Circuit system for controlling light emitting diodes

Abstract

The embodiment of the invention relates to a circuit system for controlling a light emitting diode. In described examples, a circuit (100) includes a plurality of line switches (114, 116, 118), each line switch having a line input terminal, a line terminal, and a line control terminal. Each of the line input terminals is coupled to a light emitting diode (LED) voltage terminal (120), and each line terminal is coupled to a respective LED line terminal (104, 106, 108) of the plurality of LED line terminals. The discharge circuit (102) has a plurality of discharge inputs, wherein each discharge input is coupled to a respective line terminal (104, 106, 108). The discharge circuit (102) includes a plurality of discharge switches (122, 124, 126), each discharge switch having a discharge input terminal, a discharge output terminal, and a discharge control terminal, where each discharge input terminal is coupled to a respective LED line terminal (104, 106, 108). The discharge circuit (102) also includes a current sink circuit (128) coupled between each discharge output terminal and a ground terminal.

Description

Technical Field

[0001] The present description relates to circuits for controlling light emitting diodes to reduce ghosting. Background Art

[0002] Light emitting diodes (LEDs) are used for various purposes. For example, LEDs are used as light sources for displays, for automobiles, and as light sources for other lighting. In some examples, a display includes a plurality of LED modules, wherein respective modules include LEDs and LED drivers. An LED driver is a circuit configured to drive an LED and provide lighting in response to switching operation of one or more switching devices. In some cases, parasitic (e.g., stray) capacitance of an associated circuit system may store energy that may result in faint illumination or "ghosting" of an LED that is intended to be turned off. Summary of the invention

[0003] In the described examples, a circuit includes a plurality of line switches, each having a line input terminal, a line terminal, and a line control terminal. Each of the line input terminals is coupled to a light emitting diode (LED) voltage terminal, and each line terminal is coupled to a corresponding LED line terminal of a plurality of LED line terminals. A discharge circuit has a plurality of discharge inputs, wherein each discharge input is coupled to a corresponding line terminal. The discharge circuit includes a plurality of discharge switches, each having a discharge input terminal, a discharge output terminal, and a discharge control terminal, wherein each discharge input terminal is coupled to a corresponding LED line terminal. The discharge circuit also includes a current sink circuit coupled between each discharge output terminal and a ground terminal.

[0004] In another described example, a circuit includes a switch network configured to couple a light emitting diode (LED) voltage terminal to a corresponding LED line terminal of a plurality of LED line terminals in response to a corresponding switch control signal. A discharge circuit is configured to release stored energy associated with a given LED line terminal during a line switch time interval in response to closing a corresponding line switch to disconnect the corresponding LED voltage terminal from the given LED line terminal. The line switch time interval may represent a time interval between closing the given LED line terminal and opening the next LED line terminal. A precharge circuit is configured to provide a precharge voltage to one or more corresponding channel output terminals in response to closing the one or more corresponding channel output terminals.

[0005] In another described example, a system includes a controller configured to provide a channel control signal to turn on or off a corresponding channel. A current sink circuit is configured to apply a drive current to one or more channel output terminals in response to the channel control signal. A switch circuit is configured to couple an LED voltage terminal to a corresponding line terminal in response to a line switch control signal. A discharge circuit is configured to release stored energy associated with a given LED line terminal in response to controlling the switch circuit to disconnect the corresponding LED voltage terminal from the given LED line terminal. An LED matrix has a plurality of line inputs and a plurality of line outputs, wherein each of the line inputs is coupled to a corresponding one of the line terminals, and each of the line outputs is coupled to a corresponding one of the channel output terminals. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 Describes an example circuit that includes a discharge circuit.

[0007] Figure 2 Is displayed for Figure 1 A signal graph of example waveforms for a circuit.

[0008] Figure 3 Describes an example circuit that includes a precharge circuit.

[0009] Figure 4 Is displayed for Figure 3 A signal graph of example waveforms for a circuit.

[0010] Figure 5 An example circuit including a discharge circuit and a pre-charge circuit is described.

[0011] Figure 6 Is displayed for Figure 5 A signal graph of example waveforms for a circuit.

[0012] Figure 7 and 8 Is displayed for Figure 5 A graph of the simulated signal of the circuit.

[0013] Fig. 9 is a block diagram showing an example LED system.

[0014] Fig.10 is a block diagram showing another example LED system. DETAILED DESCRIPTION

[0015] The present specification relates to circuits for controlling light emitting diodes (LEDs) so as to reduce ghosting. The circuits may be configured to reduce or eliminate ghosting caused by LEDs in an LED matrix, where the LED matrix may include, for example, rows and columns of LEDs. Examples of LED matrices include displays such as LED panels or backlit displays. The circuits may be configured to reduce ghosting by discharging and / or precharging parasitic (e.g., stray) capacitances that may be present in lines and / or channels of the LED matrix. The methods described herein may be used to reduce or eliminate ghosting for common anode, common cathode, or other LED matrix topologies.

[0016] As an example, the circuit includes a plurality of line switches and a discharge circuit. The circuit may be implemented as an LED driver, for example, including one or more of an integrated circuit, a system on chip, and / or a printed circuit board. Each of the line switches has a line input terminal, a line terminal, and a line control terminal. The line input terminal of each of the line switches may be coupled to a light emitting diode (LED) voltage terminal, and the LED voltage terminal may be coupled to an LED reference voltage. The line terminal of each corresponding switch is coupled to a corresponding LED line terminal of a plurality of LED line terminals. Thus, a first LED terminal (e.g., an anode or cathode) of each LED in a given line (e.g., a row or column) of a matrix may be coupled to a corresponding LED line terminal of an LED line terminal. A second LED terminal of each LED in a given channel (e.g., a column or row) of a matrix may be coupled to a corresponding channel output terminal of a plurality of channel output terminals.

[0017] The discharge circuit has a plurality of discharge inputs, wherein each discharge input is coupled to a corresponding line terminal (e.g., for a separate row or column of an LED matrix). For example, the discharge circuit includes a plurality of discharge switches and a current sink circuit. Each discharge switch has a discharge input terminal, a discharge output terminal, and a discharge control terminal, wherein each discharge input terminal is coupled to a corresponding LED line terminal. The current sink circuit is coupled between the discharge output terminal of each corresponding discharge switch and a ground terminal.

[0018] As described herein, each LED line terminal may have an associated parasitic line capacitance adapted to store energy (e.g., charge) based on a voltage and / or current provided to the corresponding line during operation of the LED line terminal. The stored energy may cause ghosting of one or more LEDs coupled to the line storing such energy. Thus, the discharge circuit is configured to release the stored energy associated with a given LED line terminal in response to a given line switch being controlled (e.g., closed) to disconnect the LED voltage terminal from the given LED line terminal. Thus, the discharge circuit may activate (e.g., open or close) the corresponding discharge switch during a line switch time interval, which represents a time period between closing a given LED line terminal (e.g., disconnecting from the LED voltage terminal) and opening the next LED line terminal (e.g., coupling to the LED voltage terminal).

[0019] In addition to parasitic capacitance at the line terminals, there may also be channel parasitic capacitance that may also cause ghosting of the LEDs coupled to the corresponding channels. Therefore, the circuit may also include a pre-charge circuit. The pre-charge circuit may include a plurality of pre-charge switches coupled between the input voltage terminal and a corresponding channel output terminal of a plurality of channel output terminals. Therefore, the LED matrix may include a similar number of LED channels, each of which may be coupled to a corresponding channel output terminal of the channel output terminals. The pre-charge circuit is configured to apply a pre-charge voltage to one or more channel output terminals in response to turning off one or more channels.

[0020] Figure 1 An example circuit 100 is illustrated that includes a discharge circuit 102. The discharge circuit 102 has a plurality of discharge inputs, where each discharge input is coupled to a respective line terminal 104, 106, and 108 of a plurality of N line terminals (where N is a positive integer representing the number of LED line outputs). Each line terminal 104, 106, 108 is adapted to be coupled to a respective line of an LED matrix shown at 110. The LED matrix 110 may include any number of lines and channels, which may be referred to as rows or columns of the matrix without distinction depending on the orientation of the matrix.

[0021] The circuit 100 includes a switch network 112 including a plurality of line switches 114, 116, and 118, each of which has a line input terminal coupled to an LED voltage terminal 120. The LED voltage terminal 120 may be coupled to an LED voltage source and receive a corresponding voltage shown as VLED. Figure 1In one example shown in , the line switches 114, 116, and 118 are P-channel metal oxide semiconductor field effect transistors (PMOS transistors). In other examples, the line switches 114, 116, and 118 can be implemented as other types of switching devices, such as N-channel metal oxide semiconductor field effect transistors (NMOS transistors), bipolar junction transistors, relays, etc. In the PMOS example, each line switch 114, 116, and 118 includes a first current terminal (source) coupled to the LED voltage terminal 120 and a second current terminal (drain) coupled to the corresponding line terminal 104, 106, and 108.

[0022] Parasitic line capacitances shown at CL1, CL2, and CLN may be associated with each line. For example, in response to the corresponding line terminals 104, 106, and 108 being coupled to VLED through corresponding switches to turn on the corresponding line, each parasitic line capacitance CL1, CL2, and CLN may store energy (charge). In the absence of the discharge circuit 102, when the corresponding line is turned off, the parasitic line capacitance CL1, CL2, or CLN may cause ghosting of one or more LEDs on the line based on the stored energy.

[0023] The discharge circuit 102 is configured to release stored energy associated with a given line terminal during a line switching time interval in response to closing the corresponding line switch 114, 116, 118 (e.g., by controlling the line switch to disconnect the corresponding line terminal 104, 106, and 108 from the LED voltage terminal 120). Figure 1 In the example of, the discharge circuit 102 includes a plurality of discharge switches 122, 124 and 126. Each discharge switch 122, 124 and 126 has a discharge input terminal coupled to the corresponding LED line terminal 104, 106 and 108. Each discharge switch 122, 124 and 126 has a discharge output terminal and a discharge control terminal. A current circuit 128 is coupled between each discharge output terminal and a ground terminal. In the example, the current circuit 128 includes a plurality of current sources 130, 132 and 134, wherein each corresponding current source is coupled between the corresponding discharge output terminal of the corresponding switch 122, 124 and 126 and the ground terminal. Therefore, each current source 130, 132 and 134 is configured to absorb a corresponding discharge current from the corresponding line in response to the switch 122, 124 or 126 being closed. In other examples, other types and configurations of current source circuits can be used to provide current to release energy from the corresponding line of the LED matrix.

[0024] exist Figure 1In an example of the present invention, the discharge circuit 102 includes a plurality of Zener diodes 136, 138, and 140, each of which is coupled between a discharge input terminal of a corresponding discharge switch 122, 124, and 126 and a corresponding LED line terminal 104, 106, and 108. Each of the Zener diodes 136, 138, and 140 can be configured to set a discharge voltage at the corresponding LED line terminal 104, 106, and 108. Different Zener diodes can be used to adjust the discharge voltage to accommodate different types of LEDs in the matrix 110 and / or the number of LEDs in series per line. In some examples, the Zener diodes 136, 138, and 140 can be external to an integrated circuit (IC) implementing the LED driver circuit system and the discharge circuit 102 (e.g., the Zener diodes can be mounted to a circuit board) to further enhance the configurability of the discharge voltage for a given application and use environment. By setting the voltage to a specified discharge voltage, a voltage reversal across the LED can be reduced (or prevented) during a discharge event.

[0025] As described herein, the discharge circuit is configured to release stored energy associated with a given LED line terminal interval in response to the corresponding line switch 114, 116, or 118 being controlled (e.g., closed) to disconnect the LED voltage terminal from the corresponding LED line terminal 104, 106, or 108. The discharge switch can be activated during a line switch time interval, which represents a time interval between closing a given LED line terminal and opening the next LED line terminal. For example, the controller is configured to open and close each of the line switches according to a duty cycle and a line cycle, and to apply a line switch time interval between closing a given switch and opening the next switch. The duty cycle, line cycle, line switch time interval, and other operating parameters of each line switch 114, 116, and 118 can vary according to the number of lines and other operating parameters of the circuit 100.

[0026] The circuit 100 also includes a current drive circuit (also referred to as a current driver) 144, which is configured to provide a drive current to each of a plurality of M channel output terminals 146, 148, and 150 (where M is a positive integer representing the number of LED channel outputs). For example, the current driver 144 includes switches 152, 154, 156 and current sources 158, 160, 162 coupled between each respective channel output terminal 146, 148, 150 and a ground terminal. A control circuit 164 may be coupled to a control input of each switch 152, 154, 156 and is configured to provide a switch control signal to turn each channel on or off by connecting or disconnecting a respective current source to each channel output. For example, the control circuit 164 is configured to provide a pulse width modulation (PWM) switch control signal to a control input of each respective switch 152, 154, 156. Thus, each current source 158, 160, 162 is configured to provide a drive current based on a switch control signal to turn on a corresponding one of the channel output terminals. The circuit 100 may be implemented as an IC or a system on a chip (SOC). For example, the discharge circuit 102, the line switch network 112, and the current driver 144 are implemented as part of an LED driver IC. In some examples, the Zener diode may be implemented as part of a circuit system external to the LED driver IC.

[0027] The LED matrix 110 may be an LED panel or other form of LED display (e.g., a backlight). The LED matrix 110 includes a plurality of line inputs and a plurality of channel outputs. Each of the line inputs is coupled to a corresponding line terminal 104, 106, and 108. Each of the matrix channel output terminals is coupled to a corresponding channel output terminal in channel output terminals 146, 148, and 150. Each line and channel of LEDs includes a plurality of LEDs 166, wherein each LED has an anode coupled to a line terminal and a cathode coupled to a channel terminal. In other examples, other configurations of LEDs 166 may be used.

[0028] Figure 2 Is displayed for Figure 1 200 is a signal diagram of an example waveform of the circuit 100. Thus, Figure 2 The description also refers to Figure 1. Line select signals 202, 204 and 206 represent signals applied to the control inputs (gates) of switches (PMOS transistors) 114, 116 and 118. Signals 208, 210 and 212 represent line voltage signals at respective line terminals 104, 106 and 108 at respective anodes of the LEDs for each line. The diagram also shows signals 214 and 218 at respective channel outputs 146, 148 and 150. Also shown are signals 220 and 222 representing the voltage drop across the LEDs, i.e., the difference between signals 208 and 214 and the difference between signal 210 and the signal at output channel terminal 148 ( Figure 2 The drain currents for PMOS transistors 114 and 116 are further shown at 224 and 226, respectively.

[0029] like Figure 2 As shown in , the switch (PMOS transistor) 114 is closed at time t1, which is the beginning of the corresponding line switching time interval 230 that ends at time t2. In response to closing the switch 114, the voltage at the line terminal 104 is discharged from VLED to VDISCHARGE during the line switching time interval (from time t1 to time t2) 230. As described herein, the voltage VDISCHARGE can be set based on the Zener diode 136 and is less than VLED. In addition, the discharge rate and associated discharge time during the line switching time interval 230 can be controlled based on the discharge current (e.g., provided by the corresponding current source 130, 132, 134), such as by setting a register to set the discharge current. In some examples, the voltage 208 (at the terminal 104) can remain at VDISCHARGE until the next cycle when the switch 114 is opened. As also shown, the voltage potential of the LED across line 0 (e.g., coupled to terminal 104) decreases during the line switching time interval 230 between t1 and t2, which turns off the LED, and then increases to a voltage VDISCHARGE for a duration based on the PWM applied at switch 152 to control channel output terminal 146. For example, the duration of VDISCHARGE is set by a register, and the minimum time unit of the duration may depend on a clock signal. The on-time of the line may also be set by a register, and when a given line becomes disconnected, the next line to be turned on will wait for the line switching time interval before turning on.

[0030] At time t2, the next switch 116 is activated (e.g., for line 1), as shown by signal 204 going low, which causes signal 210 to be pulled to VLED. Thus, signal 222, which is the voltage across the LEDs, is increased to a forward voltage sufficient to turn on one or more LEDs of line 1 coupled to the LED matrix 110. At time t3 (the beginning of another line switching time interval 232), signal 204 goes high and the discharge circuit is activated to release the energy stored in the parasitic line capacitance CL2 at the line terminal 106 until time t4 (the end of the line switching time interval 232). The process is then repeated for each subsequent line N.

[0031] Figure 3 An example circuit 300 is illustrated that includes a precharge circuit 302 configured to reduce ghosting of LEDs of an LED matrix 310. The circuit 300 includes a switch network 312 having one or more inputs coupled to an LED voltage terminal 320 and outputs coupled to a plurality of N line terminals 304, 306, and 308. The LED voltage terminal 320 may be coupled to an LED voltage source and receive a corresponding voltage VLED. Each line terminal 104, 106, 108 is adapted to be coupled to a respective line (e.g., a panel, backlight, or other configuration) of the LED matrix 310.

[0032] The switch network 312 includes a plurality of line switches 314, 316, and 318, each of which has a line input terminal coupled to an LED voltage terminal 320. Figure 3 In one example shown in FIG. 1 , the line switches 314, 316, and 318 are P-channel metal oxide semiconductor field effect transistors (PMOS transistors). In other examples, the line switches 314, 316, and 318 may be implemented as other types of switching devices, such as N-channel metal oxide semiconductor field effect transistors (NMOS transistors), bipolar junction transistors, relays, etc. In the PMOS example, each line switch 314, 316, and 318 includes a first current terminal (source) coupled to the LED voltage terminal 320 and a second current terminal (drain) coupled to the corresponding line terminal 304, 306, and 308.

[0033] The circuit 300 also includes a current driver 344 configured to provide a driving current to each of a plurality of M channel output terminals 346, 348, and 350. For example, the current driver 344 includes switches 352, 354, 356 and current sources 358, 360, 362 coupled in series between each corresponding channel output terminal 346, 348, 150 and a ground terminal. A control circuit 364 may be coupled to a control input of each switch 352, 354, 356 and configured to provide a switch control signal to open or close each channel by connecting or disconnecting a corresponding current source to each channel output. For example, the control circuit 364 is configured to provide a pulse width modulation (PWM) switch control signal to the control input of each corresponding switch 352, 354, 356. Therefore, each current source 358, 360, 362 is configured to provide a driving current based on the switch control signal to open a corresponding channel output terminal in the channel output terminal.

[0034] exist Figure 3 In the example of , circuit 300 illustrates parasitic channel capacitance coupled to each channel shown at CCH0, CCH1, and CCHM, each channel coupled between a corresponding channel output terminal and a ground terminal. As described herein, precharge circuit 302 is configured to apply a precharge voltage to one or more channel output terminals 346, 348, 350 in response to closing one or more channel output terminals. Figure 3 In the example of , the precharge circuit 302 includes M switches 366, 368 and 370, each having a precharge input terminal, a precharge output terminal and a channel control terminal. Each precharge input terminal is coupled to an input voltage terminal 372 and each precharge output terminal is coupled to a corresponding channel output terminal 346, 348, 350. For example, the input voltage terminal 372 is coupled to a power supply voltage to receive a DC voltage shown as VCC. In the example, VCC is greater than VLED (e.g., VCC≈2VLED). The precharge circuit 302 is configured to apply a precharge voltage to one or more channel output terminals in response to closing one or more channel output terminals. For example, the control circuit 364 is configured to open one or more switches 366, 368 and 370 in response to closing a given driver circuit (e.g., in response to driving switches 352, 354, 356 to be turned on). Therefore, a precharge voltage is applied to one or more of the channel output terminals 346, 348, 350 to prevent (or prevent ghosting) when the channel is turned off. For example, the precharge voltage is close to the voltage VCC at terminal 372 minus the voltage drop across the corresponding one or more switches 366, 368 and 370 that are turned on.

[0035] Circuit 300 may be implemented as an IC or SOC. For example, pre-charge circuit 302, line switch network 312, and current driver 344 are implemented as part of an LED driver IC.

[0036] Figure 4 Is displayed for Figure 3 The example waveforms of the circuit are shown in Figure 400. Therefore, Figure 4 The description also refers to Figure 3 . The diagram includes line select signals 402, 404, and 406, which represent the signals applied to the control inputs (gates) of switches (PMOS transistors) 314, 316, and 318, respectively. Signals 408, 410, and 412 represent line voltage signals at respective line terminals 304, 306, and 308, which are at respective anodes of the LEDs for each line. The diagram also shows signals 414 and 418 at respective channel outputs 346 and 350. Signals 420 and 422 representing the voltage drop across the LEDs for respective lines 1 and N, i.e., the difference between signals 408 and 414 (line 1) and the difference between signals 410 and 418 (line N), are also shown. Drain currents for PMOS transistors 314 and 316 are further shown at 424 and 426, respectively.

[0037] like Figure 4As shown in FIG. 4 , the switch (PMOS transistor) 314 is closed at time t1, which is the beginning of the corresponding line switch time interval 430 that ends at time t2. In response to closing the switch 314, the voltage signal 408 at the line terminal 304 changes from VLED to Vline_off. In some examples, the line voltage signal 408 (at the terminal 304) may remain at Vline_off until the next cycle when the switch 314 is opened. At time t2, the line switch 316 is opened, and the voltage signal 410 at the line terminal 305 changes from Vline_off to VLED. Between time t2 and t3, in response to controlling one or more of the channel switches 352, 354, 356, one or more of the output channels are turned on (e.g., collectively or sequentially) during the channel on time interval. For example, the control circuit 364 provides a PWM control signal to open one or more of the switches 352, 354, 356, which pulls the voltage signals 414 and 414 at each channel output terminal 346, 348, 350 that is turned on to approximately the voltage of the ground terminal (e.g., about 0V). At time t2, the voltage signal 420 is sufficient to forward bias the LED on line 1 coupled to the corresponding channel that is also turned on. At time t3, one or more channels (e.g., up to all channels) are turned off, such as by terminating the PWM control signal, so that the current sources 358, 360, 362 are disconnected from the corresponding channel output terminals 346, 348, 350. In response to or simultaneously with the closing of one or more channels, the pre-charge circuit 302 is activated (e.g., by the control circuit 364) to apply the pre-charge voltages shown at 418 and 420 at each corresponding channel output terminal 346, 348, 350 that is turned off. In the absence of the pre-charge voltage, the voltage signals 418 and 420 will decrease accordingly, as shown by dashed lines 432 and 434, respectively. In addition, the pre-charge voltage applied at time t3 causes the voltage signals 420 and 422 based on the pre-charge voltage to further decrease. As described herein, the decrease in signal 420 based on the pre-charge voltage prevents (or prevents) ghosting of the LED of line 1 that is turned off at time t3. Based on the pre-charge voltage after the next line switching interval between time t4 and t5, the voltage signals of one or more other lines may similarly decrease, as shown in signal 422 at time t5. The process can continue by repeating the process and applying the pre-charge voltage to the corresponding channels.

[0038] Figure 5An example circuit 500 is illustrated that includes both a discharge circuit 502 and a pre-charge circuit 504. For example, the discharge circuit 502 can be implemented as an instance of the discharge circuit 102, and the pre-charge circuit 504 can be implemented as an instance of the pre-charge circuit 302. Thus, the circuit 500 is configured to implement both the discharge function and the pre-charge function to reduce ghosting of LEDs as described herein.

[0039] The circuit 500 may also include a switch network 506 coupled between the LED voltage terminal 508 and each of the plurality of corresponding line terminals 510, 512, and 514. The switch network 506 may include a plurality of line switches (e.g., PMOS or other transistors) such as described herein. For example, the switch network 506 is implemented as an instance of the switch network 112 or 312. Other switch network configurations may also be used. The circuit 500 also includes a current driver circuit 516 configured to provide a drive current to one or more of the M channel output terminals 518, 520, and 522. For example, the current driver circuit 516 is implemented as an instance of the current driver circuit 144 or 344 described herein. Other configurations of current drivers may also be used.

[0040] The circuit 500 also includes an LED matrix 524 coupled to the line terminals 510, 512, and 514 and the channel output terminals 518, 520, and 522. Thus, the LED matrix may include up to M×N LEDs that are turned on and off based on a control signal provided by a control circuit 526. For example, the control circuit may be implemented as a logic or microcontroller configured to control each of the switch network 506, the discharge circuit 502, the current driver circuit 516, and the pre-charge circuit 504 to operate the LED matrix 524, such as described herein. Thus, the discharge circuit 502 is configured to release the stored energy associated with a given LED line terminal 510, 512, or 514 based on a discharge control signal (e.g., provided by the control circuit 526) during a line switching time interval in response to controlling the switch network 506 to disconnect the given LED line terminal from the LED voltage terminal 508. In addition, or as an alternative, the pre-charge circuit 504 is configured to apply a pre-charge voltage to one or more channel output terminals 518, 520, 522 based on a pre-charge control signal (e.g., provided by a control circuit 526) in response to closing one or more channel output terminals (e.g., by the current drive circuit 516). The circuit 500 may also include an LED driver IC 530. The IC 530 may include any or all of the switch network 506, the discharge circuit 502, the control circuit 526, the pre-charge circuit 504, and the current drive circuit 516.

[0041] Figure 6Is displayed for Figure 5 The signal diagram 600 of the portion of the circuit of the example waveform 602 and 604. Therefore, Figure 6 The description also refers to Figure 5 For example, waveform 602 represents a voltage (VLINE_0) at line terminal 510, which may correspond to, for example, a voltage at PMOS (see Figure 1 and 3 ) and at the anode of the LED coupled to the line terminal 510. As shown, the voltage 602 discharges from approximately VLED to VDischarge during the line switching time interval shown at 606 between times t1 and t2. Another waveform represents the voltage (VOUT0) at the channel output terminal 518 in response to turning off the channel at time t1. Figure 6 As shown in , when the corresponding channel is turned off, the voltage 608 at the channel output terminal 518 changes from approximately ground voltage (e.g., 0V) to VPre-charge at time t1. As described herein, the discharge circuit 502 and the pre-charge circuit 504 can be further configured to control peak power consumption and adjust the potential difference between VDischarge and VPre-charge to avoid applying a reverse voltage across the corresponding LEDs of the LED matrix 524.

[0042] Figure 7 and 8 is to show that, for example, Figure 5 The circuit provides the analog signals of the graphs 700 and 800. Therefore, Figure 7 and 8 The description also refers to Figure 5 . Figure 7 Graph 700 of FIG. 800 shows, for example, a switch selection signal 702 that may be provided to the gate of a given PMOS transistor of switch network 506. Graph 700 also shows voltage signals 407, 706, and 708. Signal 704 shows the voltage at the line terminal (LED+) of a given line and voltage signal 706 at the corresponding channel output (LED-). Thus, signal 708 shows the potential across the LED, which is the difference between signals 704 and 706 (e.g., LED+-LED-). Graph 800 shows the voltage at the line terminal (LED+) of a given line. Figure 7 8, including showing a pre-charge voltage 802 provided when the corresponding channel is turned off. Voltage signal 704 also exhibits a discharge during the line switching time interval 804. Thus, the pre-charge voltage 802 and the discharge at 804 can work together to further prevent ghosting as described herein.

[0043] Fig. 99 is a block diagram showing an example LED system 900 that includes an LED matrix implemented as a backlight unit 912. The system 900 also includes a system board 902 having a graphics processing unit (GPU) 904 coupled to an LED controller 906, which can be implemented as a circuit board or SOC. The LED controller 906 is coupled to an LCD or other display panel 908 and to an arrangement of one or more LED driver ICs 910. The LED controller 906 can be configured to provide a video stream to the display panel 908 and to provide a backlight control signal to an input of one of the LED driver ICs 910. Each of the LED driver ICs 910 can have an output coupled to a respective input of the backlight unit. Each of the LED driver ICs 910 can include a pre-charge circuit and / or a discharge circuit as described herein (see, e.g., Figures 1 to 8 ) to prevent ghosting of the LEDs in the backlight unit 912.

[0044] Fig.10 1 is a block diagram showing another example LED system 1000 that includes an LED matrix implemented as an LED display panel 1002. The system also includes an arrangement of a microcontroller unit (MCU) 1004, a switch controller 1006, and LED driver ICs 1008. Each of the LED driver ICs 1008 may have an output coupled to a respective input of the display panel 1002. As described herein, each of the LED driver ICs 1008 may further include a pre-charge circuit and / or a discharge circuit (see, e.g., Figures 1 to 8 ) to prevent ghosting of the LEDs in the display panel 1002.

[0045] In view of the foregoing, the circuits and systems described herein may include a discharge circuit and / or a precharge circuit to block (or prevent) ghosting of an LED. The discharge circuit may be configured to operate during a line switching time interval. Moreover, the discharge voltage, current, and time may be configurable. For example, the discharge voltage may be adjusted by selecting or configuring the type and number of Zener diodes (e.g., configured by a register or other circuit system). The methods described herein may be implemented in existing systems with simple hardware and / or software and with very little additional power consumption. As described herein, the discharge circuit and the precharge circuit may cooperate to avoid reverse LED voltage during operation. The de-ghosting circuit system (e.g., precharge and / or discharge circuit) described herein may be further effectively implemented even in the case of VLED fluctuations. The precharge and / or discharge circuit may be further implemented to achieve high contrast and to achieve under extreme environmental conditions such as high temperature and high humidity environments.

[0046] In this specification, the term "coupled" may encompass connections, communications, or signal paths that enable a functional relationship consistent with this specification. For example, if device A generates a signal to control device B to perform an action, then: (a) in a first instance, device A is coupled to device B through a direct connection; or (b) in a second instance, device A is coupled to device B through an intermediate component C, provided that the intermediate component C does not modify the functional relationship between device A and device B, such that device B is controlled by device A through the control signal generated by device A.

[0047] The recitation “based on” means “based at least in part on.” Thus, if X is based on Y, then X may be a function of Y and any number of other factors.

[0048] Modifications are possible in the described embodiments and other embodiments are possible within the scope of the claims.

Claims

1. A circuit comprising: a plurality of line switches, each line switch having a line input terminal, a line terminal and a line control terminal, wherein each of the line input terminals is coupled to a light emitting diode (LED) voltage terminal, and each line terminal is coupled to a corresponding LED line terminal of a plurality of LED line terminals; A discharge circuit having a plurality of discharge inputs, wherein each discharge input is coupled to a respective line terminal, the discharge circuit comprising: a plurality of discharge switches, each discharge switch having a discharge input terminal, a discharge output terminal and a discharge control terminal, wherein each discharge input terminal is coupled to a corresponding LED line terminal; as well as A current sink circuit is coupled between each discharge output terminal and a ground terminal.

2. The circuit of claim 1, further comprising a plurality of Zener diodes, wherein each Zener diode is coupled between a corresponding discharge input terminal and a corresponding LED line terminal.

3. The circuit of claim 2, wherein each of the Zener diodes is configured to set a discharge voltage at the corresponding LED line terminal.

4. The circuit of claim 2, wherein the current sink circuit comprises a plurality of current sources, wherein each respective current source is coupled between a respective discharge output terminal and the ground terminal.

5. The circuit of claim 1 , wherein the discharge circuit is configured to release stored energy associated with a given LED line terminal during a line switching time interval in response to controlling a corresponding line switch to disconnect the LED voltage terminal from the given LED line terminal, wherein the line switching time interval represents a time interval between closing the given LED line terminal and opening a next LED line terminal.

6. The circuit according to claim 1 further includes a precharge circuit, which includes a plurality of precharge switches, each precharge switch having a precharge input terminal, a precharge output terminal and a channel control terminal, wherein each precharge input terminal is coupled to an input voltage terminal, and each precharge output terminal is coupled to a corresponding channel output terminal among the plurality of channel output terminals.

7. The circuit of claim 6, wherein the precharge circuit is configured to apply a precharge voltage to the one or more channel output terminals in response to closing the one or more channel output terminals.

8. The circuit of claim 6, further comprising a current driver for each LED channel, wherein each current driver is configured to provide a drive current to turn on a corresponding one of the channel output terminals.

9. The circuit of claim 6, further comprising an LED matrix having a plurality of line inputs and a plurality of channel outputs, wherein each of the line inputs is coupled to a corresponding line terminal, and each of the channel output terminals is coupled to a corresponding channel output of the channel outputs.

10. The circuit of claim 6 implemented as an integrated circuit.

11. A circuit comprising: a switch network configured to couple the light emitting diode (LED) voltage terminal to a corresponding LED line terminal of the plurality of LED line terminals in response to a corresponding switch control signal; a discharge circuit configured to release stored energy associated with a given LED line terminal during a line switch time interval in response to closing a corresponding line switch to disconnect a corresponding LED voltage terminal from the given LED line terminal, wherein the line switch time interval represents a time interval between closing the given LED line terminal and opening a next LED line terminal; as well as A precharge circuit is configured to provide a precharge voltage to the one or more corresponding channel output terminals in response to closing the one or more corresponding channel output terminals.

12. The circuit of claim 11, wherein the discharge circuit comprises: A plurality of discharge switches, wherein each discharge switch is coupled between a corresponding LED line terminal and a current circuit and is configured to open a corresponding line terminal and couple the corresponding line terminal to the current circuit in response to closing the corresponding LED line terminal.

13. The circuit of claim 12, wherein the current circuit comprises a respective current source coupled between each discharge switch and a ground terminal, wherein each current source is configured to sink current from a respective LED line terminal in response to opening a respective discharge switch.

14. The circuit of claim 12, wherein the discharge circuit further comprises a plurality of Zener diodes, wherein each of the Zener diodes is configured to set a respective discharge voltage at the respective LED line terminal in response to opening the discharge switch to couple the respective LED line terminal to the LED voltage terminal.

15. The circuit of claim 12, wherein each discharge switch is configured to close and disconnect the corresponding line terminal and the current circuit in response to opening the corresponding LED line terminal.

16. The circuit of claim 11, wherein the pre-charge circuit comprises a plurality of pre-charge switches, wherein each of the pre-charge switches is configured to couple a corresponding one of the channel output terminals to a pre-charge voltage terminal in response to closing a corresponding one of the channel output terminals, and the pre-charge voltage terminal is configured to supply the pre-charge voltage.

17. The circuit of claim 16, further comprising a current driver for each LED channel, wherein each current driver is configured to provide a drive current to turn on a corresponding one of the channel output terminals.

18. The circuit of claim 11, further comprising an LED matrix having a plurality of line inputs and a plurality of channel outputs, wherein each of the line inputs is coupled to a corresponding line terminal and each of the channel output terminals is coupled to a corresponding channel output terminal.

19. The circuit of claim 11 implemented as an integrated circuit.

20. A system comprising: a controller configured to provide a channel control signal to turn on or off a corresponding channel; a current sink circuit configured to apply a drive current to one or more channel output terminals in response to the channel control signal; a switch circuit configured to couple the LED voltage terminal to the corresponding line terminal in response to a line switch control signal; The discharge circuit is configured to control the switch circuit to connect the corresponding LED voltage terminal to a given LED line terminals are disconnected to release stored energy associated with the given LED line terminal; as well as An LED matrix has a plurality of line inputs and a plurality of line outputs, wherein each of the line inputs is coupled to a corresponding one of the line terminals, and each of the line outputs is coupled to a corresponding one of the channel output terminals.

21. The system of claim 20, wherein the LED matrix comprises an array of LEDs configured as one of a backlight and / or a display panel.

22. The system of claim 20, wherein the current sink circuit, the switch circuit, and the discharge circuit are implemented in respective integrated circuits.

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