TW591588B - Driving circuit for organic electroluminescent display - Google Patents

Abstract

A driving circuit for organic electroluminescent display is disclosed, which comprises a current mirror, a first FET, a first depletion type FET and an operational amplifier. The input end of the reference current of the current mirror is connected to the first FET and the first depletion type FET in series, and the gate of the first FET is connected to the operational amplifier in series. When the first depletion type FET functions as the current source of the driving circuit, the current source is not affected by the output of the voltage source, so that the driving circuit is highly accurate.

Description

591588 V. Description of the invention (1) [Technical field to which the invention belongs] The present invention relates to a driving circuit for an organic electroluminescent display, and more particularly to an organic electroluminescent display using an empty field-effect transistor as a current source Its drive circuit. [Previous Technology] Organic Electroluminescence Display (0LED) is a display that uses current to drive an organic film to emit light, and its light emission can be individual red, blue, green 'or even full color. Since the organic thin film used by the 0LED is self-emissive, unlike a liquid crystal display (LCD), a backlight is added behind the liquid crystal. If 0LED is compared with 1 ^ 1), 0LED can greatly reduce power consumption, simplify the process, and reduce the thickness of the panel. Therefore, 0LED has self-lighting, wide viewing angle, fast response speed, low power consumption, strong contrast, and brightness. It has the characteristics of high thickness, thin thickness, full color, and dynamic day display, and is considered as a potential flat display. In the development of this 0LED, there are still many details that need to be improved. For example, the driving cost of the 0LED is too high, and the driving current often loses its accuracy due to some reasons, causing the 0LED display to be uncoordinated on the day and time. . Please refer to Fig. 1. Fig. 1 shows a simple schematic diagram of a conventional 0LED driving circuit. The conventional LED driving circuit 100 mainly includes a constant voltage source 110, an operational amplifier 120, a current mirror 125, a MOS transistor 150, and a resistor 160. Among them, the current required for 0LED driving 丨 45 mainly

591588 V. Description of the invention (2) Provided by the current mirror 125. The current source required by the current mirror 125, that is, the current source of the OLED driving current 145, is provided by the current generated by the cross-voltage across the resistor 160. The operational amplifier 120 and the N-channel MOS transistor 150 are used to generate a negative feedback path 155, so that the voltage drop across the resistor 160 is the same as the voltage drop across the voltage source 110. However, the layout of the driving circuit 100 is actually inappropriate because the person familiar with the current mirror 125 knows that the current 145 flowing through the p-channel MOS transistor 140 will refer to the current flowing through the p-channel MOS transistor 130 135. In other words, the magnitude of the current value of 145 will refer to the magnitude of the current value of 135, and it is related to the size ratio of the two. However, since the current source of the current 1 3 5 is mainly generated by the voltage across the resistor 160, the current 135 is actually the current 161 generated by the voltage across the resistor 160, that is, the current flowing through the N-channel MOS transistor 150 154 ° But unfortunately, in order to stabilize the current generated by the voltage across the resistor '60 to produce a stable current 1 35 and the OLED drive current 1 45, the voltage source 110 must provide an accurate voltage source to make the resistor 6 A stable voltage across the two ends is provided, which in turn generates a stable current. Therefore, the voltage source 丨 i 〇 is usually provided by a reference voltage source called Bandgap, and Bandgap itself is a circuit of high complexity and occupying the area of the integrated circuit layout, so it must have a relative OLED process and cost Give. In addition, due to the process or the external temperature, the output voltage 113 of the voltage source 110 is often drifted, and the feedback voltage 155 of the operational amplifier 12 is shifted, and the resistance is shifted by 160 across the voltage, which finally causes the entire current 丨 6 1, current 丨 3 5 and the OLED driving current 145 drifts.

Page 6 591588 V. Description of the invention (3) In view of this, the present invention proposes a driving circuit for an organic electroluminescent display, so that the voltage source only needs to use a general voltage source, and no complicated 8811 (1880 mode, and allows a large (^? 8 £ 1 ') to provide a driving current that does not change with the output voltage of the voltage source. [Summary of the invention] The main object of the present invention is to provide an organic electricity The driver and circuit of the excitation light display include a current mirror, a first field-effect transistor, a first empty =% efficiency transistor, and an operational amplifier. Among them, the current mirror has a reference electric f-wheel output terminal and a corresponding current output. And the output end of the current wheel of the current mirror is coupled to the organic electroluminescent display. The first field-effect transistor has a gate, a source, and an electrode, and the drain of the first field-effect transistor is coupled to the current mirror. = Reference current output terminal. The first empty field-effect transistor also has a gate, source, and drain, and the gate and source of the first empty field-effect transistor are coupled to each other and to ground, The first empty field effect power The drain of the body is coupled to the source of the first field effect transistor at a first node. As for the operational amplifier, it has a first input terminal, a second input terminal, and an output terminal, and the first input terminal of the operational amplifier = is connected to one The voltage source, the second input terminal of the operational amplifier is coupled to the first node, and the output terminal of the operational amplifier is coupled to the gate of the first field effect transistor. | 丨 ^ In a preferred embodiment of the present invention, the driving circuit further includes There are second to N-th empty field-effect transistors. Each of the empty field-effect transistors has an interrogator, a source, and a drain, and the gate and source of each empty field-effect transistor are mutually related. Is coupled to ground, and its drain is coupled to the first node.

591588 V. Description of the invention (4) In another preferred embodiment of the present invention, the above voltage source only uses two field effect transistors. Two of the field-effect transistors each have a gate, a source, and a drain, and the field-effect transistor gate, the drain, and the source of the other field-effect transistor are lightly connected to each other at the second node. When the source of this field effect transistor is coupled to the reference circuit C ′ and the gate and drain of the other field effect transistor are lightly connected to ground, the voltage on the second power source is the output voltage of this voltage source. To sum up, the present invention provides a driving circuit for an organic electroluminescent display. By replacing a conventional resistor with an empty field effect transistor as a current source of the driving circuit, the driving circuit of the present invention has high accuracy, small layout space, and Low production cost and other advantages. [Embodiment] In order for your review committee to have a better understanding and understanding of the features, purposes and functions of the present invention, the following detailed description is given in conjunction with the drawings. The present invention is based on the conventional OLED drive circuit, its voltage source and calculation Amplifiers often drift due to process or external temperature factors. Therefore, the present invention considers using an active element such as a field-effect transistor to replace the resistance in the OLED driving circuit. By virtue of the insensitivity of the active element to the trans-voltage, a stable reference current source that does not change with the trans-voltage is generated. In order to provide OLED stable driving current. Please refer to FIG. 2A, which illustrates a simplified schematic diagram of a driving circuit of an OLED according to a preferred embodiment of the present invention. This driving circuit 200 has a current mirror 125, an M0S transistor 150, an operational amplifier 120, a voltage source 11 and an empty p-channel M0S transistor which replaces the resistor 160 compared with the conventional one shown in FIG.

Page 8 591588 V. Description of the Invention (5) Body 210. Among them, the current 220 required for driving the LED is still mainly provided by the current mirror 125. The current source required by the current mirror 125, that is, the current source of the driving circuit 200, is provided by the N-channel empty MOS transistor 210 instead. As for the voltage source 110, the operational amplifier 120, and the N-channel MOS transistor 150, they are still used to generate the negative feedback path 155. In the preferred embodiment of the present invention, the working mode of the current mirror 125 will be the same as that in FIG. 1, that is, the current 220 flowing through the P-channel MOS transistor 140 will be referred to the current 230 flowing through the P-channel MOS transistor 130. . Therefore, when the empty P-channel MOS transistor 2 1 0 is used to replace the resistor 1 60 in FIG. 1, the current source of the current 23 0 flowing through the P-channel MOS transistor 130 in the current mirror 1 25 will be the N-channel empty MOS transistor. The driving current 220 provided by 210, that is, the drive current 220 of OLED will be provided by the N-channel empty MOS transistor 210. Therefore, as a whole, when the sources of the P-channel transistors 130 and 140 are simultaneously programmed with a reference voltage (VDI), and the voltage source 110 provides an appropriate voltage to the input terminal 249 of the operation amplifier 120, the p-channel MOS transistor 130, 140, and N-channel MOS transistor 150 will be turned on in the working area (ON), and the current 240 generated by the N-channel empty MOS transistor 210 will pass through the N-channel M OS transistor 150 to become the current mirror 125. 〇LED drive current 220 refers to the current 230. 'However, the driving circuit 2 0 0 of the preferred embodiment of the present invention is compared with the conventional driving circuit 100 of FIG. 1' The special thing is that the current 240 generated by the N-channel empty Mos transistor 2 10〃 will not be affected. The voltage of node X coupled to the source 247 of the N-channel M0S transistor 150 and the differential amplifier Is 1 2 0 input terminal 2 5 1 is affected. The reason is that the current formula of the ideal N-channel empty M0S transistor 210 is:

Page 9 591588

V. Description of the invention (6) Current = 0, 5 X

Cox X (W / L) | Vgs-Vtn M, but the gate 253 and the source 255 of the N-channel-type M0s transistor 21 are coupled to each other and to ground. Therefore, the voltage of the gate 253 of the N-channel empty Mos transistor 21 〇 is equal to the source 255 voltage and is zero. The current formula of the N-channel empty M0S transistor 2 1 〇 will be changed to: Current = 0.5 XX Cox X (W / L) | -Vtn I2 Therefore, the current generated by the N-channel empty M0S transistor 210 240 will have nothing to do with the N-channel empty M0S transistor 21 〇 gate 253 voltage, source 255, drain 257 voltage, but only with the N-channel empty M0S transistor 210 parameters such as // n, Cox and its size ratio w / l related. That is, the current 240 generated by the n-channel empty MOS transistor 210 will not be affected by the voltage at node X. Therefore, even when the output voltage of the voltage source 1 1 0 is drifted by the process or the external temperature, and it also affects the output voltage of the operational amplifier 120 and the feedback path 1 5 5 voltage (ie, the voltage on the node X), the current 2 4 〇 Will not be affected by these factors. Therefore, the N-channel empty M0S transistor 210 generates a stable current source that is not affected by the output voltage of the voltage source 110, so that the reference current 230 in the current mirror 125 and the driving current 220 of the 0LED will be stabilized accordingly. Please refer to FIG. 2B, which illustrates a 0LED driving circuit according to another preferred embodiment of the present invention. According to the present invention, an N-channel empty-type MOS transistor 210 is used instead of the concept of resistor 160 in FIG. 1. The present invention can further propose to connect a plurality of N-channel empty-type MOS transistors 2 10 in parallel to the node X, and use an integrated body. In the layout of the circuit, the option of metal options is used to select the number of transistors 210 connected in parallel, and the purpose of fine-tuning the current 245 has been achieved.

In FIG. 2B, a total of N P channels M0S are connected in parallel to node X in FIG. 2A.

Page 10 591588 V. Description of the invention (7) ^-Transistor 21 0. Compared with Fig. 2a, N parallel P-channel MOS transistors 2 1 0 will be able to use the jumper to fine-tune the current 2 45. Increasing the equivalent resistance Rin seen from the 10-terminal of the N-channel empty MOS transistor 2 will reduce the current drift of the current 230 in the current mirror 125 due to the voltage variation at the Y point. The reason is that, in addition to the current source of the current mirror 125, the mirror current 220 is caused by the channel length modulation effect (Channel Length Modulation), and is also affected by the node gamma voltage. When the N-channel empty mS transistor element is used to replace the resistor, the equivalent resistance seen from the γ point is relatively increased, which can improve the current drift of the current 230 in the current mirror 25 due to the change in the equivalent resistance at the Υ point. Makes the current _ 2 2 0 in the current mirror 丨 2 5 very stable. In addition, when the N-channel empty M0S transistor 210 forms a stable current source that is not affected by the output voltage of the voltage source 110, and the driving current 220 of the LED is also not affected by the voltage source 10 rounds of output voltage, the LED The driving current 2 2 0 will tolerate a large range of output voltage drift. Therefore, the voltage source 110 may not use a Bandgap reference voltage source with high complexity and occupying layout area as conventionally used, but instead uses a simple circuit such as two series connected p-channel Mos transistors as the voltage source 110. Please refer to FIG. 2C, which illustrates a 0LED driving circuit of another preferred embodiment of the present invention. In Fig. 2c, only two serially connected p-channel Mos transistors 260, 270 are used as the voltage source 11. Among them, the p-channel MOS transistor 260 gate 261, the drain 263 and the P-channel MOS transistor 270 source 271 are coupled to the node Y. And when the P-channel M0S transistor 260 source 26 5 is coupled to the reference voltage VDD and?

Page 11 591588 V. Description of the invention (8) '' '^ When the gate 273 and the drain 275 of the channel MOS transistor 270 are coupled to each other, the voltage at the node Y is the output voltage of the voltage source 110. According to this, the OLED driving circuit of the present invention has the following advantages: 1. Replace the conventional resistor with an empty field-effect transistor as the motor source of the 0LED driving circuit. Therefore, this current source will not follow the internal voltage of the 0LED driving circuit. The source output drifts and changes. 2. When the conventional resistor is replaced with an empty type% efficiency transistor, the daughter-in-law driving circuit of the present invention and! Knowing phase & has a larger output resistance and improves the matching of the current in the current mirror inside the driving circuit. 3. · Use a simple circuit to replace the internal voltage source of the conventional OLED to save its layout space and production costs. 〃 = as above. 'The present invention proposes an organic electro-optic display to resist a snow :: dynamic circuit. Xiao don't replace the circuit with an empty field-effect transistor: P electricity 2; $: ΐ source' so the current mirror current source will not Changed by the influence of driving electric drift. Therefore, in addition to the conventional driving circuit, the driving circuit of the invention has the advantages of high accuracy, small movement, low production cost, and the like. The layout size is only the above, which is only a preferred embodiment of the present invention. ^ At limits of the scope of the present invention: 1 According to the present invention::-: equal changes and modifications, will still not lose the present invention Around the situation. Therefore, it should be regarded as a further implementation of the present invention 591588 ----- Simple illustration of the diagram [Simplified illustration of the diagram] n shows a simple schematic diagram of the conventional LED driving circuit; the simple is the preferred embodiment of the present invention. The electric circuit of the circuit is based on the 0-led drive circuit of another-preferred embodiment of this creation. Figure 2C shows the LED-driven circuit of another preferred embodiment of this creation.

Explanation of drawing numbers: 100, 200: OLED driving circuit 110, voltage source 120, operational amplifier 125, current mirror 130, 140, 260, 270: p-channel MOS transistor 135, 145, 154, 161 '220, 230, 240, 245: current 1 51, 2 5 3, 2 6 1, 2 7 3: Gate electrode

15 3, 247 '255-265 ^ 271: source 1 5 5: feedback path 1 6 0: resistance 210: N-channel empty MOS transistor 257 ^ 263 ^ 275: drain 249, 251: input X, Y: node

Page 13

Claims (1)

591588 6. Scope of patent application 1. A driving circuit for an organic electroluminescent display, comprising: a current mirror with a reference current wheel output end and a corresponding end, and the current output end of the current mirror is coupled to the wheel output device; The electric excitation light shows a first field-effect transistor, which has a gate, a source, and a drain of the first field-effect transistor coupled to the current mirror> and the pole ', the terminal; a reference current turns out a first empty Type field-effect transistor, which has a gate electrode, a green gate, a gate electrode, a gate electrode, and an electrode, and is coupled to the ground. The source of the first empty-type field-effect transistor is mutually coupled. The source connected to the first field-effect transistor is in a first section ^; and the op amp is connected to the op amp with a first input terminal and a second X = terminal, where the first input terminal of the op amp is And the second input terminal outputting the operational amplifier is coupled to the -p ^ voltage source 'output terminal of the amplifier is coupled to the first field effect transistor, 卩 ^ the operation • as described in the first item of the scope of patent application Organic electrical excitation light circuit The driving circuit further includes: X ", a second empty field-effect transistor driven by a driver, having a gate, a source, and a gate electrode of the second empty field-effect transistor. / 和 pole 'and coupled to the ground, the second empty field effect transistor is coupled to the first node with each other. The body and pole are coupled to the organic electrical excitation tamping age as described in item 2 of the patent application scope. A circuit, wherein the driving circuit further includes: nine ,,,, and driver of the indicator and > and pole, Page 14 N-Empty Field-Effect Transistor with Gate and Source 591588 6. Application for Patent ΐ: Ϊ! \ Empty-Effect Field-Effect Transistor The Gate and Source of the N-Empty-Effect Field Coupling Ground The drain of the effect transistor is lightly connected to the coiling circuit of the organic electroluminescent display described in item 1 of the special scope, wherein the current mirror includes: 3 of the driver J 1? The effect transistor has a gate, a source, and a drain. The field J transistor is the reference current output terminal of the current mirror. The source of the first% efficiency transistor is coupled to a reference voltage. One! The "body" has a gate terminal, a source terminal, and a drain terminal, and the complex phase = f = the field-effect transistor gate and the second field-effect transistor gate i 4 φ: touch and couple to the second field-effect transistor. Crystal drain, the second source is lightly connected to the reference voltage, the third field effect is: and the current output terminal of the current mirror. Body 5 · As claimed in the scope of patent application [...] . # &# + The driving circuit of the organic electro-optical display device described in item 1, wherein the voltage source includes: < ^ = 四 :: 文 电 晶 胄 'has a gate, a source, and a drain, Fourth: the gate and the drain of the effect transistor are mutually coupled to a second "a" and the source of the fourth field effect transistor is coupled to the reference voltage; the fifth, the effect transistor has a gate and a source And the drain, the gate and the drain of the transistor are coupled to each other and to ground f =, and the source of the four field effect transistor is coupled to the second node. = The driving of the organic electro-optical display device described in item 1 of the scope of patent application, wherein the first field effect transistor is an N-channel MOS transistor. • Ru stated that the drive of the organic electroluminescent display described in item 1 of the patent scope Page 15 591588 6. Scope of patent application The dynamic circuit, wherein the first empty field effect transistor is an N-channel empty type MOS transistor. 8. The driving circuit of the organic electroluminescent display according to item 4 of the scope of patent application, wherein the second field effect transistor and the third field effect transistor are both P-channel MOS transistors. Page 16