JP3976704B2 - Driving circuit for electroluminescent display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a drive circuit, and more particularly to a drive circuit for driving an electroluminescent display device.
[0002]
[Prior art]
With the development of information technology, flat panel displays (FPD) are gradually becoming mainstream among electronic application products. For example, various electric products in daily life are used in televisions, automobiles, etc. Dashboards, watches, announcement signs, mobile phones, computer screens, etc. Currently, there are three types of flat panel display devices: a liquid crystal display (LCD), a plasma display panel (PDP), and an electroluminescent display (ELD). ).
[0003]
Liquid crystal display devices are not only used for notebook computers but also for desktop computers because of their low production costs and low electricity consumption, and desktop applications are gradually becoming mainstream. It has become to. However, there are still many technical problems to be solved in the liquid crystal display device. For example, the viewing angle is poor, the reaction time is long, and the structure is complicated. Is difficult. On the other hand, the electroluminescent display device has no limitation in viewing angle, no heat generation during light emission, and has advantages such as flexibility and lightweight compactness. Therefore, the electroluminescent flat panel display device will be greatly developed from now on. Expected.
[0004]
The electroluminescent panel does not require a background light source because it emits light spontaneously when the illuminant is excited. Since the reaction time and viewing angle are not limited, the moving image display has an effect superior to that of the liquid crystal display device. In addition, since the electroluminescent panel is formed by applying a light emitter to the outside of the conductive layer or by sputtering, the electroluminescent panel can be manufactured with a smaller volume than the liquid crystal display panel. Therefore, the electroluminescent panel is more competitive than the liquid crystal panel in terms of electricity consumption, reaction speed, and volume.
[0005]
Currently, in an electroluminescent display device using current programming, it is necessary to supply a current from a power source to a data line in order to drive a pixel. Since it is necessary to supply different currents in order to provide different layers, a circuit for converting digital voltage to analog current (Digital to Analog Current Converter: DCC) must be provided in the drive circuit. Don't be. A block diagram showing such a driving circuit is shown in FIG. 1 and takes a 6-bit signal as an example.
[0006]
As shown in the figure, a conventional driving circuit includes a shift register 10, a data register 20, a voltage data latch 30, a current source 40, a digital- An analog current converter (Digital to Analog Current Converter) 50, a shift register 60, and a current latch 70 are provided. The shift register 10 is an n-bit shift register and is connected to the data resist 20. The data register 20 is a 6-bit data register and is connected to the voltage data latch 30. The voltage data latch 30 is a 6-bit latch and is connected to the digital-analog current converter 50. The power source 40 is a 2-bit power source and is connected to the digital-analog current converter 50. A current latch 70 is also connected to the digital-to-analog current converter 50. The shift register 60 is an m-bit shift register and is connected to the digital-analog current converter 50. In the drawing, a solid line indicates a voltage signal, and a dotted line indicates a current signal.
[0007]
Therefore, after the data shift signal is input from the data shift register 10, the voltage signal is output from the data resist 20 and the voltage data latch 30, and further converted into a current signal by the digital-analog current converter 50. Finally, m × n output currents are output via the m-bit shift register 60 and the current latch 70.
[0008]
The drive circuit in FIG. 1 is characterized in that a reference current is supplied from a 2-bit power supply 40 to a 6-bit digital-analog current converter 50. Then, different standard currents are generated by utilizing the difference in element area by a current mirror method. Further, the digital voltage is converted into an analog current by selecting the magnitude of the current based on the voltage of the voltage latch.
[0009]
[Non-Patent Document 1]
M.M. Mizukami et al. SID 2000 Digest 924 pages [Non-Patent Document 2]
R. Dawson et al. IEEE IEDM 1998, page 875 [Non-patent Document 3]
T.A. Sasaoka et al. SID 2001 Digest 384 pages [0010]
[Problems to be solved by the invention]
However, since such a configuration uses the same reference potential to generate a current, each element has a different distribution in the threshold voltage (Vth) of the transistor due to the manufacturing process or other reasons. . Eventually, an error occurs because the standard current to be output is changed with a relative influence. Since an error of the drive circuit occurs due to such an error, it is necessary to stabilize the output current of the drive circuit by suppressing the error or reducing the error using another circuit. . Another problem in generating current using the current mirror method is that the two transistors must be perfectly matched to each other. If there is no matching, a difference will occur.
[0011]
In view of the above problems, the main object of the present invention is to solve the error problem caused by the threshold voltage in the conventional driving circuit by providing the driving circuit of the electroluminescent display device.
[0012]
In order to solve the above-described problem, the present invention generates a threshold voltage Vth by generating an analog current using a reference power source and a current copy method instead of a conventional current mirror. Reduce errors caused by changes. That is, since the circuit structure of the current replication system is mainly used, the transistor is relatively insensitive to changes in the threshold voltage Vth. Therefore, errors caused by changes in threshold voltage Vth can be effectively reduced, and the entire drive circuit and system can be stabilized.
[0013]
[Means for Solving the Problems]
In order to achieve the above-described object, a driving circuit for an electroluminescent display device according to the present invention includes an n-bit shift register, a p-bit data register, a voltage data latch, a power supply, and an n + 1 bit shift. A first current connected to the n + 1 bit shift register, comprising: a register; n digital-analog current converters; an m-bit shift register; and a current latch. Having a storage unit and providing a current from the power source when the first current storage unit is turned on and storing a current from the power source when the first current storage unit is turned off; and in an n + 1 bit shift register Has a second current storage unit connected and stores the current stored in the first current storage unit when the second current storage unit is turned on
[0014]
In the following, the features and functions of the present invention will be described in detail by way of the best embodiments with reference to the drawings.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The current copy circuit used in the present invention is a 1-bit circuit as shown in FIG. This circuit has a first current storage unit CM1 and a second current storage unit CM2. Each first current unit includes three transistors and one storage capacitor. The first current storage unit includes a first field effect transistor (FET) M1, a second field effect transistor M2, and a third field effect transistor M3.
[0016]
In general, field effect transistors are mainly divided into two types: metal oxide semiconductor field effect transistors (MOSFETs) and junction field effect transistors (JFETs). Such a field effect transistor is a voltage-controlled power source because the current is controlled using an external electric field. The present invention has a metal oxide semiconductor field effect transistor as a main element, the first field effect transistor M1 is an N-type metal oxide semiconductor field effect transistor (NMOS), and the second field effect transistor M2 is also an N-type metal. It is an oxide semiconductor field effect transistor, and the third field effect transistor M3 is a P-type metal oxide semiconductor field effect transistor (PMOS). The gate of the first field effect transistor M1 is connected to the gate of the second field effect transistor M2, and is further connected to the output terminal of the data shift register. The source of the first field effect transistor M1 is connected to the sources of the second field effect transistor M2 and the third field effect transistor M3, and the drain of the second field effect transistor M2 is connected to the third field effect transistor M3. It is connected to the gate of M3. The drain of the third field effect transistor M3 is connected to a power supply line (Vdd line). A first storage capacitor Cs1 is connected between the gate and drain of the third field effect transistor M3.
[0017]
The second current storage unit CM2 includes a fourth transistor M4, a fifth transistor M5, and a sixth transistor M6, all of which are N-type metal oxide semiconductor field effect transistors. The source of the fourth transistor M4 is connected to the sources of the first transistor M1, the second transistor M2, and the third transistor M3, and the gate of the fourth transistor M4 is connected to the gate of the fifth transistor M5. The drain of the transistor M4 is connected to the drains of the fifth transistor M5 and the sixth transistor M6. The source of the fifth transistor M5 is connected to the gate of the sixth transistor M6, the source of the sixth transistor M6 is connected to the ground line (Vss Line), and between the gate and the source of the sixth transistor M6. A second storage capacitor Cs2 is connected.
[0018]
Next, the operation of the first current storage unit CM1 and the second current storage unit CM2 will be described.
[0019]
When the first current storage unit CM1 is at a high potential, the first transistor M1 and the second transistor M2 are turned on and turned on. At this time, the first current storage unit CM1 is turned on. Therefore, the reference current Iref provided from the outside is conducted through the third transistor M3 and the first transistor M1. On the other hand, when the first current storage unit CM1 is at a low potential, the first transistor M1 and the second transistor M2 are not conducted and are turned off. At the same time, the first storage capacitor Cs1 stores the voltage Vgs corresponding to the current Iref when the third transistor M3 is conductive. Then, at the next time point, the second current storage unit CM2 is turned on, and the first current storage unit CM1 uses the reference current Iref stored in the first current storage unit at the previous time point as the second current storage unit CM2. And stored in the second current storage unit CM2. At this time, whether the output current Iout is zero or the reference current Iref is determined by controlling on / off of the seventh transistor M7 using the control signal. Here, since the action of the seventh transistor M7 is like a switch, it can be regarded as a switch. When this is on, a reference current Iref is output.
[0020]
In FIG. 2, the first current storage unit CM <b> 1 and the second current storage unit CM <b> 2 are connected to each other in a serial manner, but can also be connected to each other in a parallel manner. is there.
[0021]
Next, a method for applying the current replication unit of the present invention to a drive circuit will be described in detail. FIG. 3 is a circuit block diagram showing a drive circuit of the electroluminescent display device according to the present invention.
[0022]
Compared with the conventional driving circuit shown in FIG. 1, the present invention generates an analog current by a digital-analog current converter using a current mirror, and the generated analog current is supplied to a current latch. After being sent and stored, it is output to the pixels of the panel. In the drive circuit shown in FIG. 3, a set of standard power supplies is used as a reference current for the entire panel, and is stored in the converter in a current duplicating manner. Thereafter, the magnitude of the output current is selected based on the digital signal, and the current duplication unit stores the same reference current by storing in the current latch. In addition, since the circuit structure having the current replication configuration is relatively insensitive to the change of the threshold voltage Vth, it is possible to effectively reduce errors caused by the change of the threshold voltage Vth, and the overall uniformity. Can be increased.
[0023]
Further, as shown in FIG. 3, the embodiment of the drive circuit using the digital-analog current converter of the present invention uses 6-bit data, and includes a shift register 10, a data register 20, A voltage data latch 30, a power supply 41, a digital-analog current converter 51, a shift register 60, a current latch 70, and a shift register 80 are included. The shift register 10 is an n-bit shift register and is connected to the data register 20. The data register 20 is a 6-bit data register and is connected to the voltage data latch 30. The voltage data latch 30 is a 6-bit latch and is connected to the digital-analog current converter 51. The power source 41 is a 6-bit power source and is connected to the digital-analog current converter 51. A current latch 70 is also connected to the digital-analog current converter 51. The shift register 60 is an m-bit shift register and is connected to the digital-analog current converter 51. The shift register 80 is an n + 1-bit shift register and is connected to the digital-analog current converter 51.
[0024]
Therefore, after the data shift signal is input from the data shift register 10, the voltage signal is further output via the data register 20 and the voltage data latch 30, and converted into a digital current signal via the digital-analog current converter 51. In total, n digital current signals are output. Finally, m × n analog output currents are output via the m-bit shift register 60 and the current latch 70 to drive the panel pixels.
[0025]
“FIG. 4” is a detailed circuit diagram of the drive circuit shown in “FIG. 3”. As shown, a 6-bit power supply 41 supplies a 6-bit power supply to a 6-bit digital-analog current converter 51. The first bit power supply provides a first bit current replication unit to the digital-analog current converter 51, and the drain of the first transistor M 1 in the first current storage unit CM 1 Connected to the bit output. The first current storage unit CM1 is turned on when it is at a high potential, and this high potential is provided from the output terminal of the first bit in the shift register 80. The second current storage unit CM <b> 2 is turned on when it is at a high potential, and this high potential is provided from the n + 1 bit output terminal of the shift register 80. Therefore, when the driving circuit of the present invention is applied to n pieces of data, another n + 1 bit shift register is required. Thereby, the ON state of the current storage unit in the digital-analog current converter 51 can be controlled. At the same time, an n-bit digital-analog current converter is also required. If each data is recorded with 6 bits, the data register 20, the voltage data latch 30, the power supply 41, and the digital-analog current converter 51 must all be 6 bits. The shift register 10 and the shift register 80 should be matched with the number of data.
[0026]
The power supply 41 shown in FIG. 4 has six reference currents Iref, Irefx2, Irefx4, Irefx8, Irefx16, and Irefx32 having different bits. The operating voltages of the first current storage unit CM1 and the second current storage unit CM2 are as follows: Provided from the shift register 80. The first current storage unit CM1 is turned on when the 6-bit first current storage unit CM1 stores current, and the second current storage unit CM2 is turned on when the second current storage unit CM1 is turned on. This is when CM2 stores the current. When the control signal of the seventh transistor M7 is at a high potential, a different current value is output using the 6-bit control signal and data is recorded in the current latch 70. When the active signal of the current latch 70 is at a high potential, the current latch 70 outputs data to the pixel.
[0027]
In the present invention, the current duplication method is used as a basic unit of the current duplication unit in the digital-analog current converter, and the area is reduced by the method of more than one pair, and the stability of the entire drive circuit is increased so that the element difference can be ignored be able to.
[0028]
Although the present invention has been described with reference to the embodiments described above, these embodiments do not limit the present invention. Those skilled in the art can make modifications and additions to the present invention without departing from the spirit and scope of the present invention. Accordingly, the protection scope of the present invention should be based on the boundaries defined by the claims appended hereto.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a driving circuit in a conventional electroluminescent display device.
FIG. 2 is a circuit diagram when the current replication unit of the present invention is applied to a digital-analog current converter.
FIG. 3 is a block diagram showing a driving circuit in the electroluminescent display device of the present invention.
FIG. 4 is a detailed circuit diagram illustrating a driving circuit in the electroluminescent display device of the present invention.
[Explanation of symbols]
10 ··· Shift register 20 ··· Data register 30 ··· Voltage data latch 40 ··· Power supply 41 ··· Power supply 50 ··· Digital-analog current converter 51 Digital-analog current converter 60 Shift register 70 Current latch 80 Shift register CM1 ... 1st current storage unit CM2 ... 2nd current storage unit M1 ... 1st transistor M2 ... 2nd transistor M3 ... 3rd transistor Cs1 ... the first storage capacitor M4 ... the fourth transistor M5 ... the fifth transistor M6 ... the sixth transistor Cs2 ... the second storage Capacitor M7 ... ... seventh transistor Vdd line ··· power line Vss line ··· ground line Iref ······· low current Iout ······· output current

Claims (2)

An n-bit shift register that outputs n shift voltage signals based on the data shift signal;
a p-bit data register connected to the n-bit shift register and outputting n p-bit data shift signals based on the p-bit digital signal and the n shift voltage signals;
A voltage data latch that outputs n p-bit voltage data signals based on the latch signal and n p-bit data shift signals;
a current source for supplying p-bit current;
an n + 1 bit shift register that outputs n + 1 shift voltage signals;
Wherein n + 1 is connected to a bit in the shift register and the power source, it is connected to the first to the n outputs of each of the n + 1-bit shift register, and the both current source p bits, the (n + 1) of the n + 1-bit shift register N (first to n) digital-to-analog current converters for generating n analog current signals corresponding to n p-bit data voltage signals by being connected to the output ;
an m-bit shift register that outputs m shift voltage signals;
An electronic device comprising a current latch connected to the digital-analog current converter and an m-bit shift register and outputting m × n analog current signals based on n analog current signals and m shift voltage signals In the drive circuit of the light emitting display device,
Any of the n (first to n) digital-to-analog current converters further includes p current replication units, and each of the current replication units further includes a first current storage unit and a first current storage unit . Including two current storage units,
Each of the p first current storage units of the a-th digital-analog current converter (a = 1 to n) is connected to the a-th output of the n + 1-bit shift register and the p-bit current source. , Storing the current output from the p-bit current source based on the a-th output of the n + 1-bit shift register ,
Each of the p second current storage units of the a-th digital-analog current exchanger is connected to the n + 1-th output of the n + 1-bit shift register, and is connected to the n + 1-th output of the n + 1-bit shift register. The drive circuit for the electroluminescent display device , wherein the current stored in the p first current storage units is stored . The a-th digital-analog current converter further includes first to p-th switches, and the b-th second current storage unit (b = 1 to b) of the a-th digital-analog current converter. p) is further connected to the output terminal of the a-th analog current signal through the b-th switch, and the first to p-th switches are the a-th p-bit data voltage signal of the voltage data latch output. The drive circuit of the electroluminescent display device according to claim 1, wherein the output of the a-th analog current signal is controlled by being connected to.

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