JP2007011181A - Light-emitting device and its drive circuit, electronic equipment, and adjusting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compensate for the variance in characteristics among respective parts with high accuracy, regarding a technique for controlling the behavior of a light-emitting element, such as organic light-emitting diode element. <P>SOLUTION: A current source transistor 441 generates a reference current IR, corresponding to a control voltage VRS applied to the gate. A voltage-generating transistor 443 generates a reference voltage VR, corresponding to the reference current IR. Each data output circuit 41 generates a data signal X, corresponding to the reference voltage VR generated by the voltage-generating transistor 443 based on grayscale data D and outputs the signal to a data line 14. A voltage control circuit 46 acquires a characteristic signal Sf, corresponding to the threshold voltage Vth of the current source transistor 441, generates control voltage VRS corresponding to the characteristic signal Sf, and applies the voltage to the gate of the current source transistor 441. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for controlling the behavior of a light emitting element such as an organic light emitting diode (hereinafter referred to as “OLED (Organic Light Emitting Diode)”) element.

2. Description of the Related Art A light emitting device in which this type of light emitting element is arranged in a planar shape or a linear shape has been proposed as a display device or exposure device for various electronic devices. For example, in Patent Document 1, a reference current is generated for each block obtained by dividing an area where a plurality of light emitting elements are arranged, and the light emitting elements of each block are driven to emit light by supplying a current signal corresponding to the reference current of the block. A circuit is disclosed. Furthermore, in the configuration disclosed in this document, an adjustment current is generated by a current source installed for each block, and the reference current is adjusted for each block by adding the currents. According to this configuration, even if the characteristics of each part such as a transistor constituting the drive circuit are different from the expected values, the luminance of each light emitting element caused by this difference can be set by setting an adjustment current for each block. It is possible to suppress this variation.
JP 2004-145027 A (FIG. 5)

  However, in the technique of Patent Document 1, it is difficult to adjust the adjustment current generated by the current source of each block to the desired current value with high accuracy. There is a limit to the accuracy of the adjustment. The present invention has been made in view of such circumstances, and an object of the present invention is to solve the problem of highly accurately compensating for variations in characteristics of each part.

  In order to solve this problem, a driving circuit according to the present invention is a driving circuit of a light emitting device including a light emitting element whose luminance is controlled according to a data signal, and according to a control voltage applied to a gate. A current source transistor that generates a reference current, a voltage generation unit that generates a reference voltage corresponding to the reference current generated by the current source transistor (for example, the voltage generation transistor 443 shown in FIG. 2), and a reference that is generated by the voltage generation unit A data output circuit for generating and outputting a data signal corresponding to the voltage based on the gradation data, and a control voltage supply circuit for applying a control voltage corresponding to the characteristics of the current source transistor to the gate of the current source transistor To do.

  According to this configuration, since a control voltage corresponding to the characteristics of the current source transistor is applied to the gate of the current source transistor, the current value of the reference current or the reference current is determined regardless of the characteristics of the current source transistor. The voltage value of the reference voltage can be controlled to a desired value (design value) with high accuracy. Therefore, according to the present embodiment, it is possible to suppress variations in the data signal that specifies the luminance of each light emitting element.

  In a preferred aspect of the present invention, a measurement circuit for specifying the characteristics of the current source transistor is further provided, and the control voltage supply circuit generates a control voltage according to the characteristics specified by the measurement circuit. According to this configuration, it is possible to specify the characteristics of the current source transistor and adjust the control voltage according to the result as needed when using the light emitting device. Therefore, even when the characteristics of the current source transistor change over time, variations in the characteristics of the current source transistor can be compensated by the control voltage corresponding to the characteristics after the change.

  In a more specific aspect, the measurement circuit includes a characteristic output circuit that outputs a voltage according to the characteristics of the current source transistor, and a comparison between a plurality of reference voltages having different voltage values and the voltage output by the characteristic output circuit. A comparison circuit that selects any one of a plurality of reference voltages according to the result of the above, and a storage circuit that stores data (voltage designation data) that designates the reference voltage selected by the comparison circuit (for example, the memory 463 shown in FIG. 4) The control voltage supply circuit includes a selection circuit that selects one of a plurality of reference voltages having different voltage values based on data stored in the storage circuit, and a reference voltage selected by the selection circuit. And an output circuit that generates a control voltage according to the output voltage and outputs the control voltage to the gate of the current source transistor. According to this aspect, the voltage designation data can be generated with a simple configuration in which the reference voltage is selected according to the characteristics of the current source transistor. Furthermore, the control voltage can be generated with a simple configuration of selecting a reference voltage according to the voltage designation data.

  In another aspect of the present invention, the characteristic output circuit includes a switching element (for example, the switching element SW2 shown in FIG. 2) that diode-connects the current source transistor, and the current when diode-connected via the switching element. The voltage of the gate (or drain) of the source transistor is output. According to this aspect, it is possible to easily generate and output a voltage corresponding to the threshold voltage of the current source transistor. Further, according to the configuration in which the switching element (for example, the switching element SW3 shown in FIG. 2) that interrupts the path of the reference current when the current source transistor is diode-connected, the characteristics of the current source transistor are being measured. Thus, a situation in which the reference current and the reference voltage are generated while the control voltage is uncertain is avoided.

  In the present invention, a current source transistor, a voltage generation unit, and a control voltage supply circuit may be installed for each data output circuit (see, for example, FIG. 5). However, in a more desirable mode, the voltage generation unit generates Each of the data output circuits includes a plurality of data output circuits connected in common to a reference voltage line to which a reference voltage is applied, and each data output circuit generates a data signal corresponding to the reference voltage of the reference voltage line (for example, FIG. 1). According to this aspect, since the voltage generating means, the current source transistor, or the control voltage supply circuit is shared by the plurality of data output circuits, the configuration of the drive circuit is simplified and the manufacturing cost is reduced. There is.

  The present invention is also specified as a light-emitting device including the drive circuit of each aspect described above. The light emitting device includes a light emitting element whose luminance is controlled according to a data signal, a current source transistor that generates a reference current according to a control voltage applied to a gate, and a reference current generated by the current source transistor. Voltage generating means for generating a reference voltage, a data output circuit for generating and outputting a data signal corresponding to the reference voltage generated by the voltage generating means based on gradation data, and a control voltage according to the characteristics of the current source transistor Is supplied to the gate of the current source transistor. This light emitting device also provides the same effect as the drive circuit of the present invention.

  The light emitting device according to the present invention is used in various electronic devices. A typical example of this electronic device is a device using a light emitting device as a display device. Examples of this type of electronic device include a personal computer and a mobile phone. However, the use of the light emitting device according to the present invention is not limited to image display. For example, the light emitting device of the present invention can also be applied as an exposure device (exposure head) for forming a latent image on an image carrier such as a photosensitive drum by irradiation of light.

  Furthermore, the present invention is also specified as an apparatus (see, for example, FIG. 7) for setting the control voltage of the drive circuit. The adjustment device includes: a current source transistor that generates a reference current according to a control voltage applied to a gate; a voltage generation unit that generates a reference voltage according to a reference current generated by the current source transistor; A data output circuit that generates and outputs a data signal corresponding to the generated reference voltage based on the gradation data, and generates a control voltage based on the data stored in the storage circuit and applies it to the gate of the current source transistor A device for setting a control voltage used in a drive circuit including a control voltage supply circuit that performs measurement in which a characteristic of a current source transistor is specified and data corresponding to the characteristic specified by the measurement circuit is stored in a storage circuit. Writing means for writing.

<A: First Embodiment>
FIG. 1 is a block diagram showing a configuration of a light emitting device according to the first embodiment of the present invention. As shown in the figure, the light emitting device D includes an element array unit 10 in which a plurality of unit circuits P are arranged in a matrix, a scanning line driving circuit 20 and a data line driving circuit 40 for driving each unit circuit P. Including. In the element array portion 10, a plurality of scanning lines 12 extending in the X direction and n (n is a natural number) data lines 14 extending in the Y direction orthogonal to the X direction are formed. Each unit circuit P is arranged at a position corresponding to the intersection of the scanning line 12 and the data line 14. One unit circuit P includes an OLED element 17 in which a light emitting layer made of an organic EL (ElectroLuminescent) material is interposed in a gap between an anode and a cathode.

  The scanning line driving circuit 20 sequentially selects a plurality of unit circuits P in units of rows by outputting scanning signals to the respective scanning lines 12. On the other hand, the data line driving circuit 40 outputs data signals X (X1, X2,..., Xn) to the unit circuits P in the selected row by the scanning line driving circuit 20 via the data lines 14. The data signal Xj (j is an integer satisfying 1 ≦ j ≦ n) is a current signal that specifies the luminance (gradation) of the OLED element 17 of the unit circuit P located in the j-th column. The OLED element 17 of each unit circuit P emits light according to the data signal X supplied via the data line 14. The configuration of the unit circuit P is arbitrary, and the scanning line 12 and the data line 14 may be configured to function as an anode or a cathode of the OLED element 17 (passive matrix type) or supplied to the OLED element 17. It may be a configuration (active matrix type) including a switching element that controls the current to be generated in accordance with the data signal X.

  As shown in FIG. 1, the data line driving circuit 40 in this embodiment includes a plurality of data output circuits 41 (n corresponding to the total number of data lines 14) each connected to a separate data line 14. Includes a reference voltage generation circuit 44 and a voltage control circuit 46. FIG. 2 is a circuit diagram showing the configuration of each data output circuit 41 and reference voltage generation circuit 44. In the figure, only the configuration of the data output circuit 41 in the j-th column is shown in detail, but the configurations of the other data output circuits 41 are the same.

  The data output circuit 41 in the j-th column generates a data signal Xj based on the grayscale data Dj input from the outside for the unit circuit P in the j-th column and outputs it to the data line 14 in the j-th column. A D / A converter, four transistors Ta (Ta1 to Ta4) corresponding to the number of bits of the gradation data Dj, and four transistors Tb (Tb1 to Tb1) whose drains are connected to the source of the transistor Ta. Tb4). The drains of the transistors Ta1 to Ta4 belonging to the data output circuit 41 in the jth column are connected in common to the data line 14 in the jth column. Further, each bit of the gradation data Dj is supplied to each gate of the transistors Ta1 to Ta4. On the other hand, each of the transistors Tb1 to Tb4 has a source grounded and a gate connected to a common wiring (hereinafter referred to as “reference voltage line”) 42. The characteristics (particularly the gain coefficient) of the transistors Tb1 to Tb4 are the relative ratios of the currents I1 to I4 flowing in the transistors Tb when the voltage (hereinafter referred to as “reference voltage”) VR of the reference voltage line 42 is applied to each gate. Is selected to be “I1: I2: I3: I4 = 1: 2: 4: 8”.

  In the above configuration, the transistor Ta corresponding to each bit of the gradation data Dj among the four transistors Ta1 to Ta4 is selectively turned on. Then, a current I (one or more currents selected from I1 to I4) corresponding to the characteristics and the reference voltage VR flows to one or more transistors Tb connected to the transistor Ta turned on. A signal obtained by adding these currents flows to the data line 14 in the j-th column as the data signal Xj.

  The reference voltage generation circuit 44 is a means for generating a reference voltage VR that serves as a reference for the data signal X (X1, X2,..., Xn) generated by each data output circuit 41 and applying it to the reference voltage line 42. is there. As shown in FIG. 2, the reference voltage generation circuit 44 in this embodiment includes a p-channel transistor (hereinafter referred to as “current source transistor”) 441 whose source is connected to a power supply line (power supply voltage Vdd), a source Are n-channel type transistors (hereinafter referred to as “voltage generation transistors”) 443. The current source transistor 441 functions as a current source for generating a current (hereinafter referred to as “reference current”) IR corresponding to a voltage (hereinafter referred to as “control voltage”) VRS applied to the gate. On the other hand, the voltage generation transistor 443 has both a gate and a drain connected to the reference voltage line 42, generates a reference voltage VR corresponding to the reference current IR generated by the current source transistor 441, and applies the reference voltage VR to the reference voltage line 42. Functions as a means.

  As described above, the reference voltage VR that is the basis of each data signal X is determined according to the reference current IR. The reference current IR has a current value corresponding to the control voltage VRS (more specifically, the voltage between the gate and the source of the current source transistor 441) and the characteristics of the current source transistor 441. Here, the characteristics (for example, threshold voltage Vth) of the current source transistor 441 may differ from the expected values due to, for example, the manufacturing process. Therefore, if the voltage value of the control voltage VRS is fixedly selected regardless of the characteristics of the current source transistor 441, the reference current IR and the reference voltage VR determined according to the reference current IR are characteristics of the current source transistor 441. Accordingly, there may arise a problem that the data signal X having a desired current value cannot be supplied to each unit circuit P as a result. Therefore, in this embodiment, the characteristic (here, the threshold voltage Vth) of the current source transistor 441 is specified in advance, and the control voltage VRS is determined according to this characteristic. The characteristic output circuit 45 of FIG. 2 is means for outputting a signal (hereinafter referred to as “characteristic signal”) Sf corresponding to the threshold voltage Vth of the current source transistor 441. In the figure, the configuration in which the characteristic output circuit 45 is built in the reference voltage generation circuit 44 is illustrated, but this may be configured separately from the reference voltage generation circuit 44.

  As shown in FIG. 2, the characteristic output circuit 45 has three switching circuits in which each state is individually controlled in accordance with signals (S1, S2, S3) supplied from an external control circuit (not shown). It includes elements (SW1, SW2, SW3). Among these, the switching element SW1 is interposed between the drain of the current source transistor 441 and one end of the resistance element 445, and switches between conduction and non-conduction according to the signal S1 supplied to the gate. It is. The other end of the resistance element 445 is grounded.

  On the other hand, the switching element SW2 is an n-channel transistor that is inserted between the drain and gate of the current source transistor 441 and switches between conduction and non-conduction according to the signal S2 supplied to the gate. When the switching element SW2 is turned on, the current source transistor 441 is diode-connected. The voltage of the gate of the current source transistor 441 (that is, the voltage of the drain) when the switching element SW2 is kept on is output as the characteristic signal Sf.

  The switching element SW3 is an n-channel transistor that is inserted between the drain of the current source transistor 441 and the drain of the voltage generation transistor 443, and switches between conduction and non-conduction according to the signal S3 supplied to the gate. is there. When the switching element SW3 transitions to the on state, a path of the reference current IR is formed from the power supply line to the ground line via the current source transistor 441 and the voltage generation transistor 443. On the other hand, when the switching element SW3 transitions to the off state, the path of the reference current IR is interrupted.

  Next, FIG. 3 is a timing chart showing the operation of the characteristic output circuit 45. Each time the power of the light emitting device D is turned on, the operation of FIG. 3 is executed and the characteristic signal Sf corresponding to the threshold voltage Vth of the current source transistor 441 is output. As shown in FIG. 3, in the first period P1, the signal S1 and the signal S2 transition to a high level and the signal S3 transitions to a low level. Therefore, when the switching element SW3 is turned off, the path of the reference current IR is cut off, and the current source transistor 441 is diode-connected by the switching element SW2, and its drain is connected to the switching element SW1 and the resistance element 445. Is grounded. By this operation, the voltage Vx of the drain (gate) of the current source transistor 441 is lowered to the voltage value V0 close to the ground voltage Gnd. Further, in the first period P1, the switching element SW3 is turned off and the path of the reference current IR is cut off, so that the output of the reference voltage VR by the voltage generating transistor 443 is stopped. That is, a situation where the reference voltage VR corresponding to the control voltage VRS still in the adjustment stage is supplied to each data output circuit 41 is avoided.

  In the second period P2 following the first period P1, the signals S2 and S3 are maintained at the same level as in the first period P, and the signal S1 transits to a low level. Therefore, the switching element SW1 transitions to the off state, and the drain of the current source transistor 441 is disconnected from the ground line. Here, since the gate capacitance and the parasitic capacitance of each wiring exist in the vicinity of the current source transistor 441, the voltage Vx of the drain of the current source transistor 441 gradually increases immediately after the switching element SW1 transitions to the OFF state. Eventually, it converges to the difference value (Vx = Vdd−Vth) between the power supply voltage Vdd and the threshold voltage Vth. The converged voltage value Vx is output from the characteristic output circuit 45 as the characteristic signal Sf.

  The driving of each unit circuit P is started after the elapse of the second period P2. At this stage, the signal S1 and the signal S2 maintain the low level. Accordingly, the diode connection of the current source transistor 441 is released. Further, the signal S3 transitions to a high level. Accordingly, the switching element SW3 is turned on to form a path of the reference current IR from the current source transistor 441 to the voltage generation transistor 443, whereby the output of the reference voltage VR to each data output circuit 41 is started.

  The voltage control circuit 46 shown in FIG. 1 is means for controlling the control voltage VRS based on the characteristic signal Sf output from the characteristic output circuit 45. FIG. 4 is a block diagram showing the configuration of the voltage control circuit 46. As shown in the figure, the voltage control circuit 46 includes a comparison circuit 462, a reference voltage generation circuit 461, a memory 463, a selection circuit 464, a setting circuit 465, and an output circuit 466. The characteristic output circuit 45 shown in FIG. 2, the comparison circuit 462, the reference voltage generation circuit 461, and the memory 463 shown in FIG. 4 function as a measurement circuit C1 for specifying the characteristics of the current source transistor 441. On the other hand, the memory 463, the selection circuit 464, the setting circuit 465, and the output circuit 466 shown in FIG. 4 function as a control voltage supply circuit C2 that generates the control voltage VRS according to the characteristics specified by the measurement circuit C1. As described above, in the present embodiment, a configuration in which the reference voltage generation circuit 461 and the memory 463 are shared by the measurement circuit C1 and the control voltage supply circuit C2 is illustrated, but these elements are the measurement circuit C1 and the control voltage supply. A configuration may be adopted in which the circuit C2 is provided separately.

  The reference voltage generation circuit 461 is means for generating a plurality of voltages (hereinafter referred to as “reference voltages”) V1 to V4 having different voltage values by, for example, resistance voltage division. The comparison circuit 462 receives the reference voltages V 1 to V 4 output from the reference voltage generation circuit 461 and the characteristic signal Sf output from the characteristic output circuit 45. The comparison circuit 462 compares the voltage value Vx (= Vdd−Vth) of the characteristic signal Sf with each of the reference voltages V1 to V4, so that the voltage value Vx of the characteristic signal Sf among the reference voltages V1 to V4 is the highest. Specify a close voltage Vb. Then, the comparison circuit 462 generates data (hereinafter referred to as “voltage designation data”) Dv for identifying the voltage Vb specified here and writes it in the memory 463. That is, voltage designation data Dv corresponding to the threshold voltage Vth of the current source transistor 441 is written in the memory 463. The memory 463 is a storage circuit (for example, EEPROM) that stores the voltage designation data Dv in a nonvolatile manner.

  On the other hand, the selection voltage 464 of the control voltage supply circuit C 2 is supplied with the reference voltages V 1 to V 4 output from the reference voltage generation circuit 461 and the voltage designation data Dv read from the memory 463. The selection circuit 464 selects and outputs the voltage Vb designated by the voltage designation data Dv among the reference voltages V1 to V4. The voltage Vb selected here is a voltage corresponding to the threshold voltage Vth of the current source transistor 441.

  The setting circuit 465 is a means for setting a voltage ΔV that determines the reference current IR and the reference voltage VR. The setting circuit 465 in the present embodiment is a circuit (memory) that holds a preset voltage ΔV. However, for example, the setting circuit 465 may be configured to update the voltage ΔV in accordance with an operation on an operator (not shown) by a user or a signal supplied from an external device.

  The output circuit 466 is means for generating a control voltage VRS corresponding to the voltage Vb (any one of the reference voltages V1 to V4) output from the selection circuit 464 and outputting it to the gate of the current source transistor 441. The output circuit 466 in this embodiment generates the control voltage VRS (= Vb−ΔV) by subtracting the voltage ΔV set by the setting circuit 465 from the voltage Vb.

Here, the reference current IR that flows through the current source transistor 441 by the application of the control voltage VRS generated by the above procedure will be considered. If the current source transistor 441 operates in the saturation region, the reference current IR is expressed by the following equation (1).
IR = β / 2 · (Vgs−Vth) ² …… (1)
However, “β” in the equation (1) is a gain coefficient of the current source transistor 441. “Vgs” is a voltage between the gate and the source of the current source transistor 441. Therefore, the voltage Vgs is defined as a difference value (Vgs = Vdd−VRS) between the power supply voltage Vdd and the control voltage VRS.

If any one of the reference voltages V1 to V4 (voltage Vb) is substantially equal to the voltage value Vx (= Vdd−Vth) of the characteristic signal Sf, the control voltage VRS output from the output circuit 466 is the voltage value Vx. Since this corresponds to the difference value (Vdd−Vth−ΔV) between (= Vdd−Vth) and the voltage ΔV, the equation (1) is transformed into the following equation (2).
IR = β / 2 · {(Vdd−VRS) −Vth} ²
= Β / 2 · {Vdd− (Vdd−Vth−ΔV) −Vth} ²
= Β / 2 · (ΔV) ² …… (2)
As can be seen from Equation (2), the reference current IR is determined by the voltage ΔV set by the setting circuit 465 and does not depend on the threshold voltage Vth of the current source transistor 441.

  As described above, in this embodiment, since the control voltage VRS is adjusted according to the threshold voltage Vth of the current source transistor 441, the reference current IR that is not affected by the threshold voltage Vth of the current source transistor 441 is generated. be able to. Therefore, the reference voltage VR, which is the basis of the current value of each data signal X, is an expected value (design value) regardless of the threshold voltage Vth of the current source transistor 441. That is, according to the present embodiment, it is possible to compensate for variations in the threshold voltage Vth of the current source transistor 441 and control the luminance of each OLED element 17 to a desired value with high accuracy.

<B: Second Embodiment>
Next, a light emitting device D according to a second embodiment of the invention will be described. FIG. 5 is a block diagram showing a configuration of the data line driving circuit 40 in the present embodiment. In addition, the same code | symbol is attached | subjected about the element similar to 1st Embodiment among this embodiment, and the description is abbreviate | omitted suitably.

  In the first embodiment, the configuration in which n data output circuits 41 share one reference voltage generation circuit 44 and voltage control circuit 46 has been exemplified. On the other hand, the data line drive circuit 40 in this embodiment has n processing units U each corresponding to a separate data line 14 as shown in FIG. Each processing unit U generates a data output circuit 41 that outputs a data signal X to the data line 14, and generates a reference voltage VR that serves as a reference for the current value of the data signal X by a current source transistor 441 and a voltage generation transistor 443. And a voltage control circuit 46 for controlling the control voltage VRS for determining the reference voltage VR according to the characteristics (threshold voltage Vth) of the current source transistor 441. That is, in the present embodiment, the reference voltage generation circuit 44 and the voltage control circuit 46 described in the first embodiment are installed for each data output circuit 41 (for each data line 14).

  Also in this embodiment, since the reference voltage VR generated by each reference voltage generation circuit 44 can be set to an expected value regardless of the threshold voltage Vth of the current source transistor 441, the luminance of each light emitting element is highly accurate. It becomes possible to control with.

  Here, the configuration in which one reference voltage generation circuit 44 and one voltage control circuit 46 are provided for one data output circuit 41 is illustrated, but one reference for a plurality of data output circuits 41 is illustrated. The voltage generation circuit 44 and one voltage control circuit 46 may be installed. That is, in this configuration, the processing unit U is arranged for each block in which n data lines 14 are divided into N (N is a natural number; the configuration in FIG. 5 corresponds to N = 1). One processing unit U includes N data output circuits 41 each connected to the data line 14, and a reference voltage generation circuit 44 and a voltage control circuit 46 shared by the data output circuits 41. .

<C: Modification>
Various modifications can be made to each of the above embodiments. An example of a specific modification is as follows. In addition, you may combine each following aspect suitably.

(1) Modification 1
In each of the embodiments, the configuration in which the output of the characteristic signal Sf and the generation of the control voltage VRS corresponding to the output of the characteristic signal Sf are performed when the light emitting device D is turned on is illustrated. Is optional. For example, it may be executed every time an instruction is input by the user, or may be executed when the mode is changed to a mode in which the operation of the light emitting device D is paused.

(2) Modification 2
In each embodiment, the configuration in which the measurement circuit C1 for specifying the threshold voltage Vth of the current source transistor 441 is built in the data line driving circuit 40 is exemplified. According to this configuration, since the control voltage VRS is adjusted at any time even after the light emitting device D is shipped, for example, even when the characteristics of the current source transistor 441 change over time, There is an advantage that the control voltage VRS corresponding to the characteristics can be generated and used to generate the reference current IR and the reference voltage VR. However, it is not always necessary for the light emitting device D to include the measurement circuit C1. For example, as shown in FIG. 6, a voltage control circuit 46 including only the control voltage supply circuit C2 (a configuration not including the measurement circuit C1) may be employed. In this configuration, as shown in FIG. 7, the measurement circuit C1 prepared separately from the light emitting device D measures the characteristics of the current source transistor 441 by the same procedure as in the first embodiment. The voltage designation data Dv corresponding to the measured value is stored in the memory 463 in a nonvolatile manner by the comparison circuit 462. When the light emitting device D is used, the characteristics of the current source transistor 441 are not measured, and the control voltage VRS corresponding to the voltage designation data Dv stored in the memory 463 is the same as that of the first embodiment by the configuration of FIG. It is generated by the procedure. Even with this configuration, the effect that the intended reference voltage VR can be generated regardless of the characteristics of the current source transistor 441 is achieved.

(3) Modification 3
In each embodiment, the configuration in which the voltage designation data Dv is generated by selecting any one of the reference voltages V1 to V4 according to the characteristic signal Sf is exemplified. However, the characteristic of the current source transistor 441 is held in the memory 463. The method for doing this is not limited to this. For example, an A / D converter that generates digital data of the voltage value Vx (= Vdd−Vth) of the characteristic signal Sf may be provided in the measurement circuit C1, and this digital data may be stored in the memory 463 as voltage designation data Dv. Good.

  Further, in each embodiment, the configuration in which the control voltage VRS is generated according to the voltage Vb selected according to the voltage designation data Dv among the reference voltages V1 to V4 is exemplified. However, according to the voltage designation data Dv The method for generating the control voltage VRS is not limited to this. For example, a D / A converter that generates the voltage Vb specified by the voltage specification data is provided in the control voltage supply circuit C2, and the control voltage VRS is generated based on the voltage Vb and the voltage ΔV set by the setting circuit 465. It is good.

(4) Modification 4
In each embodiment, the configuration in which the characteristics of the current source transistor 441 are specified by detecting the drain voltage Vx when the current source transistor 441 is diode-connected is described. However, the method for specifying the characteristics of the current source transistor 441 is described below. It is not limited to this. For example, when the reference current IR flowing through the current source transistor 441 is measured while changing the control voltage VRS applied to the gate of the current source transistor 441, the change amount of the reference current IR becomes significant (ideally, The control voltage VRS (when the reference current IR starts to flow) may be specified as the threshold voltage Vth of the current source transistor 441.

(5) Modification 5
In each embodiment, the configuration in which the threshold voltage Vth of the current source transistor 441 is specified is illustrated, but the characteristic of the current source transistor 441 that serves as an index for setting the control voltage VRS is not limited to the threshold voltage Vth. For example, the carrier mobility may be specified together with (or instead of) the threshold voltage Vth, and the voltage control circuit 46 may generate the control voltage VRS based on these characteristics. That is, in the present invention, a configuration in which the control voltage VRS corresponding to the characteristics of the current source transistor 441 is applied to the gate is sufficient.

(6) Modification 6
In the above description, the light emitting device D using the OLED element 17 is exemplified, but the present invention is also applied to a light emitting device using other light emitting elements. For example, a display device using an inorganic EL element, a field emission display (FED), a surface-conduction electron emission display (SED), a ballistic electron emission display (BSD) The present invention is applied to various light emitting devices such as emitting display) and display devices using light emitting diodes.

<D: Application example>
Next, an electronic apparatus using the light emitting device according to the present invention will be described. FIG. 8 is a perspective view showing a configuration of a mobile personal computer that employs the light emitting device D according to any one of the embodiments described above as a display device. The personal computer 2000 includes a light emitting device D as a display device and a main body 2010. The main body 2010 is provided with a power switch 2001 and a keyboard 2002. Since the light emitting device D uses the OLED element 17 as a light emitting element, it is possible to display an easy-to-see screen with a wide viewing angle.

  FIG. 9 shows a configuration of a mobile phone to which the light emitting device D according to the embodiment is applied. A cellular phone 3000 includes a plurality of operation buttons 3001, scroll buttons 3002, and a light emitting device D as a display device. By operating the scroll button 3002, the screen displayed on the light emitting device D is scrolled.

  FIG. 10 shows a configuration of a personal digital assistant (PDA) to which the light emitting device D according to the embodiment is applied. The information portable terminal 4000 includes a plurality of operation buttons 4001, a power switch 4002, and a light emitting device D as a display device. When the power switch 4002 is operated, various kinds of information such as an address book and a schedule book are displayed on the light emitting device D.

  Electronic devices to which the light-emitting device according to the present invention is applied include those shown in FIGS. 8 to 10, digital still cameras, televisions, video cameras, car navigation devices, pagers, electronic notebooks, electronic papers, calculators. , Word processors, workstations, videophones, POS terminals, printers, scanners, copiers, video players, devices equipped with touch panels, and the like. Further, the use of the light emitting device according to the present invention is not limited to the display of images. For example, in an image forming apparatus such as an optical writing type printer or an electronic copying machine, a writing head that exposes a photosensitive member according to an image to be formed on a recording material such as paper is used. However, the light emitting device of the present invention is used.

It is a block diagram which shows the structure of the light-emitting device which concerns on 1st Embodiment of this invention. It is a circuit diagram which shows the structure of each data output circuit and a reference voltage generation circuit. 6 is a timing chart for explaining the operation of the characteristic output circuit. It is a block diagram which shows the structure of a reference voltage generation circuit and a voltage control circuit. It is a block diagram which shows the structure of the light-emitting device which concerns on 2nd Embodiment of this invention. It is a block diagram which shows the structure of the control voltage supply circuit which concerns on a modification. It is a block diagram which shows the structure of the measurement circuit which concerns on a modification. It is a perspective view which shows the specific form of the electronic device which concerns on this invention. It is a perspective view which shows the specific form of the electronic device which concerns on this invention. It is a perspective view which shows the specific form of the electronic device which concerns on this invention.

Explanation of symbols

D: Light emitting device, P: Unit circuit, 10: Element array section, 12: Scan line, 14: Data line, 17: OLED element, 20: Scan line drive circuit, 40: Data line Drive circuit 41... Data output circuit 42... Reference voltage line 44. Reference voltage generation circuit 441... Current source transistor 443 ... Voltage generation transistor 45 .. Characteristic output circuit 46. Control circuit 461... Reference voltage generation circuit 462... Comparison circuit 463... Memory 464... Selection circuit 465... Setting circuit 466.

Claims (9)

A driving circuit of a light emitting device including a light emitting element whose luminance is controlled according to a data signal,
A current source transistor that generates a reference current according to a control voltage applied to the gate;
Voltage generating means for generating a reference voltage corresponding to a reference current generated by the current source transistor;
A data output circuit for generating and outputting a data signal corresponding to the reference voltage generated by the voltage generating means based on gradation data;
A drive circuit for a light emitting device, comprising: a control voltage supply circuit that applies a control voltage in accordance with characteristics of the current source transistor to a gate of the current source transistor. Comprising a measurement circuit for identifying the characteristics of the current source transistor;
The light-emitting device drive circuit according to claim 1, wherein the control voltage supply circuit generates a control voltage in accordance with characteristics specified by the measurement circuit. The measurement circuit includes:
A characteristic output circuit that outputs a voltage according to the characteristic of the current source transistor;
A comparison circuit that selects any of the plurality of reference voltages according to a result of comparison between a plurality of reference voltages having different voltage values and a voltage output from the characteristic output circuit;
A storage circuit for storing data designating the reference voltage selected by the comparison circuit;
The control voltage supply circuit is
A selection circuit that selects any one of a plurality of reference voltages having different voltage values based on data stored in the storage circuit;
The drive circuit of the light emitting device according to claim 2, further comprising: an output circuit that generates a control voltage corresponding to the reference voltage selected by the selection circuit and outputs the control voltage to the gate of the current source transistor. The measurement circuit is a characteristic output circuit including a switching element that diode-connects the current source transistor, and outputs a voltage of the gate of the current source transistor when diode-connected via the switching element Including
The light-emitting device drive circuit according to claim 2, wherein the control voltage supply circuit generates a control voltage corresponding to the voltage output from the characteristic output circuit. The light emitting device driving circuit according to claim 4, wherein the characteristic output circuit includes a switching element that cuts off a path of the reference current when the current source transistor is diode-connected. A plurality of data output circuits each connected in common to a reference voltage line to which a reference voltage generated by the voltage generation means is applied, each data output circuit corresponding to a reference voltage of the reference voltage line The drive circuit of the light emitting device according to claim 1, wherein the data signal is generated. A light emitting element whose luminance is controlled according to a data signal;
A current source transistor that generates a reference current according to a control voltage applied to the gate;
Voltage generating means for generating a reference voltage corresponding to a reference current generated by the current source transistor;
A data output circuit for generating and outputting a data signal corresponding to the reference voltage generated by the voltage generating means based on gradation data;
A light-emitting device comprising: a control voltage supply circuit that applies a control voltage in accordance with characteristics of the current source transistor to a gate of the current source transistor.   An electronic apparatus comprising the light emitting device according to claim 7. A current source transistor that generates a reference current according to a control voltage applied to the gate; a voltage generation unit that generates a reference voltage according to a reference current generated by the current source transistor; and a reference generated by the voltage generation unit A data output circuit that generates and outputs a data signal corresponding to the voltage based on the gradation data, and a control voltage that generates a control voltage based on the data stored in the storage circuit and applies it to the gate of the current source transistor A device for setting a control voltage used in a drive circuit including a supply circuit,
Measuring means for specifying the characteristics of the current source transistor;
And a writing unit that writes data corresponding to the characteristics specified by the measurement circuit to the storage circuit.

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