JP2006251602A - Driving circuit, electro-optical device, and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving circuit, an electro-optical device, and an electronic apparatus which allow a voltage Vgs of driving transistor driving a light emitting element to be kept fixed regardless of the variance in the total quantity of emitted light of light emitting elements provided in a display panel. <P>SOLUTION: A variation of a supply current IEL of an electro-optical device 1 is measured by a current detection circuit 12 and a differential amplification circuit 13 to generate a differential voltage Vdif being a variation of a supply voltage VOEL. A level shifter 16 generates a reference voltage on the basis of the differential voltage Vdif and supplies it to a gradation voltage generation circuit 14 which generates a gradation voltage for writing a gradation of light emission luminance to a pixel circuit 400. The gradation voltage is given to a gate electrode of the driving transistor of the pixel circuit 400 as a voltage Vdata, and the voltage Vdata is interlocked with the variance of the supply voltage VOEL, whereby the voltage Vgs is compensated so as not to vary with the variance of the source voltage VOEL of the driving transistor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a drive circuit, an electro-optical device, and an electronic apparatus that display an image using a self-light-emitting element such as an organic light-emitting diode element (hereinafter referred to as “OLED (Organic Light Emitting Diode) element”).

  An electro-optical device including an OLED element includes a display panel in which pixel circuits including a large number of OLED elements are arranged as a two-dimensional matrix, and a scanning line that controls writing and lighting of luminance information by selecting a scanning line of the display panel. It is composed of a driver and a data line driver that supplies a writing voltage corresponding to the luminance and displays the gradation of the OLED element, and displays an image by self-emission.

In recent years, the density and the screen size of electro-optical devices have been increased, and the number of pixels of the electro-optical device has increased. When the number of pixels in the electro-optical device increases, the current consumption during image display when a large number of light-emitting elements are turned on increases, and the power supply voltage is reduced by the wiring resistance such as a power cable that supplies power from the power source to the electro-optical device. This causes a problem of lowering.
Such wiring resistance includes the contact resistance of the connector of the power cable, the resistance of a fine wiring pattern on the electro-optical device, the cable and contact resistance inside the electro-optical device, and the like from the power source to all pixel circuits. The wiring resistance existing in the route is targeted.

  As described above, when the current consumption during image display increases and the power supply voltage decreases, the luminance of the light emitting element decreases and the luminance varies depending on the display pattern. This will be described with reference to FIGS.

  FIG. 12 is a drive circuit diagram of a pixel circuit constituting the display panel. The OLED element 420, which is a light emitting element, is driven by being connected to the drain electrode of a P-channel driving transistor 401 (Tr0) whose source voltage is supplied to the source electrode VOEL. The current Ids for driving the OLED element 420 is determined by the gate-source voltage Vgs of the driving transistor 401 written through the N-channel switching transistor 403 (Tr1), and Vgs is held by the capacitance of the capacitor 410. ing. Vgs is set by a gradation voltage Vdata selected by gradation data from the outside. The N-channel switching transistor 402 is turned on when the OLED element 420 emits light. Note that the ON potential of the N-channel switching transistor 402 can be ignored.

FIG. 13 is a characteristic curve of the drive Tr0, where the vertical axis represents the drive current Ids that is the drain current, and the horizontal axis represents the source voltage. The drain current Ids of Tr0 has a relationship that can be expressed by an equation of Ids = 1 / 2β (Vgs−Vth) ² . Here, β is the mobility, and Tth is the threshold value of Tr0. Va and Vb are source voltages of Tr0 and correspond to the power supply voltage VOEL, and Vdata is a gate voltage given through the transistor 403. From the curve in FIG. 13, when the power supply voltage VOEL decreases from Va to Vb, Vgs changes from (Va−Vdata) to (Vb−Vdata), and the drive current Ids decreases from Ia to Ib. The brightness will decrease.

  FIG. 14 is a change diagram of the luminance shown in FIG. 13. When the total light emission amount of the pixels of the electro-optical device increases, the power supply voltage VOEL decreases for the above-described reason. As a result, the luminance of the entire electro-optical device is reduced. It shows a situation where it drops greatly. In particular, according to the above-described Ids equation, the decrease in luminance becomes more rapid as the power supply voltage VOEL decreases. Therefore, a driving circuit is required in which the luminance of the OLED element 420 does not vary with respect to the variation of the power supply voltage VOEL.

  As such a drive circuit, for example, a drive circuit disclosed in Patent Document 1 is disclosed. The drive circuit disclosed in Patent Document 1 suppresses a difference in light emission luminance caused by a difference in wiring resistance depending on a place where a light emitting element is arranged by controlling a lighting time.

JP 2004-45674 A

However, the drive circuit described in Patent Document 1 has a problem that complicated control is required and the configuration is complicated.
Further, the drive circuit described in Patent Document 1 is intended only for the difference in wiring resistance depending on the location of the light emitting element. Accordingly, voltage fluctuations caused by wiring resistances such as a power cable that supplies power from the power source to the electro-optical device or a cable inside the electro-optical device are not dealt with, and thus a decrease in light emission luminance caused by these is suppressed. I can't.

  Accordingly, the present invention has been made paying attention to such an unsolved problem of the conventional technology, and suppresses the luminance fluctuation of the light emitting element against the fluctuation of the power supply voltage supplied to the electro-optical device. It is an object to provide a drive circuit, an electro-optical device, and an electronic apparatus.

In order to achieve the above object, a drive circuit for driving an electro-optical device, measuring a fluctuation amount of a power supply current supplied to the electro-optical device, and calculating a reference voltage based on the measured fluctuation amount. A compensation circuit section for generating, and a gradation voltage generation section for generating a gradation voltage for performing gradation control of a light emitting element provided in the electro-optical device based on the reference voltage. To do.
According to the present invention, it is possible to realize a configuration that measures the amount of voltage fluctuation based on the fluctuation of the power supply current of the electro-optical device and suppresses the decrease in luminance of the light emitting element using the measurement result.

In order to achieve the above object, the driving circuit drives the electro-optical device, and measures a fluctuation amount of the power supply voltage supplied to the electro-optical device, and performs a reference based on the measured fluctuation amount. A compensation circuit unit that generates a voltage, and a gradation voltage generation unit that generates a gradation voltage for performing gradation control of a light emitting element provided in the electro-optical device based on the reference voltage. Features.
According to the present invention, it is possible to realize a configuration that measures the amount of voltage fluctuation based on the fluctuation of the power supply voltage supplied to the electro-optical device and suppresses the decrease in the luminance of the light emitting element using the measurement result.

The compensation circuit unit includes a holding circuit that holds a peak voltage of a power supply voltage supplied to the electro-optical device, and a difference between the voltage held by the holding circuit and the power supply voltage supplied to the electro-optical device. The variation amount of the power supply voltage is measured based on the above.
According to the present invention, it is possible to easily measure the fluctuation amount of the power supply voltage, and it is possible to realize a configuration that suppresses a decrease in luminance of the light emitting element using the measurement result.

The gradation voltage generator includes a voltage dividing circuit that divides a voltage applied to both ends, and applies the reference voltage to one of the voltage dividing circuits and a fixed voltage including a ground potential to the other. And generating a plurality of gradation voltages.
In this case, a plurality of gradation voltages for performing gradation control can be collectively generated based on the reference voltage.

The compensation circuit unit generates a first reference voltage and a second reference voltage, and the gradation voltage generation unit includes a voltage dividing circuit that divides a voltage applied to both ends, and the voltage dividing circuit A plurality of gradation voltages are generated by applying the first reference voltage to one of the first and the second reference voltage to the other.
In this case, a plurality of reference voltages for performing gradation control can be generated collectively and accurately based on the first reference voltage and the second reference voltage.

Further, the voltage dividing circuit is configured by connecting a plurality of resistors in series.
In this case, it becomes easy to configure the voltage dividing circuit in the integrated circuit. In that case, since the resistance value ratio of the plurality of resistors can be realized with high accuracy, a plurality of reference voltages for performing gradation control can be generated with high accuracy.

The gradation voltage includes a reference voltage itself applied to the voltage dividing circuit.
In this case, the components of the voltage dividing circuit can be reduced.

In order to achieve the above object, the driving circuit drives the electro-optical device, and measures a fluctuation amount of a power supply voltage or a power supply current supplied to the electro-optical device, and determines the measured fluctuation amount. And a gradation circuit for generating gradation voltage for controlling gradation by controlling a driving transistor of a light emitting element provided in the electro-optical device based on the reference voltage. And a voltage generator, wherein the gate voltage of the driving transistor is changed in conjunction with the amount of change.
In this case, it is possible to realize control that suppresses a decrease in luminance of the light emitting element.

Further, the gate voltage of the driving transistor is changed so that the voltage between the source and gate of the driving transistor is kept constant.
In this case, it is possible to realize control that suppresses a decrease in luminance of the light emitting element with high accuracy.

The light emitting device is an organic light emitting diode device.
In this case, it is possible to realize a self-luminous electro-optical device in which a decrease in luminance of the organic light-emitting diode element is suppressed.

Next, an electro-optical device according to the present invention includes a scanning line driver that controls the light emitting elements in units of rows or columns, a data line driver that controls the light emitting elements in units of columns or rows, and the drive circuit described above. It is characterized by having.
According to the present invention, it is possible to suppress a decrease in luminance of the electro-optical device, and it is possible to realize a higher density and a larger screen of the electro-optical device.

  Next, an electronic apparatus according to the present invention includes the above-described electro-optical device, and includes, for example, a monitor device, a personal computer, a mobile phone, a personal information terminal, an electronic still camera, and the like.

  Hereinafter, the present invention will be described with reference to the drawings.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. 1 to 7 are views showing a first embodiment according to the present invention.
FIG. 1 is a block diagram showing a schematic configuration of an electro-optical device 1 according to the first embodiment of the present invention.
The electro-optical device 1 includes a pixel area A, a scanning line driver 100, a data line driver 200, a current detection circuit 12, a differential amplifier circuit 13, a level shifter 16, and a gradation voltage generation circuit 14. The current detection circuit 12, the differential amplifier circuit 13, and the level shifter 16 constitute a compensation circuit unit, and its output is input as a reference voltage to the gradation voltage generation circuit 14 which is a gradation voltage generation unit. .

  The electro-optical device 1 is configured such that power is supplied to the electro-optical device 1 from a power source 500 having a source voltage VE via a power cable W having a wiring resistance having a resistance value Rw. Accordingly, the power supply voltage of the electro-optical device 1 is the power supply voltage VOEL lower than the source voltage VE.

  In the pixel region A, m write control lines 101 and m lighting control lines 102 are formed in parallel with the X direction. In addition, n data lines 103 are formed in parallel with the Y direction orthogonal to the X direction. A pixel circuit 400 is provided corresponding to each intersection of the write control line 101 and the data line 103. The pixel circuit 400 includes an OLED element. The power supply voltage VOEL is supplied to each pixel circuit 400 via the power supply line L. A detailed configuration of the pixel circuit 400 will be described later with reference to FIG.

  The control circuit 300 generates clock signals such as a Y clock signal YCLK and an X clock signal XCLK and outputs them to the scanning line driver 100 and the data line driver 200. Further, other control signals CONT are supplied to the electro-optical device 1.

  The scanning line driver 100 generates scanning signals Y1, Y2, Y3,..., Ym for sequentially selecting the plurality of write control lines 101 and generates lighting control signals Vg1, Vg2, Vg3,. The scanning signals Y1 to Ym and the lighting control signals Vg1 to Vgm are generated by sequentially transferring in synchronization with the Y clock signal YCLK. The lighting control signals Vg1, Vg2, Vg3,..., Vgm are supplied to the pixel circuits 400 via the lighting control lines 102, respectively.

  FIG. 2 shows an example of a timing chart of the scanning signals Y1 to Ym and the lighting control signals Vg1 to Vgm. The scanning signal Y1 is a pulse having a width corresponding to one horizontal scanning period (1H) from the first timing of one vertical scanning period (1F), and is supplied to the writing control line 101 in the first row. Thereafter, the pulses are sequentially shifted and supplied as scanning signals Y2, Y3,..., Ym to the write control lines 101 in the 2, 3,. In general, when the scanning signal Yi supplied to the write control line 101 in the i-th row (i is an integer satisfying 1 ≦ i ≦ m) becomes H level, the write control line 101 is selected. Show. Further, as the lighting control signals Vg1, Vg2, Vg3,..., Vgm, for example, signals obtained by inverting the logic levels of the scanning signals Y1, Y2, Y3,.

  The data line driver 200 includes a data line writing circuit 201 and a plurality of selectors 15, and supplies gradation signals X 1, X 2, X 3,..., Xn to the corresponding data lines 103. The gradation signals X1 to Xn are given as voltage signals indicating gradation luminance.

  The data line writing circuit 201 includes a shift register (not shown) and a latch circuit (not shown). The shift register sequentially transfers and stores the gradation data in synchronization with the X clock signal XCLK. Next, the latch circuit latches the gradation data using the latch signal input from the control circuit 300. As a result, the gradation data in the serial format is converted into the parallel format and output to the selector 15.

  The selector 15 is provided corresponding to each of the n data lines 103, and in cooperation with the gradation voltage generation circuit 14, converts the gradation data from a digital signal to an analog signal to obtain gradation signals X1 to Xn. Output to each data line 103. Specifically, the gradation voltages Vref1 to VrefQ supplied from the gradation voltage generation circuit 14 are used, the reference voltage corresponding to the gradation data is selected by an analog switch, and the data lines 103 are formed as gradation signals X1 to Xn. To output.

  In addition, as shown in FIG. 1, the configuration of the D / A conversion of the present embodiment is such that the n selectors 15 commonly use the gradation voltage output from one gradation voltage generation circuit 14. Yes. By sharing the gradation voltage generation circuit 14, it is possible to reduce variations in D / A conversion characteristics.

FIG. 3 shows a detailed circuit diagram of the level shifter 16 and the gradation voltage generation circuit 14. The output of the level shifter 16 is input to the gradation voltage generation circuit 14 as a reference voltage.
3A shows an example using a plurality of reference voltages VOEL2 and VOEL3 as reference voltages, and FIG. 3B shows an example using one reference voltage VOEL4.

First, the configuration example in FIG. 3A will be described.
The gradation voltage generation circuit 14 includes Q + 1 resistors R0 to RQ connected in series. The reference voltage VOEL2 and the VOEL3 having a higher potential than the reference voltage VOEL2 are supplied to the gradation voltage generation circuit 14, divided by the resistors R0 to RQ, and Q kinds of gradation voltages Vref1, Vref2 between the voltages of VOEL2 and VOEL3, ..., VrefQ is generated. When the gradation data is 6-bit data, Q = 64, and 64 kinds of gradation voltages Vref1 to VrefQ correspond respectively. The selector 15 selects one of a plurality of gradation voltages Vref1 to VrefQ based on the gradation data, and outputs the selected gradation signals X1 to Xn.
Each gradation voltage has the highest voltage of Vref1, and the voltage decreases in the order from Vref1 to VrefQ. At this time, the voltages of the gradation voltages Vref1 to VrefQ are defined by the ratio of the relative resistance values of the resistors R0 to RQ, and different resistance values are set for the respective resistors in order to realize a desired gamma characteristic. Has been.

The operational amplifier 17 and the resistances Ra and Rb connected to the operational amplifier 17 constitute a level shifter circuit, invert the phase of the differential voltage Vdif input to the input terminal Vin, and add the offset voltage Vf. Output as the reference voltage VOEL2. The operational amplifier 18 and the resistances Ra and Rb connected to the operational amplifier 18 constitute another level shifter circuit, which inverts the phase of the differential voltage Vdif input to the input terminal Vin, and the offset voltage Vh. Is added as a reference voltage VOEL3. This circuit corresponds to the level shifter 16 of FIG.
Note that since the offset voltage is set as a potential of Vh> Vf, the reference voltage has a relationship of VOEL3> VOEL2.
Since the same differential voltage Vdif is input to the two offset circuits and the amplification factor = Rb / Ra defined by the resistance value ratio is also the same, the reference voltage VOEL2 and the reference voltage VOEL3 are different from each other. It changes in conjunction with the change of the voltage Vdif with the same polarity and the same amplitude. Therefore, the potential difference between the reference voltages VOEL2 and VOEL3 is constant regardless of the differential voltage Vdif. The generation of the differential voltage Vdif will be described later with reference to FIG.

In this way, the level shifter 16 applies the reference voltages VOEL2 and VOEL3 that change in the same direction and with the same amplitude to the gradation voltage generation circuit 14, so that each gradation voltage Vref1 to VrefQ is the differential voltage Vdif. It changes with the same voltage width in conjunction with.
Under the condition that the differential voltage Vdif is a positive voltage and the absolute value of the differential voltage Vdif is smaller than the offset voltages Vf and Vh, the reference voltage VOEL2 decreases as the differential voltage Vdif increases with the offset voltage Vf as a reference. Further, the reference voltage VOEL3 decreases as the differential voltage Vdif increases with reference to the offset voltage Vh.

Next, the configuration example of FIG. 3B will be described.
The gradation voltage generation circuit 14 includes Q + 1 resistors R0 to RQ connected in series. The configuration and operation of the gradation voltage generation circuit 14 are the same as in FIG. The reference voltage VOEL4 supplied to the gradation voltage generation circuit 14 is divided by resistors R0 to RQ, and Q kinds of gradation voltages Vref1, Vref2,..., VrefQ are generated.

  The operational amplifier 19 and the resistors Rc and Rd connected to the operational amplifier 19 constitute a level shifter circuit, invert the phase of the differential voltage Vdif input to the input terminal Vin, and add the offset voltage Vk. Is output as the reference voltage VOEL4. This circuit corresponds to the level shifter 16 of FIG.

Under the condition that the differential voltage Vdif is a positive voltage and the absolute value of the differential voltage Vdif is smaller than the offset voltage Vk, the reference voltage VOEL4 decreases as the differential voltage Vdif increases with the offset voltage Vk as a reference.
As described above, the level shifter 16 applies the reference voltage VOEL4 based on the differential voltage Vdif to the gradation voltage generation circuit 14, so that the respective gradation voltages Vref1 to VrefQ are interlocked with the differential voltage Vdif. Change.
Note that the reference voltage VOEL4 is applied to the low voltage side of the gradation voltage generation circuit 14 in contrast to the method in which the low voltage side of the gradation voltage generation circuit 14 is set to the ground potential and the reference voltage VOEL4 is applied to the high potential side. A configuration may be adopted in which a fixed voltage is applied to the potential side. In this case, the voltage change width of the gradation voltage based on the differential voltage Vdif can be given larger on the VrefQ side than on the Vref1 side.

As described above with reference to FIGS. 3A and 3B, a plurality of gradation voltages are generated by applying a reference voltage based on the differential voltage Vdif to the gradation voltage generation circuit 14.
Here, the reference voltage may be included in the gradation voltage output from the gradation voltage generation circuit 14. By using the reference voltage as one of the gradation voltages, the resistance of the gradation voltage generation circuit 14 can be reduced. For example, the resistance R0 can be reduced by using the reference voltages VOEL3 and VOEL4 as the gradation voltage Vref1. The same applies to RQ.

  Next, the pixel circuit 400 will be described. FIG. 4 shows a circuit diagram of the pixel circuit 400. A pixel circuit 400 shown in the figure corresponds to the i-th row and j-th column in FIG. 1, and includes three thin film transistors TFT 401 to 403, a capacitor element 410, and an OLED element 420.

The TFT 401 as a driving transistor is a p-channel MOS transistor, and the TFTs 402 and 403 are n-channel MOS transistors. The source electrode of the TFT 401 is connected to the power supply line L, while its drain electrode is connected to the drain electrode of the TFT 402.
One end of the capacitor 410 is connected to the source electrode of the TFT 401, and the other end is connected to the gate electrode of the TFT 401 and the drain electrode of the TFT 403. The gate electrode of the TFT 403 is connected to the write control line 101. On the other hand, the gate electrode of the TFT 402 is connected to the lighting control line 102, and its source electrode is connected to the anode of the OLED element 420. A lighting control signal Vgi is supplied to the gate electrode of the TFT 402 via the lighting control line 102. Note that the cathode of the OLED element 420 is a common electrode throughout the pixel circuit 400 and has a low (reference) potential in the power supply.

  In such a configuration, when the scanning signal Yi becomes the H level, the n-channel TFT 403 is turned on, so that the potential difference between the Vdata output from the data line driver 200 and the power supply voltage VOEL is accumulated in the capacitor 410.

  When the scanning signal Yi becomes L level, the TFT 403 is turned off, and the gate-source voltage Vgs of the TFT 401 is held at the voltage when the voltage Vdata is applied. At the same time as the scanning signal Yi becomes L level, the lighting control signal Vgi becomes H level, the TFT 402 is turned on, and an injection current Ioled corresponding to the gate-source voltage flows between the source and drain of the TFT 401. Specifically, this current flows through a path of the power supply line L → TFT 401 → TFT 402 → OLED element 420.

  Here, the injection current Ioled flowing through the OLED element 420 is determined by the operating point of the TFT 401 set by the gate-source voltage of the TFT 401. The gate-source voltage Vgs is a voltage held in the capacitor 410 due to the potential difference between Vdata and the power supply voltage VOEL when the scanning signal Yi is at the H level. As described above, the pixel circuit 400 is controlled by the voltage program method, and the light emission luminance is defined by the voltage Vdata of the gradation signals X1 to Xn.

  FIG. 5 is a detailed circuit diagram of the current detection circuit 12 and the differential amplifier circuit 13 shown in FIG. These are composed of an operational amplifier and respective resistors associated therewith, and generate a differential voltage Vdif supplied to the level shifter 16 described with reference to FIG.

First, the power supply current IEL flowing through the power supply line L flows through the resistor 11 having a small resistance value r, and the voltage at both ends of the resistor 11 passes through the voltage follower-connected operational amplifiers 20 and 21 through the resistors Re, Rf, and operational amplifier 22. Are respectively input to the differential amplifier circuit. Here, the amplification factor of the differential amplifier circuit is set to 1, and the potential difference generated by the power supply current IEL flowing through the resistor 11 is obtained as the differential voltage Vdif at the output V0 of the operational amplifier 22.
Here, the circuit of the operational amplifiers 20 and 21 connected to the voltage follower is provided to prevent the flow of the power supply current IEL, and is not necessarily required if the design is taken into consideration.

FIG. 6 is an operation explanatory diagram of the drive transistor of this embodiment, and the same description as the characteristic curve of FIG. 13 will be given. The drain current Ids of the MOS transistor 401 (Tr0) on the vertical axis has a relationship represented by the equation Ids = 1 / 2β (Vgs−Vth) ² . Here, β is the mobility, and Tth is the threshold value of Tr0. Va and Vb are Tr0 source voltages, and Vdataα and Vdataβ are Tr0 gate voltages given through the MOS transistor 403.

  When the power supply voltage VOEL of the power supply line L decreases, the horizontal axis (source voltage) in FIG. 6 decreases from Va (black circle in the figure) by Vdif and becomes Vb (white circle in the figure). At this time, the reference voltage of the gradation voltage generation circuit 14 changes in conjunction with it, and the potential difference of Vdif also decreases in the gate voltage of Tr0 from Vdataα to Vdataβ. Since Vgs of Tr0 is (source voltage−Vdata) and (Va−Vdataα) and (Vb−Vdataβ) do not vary, Vgs can be made constant even when the source voltage VOEL varies.

  FIG. 7 is a graph showing the effect of compensating for the decrease in luminance of the OLED element 420. The horizontal axis indicates the total light emission amount of the entire display panel, and is substantially proportional to the current consumption of the electro-optical device. The vertical axis represents the voltage values of VOEL and Vdata and the luminance of the display panel. When the level shifter 16 has the configuration of FIG. 3A, the reference voltages VOEL2 and VOEL3 change in conjunction with Vdif. When the level shifter 16 has the configuration of FIG. 3B, the reference voltage VOEL4 interlocks with Vdif. Change.

  FIG. 7A shows a case where control is performed so that the amount of change ΔVdata between Vdif and Vdata is equal. Even if the source voltage VOEL fluctuates, Vgs is constant, so fluctuations in the drive current Ids are eliminated, and a decrease in luminance of the OLED element 420 can be compensated.

  FIG. 7B shows a case where the amount of change in Vdif and Vdata is not equal to ΔVdata, but is controlled in conjunction with Vdif and Vdata. Although the effect is smaller than that in FIG. 7A, the fluctuation of the drive current Ids becomes small even when the source voltage VOEL fluctuates, and the decrease in luminance of the OLED element 420 can be compensated. Depending on the use of the electro-optical device, the electro-optical device can be used as a problem-free level.

As described above, in this embodiment, the current detection circuit 12 and the differential amplifier circuit 13 measure the fluctuation amount of the power supply current IEL of the electro-optical device 1, and the differential voltage that is the fluctuation amount of the power supply voltage VOEL. Vdif is generated. The level shifter 16 generates a reference voltage based on the differential voltage Vdif, and supplies the reference voltage to the gradation voltage generation circuit 14 that generates a gradation voltage for writing the gradation of light emission luminance into the pixel circuit 400. The gradation voltage is given as Vdata to the gate electrode of the driving transistor of the pixel circuit 400, and Vdata is linked to the amount of fluctuation of the power supply voltage VOEL, so that Vgs does not change even if the source voltage VOEL of the driving transistor changes. Will be compensated for.
As a result, even if the power supply voltage VOEL decreases due to an increase in the power supply current IEL of the electro-optical device 1, the luminance of the display panel does not decrease.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to the drawings.
FIG. 8 is a diagram illustrating a second embodiment according to the present invention, and is different from the first embodiment in a circuit configuration for measuring the fluctuation amount of the power source of the electro-optical device. In this embodiment, the fluctuation amount of the power supply voltage is measured. Hereinafter, a different part from the said 1st Embodiment is demonstrated, the part which overlaps with the said 1st Embodiment is attached | subjected to the same code | symbol, and description is abbreviate | omitted.

FIG. 8 is a block diagram showing a schematic configuration of the electro-optical device 2 according to the second embodiment of the present invention.
The electro-optical device 2 includes a pixel area A, a scanning line driver 100, a data line driver 200, a voltage setting circuit 40, a differential amplifier circuit 13, a level shifter 16, and a gradation voltage generating circuit 14. The voltage setting circuit 40, the differential amplifier circuit 13, and the level shifter 16 constitute a compensation circuit unit, and its output is input as a reference voltage to the gradation voltage generation circuit 14 which is a gradation voltage generation unit. .

The voltage setting circuit 40 outputs a preset power supply voltage set in advance and is input to one input terminal of the differential amplifier circuit 13. Since the power supply voltage VOEL is input to the other input terminal of the differential amplifier circuit 13, the differential amplifier circuit 13 can output the differential voltage Vdif, which is a fluctuation amount of the power supply voltage VOEL, to the level shifter 16.
As the planned power supply voltage, a voltage when the electro-optical device 2 is unloaded can be used. In order to prevent the output voltage polarity of the level shifter 16 from becoming negative, it is preferable to set the planned power supply voltage to a slightly higher voltage than the no-load voltage.

  The configuration of the voltage setting circuit 40 may be an analog method in which a fixed voltage is adjusted by a variable resistor, or a digital method in which a voltage is output by a memory such as a RAM and a D / A converter.

In this way, in this embodiment, the voltage setting circuit 40 and the differential amplifier circuit 13 measure the amount of fluctuation of the power supply voltage VOEL of the electro-optical device 2 to generate the differential voltage Vdif. The level shifter 16 generates a reference voltage based on the differential voltage Vdif, and supplies the reference voltage to the gradation voltage generation circuit 14 that generates a gradation voltage for writing the gradation of light emission luminance into the pixel circuit 400. The gradation voltage is given as Vdata to the gate electrode of the driving transistor of the pixel circuit 400, and Vdata is linked to the fluctuation amount of the power supply voltage VOEL. Will be compensated for.
As a result, even if the power supply voltage VOEL decreases due to an increase in the power supply current IEL of the electro-optical device 2, the luminance of the display panel does not decrease.

(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to the drawings.
FIG. 9 is a diagram illustrating a third embodiment according to the present invention, and is different from the second embodiment in a circuit configuration for measuring a fluctuation amount of a power source of the electro-optical device. In this embodiment, as in the second embodiment, when measuring the fluctuation amount of the power supply voltage, the fluctuation amount of the power supply voltage is measured using a peak hold circuit. Hereinafter, a different part from the said 2nd Embodiment is demonstrated, the part which overlaps with the said 2nd Embodiment is attached | subjected, and description is abbreviate | omitted.

FIG. 9 is a block diagram illustrating a schematic configuration of the electro-optical device 2 according to the third embodiment of the invention.
The electro-optical device 2 includes a pixel region A, a scanning line driver 100, a data line driver 200, a peak hold circuit 42, a differential amplifier circuit 13, a level shifter 16, and a gradation voltage generation circuit 14. The peak hold circuit 42, the differential amplifier circuit 13, and the level shifter 16 constitute a compensation circuit unit, and its output is input as a reference voltage to the gradation voltage generation circuit 14 which is a gradation voltage generation unit. .

  The peak hold circuit 42 detects the peak value of the power supply voltage VOEL and holds the value for a long period. When the current consumption of the electro-optical device 2 becomes the minimum, the voltage drop is regarded as the minimum, and the power supply voltage VOEL becomes the maximum value. Therefore, the peak hold circuit 42 holds this maximum value. In addition, since no display is performed at the start of the operation of the electro-optical device 2, the current consumption is minimized, and the power supply voltage VOEL at this time can be automatically held as the maximum value. The peak hold circuit 42 can hold the holding voltage for a long period of time, but resets the peak hold at a predetermined timing while detecting the condition that the current consumption is low, and increases the detection accuracy of the peak hold value. Can do.

  The output of the peak hold circuit 42 is input to one input terminal of the differential amplifier circuit 13, and the power supply voltage VOEL is input to the other input terminal of the differential amplifier circuit 13. A differential voltage Vdif that is a fluctuation amount of the power supply voltage VOEL can be output to the level shifter 16.

  Even if the peak hold circuit 42 is an analog system in which a voltage value is stored in a capacitor using an operational amplifier, the voltage data measured by the A / D converter is stored in a memory such as a RAM and the D / A converter. It may be a digital system that outputs a voltage using the above method.

Thus, in this embodiment, the peak hold circuit 42 and the differential amplifier circuit 13 measure the amount of fluctuation of the power supply voltage VOEL of the electro-optical device 2 to generate the differential voltage Vdif. The level shifter 16 generates a reference voltage based on the differential voltage Vdif, and supplies the reference voltage to the gradation voltage generation circuit 14 that generates a gradation voltage for writing the gradation of light emission luminance into the pixel circuit 400. The gradation voltage is given as Vdata to the gate electrode of the driving transistor of the pixel circuit 400, and Vdata is linked to the amount of fluctuation of the power supply voltage VOEL, so that Vgs does not change even if the source voltage VOEL of the driving transistor changes. Will be compensated for.
As a result, even if the power supply voltage VOEL decreases due to an increase in the power supply current IEL of the electro-optical device 2, the luminance of the display panel does not decrease.

  If the electro-optical device has a large number of pixels, it is assumed that a plurality of data line drivers 200 are used for the configuration of the electro-optical device. In this case, each data line driver 200 may include the gradation voltage generation circuit 14 and supply a reference voltage to each gradation voltage generation circuit.

  In addition, the level shifter 16 and the gradation voltage generation circuit 14 described above are shown as analog circuits, but may be configured using an A / D converter, a D / A converter, and a digital circuit. Needless to say.

(Application examples)
Next, an electronic apparatus to which the electro-optical device according to the above-described embodiment is applied will be described. 10 and 11 use the electro-optical device 1, it goes without saying that the electro-optical device 2 is also equivalent.
FIG. 10 shows a configuration of a monitor device to which the electro-optical device 1 is applied. The monitor device 1000 includes the electro-optical device 1 as a display unit. The monitor device 1000 inputs information of still images and moving images from an information processing device such as a personal computer or a video device through a display interface, and displays the information on the electro-optical device 1. The power source of the monitor device 1000 may be installed outside the monitor device 1000 or may be built in the monitor device 1000. Since the electro-optical device 1 uses the OLED element 420, a large-screen image can be easily displayed with a wide viewing angle.

  FIG. 11 shows the configuration of a mobile personal computer to which the electro-optical device 1 is applied. The personal computer 2000 includes the electro-optical device 1 as a display unit and a main body 2010. The main body 2010 is provided with a power switch 2001 and a keyboard 2002. Since the electro-optical device 1 uses the OLED element 420, an easy-to-see screen can be displayed with a wide viewing angle.

  Note that electronic devices to which the electro-optical device 1 is applied include those shown in FIGS. 10 to 11, digital still cameras, televisions, viewfinder type and monitor direct-view type video tape recorders, car navigation devices, pagers, and electronic notebooks. , Calculators, word processors, workstations, videophones, POS terminals, devices equipped with touch panels, and the like. The electro-optical device described above can be applied as the display unit of these various electronic devices.

1 is a block diagram of an electro-optical device according to a first embodiment of the invention. The timing chart of a scanning signal and a lighting control signal. The detailed circuit diagram of a level shifter and a gradation voltage generation circuit. (A) shows a case where 2 reference voltages are used, and (b) shows a case where one reference voltage is used. The circuit diagram of a pixel circuit. The detailed circuit diagram of a current detection circuit and a differential amplifier circuit. FIG. 6 is an operation explanatory diagram of a driving transistor. The graph which shows the effect of invention. FIG. 9 is a block diagram of an electro-optical device according to a second embodiment of the invention. FIG. 10 is a block diagram of an electro-optical device according to a third embodiment of the invention. 1 is a front view of a monitor device to which an electro-optical device of the invention is applied. 1 is a perspective view of a mobile personal computer to which an electro-optical device of the invention is applied. FIG. 6 is a drive circuit diagram of a pixel circuit. Drive transistor characteristic curve. FIG. 14 is a change diagram of luminance shown in FIG. 13.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 ... Electro-optical device, 12 ... Current detection circuit, 13 ... Differential amplifier circuit, 14 ... Gradation voltage generation circuit, 15 ... Selector, 16 ... Level shifter, 40 ... Voltage setting circuit, 42 ... Peak hold circuit, 100 DESCRIPTION OF SYMBOLS ... Scanning line driver, 101 ... Write control line, 102 ... Lighting control line, 103 ... Data line, 200 ... Data line driver, 300 ... Control circuit, 400 ... Pixel circuit, 420 ... OLED element as a light emitting element, 500 ... Power supply, A ... pixel area, L ... power supply line, VE ... power supply voltage, VOEL ... power supply voltage, VOEL2, VOEL3, VOEL4 ... reference voltage.

Claims (12)

A drive circuit for driving an electro-optical device,
A compensation circuit unit that measures a fluctuation amount of a power supply current supplied to the electro-optical device, and generates a reference voltage based on the measured fluctuation amount;
A gradation voltage generator that generates a gradation voltage for performing gradation control of a light emitting element provided in the electro-optical device based on the reference voltage;
A drive circuit comprising: A drive circuit for driving an electro-optical device,
A compensation circuit unit that measures a fluctuation amount of a power supply voltage supplied to the electro-optical device and generates a reference voltage based on the measured fluctuation amount;
A gradation voltage generator that generates a gradation voltage for performing gradation control of a light emitting element provided in the electro-optical device based on the reference voltage;
A drive circuit comprising: The compensation circuit unit includes a holding circuit that holds a peak voltage of a power supply voltage supplied to the electro-optical device,
The drive circuit according to claim 2, wherein a fluctuation amount of the power supply voltage is measured based on a difference between a voltage held by the holding circuit and a power supply voltage supplied to the electro-optical device. The gradation voltage generator includes a voltage dividing circuit that divides a voltage applied to both ends,
4. A plurality of gradation voltages are generated by applying the reference voltage to one of the voltage dividing circuits and applying a fixed voltage including a ground potential to the other. The drive circuit described. The compensation circuit unit generates a first reference voltage and a second reference voltage,
The gradation voltage generator includes a voltage dividing circuit that divides a voltage applied to both ends,
4. A plurality of gradation voltages are generated by applying the first reference voltage to one of the voltage dividing circuits and applying the second reference voltage to the other. The drive circuit according to one item.   6. The drive circuit according to claim 4, wherein the voltage dividing circuit is configured by connecting a plurality of resistors in series.   The drive circuit according to claim 4, wherein the grayscale voltage includes a reference voltage itself applied to the voltage dividing circuit. A drive circuit for driving an electro-optical device,
A compensation circuit unit that measures a fluctuation amount of a power supply voltage or a power supply current supplied to the electro-optical device, and generates a reference voltage based on the measured fluctuation amount;
A gradation voltage generator for controlling a driving transistor of a light emitting element provided in the electro-optical device based on the reference voltage to generate a gradation voltage for performing gradation control;
The drive circuit is characterized in that the gate voltage of the drive transistor is changed in conjunction with the fluctuation amount.   9. The drive circuit according to claim 8, wherein a gate voltage of the drive transistor is changed so as to keep a voltage between a source and a gate of the drive transistor constant.   The drive circuit according to claim 1, wherein the light emitting element is an organic light emitting diode element. A scanning line driver for controlling the light emitting elements in units of rows or columns;
A data line driver for controlling the light emitting elements in columns or rows, and
The drive circuit according to any one of claims 1 to 10,
An electro-optical device comprising: An electronic apparatus comprising the electro-optical device according to claim 11.

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