JP4409193B2 - Current-driven active matrix display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an active matrix display device, and more particularly to a current driven active matrix display device using a current driven light emitting element such as electroluminescent (hereinafter referred to as EL) as a light emitting element.
[0002]
[Prior art]
A display device using EL as a light-emitting element is a spontaneous emission type display device that changes the light emission luminance by controlling the current flowing through the light-emitting element, and does not require a backlight like a liquid crystal display device, and has a thin structure. Attention has been paid to the fact that the display element is easy to handle, the response characteristics of the display element are good, and the viewing angle dependency is small. In recent years, research and development as a flat display panel have been advanced and put into practical use.
[0003]
FIG. 8A is a circuit configuration diagram of a conventional current-driven active matrix display device using an organic EL as a light emitting element, and FIG. 8B is a detailed view of a pixel portion in FIG. 8A. In the figure, 1 is a display unit, 2 is a pixel unit, 3 is a data line driving circuit, 4 is a scanning line driving circuit, 5 is a power supply circuit, Q2 is an EL element driving transistor, Q1 is a control transistor, Cs is a capacitor, OLED is an organic light emitting diode, S1 to SN are scanning lines, and D1 to DM are data lines. Next, the circuit operation of FIG. 8 will be briefly described.
[0004]
The scanning line driving circuit 4 is generally composed of a shift register or the like, starts its operation by a start pulse GSI, and performs N stages of shift operations by a shift clock GCLK. The scanning line driving circuit 4 sequentially sends scanning pulses SCAN to the scanning lines S1, S2, S3,... SN for each stage shift operation, and controls the pixel unit 2 connected to the scanning line. Transistor Q1 is operated. A scanning pulse SCAN is sent from the scanning line driving circuit 4 to one scanning line, and the data line driving circuit 3 performs control while the control transistor Q1 of the pixel unit 2 connected to the scanning line is operating. The data signal voltage DATA is applied to the capacitor Cs via the transistor Q1. A current proportional to the data signal voltage flows from the power supply line VDDA to the organic light emitting diode OLED via the EL element driving transistor Q2, and causes the light emitting diode OLED to emit light. The voltage applied to the capacitor Cs is held for one frame. In FIG. 8, in addition to the power supply circuit 5 for supplying current to the organic light emitting diode OLED, a power supply for operating the scanning line drive circuit 4, the data line drive circuit 3 and the like is also necessary but omitted. The start pulse GSI and the shift clock GCLK are output from a control circuit (not shown) that controls the entire display device.
[0005]
Conventional current-driven active matrix display devices using organic EL as such light emitting elements are described in, for example, Japanese Patent Application Laid-Open Nos. 2000-305522 and 2001-5426.
FIG. 9 is a schematic cross-sectional view for simply explaining an example of the pixel portion 2 in such a display device. In the figure, 6 is a cathode (reflective layer), 7 is an EL light emitting layer, 8 is an anode (transparent electrode), 9 is an insulating layer, 10 is a conductor, 11 is an electrode, 12 is a glass substrate, and 13 is scattered light. In FIG. 9, the capacitor Cs in the pixel portion is omitted. Light from the EL light emitting layer 7 is reflected by the reflective layer of the cathode 6, passes through the transparent electrode of the anode 8, and exits from the surface of the glass substrate 12. A part of the light is reflected by the surface of the glass substrate 12 and becomes scattered light 13.
[0006]
In recent years, thin film transistor formation technology has progressed, and in particular, a drive circuit for driving the display unit on the same substrate as the display unit is formed in an active matrix display device by using a polysilicon TFT (Thin Film Transistor). It is possible to do.
[0007]
[Patent Document 1]
JP 2000-305522 A [Patent Document 2]
Japanese Patent Laid-Open No. 2001-5426
[Problems to be solved by the invention]
Unlike the liquid crystal display device, a display device using such an organic light emitting diode OLED has a separate power supply circuit for supplying current to the EL light emitting element, and a steady current is supplied from the power supply circuit. since flows, current variation even if the holding voltage variation of capacitor C _S in elements other than the video signal (data signal) occurs occurs. In control transistor Q1 in the circuit of FIG. 8, the control transistor Q1 is the in the off (when not in operation) is the leakage current (leakage current), the holding voltage of the capacitor C _S is varied. This variation is no problem in the time order of the normal frame period of the pixel section 2, the hold voltage of the capacitor C _S is no longer updated when the scanning pulse from the scanning line driving circuit 4 for some reason will stop, control hold voltage of the capacitor C _S for the leakage current of the transistor Q1 varies. In the circuit of FIG. 8, when the holding voltage fluctuates in the ground (earth) direction, the current flowing through the organic light emitting diode OLED through the EL element driving transistor Q2 changes, and the luminance of the organic light emitting diode OLED increases. It becomes brighter. As the organic light emitting diode OLED becomes brighter, the scattered light 13 that hits the control transistor Q1 also increases, as is apparent from the structure shown in FIG. Since the leakage current of the control transistor Q1 is increased and the light hits, the holding voltage of the capacitor C _S is further current of the organic light emitting diode OLED is changed in a direction to increase. Finally, the current that can be withstood is exceeded, and there is a problem that the EL element driving transistor Q2 and the organic light emitting diode OLED are permanently damaged, such as disconnection or short circuit. Japanese Patent Application Laid-Open No. 2000-305522, which is a patent document, describes an invention that prevents an inappropriate voltage from being applied to a circuit when the power is turned on to destroy the circuit portion. However, the two patent documents do not describe any preventive measures against circuit destruction when the scanning pulse stops.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, according to one aspect of the present invention, a display unit in which a plurality of pixel units are arranged in a matrix, a data line driving circuit that supplies a data signal, and a scanning line driving circuit that generates a scanning pulse In the current-driven active matrix display device that displays images by time-division driving in this display unit, a scanning pulse detection circuit that detects the presence or absence of scanning pulse output from the scanning line driving circuit, and data in the display unit A power supply control circuit for controlling the current from the power supply circuit that supplies the signal current is provided, and when the scan pulse detection circuit detects no scan pulse, the power supply control circuit is operated to cut off the current from the power supply circuit. And
[0010]
In the current driven active matrix display device using a current driven light emitting element such as an EL, even when the scanning pulse from the scanning line driving circuit is stopped, the present invention is configured as described above. Since the current detected and supplied to the display portion is cut off, it is possible to prevent permanent destruction such as disconnection / short circuit of the EL element driving transistor and the EL light emitting element.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
1 is a circuit configuration diagram of a current-driven active matrix display device according to an embodiment of the present invention, FIG. 2 is a scan pulse detection circuit diagram according to an embodiment of the present invention, and FIG. 3 is a scan pulse according to the embodiment of the present invention. FIG. 4 is a power supply control circuit diagram according to the first embodiment of the present invention, and FIG. 5 is a power supply control circuit diagram according to the second embodiment of the present invention.
[0012]
As shown in FIG. 1, the circuit configuration of the current drive type active matrix display device according to the embodiment of the present invention includes a scan pulse detection circuit 14 and a power supply control circuit 15 as compared with the configuration of the conventional display device. As shown in FIG. 2, the scanning pulse detection circuit 14 is constituted by a D-type flip-flop (DFF) circuit. As shown in the operation time chart of FIG. 3, the circuit operation of the scan pulse detection circuit 14 is set by the shift-out pulse holding signal GSOHLD at the rising edge of the shift-out pulse GSO, and the shift-out pulse holding signal GSOHLD is reset by the start pulse GSI. The When the shift-out pulse holding signal GSOHLD is on, the power supply control signal PowCNT is turned on by the rising edge of the start pulse GSI. When the shift clock GCLK supplied to the scanning line driving circuit 4 stops, the shift-out pulse GSO from the shift register in the scanning line driving circuit 4 is not output, the shift-out pulse holding signal GSOHLD is not set, and the next start The power control signal PowCNT is turned off at the rising edge of the pulse GSI.
[0013]
The shift-out pulse GSO is a signal output by the (N + 1) th shift clock in the N-stage shift register. The power-on reset signal PonRST is a signal that resets the scan pulse detection circuit 14 to an initial state, and is output from a control circuit (not shown) that controls the entire display device.
As shown in FIG. 4, the power supply control circuit 15 includes an inverter IN and a P-channel MOS type switching transistor Q3. Upon receipt of the power control signal PowCNT on signal from the scan pulse detection circuit 14, the transistor Q3 is turned on, and power is supplied from the power circuit 5 to each pixel unit 2 via the power line VDDA. When the shift clock GCLK supplied to the scanning line driving circuit 4 stops, the power control signal PowCNT is turned off, the transistor Q3 of the power control circuit 15 is turned off, and the power is supplied from the power circuit 5 to each pixel unit 2 of the display unit 1. Shut off the current that is flowing. Therefore, even if the holding voltage of the capacitor C _S for the leakage current of the control transistor Q1 in the pixel portion 2 is changed to the ground side, since no current flows to the organic light emitting diode OLED through the EL element driving transistor Q2, These elements are not destroyed.
[0014]
FIG. 5 shows a second embodiment of the power supply control circuit 15. Two switching transistors Q31 and Q32 are provided, and the current from the power supply circuit 5 is divided into two systems (VDDA1 and VDDA2). 2 is supplied with current. With this configuration, the current handled by each of the switching transistors Q31 to Q32 is reduced, and for example, a polysilicon TFT can be used. 5 is an example in which two switching transistors Q31 and Q32 are provided. However, the number of switching transistors is increased, and the power supply control circuit 15 is divided into multiple systems. A current may be supplied.
[0015]
FIG. 6 is a plan view of a display panel of a current-driven active matrix display device according to an embodiment of the present invention. The display unit 1 and the scanning line driving circuit 4 are formed on the same display substrate 16 using polysilicon TFT technology. The scan pulse detection circuit 14 and the power supply control circuit 15 are formed. Even when the current flowing through the display unit 1 is large, each switching transistor can be formed of polysilicon TFTs by supplying currents in multiple systems using the power supply control circuit shown in FIG. It can be formed on the same display substrate 16.
[0016]
FIG. 7 is a plan view of a display panel of a current-driven active matrix display device according to another embodiment of the present invention. The display unit 1 and scanning line driving are performed on the same display substrate 16 using polysilicon TFT technology. A circuit 4 and a scanning pulse detection circuit 14 are formed. The power supply control circuit is provided on a separate substrate (printed substrate) 17 (not shown) on which a power supply unit and the like are mounted. In this case, since the power supply control circuit 15 is mounted on a printed circuit board, a single crystal transistor can be used as a switching transistor, and a large current can be controlled with a small switching resistance.
[0017]
Note that if a mechanical switching element such as a relay is used instead of the switching transistor of the power supply control circuit 15, a larger current can be controlled with a smaller switching resistance.
In addition to the embodiment of FIG. 6 or FIG. 7, a data line driving circuit may be formed on the same display substrate 16.
[0018]
6 and 7, the scanning pulse detection circuit 14 and the power supply control circuit 15 directly related to the scanning line driving circuit 4 are formed on the same display substrate 16 as the scanning line driving circuit 4. The display device can be easily manufactured without the need of soldering or connecting the signal lines.
[0019]
【The invention's effect】
As described above, according to the present invention, in a current drive type active matrix display device using a current drive type light emitting element such as an EL, the presence / absence of a scan pulse output from the scan line drive circuit is detected and the scan pulse is detected. When the absence is detected, the current from the power supply circuit is cut off, so even if the scanning pulse from the scanning line driving circuit stops, the EL element driving transistor and the EL light emitting element are permanently damaged, such as disconnection or short circuit. There is an effect that can prevent the occurrence of. In addition, manufacture is easy despite the addition of new circuits.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram of a current-driven active matrix display device according to an embodiment of the present invention.
FIG. 2 is a scanning pulse detection circuit diagram according to an embodiment of the present invention.
FIG. 3 is an operation time chart of the scanning pulse detection circuit according to the embodiment of the present invention.
FIG. 4 is a power supply control circuit diagram according to the first embodiment of the present invention.
FIG. 5 is a power supply control circuit diagram according to a second embodiment of the present invention.
FIG. 6 is a plan view of a display panel of a current driven active matrix display device according to an embodiment of the present invention.
FIG. 7 is a plan view of a display panel of a current driven active matrix display device according to another embodiment of the present invention.
FIG. 8 is a circuit configuration diagram of a conventional current-driven active matrix display device.
FIG. 9 is a schematic cross-sectional view of a pixel portion of a current-driven active matrix display device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Display part 2 Pixel part 3 Data line drive circuit 4 Scan line drive circuit 5 Power supply circuit 6 Cathode (reflection layer)
7 EL light emitting layer 8 Anode (transparent electrode)
9 Insulating layer 10 Conductor 11 Electrode 12 Glass substrate 13 Scattered light 14 Scanning pulse detection circuit 15 Power supply control circuit 16 Display substrate 17 Separate substrate

Claims (3)

A display portion having a plurality of pixel portions arranged in a matrix; a data line driving circuit for supplying a data signal; and a scanning line driving circuit for generating a scanning pulse based on a shift operation of a shift register . In a current-driven active matrix display device that displays images by time-division driving,
A scan pulse detection circuit that detects whether or not a shift-out pulse is output from the shift register and a current from a power supply circuit that supplies a data signal current to the display unit are divided into a plurality of systems by a plurality of switching elements. A power supply control circuit for controlling to supply to the display unit is provided, and the power supply control circuit is operated to cut off a current from the power supply circuit when the scan pulse detection circuit detects no shift-out pulse. A current-driven active matrix display device. Wherein a display unit, a scanning line driving circuit, the scanning pulse detection circuit and, claim 1 Symbol placing current-driven active matrix display device, characterized in that the power supply control circuit are formed on the same substrate. 2. The current-driven active matrix display according to claim 1, wherein the display unit, the scanning line driving circuit, and the scanning pulse detection circuit are formed on the same substrate, and the power supply control circuit is provided on another substrate. apparatus.

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