In general, electrochromic display elements use chemical reactions to display their images, so once they are colored, they have a so-called memory property of maintaining the colored state even if the power is turned off. It is necessary to individually apply voltages of opposite polarity in response to color removal and decolorization. In order to apply such a voltage, it is possible to have the power supply unit output multiple types of voltage values and use the drive circuit to switch between these voltages.
For example, if the entire system could be driven by a single TTL-level 5V power supply, the circuit configuration of the entire display device could be simplified.
It also becomes possible to reduce manufacturing costs.

In response to the above request, a conventional drive circuit 50 as shown in FIG.
is proposed. This circuit 50 individually connects the output end of the display pole drive section 5 to each display pole 3 of the display section 1, keeps each output end in an open state at all times, and provides common equipment for each display pole 3. A counter electrode drive unit 51 is connected to the counter pole 4.
Connect.

Here, when coloring, the display S3 to be colored is Ov, the other display electrodes are in the oven state, and the opposite electrode 4 is set to about IV, and a coloring voltage V is applied to the display part 1, and conversely, when decoloring, By setting all the displays t4i3 to 5V and the counter electrode 4 to about 4V, the color erasing voltage vb is applied to the display section 1 to 5V.
v can be applied using a single power supply 11.

[Problems to be Solved by the Invention C] By the way, when the drive circuit 50 described above is used and a display operation is performed while changing various conditions, the display element itself constituting the display section 1 deteriorates more than during normal use. It is known to be large. In order to investigate this cause, the present inventors varied the temperature of the entire display device between OoC and 60°C and observed changes in the coloring voltage V and the color erasing voltage V, and found that the temperature increased. It was found that both voltages increased significantly as the temperature increased. That is, the coloring voltage V generated by the conventional counter electrode drive section 51 is the voltage obtained by dividing the power supply voltage v0 by the resistor 52 and simply amplifying it by the Darlington-connected transistor 53, and the coloring voltage V generated by the conventional counter electrode drive section 51 is the voltage obtained by dividing the power supply voltage v0 by the resistor 52 and simply amplifying it by the Darlington-connected transistor 53. v2 uses the forward voltage of the diode 54 connected in series, and does not specifically compensate for voltage fluctuations due to temperature changes, and the lack of measures against this temperature rise exceeds expectations at high temperatures. As well as causing a voltage increase,
Combined with the characteristics of the display element itself at high temperatures,
We have come to the conclusion that this accelerates the deterioration of display elements.

To solve the above problem, it is possible to perform constant current coloring so that the current value per unit area of the display element is constant.
Providing one set of constant current circuits for all display electrodes is not only extremely expensive, but also unrealistic, as it increases the size of the entire circuit board.

The present invention has been made in view of the above problems, and aims to make the current value flowing into the display section at the time of coloring as constant as possible and to stabilize it against temperature changes, thereby driving the display section at a constant current. The purpose of this invention is to prevent deterioration of the element itself due to abnormally high voltage application, and to improve display quality.

[Means for Solving the Problems] FIG. 1 is a block diagram schematically showing an electrochromic display device according to the present invention, which includes a display section 1 and a display section L that controls coloring and decoloring operations. It is composed of a driving section 2 that applies a driving voltage, and a constant current means interposed between the driving section 2 and the display section 1.

The display section 1 is composed of an electrochromic display element having a display electrode 3 and a counter electrode 4, and repeats coloring and decoloring by reversing the direction of the voltage applied to both electrodes.

The constant current means is a FET 20 connected with a constant current, and is interposed between the display electrode 3 of the display section 1 and the drive section 2, and
The gate-source voltage when the FET 20 is colored is set to a value at which the temperature coefficient is approximately zero.

[Operation] In the above configuration, when a coloring cycle is first entered based on data sent from the control unit 10, the display electrode 3 to be colored is selected from the drive unit 2, and the corresponding display electrode 3 and the opposing electrode 4 are selected. A predetermined driving voltage is applied between them. At this time, drive section 2
A constant current means is interposed between the display electrode 3 and the display electrode 3, and the constant current means absorbs all various current fluctuation factors such as fluctuations in the drive voltage output from the drive section 2 and changes over time in the characteristics of the display section 1. However, a substantially constant current continues to flow to the display electrode 3.

Here, when the temperature of the entire device changes, the operating characteristics of the FET 20 itself, which constitutes the constant current means, as well as the display section 1 and the drive section 2 also change, but the bias voltage applied between the gate and source of the FET 20 is is set in advance to a value that is approximately zero, the set current value of the constant current means does not change regardless of temperature changes, and stable constant current driving of the display section l is performed.

[Example] FIG. 2 is an electric circuit diagram showing an example of a concrete implementation of the display device according to the present invention, in which the display unit 1 and the display unit 1
a drive section 2 that applies a predetermined voltage to the drive section 2, a control section 10 that controls the entire device, and a predetermined power supply voltage V. The power supply section 11 supplies power to each circuit.

The display unit 1 is composed of one or more electrochromic display elements, which are divided into a plurality of displays faj3, 3, etc. corresponding to the shape to be displayed, and a total display w&3.
By changing the direction and value of the voltage applied to both electrodes 3 and 4, it is possible to control the reversible chemical change between, for example, tungsten oxide and lithium ions, which occurs between the two electrodes. Coloring and decoloring each display electrode 3 to blue is performed to enable a predetermined display operation.

The control unit 10 includes, for example, a central processing unit and its operation is regulated by a program, and sends various signals such as data signals, control signals, and address signals to the drive unit 2.
The power supply unit 11 outputs a sufficiently stabilized unipolar voltage vo of, for example, about 5 V, regardless of temperature changes or load conditions, by appropriately sending signals S and -S2 to control the operation of the entire device. do.

The drive section 2 includes a display electrode drive section 5 connected to the display electrode 3 and a counter electrode drive section 6 connected to the counter electrode 4.

The display pole drive unit 5 includes output terminals corresponding to at least the number of display poles 3 and receives various signals 31 .
Its output voltage is controlled by That is, the output terminal of the display electrode 3 that does not require data writing maintains a high impedance state, while the output terminal that performs data writing is grounded to set the output voltage to Ov, which is output from the counter electrode drive unit 6. The display section shows the difference voltage v8 between the voltage value V and the voltage value V8.
to drive. Conversely, when erasing is performed, all output terminals are set to about 5V, and the voltage value V output from the counter electrode drive unit 6.

The display section l is driven by the voltage difference V between the two.

The counter electrode drive unit 6 has the coloring voltage V, which is a power supply voltage v0.
The decoloring voltage v2 is formed by dividing it with the variable resistor 13 as it is, and then is sent to the voltage buffer circuit 16 via the analog switches 14 and 15.

The analog switches 14 and 15 are devices such as C-MOS Quib transmission gates or FET-based electronic switches, which open and close the gates at high speed in conjunction with the presence or absence of a signal to the control end, allowing the input voltage value to be output as is. It is.

Both analog switches 14 and 15 are normally off, but are turned on individually in conjunction with the coloring control signal SI and decoloring control signal S2 being sent from the control unit IO, and the coloring voltage v1 or decoloring voltage V1 or decoloring voltage is turned on. The operating voltage V2 is alternatively output for a certain period of time.

The voltage a-circuit circuit 16 is constructed by providing a feedback circuit 18 using a resistor between the opposing pole 4 and the negative pole of the OP amplifier 17, so that the voltage input to the positive pole of the OP amplifier 17 is controlled by changes in temperature or display element drive current. Despite fluctuations in operating conditions such as an increase or decrease in the value, the value is kept unchanged and is applied as it is, or after being amplified by a predetermined ratio, it is applied to the opposite S4.

The present invention is characterized in that a constant current circuit 19 is interposed between the display electrode drive section 5 and each display electrode 3 of the display section 1.

The constant current circuit 19 uses an FET 20 such as an N-type junction type or MOS type, and connects the FET node to the display electrode 3, connects the source and gate with a variable resistor 21, and further connects the gate to the display electrode 3. By connecting to the output end of the display electrode drive unit 5, when coloring, that is, when current flows from the opposing electrode 4 toward the display electrode 3 in this embodiment,
A voltage higher than the pinch-off voltage is applied between the source and drain of the FET 20, and the FET 20 is configured to operate as a constant current element in the saturation region.

Furthermore, a variable resistor 21 through which drain current flows is used to
Gate rI! I voltage: JR adjustment, FET20 when coloring
By setting the voltage value such that the temperature coefficient of
The constant current circuit 19 always maintains the set current value regardless of temperature changes in the entire device, absorbs current fluctuation factors such as changes in the output voltage from the drive unit 2 or deterioration of the display unit 1 itself, and maintains the current value in the display unit 1. constant current drive is performed stably.

Next, when decoloring, the direction of the voltage applied to the display section l is opposite to that when coloring, but if the FET 20 is a junction type, the PN junction between the drain and gate becomes a forward diode. , it becomes possible to drive at a constant voltage in substantially the same way as before. However, if the FET 20 is a MOS type and does not have a PN junction and the current value is limited, or if the current itself is insufficient during erasing, the diode 22 is disconnected between the display electrode drive unit 5 and the display electrode 3. By connecting the diode 22 in the forward direction when it is colored, the extracted current is bypassed by the diode 22 and the current value is increased, thereby making it possible to perform a reliable color erasing operation.

Note that if the FET 20 is P type or the direction of voltage application during coloring/decoloring is reversed, the connection direction of the FET 20 must be reversed from the above.

In addition, when the area of each display electrode 3 is different, the characteristics of the FET 20 can be appropriately changed in design so that a constant current value proportional to the area can be obtained.
Coloring operation using constant current density can be performed without any modification to the coloring process.

[Experimental Example] Using the drive unit 2 having the configuration shown in FIG. 2 and a 7C segment display element, the temperature dependence of the amount of electricity injected during coloring was investigated. In the experiment, the temperature was 25°C and the current value during coloring was 8.3m.
After adjusting the amount of electricity to 5.0 mC and setting the erasing voltage to 1.7 V, the change in the amount of electricity injected was examined while changing the temperature between 0'C and 60°C. The repetition time for coloring and decoloring is 0.6 seconds each.

For comparison, we used the circuit shown in Figure 3, which is a conventional example, and the temperature was 2.
The coloring voltage at 5°C is 1. The results of an experiment under the same conditions except that the voltage was set to lV are shown.

In the comparative example, the value of the amount of injected electricity was 5.0 at 25°C.
What is called rrrC is 2.2+nC160' at 0°C.
In contrast, in this example, the value set at 5.0 mG at 25°C was 0.
The variation width was small, 4.8 DIG at °C, and 5.1 mC at 60'C, and it was confirmed that sufficient constant current control was performed.

[Effects of the Invention] As described above, the present invention interposes a constant current means with a temperature coefficient of approximately zero during coloring between the drive unit 2 and the display electrode 3, so that no special control means is required. In fact, even if the configuration of the drive unit 2 is simplified, the display unit 1 can always be driven at a constant current even when the drive voltage changes due to temperature changes or the operating characteristics of the display element change, and the element is not damaged due to high voltage application. can also be prevented.

In addition, by simply setting the characteristics of the FET 20 so that the set current value of the constant current means is proportional to the area of each display electrode 3, the display element can be driven by the constant current density without any modification or modification of other configurations. By simply controlling the pulse width of the driving voltage, coloring can be achieved with a constant amount of electricity, and display quality can be improved.

Further, the constant current means of the present invention can be easily integrated into an IC, and has many advantages such as being integrated with the display electrode driving section 5 to reduce the size of the circuit configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an outline of the present invention, and FIG. 2 is an electric circuit diagram showing an example of implementing the present invention. FIG. 3 is an electrical circuit diagram showing a conventional example. 1...Display part, 2...Drive part, 3...Display pole, 4...Counter pole, 5...Display W & drive part, 6...Counter pole drive Part, 10... Control part, 11... Power supply part. Inventor Nagaben Kitakai Toshikatsu Manabe No. 3 +'A/"s1"

Claims (3)

[Claims] (1) An electrochromic display device comprising a display section 1 having a display section 3 and a counter electrode 4, and a drive section 2 that applies a drive voltage that regulates coloring and decoloring operations of the display section 1. A constant current means is interposed between the driving section 2 and the display electrode 3, and the constant current means is constituted by a constant current connected FET 20, and the gate-source voltage at the time of coloring of the FET 20 is determined by a temperature coefficient. An electrochromic display device characterized in that the value is set to approximately zero. (2) The electrochromic display device according to claim 1, wherein the FET 20 is connected in parallel with a diode 22 so that it can be turned on when decoloring. (3) The electrochromic display device according to claim 1 or 2, wherein each FET 20 is formed so that a constant current value flowing during coloring is proportional to the area of the display section 3.