LED driving device and LED driving method

Abstract

The present application provides an LED driving device and an LED driving method, and relates to the LED driving technology. The present application provides the technology that measures the time for reaching the forward voltage of the LED driven currently by comparing the forward voltage sensed in the previous scanning line and the LED voltage sensed in the current scanning line, and compensates the ON time period of the PWM signal, i.e. the pulse width modulation signal, according to the measured time for reaching the forward voltage.

Description

TECHNICAL FIELD

[0001] Various embodiments relate generally to LED driving technology. BACKGROUND

[0002] With the development of informatization, various display apparatuses capable of visualizing information are being developed. Liquid crystal display (LCD), organic light emitting diode (OLED) display apparatuses, and plasma display panel (PDP) display apparatuses are representative examples of display apparatuses that have been developed or are being developed to date. These display apparatuses are being developed to properly display high-resolution images.

[0003] However, the above-described display apparatuses have advantages in terms of high resolution, but have disadvantages in that it is difficult to manufacture large-sized display apparatuses. For example, since large-sized OLED display apparatuses developed to date have sizes of 80 inches (about 2 m) and 100 inches (about 2.5 m), they are not suitable for manufacturing large-sized display apparatuses having a width greater than 10 m.

[0004] As a method of solving such a large size aspect, recently, attention to light emitting diode (LED) display apparatuses is increasing. In LED display apparatus technology, since modular LED pixels are arranged in a desired number, one large panel can be configured. In other aspects, in LED display apparatus technology, since unit panels each configured of a plurality of LED pixels are arranged in a desired number, one large panel structure can be formed. Thus, in LED display apparatus technology, by arranging LED pixels by increasing the number of LED pixels as much as desired, a large display apparatus can be easily implemented.

[0005] An LED display apparatus is advantageous not only in terms of large size, but also in terms of various panel sizes. In LED display apparatus technology, various adjustments can be made to horizontal and vertical sizes according to proper arrangement of LED pixels.

[0006] On the other hand, an LED display apparatus supplies a driving current to an LED during an ON period of a PWM (pulse width modulation) signal. The ON period of the PWM signal is determined according to a gray value of the LED. However, the LED does not emit light as soon as a driving current is supplied, and normal emission is achieved only when a voltage across the LED reaches a forward voltage. Thus, when a driving current is supplied during the ON period of the PWM signal, the actual brightness of the LED does not reach the gray value. SUMMARY

[0007] In this context, in an aspect, the present application provides a technique for more accurately controlling an ON period of a PWM signal so that a brightness of an LED can match a gray scale value. In another aspect, the present application provides a technique for compensating a PWM signal for a forward voltage reaching time of an LED so that a loss of a gray scale value does not occur. In still another aspect, the present application provides a technique for simply measuring a forward voltage reaching time of an LED without using a separate sequence. In yet another aspect, the present application provides a technique for accurately measuring a forward voltage reaching time of an LED by continuously updating a forward voltage of an LED regardless of a change in a characteristic of a panel.

[0008] In an aspect, the present application provides an LED driving apparatus including: a driving current source configured to supply a driving current to a driving line to which a plurality of LEDs are connected; a driving control circuit configured to control a supply time of the driving current to the driving line according to a pulse width modulation signal (PWM signal); a sample-and-hold circuit configured to sense a one-side voltage of an LED and hold a voltage corresponding to a forward voltage; and a PWM compensation circuit configured to measure a first time for a one-side voltage of one LED to reach a voltage held for another LED during a time period in which the one LED is connected to the driving line, and compensate the PWM signal according to the first time.

[0009] The one-side voltage can be an anode voltage of an LED, and a cathode of the LED can be connected to a ground voltage.

[0010] In another aspect, embodiments can provide an LED driving apparatus including: a driving current source configured to supply a driving current to a first LED during a first scan time and to supply the driving current to a second LED during a second scan time; a sample-and-hold circuit configured to sense a one-side voltage of the first LED during the first scan time and hold a voltage corresponding to a forward voltage; and a compensation circuit configured to measure a first time for a one-side voltage of the second LED to reach the voltage held for the first LED during the second scan time, and control a supply time of the driving current to the second LED according to the first time.

[0011] In still another aspect, embodiments can provide a driving method for a plurality of LEDs arranged in a panel, the driving method including connecting a first LED to one driving line according to a first scan signal, supplying a driving current to the first LED through the one driving line and sensing and maintaining a forward voltage of the first LED, connecting a second LED to the one driving line according to a second scan signal, supplying the driving current to the second LED through the one driving line and measuring a first time for which a one-side voltage of the second LED reaches the forward voltage of the first LED, and controlling a supply time of the driving current to the second LED according to the first time.

[0012] The method can further include, while supplying the driving current to the second LED through the one driving line, sensing and maintaining a forward voltage of the second LED, connecting a third LED to the one driving line according to a third scan signal, supplying the driving current to the third LED through the one driving line and measuring a second time for which a one-side voltage of the third LED reaches the forward voltage of the second LED, and increasing the supply time of the driving current to the third LED according to the second time.

[0013] As is apparent from the above description, according to embodiments, an ON time period of a PWM signal can be more accurately controlled so that a brightness of an LED can match a gray value. Also, according to embodiments, a PWM signal can be compensated for a forward voltage reaching time of an LED so that a loss of a gray value is not caused. Also, according to embodiments, a forward voltage reaching time of an LED can be simply measured without using a separate sequence. Also, according to embodiments, a forward voltage reaching time of an LED can be accurately measured by continuously updating a forward voltage of an LED regardless of a change in a characteristic of a panel. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a configuration diagram of a display apparatus according to embodiments.

[0015] Figure 2 is a diagram illustrating waveforms of scan signals in a display apparatus according to embodiments.

[0016] Figure 3 is a configuration diagram of an LED driving apparatus according to embodiments.

[0017] Figure 4 is a configuration diagram of a PWM compensation circuit according to embodiments.

[0018] Figure 5 is a configuration diagram of a reaching time measurement circuit according to embodiments.

[0019] Figure 6 is a block diagram of a time extension circuit according to an embodiment.

[0020] Figure 7 is a graph showing Figure 5 and Figure 6 main waveforms of the circuit shown in

[0021] Figure 8 is a flowchart of an LED driving method according to an embodiment. DETAILED DESCRIPTION

[0022] Figure 1 is a block diagram of a display device according to an embodiment.

[0023] Referring to Figure 1 , the display device 100 can include a driving device 110 and a panel 120.

[0024] In the panel 120, a plurality of pixels P can be arranged in a case where a matrix is formed along a first direction (e.g., a horizontal direction in Figure 1 and a second direction (e.g., a vertical direction in Figure 1 ).

[0025] At least one LED (Light Emitting Diode) can be arranged in each pixel P, and the luminance of the pixel P can be determined according to the luminance of the LED.

[0026] A driving line DL and a scan line SL can be arranged in the panel 120. Each driving line DL can connect one side of the pixel P along the second direction, and each scan line SL can connect the other side of the pixel P along the first direction. For example, the anode side of the LED arranged in the pixel P can be electrically connected to the driving line DL, and the cathode side of the LED can be electrically connected to the scan line SL. In the aspect in which the cathode sides of the LEDs are commonly connected, Figure 1 the structure shown in is referred to as a common cathode structure, but it should be noted that the present embodiment is not limited to such a structure.

[0027] A scan switch SWc1, SWc2, …, and SWcN can be arranged in the scan line SL, respectively, and the scan line SL to which the driving current Ie is to be supplied can be determined according to the opening and closing of the scan switches SWc1, SWc2, …, and SWcN.

[0028] Figure 2 is a graph showing waveforms of a scan signal in a display device according to an embodiment.

[0029] Referring to Figure 1 and Figure 2 , in each frame, the scan signals Scan<1>, Scan<2>, …, and Scan<n>are sequentially supplied to the scan switches SWc1, SWc2,..., and SWcN, respectively. The scan signals Scan<1>, Scan<2>,..., and Scan <n>The drive current Ie is sequentially supplied to the first scan line SL, the second scan line SL,..., and the Nth scan line SL.

[0030] The scan line SL can be connected to a low voltage part such as a ground line in the display device 100. The scan switches SWc1, SWc2,..., and SWcN can be formed in the panel 120 or a separate substrate. According to an embodiment, the scan switches SWc1, SWc2,..., and SWcN can be formed in the driving device 110.

[0031] The scan signals Scan<1>, Scan<2>,..., and Scan <n>The driving device 110 can supply the driving current Ie, or a separate control device can supply the driving current Ie.

[0032] The brightness of the LED arranged in each pixel P can be determined according to the amount of driving power supplied within a predetermined time. The LED can be PWM (Pulse Width Modulation) driven, and the brightness of the LED can be determined according to the ratio of the on-time within the PWM control time. When the LED is turned on by the driving current Ie, a forward voltage can be formed in the LED. The amount of driving power supplied to the LED can be obtained by accumulating the product of the forward voltage and the driving current Ie during the on-time within the PWM control time, and the brightness of the LED can be determined according to the amount of driving power. Assuming that the magnitude of the forward voltage of the LED and the driving current Ie are fixed variables, the amount of driving power can be considered to have a value proportional to the on-time within the PWM control time. According to this principle, the driving device 110 can control the brightness of the LED and the brightness of the pixel P by controlling the on-time within the PWM control time.

[0033] The driving device 110 can include a plurality of channels N connected to the driving line DL, and can supply the driving current Ie to each pixel P in each channel.

[0034] On the other hand, the LED display device supplies a driving current to the LED during an ON time period of a PWM (Pulse Width Modulation) signal. The ON time period of the PWM signal is determined according to the gray value of the LED. However, the LED does not emit light just as the driving current is supplied, and normal emission is achieved only when the voltage across the LED reaches the forward voltage. Therefore, when the driving current is supplied during the ON time period of the PWM signal, the actual brightness of the LED does not reach the gray value.

[0035] To solve such a problem, the embodiment provides a technology for compensating for the PWM signal with respect to the forward voltage reaching time of the LED, so that the brightness of the LED can match the gray value.

[0036] Figure 3 FIG. 1 is a block diagram of an LED driving device according to an embodiment.

[0037] Reference Figure 3 The LED driving device 110 (hereinafter referred to as a driving device) can include a driving current source 310, a driving control circuit 320, a sample-and-hold circuit 330, a PWM compensation circuit 340, and a PWM generation circuit 350.

[0038] The driving current source 310 can supply a driving current Ie to a driving line DL to which a plurality of LEDs LED1 to LED3 are connected. The driving current Ie can be supplied to one LED of the plurality of LEDs LED1 to LED3 connected to the driving line DL.

[0039] The LED to which the drive current Ie is to be supplied can be determined by the scan signals Scan<1> to Scan<3>. For example, when the first scan signal Scan<1> is supplied, the first LED LED1 can be connected to the drive line DL and the drive current Ie can be supplied to the first LED LED1, and when the second scan signal Scan<2> is supplied, the second LED LED2 can be connected to the drive line DL and the drive current Ie can be supplied to the second LED LED2.

[0040] The drive control circuit 320 can control the supply time of the drive current Ie to the drive line DL. As an example, the drive control circuit 320 can control the connection between the drive current source 310 and the drive line DL. When the drive control circuit 320 connects the drive current source 310 and the drive line DL, the drive current Ie generated by the drive current source 310 can be supplied to the drive line DL, and when the drive control circuit 320 disconnects the drive current source 310 and the drive line DL, the supply of the drive current Ie to the drive line DL can be stopped.

[0041] The drive control circuit 320 can include a switching circuit SWp that controls the connection between the drive current source 310 and the drive line DL. The switching circuit SWp can connect or disconnect the drive current source 310 and the drive line DL according to a PWM (Pulse Width Modulation) signal. The PWM signal can have an ON period and an OFF period. In general, in the PWM signal, the period in which the voltage has a high level can be the ON period, and the period in which the voltage has a low level can be the OFF period. The switching circuit SWp can connect the drive current source 310 to the drive line DL during the ON period of the PWM signal, and can disconnect the drive current source 310 and the drive line DL during the OFF period of the PWM signal.

[0042] The sample-and-hold circuit 330 can sense the one-side voltage of the LEDs LED1 to LED3. The one side of the LEDs LED1 to LED3 can be connected to the drive line DL, and the sample-and-hold circuit 330 can sense the one-side voltage of the LEDs LED1 to LED3 through the drive line DL. One terminal To of the LED driving device 110 can be connected to the drive line DL, and the sample-and-hold circuit 330 can sense the voltage formed at the one terminal To. In the following description, the voltage Vt formed at the one terminal To is referred to as a terminal voltage. The terminal voltage Vt can correspond to the voltage of the drive line DL, and can correspond to the one-side voltage of the LEDs LED1 to LED3. The drive current Ie can be supplied to the drive line DL through the one terminal To.

[0043] The sample-and-hold circuit 330 can sense a one-side voltage of the LEDs LED1 to LED3, and can hold a voltage corresponding to a forward voltage among the sensed voltages. The forward voltage can mean a voltage difference between both ends (anode and cathode) of each of the LEDs LED1 to LED3 when each of the LEDs LED1 to LED3 is normally turned on. The LED driving apparatus 110 can determine that each of the LEDs LED1 to LED3 normally emits light when the voltage of both ends of each of the LEDs LED1 to LED3 reaches the forward voltage. The one-side voltage of each of the LEDs LED1 to LED3 can be the same as the voltage of both ends of each of the LEDs LED1 to LED3, in a case where the one-side voltage of each of the LEDs LED1 to LED3 is a voltage formed at the anode of each of the LEDs LED1 to LED3 and the cathode of each of the LEDs LED1 to LED3 is connected to a base voltage (for example, a ground).

[0044] The sample-and-hold circuit 330 can hold the voltage at a point in time when it is determined that the one-side voltage of the LEDs LED1 to LED3 reaches the forward voltage. For example, when a predetermined time elapses after the driving current Ie is supplied to the LEDs LED1 to LED3, it can be determined that the LEDs LED1 to LED3 normally emit light. At this point in time, the sample-and-hold circuit 330 can sample and hold the one-side voltage of the LEDs LED1 to LED3 as the forward voltage.

[0045] As an example, the sample-and-hold circuit 330 can sample and hold the one-side voltage of the LEDs LED1 to LED3 at a point in time when the supply of the driving current Ie to the LEDs LED1 to LED3 ends, and thus can sample and hold the forward voltage of the LEDs LED1 to LED3. The driving current Ie can be supplied to the LEDs LED1 to LED3 during an ON time period of the PWM signal, and the sample-and-hold circuit 330 can sample and hold the forward voltage of the LEDs LED1 to LED3 at or near a falling edge of the PWM signal.

[0046] The sample-and-hold circuit 330 can measure the forward voltage reach time by sensing the terminal voltage Vt (a voltage corresponding to the one-side voltage of the LEDs LED1 to LED3) during an early stage of driving the LEDs LED1 to LED3, and can hold the forward voltage by sensing the terminal voltage Vt during a later stage of driving the LEDs LED1 to LED3.

[0047] When the ON period of the PWM signal starts (for example, when the rising edge of the PWM signal is checked), the sample-and-hold circuit 330 can sense the terminal voltage Vt and compare the terminal voltage Vt with the previously stored (previously held) forward voltage. The sample-and-hold circuit 330 can store the terminal voltage Vt for the time taken by the forward voltage. When such a time is referred to as a forward voltage reaching time, the LED driving apparatus 110 can compensate for the supply time of the driving current Ie by using the forward voltage reaching time.

[0048] At a point in time when the ON period of the PWM signal ends (for example, at a point in time when the falling edge of the PWM signal is checked), the sample-and-hold circuit 330 can sense the terminal voltage Vt and can store (hold) the terminal voltage Vt as a forward voltage. The held voltage can be used to drive the next scan line.

[0049] For convenience of explanation, hereinafter, the terminal voltage sensed during the Kth scan time for driving the Kth scan line is denoted as Vt[k].

[0050] The sample-and-hold circuit 330 can sense the terminal voltage Vt[k-1] according to the PWM signal during the (K-1)th scan time and can hold a voltage corresponding to a forward voltage. The held voltage can be denoted as Vf[k-1]. The voltage to be held can be updated for each scan time. The sample-and-hold circuit 330 can sense the terminal voltage Vt[k] according to the PWM signal during the Kth scan time and can update a voltage corresponding to a forward voltage. The sample-and-hold circuit 330 can include a holding element (for example, a capacitor) and can hold and update the forward voltage in the holding element.

[0051] The sample-and-hold circuit 330 can sense the terminal voltage Vt[k] according to the PWM signal during the Kth scan time. The sample-and-hold circuit 330 can transfer the terminal voltage Vt[k] sensed during the Kth scan time and the voltage Vf[k-1] held during the (K-1)th scan time to the PWM compensation circuit 340.

[0052] The PWM compensation circuit 340 can measure the forward voltage reaching time of the LED driven among the LEDs LED1 to LED3 and can increase the supply time of the driving current Ie by the forward voltage reaching time.

[0053] The PWM compensation circuit 340 can measure a time for a one-side voltage of one LED to reach a voltage maintained for another LED as a forward voltage reaching time during a time period in which the one LED is connected to the driving line DL. For example, the PWM compensation circuit 340 can measure a time for a one-side voltage Vt[2] of the second LED LED2 to reach a voltage Vt[1] maintained for the first LED LED1 as a forward voltage reaching time of the second LED LED2 during a scan time of the second LED LED2.

[0054] The PWM compensation circuit 340 can store the forward voltage reaching time in one element (e.g., a capacitor), and can compensate for the PWM signal such that an ON time period of the PWM signal is increased. The forward voltage reaching time can have little or no contribution to brightness of the LEDs LED1-LED3. Accordingly, the PWM compensation circuit 340 can increase a driving time of the LEDs LED1-LED3 by increasing the ON time period of the PWM signal by the forward voltage reaching time.

[0055] The PWM compensation circuit 340 can generate a secondary PWM signal SPb by compensating for a primary PWM signal Spa delivered from the PWM generation circuit 350, and can deliver the secondary PWM signal SPb to the driving control circuit 320.

[0056] The PWM generation circuit 350 can generate the primary PWM signal Spa according to a gray value included in image data. The image data can be received from an external device (e.g., a host device or a timing controller, etc.), and can include a gray value indicating brightness that each LED needs to display in the image data. The PWM generation circuit 350 can generate the primary PWM signal Spa according to the gray value. The PWM compensation circuit 340 can generate the secondary PWM signal SPb by compensating for the primary PWM signal Spa.

[0057] Figure 4 is a block diagram of a PWM compensation circuit according to an embodiment.

[0058] Referring to Figure 4 The PWM compensation circuit 340 can include a reaching time measurement circuit 410 and a time extension circuit 420.

[0059] The reach time measurement circuit 410 can receive a forward voltage held during another scan time (e.g., the forward voltage Vt[k-1] held during the (K-1)th scan time) and a terminal voltage sensed during a current scan time (e.g., the terminal voltage Vt[k] sensed during the Kth scan time). The reach time measurement circuit 410 can measure a time taken for the terminal voltage sensed during the current scan time to reach the forward voltage held during the other scan time while comparing the terminal voltage with the forward voltage using a comparator. A start point of the measurement can be a point of time corresponding to a rising edge of the primary PWM signal SPa, and an end point of the measurement can be a point of time when the output of the comparator is inverted.

[0060] The forward voltage reach time can be stored as a voltage value Va. An example of the voltage value Va will be described later with reference to Figures 5 to 7

[0061] The time extension circuit 420 can receive the primary PWM signal SPa and the voltage value Va corresponding to the forward voltage reach time, and can generate the secondary PWM signal SPb by increasing an ON period of the primary PWM signal SPa according to the forward voltage reach time.

[0062] Figure 5 FIG. 10 is a block diagram of a reach time measurement circuit according to an embodiment.

[0063] Referring to Figure 5 , the reach time measurement circuit 410 can receive a terminal voltage Vt[k] being sensed during the Kth scan time (current scan time) and a forward voltage Vf[k-1] sampled and held during the (K-1)th scan time (scan time of a previous scan line), and can input the two voltages to a first comparator CMP1. The reach time measurement circuit 410 can input an output of the first comparator CMP1 to a first buffer BF1, and can input an inverted output of the first buffer BF1 to one terminal of a first AND circuit AND1. The reach time measurement circuit 410 can input the primary PWM signal SPa to the other terminal of the first AND circuit AND1, can input an inverted output of the first AND circuit AND1 to a second buffer BF2, and can control disconnection of the first charge / discharge switch SWa by using the inverted output of the second buffer BF2.

[0064] ​When the first charge / discharge switch SWa is closed, the charged charge in the first capacitor Ca is discharged at a constant rate by the first discharge current source Ir1, and when the first charge / discharge switch SWa is opened, the discharge of the first capacitor Ca is stopped. The first charge / discharge switch SWa can be closed from a rising edge of the primary PWM signal Spa until a time point at which the terminal voltage Vt[k] becomes the same as the forward voltage Vf[k-1] by the first comparator CMP1. The voltage Va of the first capacitor Ca after the first charge / discharge switch SWa is opened can be a voltage value Va corresponding to the forward voltage reaching time.

[0065] The initial charge voltage of the first capacitor Ca can be determined by the first reference voltage Vr1, and the voltage of the first capacitor Ca can be reset to the first reference voltage Vr1 by the first reset switch SWr1.

[0066] Figure 6 is a block diagram of a time extension circuit according to an embodiment.

[0067] Referring to Figure 6 The time extension circuit 420 can reset the second capacitor Cb to the second reference voltage Vr2, and can compensate for the PWM signal with a time at which the voltage Vb of the second capacitor Cb becomes the same as the voltage Va of the first capacitor Ca while discharging the second capacitor Cb according to the second discharge current source Ir2.

[0068] In detail, the time extension circuit 420 can input the voltage Vb of the second capacitor Cb reset to the second reference voltage Vr2 and the voltage Va of the first capacitor Ca to the second comparator CMP2, and can input an output of the second comparator CMP2 to one terminal of the second AND circuit AND2. The time extension circuit 420 can invert the primary PWM signal Spa by the third buffer BF3, and can input the inverted signal of the third buffer BF3 to the other terminal of the second AND circuit AND2.

[0069] The time extension circuit 420 can input an inverted output of the second AND circuit AND2 to the fourth buffer BF4, and can control the second charge / discharge switch SWb according to the inverted output of the fourth buffer BF4.

[0070] When the second charge / discharge switch SWb is closed, the charged electric charge in the second capacitor Cb is discharged at a constant rate by the second discharge current source Ir2, and when the second charge / discharge switch SWb is opened, the discharge of the second capacitor Cb stops. The second charge / discharge switch SWb can be closed from the falling edge of the primary PWM signal SPa until the time point at which the second capacitor voltage Vb becomes the same as the first capacitor voltage Va by the second comparator CMP2.

[0071] The initial charge voltage of the second capacitor Cb can be determined by the second reference voltage Vr2, and the voltage of the second capacitor Cb can be reset to the second reference voltage Vr2 by the second reset switch SWr2.

[0072] Referring to Figure 5 and Figure 6 , the capacity of the first capacitor Ca and the capacity of the second capacitor Cb can be the same, and the magnitude of the current discharged by the first discharge current source Ir1 and the magnitude of the current discharged by the second discharge current source Ir2 can be the same, and the voltage of the first reference voltage Vr1 and the voltage of the second reference voltage Vr2 can be the same. According to such a setting, the forward voltage reaching time can be the same as the closing time of the second charge / discharge switch SWb.

[0073] The time extension circuit 420 can generate the secondary PWM signal SPb by OR operating the primary PWM signal SPa and the control signal for the second charge / discharge switch SWb with the OR (OR) circuit OR1.

[0074] Figure 7 is a graph showing Figure 5 and Figure 6 the main waveforms of the circuit shown in FIG. 8.

[0075] Referring to Figure 7 , the forward voltage Vf[k-1] maintains a constant level. Although the forward voltage Vf is updated during each scan time, the value of the forward voltage Vf can be maintained at a constant level when the LED is placed under similar conditions. There can be a certain tendency of change in the forward voltage Vf over time.

[0076] During the time of driving the LED, the terminal voltage Vt[k] can rise from the rising edge of the PWM signal SP, and can maintain a constant level after reaching the forward voltage. The terminal voltage Vt[k] can fall from the falling edge of the PWM signal SP.

[0077] The first capacitor voltage Va can be reset to the reference voltage Vr, and can start to decrease from a rising edge of the PWM signal SP. The first capacitor voltage Va can stop decreasing at a time point at which the terminal voltage Vt[k] becomes the same as the forward voltage Vf[k-1]. A time from the rising edge of the PWM signal SP until the time point at which the terminal voltage Vt[k] becomes the same as the forward voltage Vf[k-1] can be the forward voltage reaching time Ta.

[0078] The second capacitor voltage Vb can be reset to the reference voltage Vr, and can start to decrease from a falling edge of the primary PWM signal. The second capacitor voltage Vb can stop decreasing at a time point at which the second capacitor voltage Vb becomes the same as the first capacitor voltage Va. A time from the falling edge of the primary PWM signal until the time point at which the second capacitor voltage Vb becomes the same as the first capacitor voltage Va can be the compensation time Tb.

[0079] The PWM signal SP can be compensated to a state in which an ON time period thereof is increased by the compensation time Tb.

[0080] Figure 8 is a flowchart of an LED driving method according to an embodiment.

[0081] Reference Figure 8 The LED driving apparatus can connect the first LED to the driving line according to the first scan signal. The LED driving apparatus (e.g., a driving current source) can supply a driving current to the first LED during a first scan time in which the first LED is connected to the driving line (S800). A supply time of the driving current to the first LED can be controlled by the LED driving apparatus (e.g., a driving control circuit).

[0082] The LED driving apparatus (e.g., a sample-and-hold circuit) can sample and hold a forward voltage of the first LED during the first scan time (S802). The LED driving apparatus can sense a one-side voltage of the first LED through the driving line, and can hold a voltage corresponding to the forward voltage among the sensed voltages.

[0083] The LED driving apparatus can connect the second LED to the driving line according to the second scan signal. The LED driving apparatus (e.g., a driving current source) can supply a driving current to the second LED during a second scan time in which the second LED is connected to the driving line (S804). A supply time of the driving current to the second LED can be controlled by the LED driving apparatus (e.g., a driving control circuit).

[0084] When the second LED is driven, the LED driving apparatus (e.g., a sample-and-hold circuit) can sense a one-side voltage of the second LED. The LED driving apparatus (e.g., a compensation circuit) can measure a time for which the one-side voltage of the second LED reaches the voltage held for the first LED, and can compensate for a supply time of a driving current to the second LED according to the time (S806).

[0085] The LED driving apparatus (e.g., a sample-and-hold circuit) can input the voltage held for the first LED to one terminal of a comparator, and can connect the one-side voltage of the second LED to the other terminal of the comparator. The LED driving apparatus (e.g., a compensation circuit) can measure a forward voltage reach time of the second LED according to an output of the comparator. The LED driving apparatus (e.g., a compensation circuit) can compensate for an ON time period of a PWM signal corresponding to the second LED according to the forward voltage reach time.

[0086] At step S802, the LED driving apparatus (e.g., a sample-and-hold circuit) can hold a voltage corresponding to a forward voltage of the first LED in a holding element. The LED driving apparatus (e.g., a sample-and-hold circuit) can update the holding element with a voltage corresponding to a forward voltage of the second LED during a second scan time (S808). The update time point can be a time point corresponding to a falling edge of a PWM signal before compensation or a PWM signal after compensation during the second scan time.

[0087] The first LED can be an LED disposed on a previous scan line, and the second LED can be an LED disposed on a current scan line. The above-described process can be repeated for all scan lines. For example, after step S808, the LED driving apparatus can connect a third LED to a driving line according to a third scan signal, can supply a driving current to the third LED, and can measure a time for which a one-side voltage of the third LED reaches the forward voltage of the second LED. The LED driving apparatus can increase a supply time of a driving current to the third LED according to the time.

[0088] As is apparent from the above description, according to an embodiment, the ON time of a PWM signal can be more accurately controlled so that the brightness of an LED can match a gray value. Further, according to an embodiment, a PWM signal can be compensated for a forward voltage reach time of an LED so that a loss of a gray value is not caused. Further, according to an embodiment, a forward voltage reach time of an LED can be simply measured without using a separate sequence. Further, according to an embodiment, a forward voltage reach time of an LED can be accurately measured by continuously updating a forward voltage of an LED regardless of a change in a characteristic of a panel.

[0089] Cross Reference to Related Applications

[0090] This application claims priority to Korean Patent Application No. 10-2020-0107669, filed on August 26, 2020, which is incorporated by reference herein in its entirety as if fully set forth herein for all purposes.< / n> < / n> < / n>

Claims

1. An LED driving apparatus comprising: a driving current source configured to supply a driving current to a driving line to which a plurality of LEDs are connected; a driving control circuit configured to control a supply time of the driving current to the driving line in accordance with a pulse width modulation signal (PWM signal); a sample-and-hold circuit configured to sense a one-side voltage of an LED and hold a voltage corresponding to a forward voltage; and a PWM compensation circuit configured to measure, during a time period in which one LED is connected to the driving line, a first time taken for a one-side voltage of the one LED to reach a voltage held for another LED, and compensate the PWM signal in accordance with the first time, wherein the sample-and-hold circuit transfers, to the PWM compensation circuit, a voltage sensed during a Kth scan time of the one-side voltage of the one LED and a voltage held during a (K-1)th scan time of the one-side voltage of the another LED, wherein the PWM compensation circuit measures a time taken for the voltage sensed during the Kth scan time to reach the voltage held during the (K-1)th scan time, wherein at a point in time at which the supply of the driving current to the one LED ends, a voltage to be held is updated from a voltage for another LED to a voltage for the one LED, and wherein K is a natural number of 2 or more.

2. The LED driving apparatus according to claim 1, wherein the driving control circuit includes: a switching circuit configured to control connection between the driving current source and the driving line, wherein the switching circuit connects the driving current source and the driving line during a turn-on time period of the PWM signal compensated by the PWM compensation circuit.

3. The LED driving apparatus according to claim 1, further comprising a PWM generation circuit configured to generate a primary PWM signal in accordance with a gray value included in image data, wherein the PWM compensation circuit generates a secondary PWM signal by increasing a turn-on time period of the primary PWM signal by the first time, and wherein the driving control circuit controls the supply time of the driving current in accordance with a turn-on time period of the secondary PWM signal.

4. The LED driving apparatus according to claim 1, wherein the one-side voltage is an anode voltage of an LED, and a cathode of the LED is connected to a ground voltage.

5. The LED driving apparatus according to claim 1, wherein the sample-and-hold circuit senses the one-side voltage of an LED by sensing a voltage formed on the driving line in each scan time.

6. An LED driving apparatus comprising: a driving current source configured to supply a driving current to a first LED during a first scan time and to a second LED during a second scan time; a sample-and-hold circuit configured to sense a one-side voltage of the first LED during the first scan time and hold a voltage corresponding to a forward voltage; and a PWM compensation circuit configured to measure, during a time period in which one LED is connected to the driving line, a first time taken for a one-side voltage of the one LED to reach a voltage held for another LED, and compensate the PWM signal in accordance with the first time, wherein the sample-and-hold circuit transfers, to the PWM compensation circuit, a voltage sensed during a Kth scan time of the one-side voltage of the one LED and a voltage held during a (K-1)th scan time of the one-side voltage of the another LED, wherein the PWM compensation circuit measures a time taken for the voltage sensed during the Kth scan time to reach the voltage held during the (K-1)th scan time, wherein at a point in time at which the supply of the driving current to the one LED ends, a voltage to be held is updated from a voltage for another LED to a voltage for the one LED, and wherein K is a natural number of 2 or more. a compensation circuit configured to measure a first time taken for a voltage on one side of the second LED to reach a voltage held for the first LED during the second scan time, and control a supply time of the drive current to the second LED in accordance with the first time, wherein the sample-and-hold circuit transfers a voltage sensed during a Kth scan time of a voltage on one side of the first LED and a voltage held during a (K-1)th scan time of a voltage on one side of the second LED to the compensation circuit, wherein the compensation circuit measures a time taken for the voltage sensed during the Kth scan time to reach the voltage held during the (K-1)th scan time, wherein at a point in time at which the supply of the drive current to the first LED ends, the voltage to be held is updated from a voltage for the second LED to a voltage for the first LED, and wherein K is a natural number of 2 or more.

7. The LED driving device according to claim 6, further comprising: a drive control circuit configured to control a supply time of the drive current in accordance with a pulse width modulation signal (PWM signal).

8. The LED driving apparatus according to claim 7, wherein The compensation circuit compensates for an on period of a PWM signal corresponding to the second LED in accordance with the first time.

9. The LED driving apparatus according to claim 8, wherein The sample-and-hold circuit holds a voltage corresponding to a forward voltage of the first LED in a holding element during the first scan time, and updates the holding element with a voltage corresponding to a forward voltage of the second LED during the second scan time.

10. The LED driving apparatus according to claim 9, wherein The sample-and-hold circuit updates the holding element with a voltage on one side of the second LED sensed at a falling edge of a PWM signal before compensation or a PWM signal after compensation during the second scan time.

11. The LED driving apparatus according to claim 6, wherein The sample-and-hold circuit inputs a voltage held for the first LED to one terminal of a comparator, and inputs a voltage on one side of the second LED to the other terminal of the comparator, and the compensation circuit measures the first time in accordance with an output of the comparator.

12. A driving method for a plurality of LEDs arranged in a panel, the driving method comprising: connecting a first LED to one drive line in accordance with a first scan signal; supplying a drive current to the first LED through the one drive line, and sensing and holding a forward voltage of the first LED; connecting a second LED to the one drive line in accordance with a second scan signal; supplying the drive current to the second LED through the one drive line, and measuring a first time taken for a voltage on one side of the second LED to reach the forward voltage of the first LED; controlling a supply time of the drive current to the second LED in accordance with the first time; and transferring a voltage sensed during a Kth scan time of a voltage on one side of the first LED and a voltage held during a (K-1)th scan time of a voltage on one side of the second LED to a PWM compensation circuit, ​ wherein the PWM compensation circuit measures a time at which the voltage sensed during the Kth scan time reaches the voltage held during the (K-1)th scan time, wherein at a time point at which the supply of the drive current to the first LED ends, the voltage to be held is updated from a voltage for a second LED to a voltage for the first LED, and wherein K is a natural number of 2 or more.

13. The driving method according to claim 12, further comprising: sensing and holding a forward voltage of the second LED while the drive current is supplied to the second LED through the one drive line; connecting a third LED to the one drive line according to a third scan signal; supplying the drive current to the third LED through the one drive line, and measuring a second time taken for a one-side voltage of the third LED to reach the forward voltage of the second LED; and increasing a supply time of the drive current to the third LED according to the second time.

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