Light-emitting device and printer

Abstract

A light-emitting device (10) comprises a light-emitting element (13), a current supply circuit (14) having first to sixth switching elements (TR1-TR6), and a drive control unit (15). During an OFF period in which the fifth and sixth switching elements are turned off, the drive control unit controls the first to sixth switching elements so that a first ON period in which the second and third switching elements are turned on, a second ON period in which the first switching element is turned on, and a third ON period in which the second and third switching elements are turned on are disposed.

Description

Light-emitting device and printer

[0001] The present disclosure relates to a light emitting device and a printer.

[0002] A technology for a light-emitting device that uses a pixel circuit to cause a light-emitting element such as an EL element to emit light has been developed (see Patent Document 1). By using a pixel circuit, it is possible to reduce variations in light-emitting characteristics among light-emitting elements when a plurality of light-emitting elements are caused to emit light.

[0003] WO2020 / 194647 publication

[0004] As a result of extensive research, the inventors have found that when a pixel circuit is used to make a light-emitting element emit light, the light emission history can affect the intensity of the light emission thereafter. That is, it has been found that the light emission intensity of a light-emitting element differs depending on whether or not the light-emitting element emits light within a few seconds immediately before the light-emitting element emits light.

[0005] An object of one aspect of the present disclosure is to realize a light emitting device and a printer that reduce the influence of the light emission history on the light emission intensity.

[0006] A light-emitting device according to one aspect of the present disclosure includes a light-emitting element, a current supply circuit that supplies a current to the light-emitting element, and a drive control unit that controls driving of the current supply circuit, wherein the current supply circuit includes: a capacitor having one end connected to a power supply line to which a voltage is applied, a first switching element having a control end to which a first control signal is input, one end connected to the other end of the capacitor, and the other end connected to an initialization voltage source, a second switching element having a control end to which a second control signal is input and one end connected to the other end of the capacitor and the one end of the first switching element, a third switching element having a control end to which the second control signal is input and one end connected to a data line to which a data signal is supplied, and a control circuit that controls the other end of the capacitor, the one end of the first switching element, and the a fourth switching element having a control terminal connected to the one end of the second switching element and one end connected to the other end of the third switching element; a fifth switching element having a control terminal to which a third control signal is input, one end connected to the other end of the third switching element and the one end of the fourth switching element, and the other end connected to the power supply line and the one end of the capacitor; and a sixth switching element having a control terminal to which the third control signal is input, one end connected to the other end of the second switching element and the other end of the fourth switching element, and the other end connected to the light-emitting element. The drive control unit executes a first control process in which the second switching element and the third switching element are changed from an OFF state via an ON state to an OFF state using the second control signal; a second control process in which the first switching element is changed from an OFF state via an ON state to an OFF state using the first control signal; a third control process in which the second switching element and the third switching element are changed from an OFF state via an ON state to an OFF state using the second control signal; and a fourth control process in which the fifth switching element and the sixth switching element are changed from an OFF state via an ON state to an OFF state using the third control signal.The drive control unit controls the fifth and sixth switching elements to be in the OFF state by the third control signal during a first ON period in which the second and third switching elements are in the ON state in the first control process, during a second ON period in which the first switching element is in the ON state in the second control process, and during a third ON period in which the second and third switching elements are in the ON state in the third control process.

[0007] According to the present disclosure, it is possible to realize a light emitting device that reduces the influence of the light emission history on the light emission intensity.

[0008] 1 is a schematic diagram illustrating a printer according to an embodiment of the present disclosure; FIG. 2 is a plan view illustrating a printer head according to an embodiment of the present disclosure; FIG. 3 is a circuit diagram illustrating an example of a pixel circuit; FIG. 4 is a timing chart illustrating the timing of control signals according to Comparative Example 1; FIG. 5 is a graph illustrating temporal changes in light emission according to Comparative Example 1; FIG. 6 is a graph illustrating an example of a mechanism for changing light emission intensity; FIG. 7 is a timing chart illustrating the timing of control signals according to Comparative Example 2; FIG. 8 is a graph illustrating temporal changes in light emission according to Comparative Example 2; FIG. 9 is a timing chart illustrating the timing of control signals according to Embodiment 1; FIG. 10 is a graph illustrating temporal changes in light emission according to Embodiment 1; FIG. 11 is a timing chart illustrating the timing of control signals according to Embodiment 2-1; FIG. 12 is a timing chart illustrating the timing of control signals according to Embodiment 2-2; FIG. 13 is a timing chart illustrating the timing of control signals according to Embodiment 3; and FIG. 14 is a graph illustrating the relationship between a first ON period and a step response.

[0009] (Embodiment) A light emitting device according to an embodiment of the present disclosure will be described below. Fig. 1 is a schematic diagram showing a printer 10. The printer 10 is one aspect of the light emitting device according to the present disclosure.

[0010] The printer 10 is an image forming device that forms an image on a sheet (for example, a paper surface), and includes a photosensitive drum 11 and a printer head 12 .

[0011] As the photosensitive drum 11 rotates, it is exposed to light by the printer head 12, and a latent image of the print data is formed. When the photosensitive drum 11 is charged and a photosensitive pattern corresponding to the image pattern is formed by the printer head 12, a charged pattern (latent image) is formed on the photosensitive drum 11, making it possible to form an image on a sheet using toner or the like.

[0012] 2 is a plan view illustrating a printer head 12 according to an embodiment of the present disclosure. The printer head 12 is one aspect of the light-emitting device according to the present disclosure, and includes a light-emitting unit 13, a current supply unit 14, a drive control unit 15, and a data supply unit 16.

[0013] The light-emitting unit 13 has a plurality of light-emitting elements 13(i,j). The plurality of light-emitting elements 13(i,j) are composed of light-emitting elements, for example, OLEDs (organic light-emitting diodes) or LEDs (light-emitting diodes), and are arranged in a matrix in a first direction (in this example, the X-axis direction) and a second direction (in this example, the Y-axis direction). Light emitted from the light-emitting unit 13 is concentrated on the photosensitive drum 11, forming dots D that constitute a charge pattern (latent image). For ease of understanding, FIG. 2 shows the dots D formed on the photosensitive drum 11 superimposed on the light-emitting elements 13(i,j).

[0014] The current supply unit 14 has a plurality of pixel circuits 14(i,j). The plurality of pixel circuits 14(i,j) function as current supply circuits, and each supply current to a light-emitting element 13(i,j) to cause it to emit light. For this reason, the light-emitting element 13(i,j) is connected to the pixel circuit 14(i,j) by wiring. Here, for ease of understanding, the wiring is not shown.

[0015] The drive control unit 15 controls the pixel circuit 14(i,j) (ultimately, the transistors TR1 to TR3, TR5 to TR6 described below) using a first control signal (dis(j)), a second control signal (scan(j)), and a third control signal (em(j)).

[0016] The data supply unit 16 supplies data signals DA(i) (DA(1) to DA(m)) to the data lines DL(i) (DL(1) to DL(m)). The data signals DA(i) include time-division data signals DA(i,1)..., DA(i,j)..., DA(i,n). The data signals DA(i,j) correspond to the pixel circuits 14(i,j).

[0017] 3 is a circuit diagram showing an example of pixel circuit 14(i,j). Pixel circuit 14(i,j) is controlled by drive control unit 15 and outputs light-emitting current Iij to light-emitting element 13(i,j) based on a data signal supplied from data supply unit 16.

[0018] The pixel circuit 14(i,j) has a capacitor C1 and transistors TR1 to TR7, and is connected to a power supply line PL to which a voltage is applied and a data line DL(i) (data supply unit 16) to which a data signal is supplied.

[0019] The capacitor C1 has one end connected to a power supply line PL to which a voltage (power supply voltage VDD) is applied.

[0020] The transistor TR1 functions as a first switching element having a control end (gate) to which a first control signal (dis(j)) is input, one end (source) connected to the other end of the capacitor C1, and the other end (drain) connected to the initialization power supply VINI1.

[0021] The transistor TR2 functions as a second switching element having a control terminal (gate) to which a second control signal (scan(j)) is input, and one terminal (source or drain) connected to the other terminal of the capacitor C1 and one terminal (source) of the first switching element (TR1). Note that the source and drain of the transistor TR2 are switched depending on the state.

[0022] The transistor TR3 functions as a third switching element having a control end (gate) to which a second control signal (scan(j)) is input, and one end (source) connected to a data line DL(i) to which a data signal DA(i) is supplied.

[0023] The transistor TR4 functions as a fourth switching element having a control end (gate) connected to the other end of the capacitor C1, one end (source) of the first switching element (TR3), and one end (source or drain) of the second switching element, and one end (source) connected to the other end (drain) of the third switching element (TR3).

[0024] The transistor TR5 functions as a fifth switching element having a control end (gate) to which a third control signal (em(j)) is input, one end (drain) connected to the other end (drain) of the third switching element (TR3) and one end (source) of the fourth switching element (TR4), and the other end (source) connected to the power supply line PL and one end of the capacitor C1.

[0025] The transistor TR6 functions as a sixth switching element having a control end (gate) to which the third control signal (em(j)) is input, one end (source) connected to the other end (drain) of the second switching element (TR2) and the other end (drain) of the fourth switching element (TR4), and the other end (drain) connected to the light-emitting element 13(i, j).

[0026] The transistor TR7 functions as a seventh switching element having a control end (gate) to which the first control signal (dis(j)) is input, the other end (drain) of the sixth switching element, one end (source) connected to the light-emitting element 13(i, j), and the other end (drain) connected to the initialization power supply VINI2.

[0027] The drive control unit 15 controls the pixel circuit 14(i, j) by executing the following first to fourth control processes (1) to (4). Note that the drive control unit 15 may execute the first to fourth control processes (1) to (4) in order. (1) A first control process in which the second switching element and the third switching element are changed from an OFF state to an ON state and then to an OFF state by a second control signal (scan(j)) (here, the second control signal is set to an H state, an L state, and an H state in this order); (2) A second control process in which the first switching element is changed from an OFF state to an ON state and then to an OFF state by a first control signal (dis(j)) (here, the first control signal is set to an H state, an L state, and an H state in this order); (3) A third control process in which the second switching element and the third switching element (TR2, TR3) are changed from an OFF state to an ON state and then to an OFF state by a second control signal (scan(j)) (here, the second control signal is set to an H state, an L state, and an H state in this order); (4) A fourth control process in which the fifth switching element and the sixth switching element (TR5, TR6) are changed from an OFF state to an ON state and then to an OFF state by a third control signal (em(j)) (here, the third control signal is changed to an H state, an L state, and an H state in this order).

[0028] At this time, the drive control unit 15 controls the fifth and sixth switching elements (TR5, TR6) to be in the OFF state using the third control signal (em(j)) during the next first to third ON periods (here, the third control signal is set to the L state).

[0029] The first ON period is the first ON period in the first control process during which the second and third switching elements (TR2, TR3) are in the ON state. The second ON period is the second ON period in the second control process during which the first switching element (TR1) is in the ON state. The third ON period is the third ON period in the third control process during which the second and third switching elements (TR2, TR3) are in the ON state.

[0030] The data supply unit 16 supplies a data signal DA(i) to the data line DL(i). As described above, the data signal DA(i) includes time-division data signals DA(i,1)..., DA(i,j)..., DA(i,n). The data supply unit 16 sequentially repeats data supply periods T1 to Tn in which it supplies the first to nth data signals DA(i,1) to DA(i,n) to the data line DL(i). That is, the data supply unit 16 supplies the jth data signal DA(i,j) to the data line DL(i) during the jth data supply period Tj.

[0031] Hereinafter, these repeated data supply periods T1 to Tn may be arranged in chronological order and represented as T(k) (k: integer). For example, when n=4 (when data supply periods T1 to T4 are repeated), the integer k may be a negative number or a number greater than 4. In this way, the repeated data supply periods T1 to Tn can be generally represented as data supply periods T(k), making it possible to clarify the temporal relationship. For example, when n=4, if data supply period T1 is represented as T(k), the previous data supply period T4 is represented as T(k-1). For ease of understanding, the following Figures 4, 7, 9, 11 to 13 use the notations T1 to Tn and T(k).

[0032] Comparative Example 1 FIG. 4 is a timing chart showing timings of control signals according to Comparative Example 1. In FIG.

[0033] In the following description, n=4. That is, data supply periods T1 to T4 in which data signals DA(i,1) to DA(i,4) (hereinafter also referred to as "data signals D1 to D4") are supplied to data line DL(i) are repeated in sequence. As a result, in period T0 (frame period) corresponding to data supply periods T1 to T4, light-emitting elements 13(i,1) to 13(i,4) emit light in sequence in response to data signals DA(i,1) to DA(i,4) of one frame FL. This also applies to Comparative Example 2 and Embodiments 1 to 3 described below.

[0034] In Comparative Example 1, the second to fourth control processes are executed, but the first control process is not executed, as will be described below. In this respect, Comparative Example 1 differs from Comparative Example 2 and Embodiments 1 to 3, which will be described later.

[0035] 4, between times td1 and td2 (second ON period), the first control signal (dis(j)) is in the L state, and the first switching element (TR1) is in the ON state (second control process). Between times ts1 and ts2 (third ON period), the second control signal (scan(j)) is in the L state, and the second and third switching elements (TR2, TR3) are in the ON state (third control process). Between time te2 and the next time te1, the third control signal (em(j)) is in the L state, and the fifth and sixth switching elements (TR5, TR6) are in the ON state (fourth control process).

[0036] Here, between times te1 and te2 (hereinafter referred to as the OFF period), the third control signal (em(j)) is in the H state, and the fifth and sixth switching elements (TR5, TR6) are in the OFF state. This OFF period between times te1 and te2 includes the second ON period between times td1 and td2 and the third ON period between times ts1 and ts2. However, the OFF period between times te1 and te2 does not include the first ON period before the second ON period between times td1 and td2, in which the second control signal (scan(j)) turns the second switching element and the third switching element (TR2, TR3) ON. As a result, as will be described later, the history of light emission is more likely to affect the intensity of light emission.

[0037] Between times td1 and td2 (second ON period), the control signals dis(j), scan(j), and em(j) are L level, H level, and H level, respectively. As a result, transistors TR1, TR4, and TR7 are ON, and transistors TR2, TR3, TR5, and TR6 are OFF. Although the control signals dis(j), scan(j), and em(j) are not input to transistor TR4, because transistor TR1 is ON, the gate of transistor TR4 is connected to VINI1, goes L level, and transistor TR4 is ON. Between times td1 and td2 (second ON period), because transistor TR3 is OFF, the data signal DA(i, j) does not flow into pixel circuit 14.

[0038] Between times ts1 and ts2 (third ON period), the control signal scan(j) is at L level, and transistors TR2 and TR3 are in the ON state. As a result, the data signal DA(i,j) flows into capacitor C1 via transistors TR3, TR4, and TR2 and is stored as a charge in capacitor C1.

[0039] From time te2 to the next time te1, the control signal scan(j) is at H level, and transistors TR2 and TR3 are in the OFF state. Furthermore, the control signal em(j) is at L level, and transistors TR5 and TR6 are in the ON state. As a result, the data signal DA(i,j) stored as a charge in capacitor C1 causes light-emitting current Iij to be injected into light-emitting element 13(i,j) via transistors TR5, TR4, and TR6. This causes light-emitting element 13(i,j) to emit light with an intensity corresponding to the data signal DA(i,j).

[0040] 5 is a graph showing temporal changes in light emission according to Comparative Example 1. This graph shows a case where light is emitted continuously in a combination of a pair of light-emitting element 13(i,j) and pixel circuit 14(i,j). Specifically, a non-light-emitting frame FL1 and light-emitting frames FL2 to FL4 are executed in sequence.

[0041] In this sequential light emission, when transitioning from a non-light-emitting frame FL1 (dark state) to light-emitting frames FL2 to FL4 (bright state), a phenomenon (hereinafter also referred to as step response) was discovered in which the light emission intensity B1 of the first light-emitting frame FL2 becomes lower than the original light emission intensity (for example, the light emission intensity B2 of frames FL3 to FL4).

[0042] More specifically, when the device transitions from a non-light-emitting state that continues for a predetermined period Ts (e.g., 5 seconds) or more to a light-emitting state, the light intensity in the first light-emitting frame decreases. This decrease can be expressed by the intensity ratio R (R=B1 / B2) between the light intensity B1 in the first light-emitting frame and the light intensity B2 in the immediately following light-emitting frame.

[0043] In this way, the change in light emission intensity depending on the light emission history can be understood as being due to the fact that the characteristics of the pixel circuit 14(i, j), in particular the transistor TR4, for example, the threshold voltage Vth, change depending on the light emission history.

[0044] As shown in Figure 3, the threshold voltage Vth of transistor TR4 is thought to shift due to a voltage Vgs corresponding to the light emission history. The voltage Vgs is the voltage between the control terminal (gate) and one terminal (source) of transistor TR4. The threshold voltage Vth of transistor TR4 is thought to differ between when not emitting light (Bk) and when emitting light (W). In other words, the threshold voltage Vth of transistor TR4 can be thought of as being large when not emitting light (Bk) and small when emitting light (W) (Vth(Bk)>Vth(W)).

[0045] When transitioning from frame FL1 (non-emission) to frame FL2 (emission), the signal voltage during emission, "Vdata(W)-Vth(Bk)," is written to the gate terminal of transistor TR4 in accordance with the threshold voltage Vth(Bk) of the IV characteristic (G(Bk)) immediately before the non-emission state. After that, as shown by the dashed line, the IV characteristic (G(W)), i.e., Vth, shifts, causing the emission intensity B1 to decrease below the original emission intensity B2.

[0046] On the other hand, from frame FL2 onwards, the IV characteristic (G(W)) corresponds to Vth(W) during light emission, and therefore the signal voltage "Vdata(W)-Vth(W)" is written to the gate terminal of transistor TR4. Since the threshold voltage Vth(W) remains unchanged thereafter, the original light emission intensity B2 is maintained. Thus, in Comparative Example 1, it is believed that the light emission intensity at the first light emission changes depending on the light emission history due to the difference between the threshold voltages Vth(Bk) and Vth(W) of transistor TR4 during non-light emission (Bk) and light emission (W).

[0047] Comparative Example 2 FIG. 7 is a timing chart showing the timing of control signals according to Comparative Example 2. In this example, in addition to the second to fourth control processes, the first control process is executed before the second control process, and the zeroth control process is executed before the first control process. The zeroth and first control processes correspond to the second and third control processes. That is, in Comparative Example 2, the OFF period between times te1 and te2 includes the time td1 and td2 (the zeroth ON period) when the control signal dis(j) is in the L state, the time ts1 and ts2 (the first ON period) when the control signal scan(j) is in the L state, the time td3 and td4 (the second ON period) when the control signal dis(j) is in the L state, and the time ts3 and ts4 (the third ON period) when the control signal scan(j) is in the L state. That is, in Comparative Example 2, the second and third ON periods are repeated twice during the OFF period.

[0048] 8 is a graph showing the change in light emission over time according to Comparative Example 2. It can be seen that the step response of Comparative Example 2 is improved compared to Comparative Example 1. In Comparative Example 1, the intensity ratio R (the intensity ratio R (=B1 / B2) between the light emission intensity B1 in the first light emission frame and the light emission intensity B2 in the immediately following light emission frame) is about 92.0%, whereas in Comparative Example 2 the intensity ratio R is about 99.2%.

[0049] On the other hand, the addition of an ON period increases the OFF period. During the ON period, it is necessary to maintain the OFF state of the control signal em(j) in order to limit unnecessary light emission of the light-emitting element 13(i,j). Specifically, since the 0th to 3rd ON periods are allocated to the three data supply periods T3, T4, and T1, the OFF period also spans the three data supply periods T3, T4, and T1. This may lead to a reduction in the light-emitting time of the light-emitting element 13(i,j) (from time te2 to the next time te1), and ultimately a reduction in the amount of light (the product of the light-emitting intensity and the light-emitting time).

[0050] For example, in a display device such as an EL display device, since there are a large number of scanning lines (e.g., several hundred to several thousand), it is relatively easy to ensure the light-emitting time of light-emitting element 13(i,j). Therefore, in the display device, even if multiple ON periods of the control signal scan and the control signal dis are provided immediately before the frame FL1 in which light is emitted or in the frame FL before that, the step response can be reduced without substantially reducing the light amount of light-emitting element 13(i,j). In other words, in a display device, it is easy to reduce the step response by applying Comparative Example 2.

[0051] On the other hand, in a printer head, the number of scanning lines (number n in FIG. 2) is relatively small (for example, 1 to 8 lines), so it is not easy to ensure the light emission time of light-emitting element 13(i, j). In other words, if Comparative Example 2 is applied to a printer head, the amount of light emitted by light-emitting element 13(i, j) may be significantly reduced, which may result in a decrease in printing speed.

[0052] 9 is a timing chart showing the timing of control signals according to the first embodiment. Here, the OFF period from time te1 to time te2 includes the time between times ts1 and ts2 (first ON period) when the control signal scan(j) is in the L state, the time between times td1 and td2 (second ON period) when the control signal dis(j) is in the L state, and the time between times ts3 and ts4 (third ON period) when the control signal scan(j) is in the L state. Unlike Comparative Example 2, this OFF period does not include the zeroth ON period. That is, the OFF period during which the fifth and sixth switching elements (TR5, TR6) are turned OFF by the third control signal (em) does not include the zeroth ON period during which the first switching element (TR1) is turned ON by the first control signal (dis) before the first ON period. As a result, the reduction of the ON period of the control signal em(j) is limited, and the step response can be reduced while maintaining the light intensity of the light-emitting element 13(i,j).

[0053] 10 is a graph showing temporal changes in light emission according to embodiment 1. Here, the control signal dis(j) is in the L state (first ON period) without providing an ON period (zeroth ON period) of the control signal dis(j).

[0054] As described above, during the 0th ON period, transistor TR1 is turned ON, and the gate terminal of transistor TR4 is initialized. In the first embodiment, this initialization is not performed, and the control signal scan(j) is turned ON. That is, transistors TR2 and TR3 are turned ON while transistor TR4 is not completely ON. As a result, there is a possibility that the data signal passing through transistors TR3, TR4, and TR2 may not be read completely.

[0055] However, experiments have shown that the step response can be reduced even when the first ON state is executed without passing through the 0th ON state. The reason why the step response can be reduced by only the first ON state without passing through the 0th ON state can be explained as follows. That is, by providing the first ON period (without passing through the 0th ON state) before the second and third ON periods (the original processing combination) and writing the data signal DA(i, j), the gate-source voltage Vgs of transistor TR4 can be induced in the negative direction, bringing the gate-source voltage Vgs closer to 0 (see FIG. 6). As a result, the threshold voltage Vth can be brought closer to the IV characteristics during light emission, reducing the reduction in the amount of light in the light-emitting frame FL2.

[0056] In the first embodiment, the (k-1)th data supply period T(k-1) immediately preceding the kth data supply period T(k) includes the first ON period and at least a portion of the second ON period, and the kth data supply period includes the third ON period. That is, the first to third ON periods are allocated to two data supply periods T(k-1) and T(k), and the OFF period also spans the two data supply periods T(k-1) and T(k). Compared to the second comparative example, in which the zeroth to third ON periods are allocated to three data supply periods T3, T4, and T1, and the OFF period also spans the three data supply periods T3, T4, and T1, the OFF period can be shortened, making it easier to increase the light intensity of the light-emitting element 13(i, j).

[0057] As described above, the light emitting device according to the first embodiment includes a light emitting element, a current supply circuit for supplying a current to the light emitting element, and a drive control unit for controlling the drive of the current supply circuit. The current supply circuit includes a capacitor having one end connected to a power supply line to which a voltage is applied, a first switching element having a control end to which a first control signal is input, one end connected to the other end of the capacitor, and the other end connected to an initialization voltage source, a second switching element having a control end to which a second control signal is input and one end connected to the other end of the capacitor and the one end of the first switching element, a third switching element having a control end to which the second control signal is input and one end connected to a data line to which a data signal is supplied, and a control circuit for controlling the other end of the capacitor, the one end of the first switching element, and the other end connected to an initialization voltage source. a fourth switching element having a control terminal connected to the one end of the second switching element and one end connected to the other end of the third switching element; a fifth switching element having a control terminal to which a third control signal is input, one end connected to the other end of the third switching element and the one end of the fourth switching element, and the other end connected to the power supply line and the one end of the capacitor; and a sixth switching element having a control terminal to which the third control signal is input, one end connected to the other end of the second switching element and the other end of the fourth switching element, and the other end connected to the light-emitting element. The drive control unit executes a first control process in which the second switching element and the third switching element are changed from an OFF state via an ON state to an OFF state using the second control signal; a second control process in which the first switching element is changed from an OFF state via an ON state to an OFF state using the first control signal; a third control process in which the second switching element and the third switching element are changed from an OFF state via an ON state to an OFF state using the second control signal; and a fourth control process in which the fifth switching element and the sixth switching element are changed from an OFF state via an ON state to an OFF state using the third control signal.The drive control unit controls the fifth and sixth switching elements to be in the OFF state by the third control signal during the first ON period in which the second and third switching elements are in the ON state in the first control process, during the second ON period in which the first switching element is in the ON state in the second control process, and during the third ON period in which the second and third switching elements are in the ON state in the third control process.

[0058] This makes it possible to realize a light-emitting device that reduces the influence of the light emission history on the light emission intensity. Compared to Comparative Example 2, it is easier to ensure the light-emitting period of light-emitting element 13(i, j) (the time from time te2 to the next time te1), and the decrease in the light intensity of light-emitting element 13(i, j) is suppressed.

[0059] (Embodiment 2-1) FIG. 11 is a timing chart showing the timing of control signals according to embodiment 2-1.

[0060] 11 , the (k-1)th data supply period T(k-1) immediately preceding the kth data supply period T(k) includes at least a portion of the first ON period, and the kth data supply period includes at least a portion of the second ON period and the third ON period. That is, the number of ON periods included in the data supply period T(k-1) is one. In the first embodiment, compared to when the number of ON periods included in the data supply period T(k-1) is two, it is easier to shorten the OFF period and increase the light intensity of the light-emitting element 13(i, j).

[0061] Here, the first to third ON periods are substantially continuous. That is, the end of the first ON period (time ts2) and the start of the second ON period (time td1) are close to each other (substantially simultaneous), and the end of the second ON period (time td2) and the start of the third ON period (time ts3) are close to each other (substantially simultaneous). This makes it easier to shorten the OFF period (times te1 to te2) and ensure the light emission period (the time from time te2 to the next time te1). Note that close (substantially simultaneous) means that the difference between the end (e.g., time ts2) and the start (e.g., time td1) of these periods is, for example, ±3 μsec or less.

[0062] (Embodiment 2-2) FIG. 12 is a timing chart showing the timing of control signals according to embodiment 2-2.

[0063] 12, the kth data supply period T(k) includes at least a portion of the first ON period (times ts1 to ts2), the second ON period (times td1 to td2), and the third ON period (times ts3 to ts4). That is, the first to third ON periods are substantially included in one data supply period T(k). In embodiments 2-1 and 2-2, the relationship between the first to third ON periods and the data supply period T(k) is different. Note that in embodiments 2-1 and 2-2, the lengths of the first to third ON periods may be the same.

[0064] As in embodiment 2-1, the first to third ON periods are substantially continuous. That is, the end of the first ON period (time ts2) and the start of the second ON period (time td1) are close to each other (substantially simultaneous), and the end of the second ON period (time td2) and the start of the third ON period (time ts3) are close to each other (substantially simultaneous). This makes it easier to shorten the OFF period (times te1 to te2) and ensure a sufficient light-emitting period (the time from time te2 to the next time te1).

[0065] (Embodiment 3) Figure 13 is a timing chart showing the timing of control signals according to embodiment 3. As shown in Figure 13, in embodiment 3, similar to embodiment 2-1, the (k-1)th data supply period T(k-1) immediately preceding the kth data supply period T(k) includes at least a portion of the first ON period, and the i-th data supply period includes at least a portion of the second ON period and the third ON period. In embodiment 3, the first ON period is shorter than the third ON period. Note that the relationship between the data supply period and the first to third ON periods can be defined as appropriate.

[0066] As in embodiment 2-1, the first to third ON periods are substantially continuous. That is, the end of the first ON period (time ts2) and the start of the second ON period (time td1) are close to each other (substantially simultaneous), and the end of the second ON period (time td2) and the start of the third ON period (time ts3) are close to each other (substantially simultaneous). This makes it easier to shorten the OFF period (times te1 to te2) and ensure a sufficient light-emitting period (the time from time te2 to the next time te1).

[0067] In addition, in the third embodiment, the first ON period is shorter than the third ON period. As a result, in the third embodiment, it is easier to shorten the OFF period and increase the light intensity of the light-emitting element 13(i, j).

[0068] FIG. 14 is a graph showing the relationship between the first ON period and step response. "ds" corresponds to Comparative Example 1, in which the first ON period is not provided. "s(**μ)ds" means a combination of the first ON period of "** [μ seconds]" and the third ON period. Here, the third ON period is set to 3 [μ seconds], and the first ON period is changed.

[0069] As shown in FIG. 14, when the first ON period is 0.06 μsec or longer, the step response is 95% or higher, and it is clear that it is preferable that the second ON period is 0.06 μsec or longer.

[0070] Furthermore, considering the ratio of the first ON period to the third ON period, it is preferable that the first ON period be 2% (=100*0.06 / 3) or more of the third ON period. When the first ON period is 3 μsec, it is preferable that the second ON period be 0.06 μsec or more.

[0071] (Modification) The light-emitting device according to the present disclosure has been described above using a printer (printer head) as an example. The light-emitting device according to the present disclosure is not limited to a printer, and may be any light-emitting device in which a plurality of light-emitting elements are aligned vertically and horizontally and which scans these light-emitting elements to emit light sequentially. An example of such a light-emitting device is a display device that displays an image.

[0072] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure.

[0073] 10 Printer (light emitting device) 11 Photosensitive drum 12 Printer head (light emitting device) 13 Light emitting section 13 (i, j) Light emitting element 14 Current supply section 14 (i, j) Pixel circuit 15 Drive control section 16 Data supply section T1 to T4 Data supply period

Claims

1. A light-emitting element, a current supply circuit that supplies current to the light-emitting element, and a drive control unit that controls the drive of the current supply circuit, wherein the current supply circuit comprises: a capacitor having one end connected to a power supply line to which a voltage is applied; a first switching element having a control end to which a first control signal is input, one end connected to the other end of the capacitor, and the other end connected to an initialization voltage source; a second switching element having a control end to which a second control signal is input and one end connected to the other end of the capacitor and the one end of the first switching element; a third switching element having a control end to which the second control signal is input and one end connected to a data line to which a data signal is supplied; and a fourth switching element having a control end connected to the other end of the capacitor, the one end of the first switching element, and the one end of the second switching element, and one end connected to the other end of the third switching element. a fifth switching element having a control terminal to which a third control signal is input, one end connected to the other end of the third switching element and the one end of the fourth switching element, and the other end connected to the power supply line and the one end of the capacitor; and a sixth switching element having a control terminal to which the third control signal is input, one end connected to the other end of the second switching element and the other end of the fourth switching element, and the other end connected to the light-emitting element, wherein the drive control unit performs: a first control process to change the second switching element and the third switching element from an OFF state via an ON state to an OFF state in accordance with the second control signal; a second control process to change the first switching element from an OFF state via an ON state to an OFF state in accordance with the first control signal; and a third control process to change the second switching element and the third switching element from an OFF state via an ON state to an OFF state in accordance with the second control signal.and a fourth control process for changing the fifth switching element and the sixth switching element from an OFF state to an ON state and then back to an OFF state by the third control signal, wherein the drive control unit controls the fifth and sixth switching elements to be in the OFF state by the third control signal during a first ON period in which the second and third switching elements are in the ON state in the first control process, a second ON period in which the first switching element is in the ON state in the second control process, and a third ON period in which the second and third switching elements are in the ON state in the third control process.

2. The light emitting device of claim 1, wherein the OFF period in which the fifth and sixth switching elements are turned OFF by the third control signal does not include the zeroth ON period in which the first switching element is turned ON by the first control signal before the first ON period.

3. A light-emitting device according to claim 1 or 2, further comprising: a data supply unit that supplies data signals to the data lines; the data supply unit sequentially repeats data supply periods in which it supplies first to nth data signals to the data lines (n: an integer of 2 or more), thereby supplying a jth data signal to the data lines in a kth data supply period (k: an integer of 1 or more and may be greater than n); and the current supply circuit causes the light-emitting element to emit light based on the jth data signal in the kth data supply period.

4. The light emitting device of claim 3, wherein the (k-1)th data supply period immediately preceding the kth data supply period includes the first ON period and at least a portion of the second ON period, and the kth data supply period includes the third ON period.

5. The light emitting device of claim 3, wherein the (k-1)th data supply period immediately preceding the kth data supply period includes at least a portion of the first ON period, and the kth data supply period includes at least a portion of the second ON period and the third ON period.

6. The light emitting device according to claim 5, wherein the first ON period is shorter than the third ON period.

7. The light emitting device according to claim 3, wherein the kth data supply period includes at least a part of the first ON period, the second ON period, and the third ON period.

8. The light emitting device according to claim 7, wherein the first ON period is 2% or more of the third ON period.

9. The light emitting device according to claim 6, wherein the first ON period is 0.06 [μsec] or longer.

10. A light emitting device according to any one of claims 3 to 9, wherein the end of the first ON period and the start of the second ON period are close to each other, and the end of the second ON period and the start of the third ON period are close to each other.

11. The light emitting device according to any one of claims 3 to 10, comprising: first to nth current supply circuits having data lines to which the first to nth data signals are respectively supplied from the data supply unit; and first to nth light emitting elements to which current is supplied from the first to nth current supply circuits, respectively.

12. A printer comprising the light-emitting device according to any one of claims 1 to 11.

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