CN116110329A

CN116110329A - VF detection compensation circuit, driving chip and display device

Info

Publication number: CN116110329A
Application number: CN202310038123.3A
Authority: CN
Inventors: 唐永生; 黄立; 申石林; 刘阿强
Original assignee: Chengdu Lipson Microelectronics Co ltd
Current assignee: Chengdu Lipson Microelectronics Co ltd
Priority date: 2022-07-07
Filing date: 2023-01-10
Publication date: 2023-05-12
Also published as: CN115985231A

Abstract

The embodiment of the invention provides a VF detection compensation circuit, a driving chip and display equipment, and relates to the technical field of LED display driving. The VF detection compensation circuit comprises a VF detection circuit, a processing circuit, a precharge compensation circuit and/or a current compensation circuit, wherein the VF detection circuit is used for collecting the VF value of each lamp bead and outputting the VF value to the processing circuit; the processing circuit determines a compensation coefficient of the precharge and/or driving current of each lamp bead based on the VF value of each lamp bead; in the display process, when a certain row of lamp beads is scanned, the precharge compensation circuit and/or the current compensation circuit performs display correction on each lamp bead of the row based on respective compensation coefficients. The embodiment of the invention can correct the display effect difference caused by the forward conduction voltage VF difference of each lamp bead point by point in the chip, and has high correction precision and good low-gray display effect.

Description

VF detection compensation circuit, driving chip and display device

Technical Field

The invention relates to the technical field of LED display driving, in particular to a VF detection compensation circuit, a driving chip and display equipment.

Background

The light-emitting brightness of the LED display screen beads is related to the magnitude of the driving current, and in theory, in order to ensure that the light-emitting brightness of the LED beads of the same model is the same, each LED bead needs to provide constant driving current. However, even though there is a strictly screened LED bead, there is still a difference in the forward on voltage VF of the different beads, resulting in a difference in the luminous efficiency of the different beads. Therefore, even if the LED display driving chip provides a constant driving current for each LED bead, the brightness generated by each bead still varies.

In order to solve the above problems, the method in the prior art is to correct the gray scale of the lamp beads of the LED display screen point by point. Firstly, detecting the actual display brightness of each lamp bead when the lamp beads are full of gray scales by a special instrument, and then multiplying each lamp bead gray scale by a corresponding coefficient to ensure that all the lamp beads can display the same display brightness after gray scale modulation. However, this approach tends to result in low gray scale sacrifice based on the inherent configuration of current control cards and driver chips, making the low gray scale display of the light beads poor.

Disclosure of Invention

The invention aims to provide a VF detection compensation circuit, a driving chip and display equipment, which can correct the display effect difference caused by the forward conduction voltage VF difference of each lamp bead point by point in a chip, and have high correction precision and good low-gray display effect.

Embodiments of the invention may be implemented as follows:

in a first aspect, the present invention provides a VF detection compensation circuit, including a VF detection circuit, a processing circuit, and a precharge compensation circuit and/or a current compensation circuit;

the VF detection circuit is used for collecting the VF value of each lamp bead and outputting the VF value to the processing circuit;

the processing circuit determines a compensation coefficient of the precharge and/or driving current of each lamp bead based on the VF value of each lamp bead;

In the display process, when a certain row of lamp beads is scanned, the precharge compensation circuit and/or the current compensation circuit performs display correction on each lamp bead of the row based on respective compensation coefficients.

In practice, the VF value represents the forward voltage value of the lamp bead, and there may be differences between VF values corresponding to different lamp beads. Based on the difference, the inventor finds that monotonicity exists between the VF value of the lamp beads and the brightness of the lamp beads, so that the thought of determining the compensation coefficient of the precharge and/or driving current of each lamp bead based on the VF value of each lamp bead and performing display correction on each lamp bead of the row based on the respective compensation coefficient by utilizing a precharge compensation circuit and/or a current compensation circuit when a certain row of lamp beads is scanned in the display process is provided. That is, the precharge compensation circuit performs display correction on each of the beads of the row based on the compensation coefficient of the respective precharge, and the current compensation circuit performs display correction on each of the beads of the row based on the compensation coefficient of the respective drive current.

The embodiment of the invention corrects the display effect difference caused by the VF value difference of different lamp beads under the same constant current driving current and the same gray scale, so that the display effect difference of different lamp beads is not too large. The compensation coefficient of the embodiment of the present invention is directly related to the display effect of each bead, that is, the VF value of the bead, so that the display correction of the bead based on the compensation coefficient of the precharge and/or drive current of each bead according to the embodiment of the present invention can be understood as a fine adjustment of the display effect of the bead, and the correction accuracy is very high. Because the embodiment of the invention adopts the compensation coefficient of the precharge and/or the driving current to carry out display correction on the lamp beads, compared with the prior mode of carrying out point-by-point correction on the gray values of the lamp beads, the correction mode of the invention has no relation with the gray scale of each lamp bead, can avoid the sacrifice of low gray scale, has good display correction effect of low gray scale and can improve the display effect of the whole display screen. In addition, in the embodiment of the invention, when a certain row of lamp beads is scanned in the display process, the display correction is carried out on the row of lamp beads, so that the precharge compensation circuit and the current compensation circuit are both positioned in the driving chip, namely the invention belongs to an on-chip point-by-point correction mode, and the real-time performance is higher.

Further, the precharged compensation coefficient includes at least one of a precharged voltage compensation coefficient, a precharged speed compensation coefficient and a precharged time compensation coefficient;

the precharge compensation circuit comprises at least one of a precharge voltage compensation module, a precharge speed compensation module and a precharge time compensation module; wherein:

the precharge voltage compensation module corrects the precharge voltage of the lamp bead based on the voltage compensation coefficient of the lamp bead and outputs a target precharge voltage;

the precharge speed compensation module corrects the charge speed of the precharge voltage of the lamp beads based on the precharge speed compensation coefficient of the lamp beads;

the precharge time compensation module corrects a duration of a precharge voltage of a lamp bead based on a precharge time compensation coefficient of the lamp bead.

Further, the compensation coefficient of the driving current comprises at least one of a current compensation coefficient, a constant-current opening speed compensation coefficient and a constant-current closing speed compensation coefficient of the driving current;

the current compensation circuit comprises a current compensation module and/or a constant current speed compensation module;

the current compensation module corrects the driving current of the lamp bead based on the current compensation coefficient of the lamp bead;

The constant current speed compensation module corrects the opening speed of the constant current switching tube for controlling the output of the driving current based on the constant current opening speed compensation coefficient, and/or

The constant-current speed compensation module corrects the closing speed of the constant-current switching tube based on the constant-current closing speed compensation coefficient.

Optionally, the precharge voltage compensation module includes: the first selector, the second selector, a plurality of fixed resistors and a current source;

the plurality of fixed resistors are sequentially connected in series and connected into a current source, the first selector selects one resistor node in the plurality of fixed resistors as an input end of the precharge voltage based on the input first selection signal, and the second selector selects the voltage at the one resistor node in the plurality of fixed resistors as a target precharge voltage output of the lamp bead based on the voltage compensation coefficient of the lamp bead.

Optionally, the current compensation module includes: a third selector, a fourth selector, an intermediate resistor, and a variable current source;

the third selector is connected with the first end of the intermediate resistor, the fourth selector is connected with the second end of the intermediate resistor, and the variable current source provides variable current for the intermediate resistor according to the current compensation coefficient of the lamp bead;

the third selector selects the first end of the intermediate resistor as an input end or an output end based on the input second selection signal, and the fourth selector selects the second end of the intermediate resistor as an output end or an input end based on the corresponding input second selection signal;

The input end is connected with the voltage VDI, and the voltage VDO output by the output end is the bias voltage of the constant current driving channel of the driving chip.

Optionally, the VF detection compensation circuit further includes a memory and M groups of N-bit latch circuits, where the M groups of N-bit latch circuits are in one-to-one correspondence with M constant current driving channels of the driving chip, and each group of latch circuits is connected with a precharge compensation circuit and/or a current compensation circuit in the corresponding constant current driving channel;

each set of latch circuits includes: a first latch and a second latch;

in the ith display row, the first latch in the M groups of N-bit latch circuits latches the compensation coefficients of the lamp beads in the ith (i+1) th row read from the memory;

in the ith display row and in the ith display row, a second latch in the M groups of N-bit latch circuits latches the compensation coefficients of the ith row and the (1) th row of lamp beads output by the first latch and then sends the compensation coefficients into a precharge compensation circuit or a current compensation circuit so as to carry out display correction on the ith row and the (1) th row of lamp beads.

Optionally, the VF detection compensation circuit further includes a memory, where the memory is connected to a plurality of constant current driving channels, and each constant current driving channel includes a precharge compensation circuit and/or a current compensation circuit;

in the ith display row, the compensation coefficients of the ith row lamp beads read from the memory are respectively sent to a precharge compensation circuit or a current compensation circuit in a plurality of constant current driving channels so as to carry out display correction on the ith row lamp beads.

Further, the processing circuit is configured to:

calculating a first average value based on the VF value of each lamp bead;

screening out a VF value with the deviation degree meeting a preset condition from the first mean value, and calculating to obtain a second mean value according to the screened VF value;

and calculating the difference value of the VF value of each lamp bead and the second average value, and determining and storing the compensation coefficient of the precharge of each lamp bead and the compensation coefficient of the driving current based on the difference value and the respective preset coefficients of the precharge and the driving current.

In a second aspect, the present invention provides a driving chip, including a VF detection compensation circuit according to any one of the foregoing embodiments.

In a third aspect, the present invention provides a display device comprising a driving chip as described in the previous embodiments.

The embodiment of the invention provides a VF detection compensation circuit, a driving chip and display equipment, wherein the VF detection circuit is used for collecting the VF value of each lamp bead and outputting the VF value to a processing circuit; the processing circuit determines a compensation coefficient of the precharge and/or driving current of each lamp bead based on the VF value of each lamp bead; in the display process, when a certain row of lamp beads is scanned, the precharge compensation circuit and/or the current compensation circuit carry out display correction on each lamp bead of the row based on respective compensation coefficients, so that the embodiment of the invention can carry out on-chip point-by-point correction on the display effect difference caused by the forward conduction voltage VF difference of each lamp bead, and has high correction precision and good low-gray display effect.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic diagram of a VF detection compensation circuit according to one embodiment of the present invention;

FIG. 2 is a schematic diagram of a display line according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a common anode driving chip channel circuit;

FIG. 4 is a schematic diagram of a precharge compensation circuit according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a precharge mode according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of a precharge voltage compensation module according to an embodiment of the present invention;

FIG. 7 is a schematic diagram of a current compensation circuit according to an embodiment of the present invention;

FIG. 8 is a schematic diagram of a current compensation module according to an embodiment of the present invention;

FIG. 9 is a schematic diagram of an M-bit latch circuit according to an embodiment of the present invention;

FIG. 10 is a schematic diagram of a set of latch circuits according to an embodiment of the present invention;

FIG. 11 is a schematic diagram of a precharge voltage correction sequence according to an embodiment of the present invention;

fig. 12 is a schematic diagram of a part of a driving chip according to an embodiment of the present invention.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.

It should be noted that the terms "first," "second," and the like, if any, are used solely for distinguishing between descriptions and should not be construed as indicating or implying a relative importance.

It should be noted that the features of the embodiments of the present invention may be combined with each other without conflict.

Referring to fig. 1, fig. 1 is a schematic diagram illustrating a structure of a VF detection compensation circuit according to an embodiment of the present invention. The VF detection compensation circuit comprises a VF detection circuit, a processing circuit, a precharge compensation circuit and a current compensation circuit.

The VF detection circuit is electrically connected with the processing circuit. The VF detection circuit is used for collecting the VF value of each lamp bead and outputting the VF value to the processing circuit. The VF detection circuit and the processing circuit can be both positioned in the driving chip.

The processing circuit obtains a corresponding precharged compensation coefficient and a corresponding driving current compensation coefficient of the corresponding lamp beads based on the VF value of each lamp bead, or obtains a corresponding precharged compensation coefficient or a corresponding driving current compensation coefficient of the corresponding lamp beads.

In the embodiment of the present invention, when a row of beads is scanned, the moment of scanning the row of beads is not understood to be the moment when a row is displayed. Wherein time of one display row = 1/frame rate/display grouping/row sweep, which includes display time, precharge time, and other latency of the row of light beads.

Referring to fig. 2, a schematic diagram of one display line is shown. I.e. 1/frame rate = one complete display frame with a number of display packets, P display packets as shown in fig. 2, one complete display packet being the time to scan at least once the row 1 to the last row of beads, scan row 1 to scan row m as shown in fig. 2. The time of scanning a certain line is a complete display line in a display group, wherein the complete display line comprises a plurality of display areas, and a blank time is arranged between the display areas. The display area may understand the time for which the beads are displayed based on the PWM signal, which may be greater than 0 or equal to 0, of course. The lamp beads can be precharged or scanned in the blank time, and the lamp beads can be precharged for a plurality of times in the time of a complete display line, and when the PWM signal of a certain display area is 0, the lamp beads can still be precharged in the display area.

For example, for a driving chip applying 64 rows of scanning, one constant current driving channel of the driving chip can display the light beads of the maximum loaded 64 rows, and the time of each display row=1/60/64/64≡4us, i.e. the embodiment can display and correct each light bead of the row based on the respective compensation coefficient in the time of 4 us.

Because the driving chip is a multi-constant current driving channel chip, each constant current driving channel is connected with the lamp beads of the column through the column line, when a certain row of lamp beads is scanned, each lamp bead driven by the constant current driving channel is fixed in the display row, namely, each lamp bead of the row is subjected to display correction based on the respective compensation coefficient in the time of 4us, and the fact that a plurality of constant current driving channels drive the respective corresponding lamp beads simultaneously in the time of 4us is understood. In other words, the time for performing display correction based on the compensation coefficient of each of the beads is 4us, and within the 4us, the display correction may be performed on the beads based on the compensation coefficient of at least one of the driving current and the precharge of the beads.

In practical display panels, each group of beads generally includes 3 kinds of beads of red (R), green (G) and blue (B) with anodes or cathodes connected together. The display correction of each lamp bead is performed on the single-color lamp beads in each group of lamp beads, such as the red lamp beads.

When a certain row of beads is scanned, the precharge compensation circuit and/or the current compensation circuit performs display correction on each bead of the row based on respective compensation coefficients, which can be further understood as: in the display row of the lamp beads, the precharge compensation circuit performs display correction on each lamp bead of the row based on a respective precharge compensation coefficient, and/or the current compensation circuit performs display correction on each lamp bead of the row based on a respective drive current compensation coefficient. It is noted that in various embodiments of the present invention, a and or B represent may have both a and B, or may be present only a or only B. For example, the VF detection compensation circuit may include both a precharge compensation circuit and a current compensation circuit, or may include only a precharge compensation circuit or a current compensation circuit.

In practice, the output end of the constant current driving circuit of the driving chip is commonly connected with the output end of the precharge circuit, and the precharge circuit outputs a precharge voltage based on the reference potential and the precharge control signal, as mentioned in the present invention, a corrected target precharge voltage; the constant current driving circuit outputs a driving current based on display data, i.e., gradation data. In the driving chip, the constant current driving circuit and the precharge circuit are not turned on at the same time, i.e., the constant current driving circuit outputs a constant current and the precharge circuit performs precharge at the same time. Therefore, the display correction of the embodiment of the invention based on the compensation coefficient of the driving current of the lamp beads is realized when the constant current driving circuit is started, and the display correction of the embodiment of the invention based on the compensation coefficient of the precharge of the lamp beads is realized when the precharge circuit is started.

Further, the precharged compensation coefficients include at least one of a precharged voltage compensation coefficient, a precharged speed compensation coefficient, and a precharge time compensation coefficient. As shown in fig. 4, the precharge compensation circuit includes a precharge voltage compensation module, a precharge speed compensation module, and a precharge time compensation module.

The current LED display screen is generally composed of m rows and n columns of lamp beads, and is respectively driven by a row driving chip and a constant current source driving chip for display, and due to parasitic capacitance on row lines and column lines, coupling phenomenon is generated in the LED display process, and besides, the parasitic capacitance can cause upper ghosting, lower ghosting and the like of the display screen. In order to reduce the influence of parasitic capacitance, the traditional mode is to clamp the lamp bead to the same voltage before display by pre-charging the lamp bead and clamp the lamp bead to the same voltage before display by the pre-charging voltage, and the voltage jump generated in the process releases the charge of the parasitic capacitance. The embodiment of the invention further considers that the parasitic capacitance to be eliminated of each lamp bead is possibly different, and can determine the voltage compensation coefficient, the precharge speed compensation coefficient and the precharge time compensation coefficient of each lamp bead based on the VF value difference of each lamp bead on the display screen, so that the precharge of each lamp bead is corrected in real time in a chip through the precharge compensation coefficients of the lamp beads, and the decoupling effect is good.

The precharge voltage compensation module corrects the precharge voltage of the lamp bead based on the voltage compensation coefficient of the lamp bead and outputs a target precharge voltage. In the embodiment of the invention, the effect of the precharge is to reduce the influence of the parasitic capacitance on the display coupling, so that the precharge voltage cannot light the lamp bead, but a voltage jump process is provided, and the electric charge generated by the parasitic capacitance is released by using the jump voltage. Based on the formula q=cv, Q represents the charge amount, C represents the capacitance, V represents the voltage, and for a certain bead, the parasitic capacitance C is fixed, so that the magnitude of the charge released by the parasitic capacitance is determined by the value of the voltage, and a voltage jump is needed to release the charge from the parasitic capacitance, so that the precharge voltage is used for manufacturing the voltage jump to release the charge from the parasitic capacitance, and when the adjacent bead of the bead is turned on, the bead is not turned on by the parasitic capacitance, thereby reducing the coupling phenomenon.

Since the output constant current and the precharge are not performed simultaneously, referring to fig. 5, an example of a precharge method is: in a display unit, when PWM is greater than 0, the working state of the precharge circuit is precharge voltage V1, precharge closing and precharge voltage V2 in sequence, the constant current drive circuit is started based on PWM in the area corresponding to the precharge closing to light up the lamp beads, and the voltage of the output end of the channel is V3; in one display unit, when PWM is equal to 0, the constant current driving circuit is turned off, and the output state of the precharge circuit is precharge voltage V4, precharge voltage V5, precharge voltage V6 in this order. One display unit shown in fig. 5 may be understood as one display area shown in fig. 2 plus the blank time on both the left and right sides thereof. In this example, in one display unit, if the PWM of the display area is greater than 0, the embodiments of the present invention may correct the precharge voltage V1 and the precharge voltage V2 based on the voltage compensation coefficient of the lamp bead; if the PWM of the display area is equal to 0, the embodiments of the present invention can perform time-sharing correction on the precharge voltage V4, the precharge voltage V5, and the precharge voltage V6 based on the voltage compensation coefficient of the lamp bead.

In one embodiment, the precharge voltage compensation module includes a first selector, a second selector, a plurality of fixed resistors, and a current source.

And a plurality of fixed resistors are sequentially connected in series and connected into the current source. Wherein the current source may be one or two. When the number of the current sources is two, the two current sources are the same, and a plurality of fixed resistors are connected in series in sequence and then connected between the two current sources. The current source mentioned in this embodiment may be a fixed current source or a variable current source, and when two variable current sources exist, the output currents of the two current sources are adjusted synchronously. When the resistance of the fixed resistor is sufficiently large, the current source may be composed of one current source. That is, when the resistance of the fixed resistor is greater than or equal to the built-in resistor of the first selector, the current source may be composed of one current source, the first end of the plurality of fixed resistors connected in series may be connected to the current source, and the other end may be grounded or VCC.

In one possible example, referring to fig. 6, the current source may include a third power source i3 and a fourth power source i4, and the third power source i3 and the fourth power source i4 are connected to both ends of a series circuit formed by a plurality of fixed resistors, respectively. That is, the third power source i3 and the fourth power source i4 may be connected to the first and last two resistor nodes among the plurality of resistor nodes, respectively.

The first selector selects one of the plurality of fixed resistors as an input terminal of the precharge voltage based on the inputted first selection signal, and the second selector selects a voltage at the one of the plurality of fixed resistors as a target precharge voltage output of the lamp bead based on a voltage compensation coefficient of the lamp bead. The first selector may be a data selector, and the second selector may be a multiplexer. The number of the fixed resistors depends on the actual adjustment requirements, and is not limited herein.

In one possible example, as shown in fig. 6, the number of the fixed resistors R is 4, and after the 4 fixed resistors R are connected in series, 5 resistor nodes n0 to n4 are formed, and the 5 resistor nodes n0 to n4 are connected to the second selector MUX2, where the positive input terminal and the negative input terminal of the first selector MUX1 are connected to the resistor nodes n0 and n4 respectively.

The first selector MUX1 is configured to determine an input terminal of the precharge voltage VPRE from the resistor nodes n0, n4 according to the first selection signal. The second selector MUX2 is configured to select one of the resistor nodes n0-n4 according to the voltage compensation coefficient, and to connect the voltage of the selected resistor node as a target precharge voltage to one input terminal of the first amplifier AMP1, and the other input terminal of the operational amplifier AMP1 is connected to an output terminal thereof, which may be connected to a pin terminal of the constant current driving channel based on a switch or not, and the output terminal outputs the target precharge voltage when the constant current driving circuit is turned off.

When vf_cal [ P ] =1, vpre=vt, at this time, vpre_cal=vpre-i×r×vf_cal [ P-1:0].

When vf_cal [ P ] =0, vpre=vb, at this time, vpre_cal=vpre+i×r×vf_cal [ P-1:0].

Wherein VF_CAL [ P ] is a first selection signal, VF_CAL [ P-1:0] is a voltage compensation coefficient, VPRE is a precharge voltage, VT is a voltage at a resistor node n0, VB is a voltage at a resistor node n4, I is a first synchronous current output by a third power supply and a fourth power supply, and VPRE_CAL is an output target precharge voltage.

That is, in the precharge voltage compensation module, the fixed resistors are used as a voltage dividing resistor, and the first synchronous current flows through each fixed resistor, and a voltage division of i×r is generated in each fixed resistor.

When the first selection signal vf_cal [ P ] is 1, the resistor node n0 is used as an input terminal of the precharge voltage, the voltage vt=vpre of the resistor node n0, the second selector MUX2 selects one resistor node ns (s is an integer from 0 to 4) from the resistor nodes n0 to n4 according to the voltage compensation coefficient, and the voltage of the resistor node ns is the target precharge voltage vpre_cal output by the second selector MUX2, and the magnitude of the voltage is the voltage of the resistor node n0 minus all the partial voltages generated by the fixed resistors existing between the resistor node n0 and the resistor node ns.

When the first selection signal vf_cal [ P ] is 0, the resistor node n4 is used as an input terminal of the precharge voltage, the voltage vb=vpre of the resistor node n4, the second selector MUX2 selects one resistor node ns (s is an integer from 0 to 4) from the resistor nodes n0 to n4 according to the voltage compensation coefficient, and the voltage of the resistor node ns is the target precharge voltage vpre_cal output by the second selector MUX2, and the magnitude of the voltage is the voltage of the resistor node n4 plus all the voltage division generated by the fixed resistor existing between the resistor node ns and the resistor node n 4.

For example, assuming VPRE is 0.4V, i is 0.1a, r is 1Ω, vf_cal [ P ] =1, and vf_cal [ P-1:0] is 3, then the target precharge voltage vpre_cal output at this time is 0.1V at the resistor node n 3. It should be noted that this example is only an example, and the data in specific application is based on the actual application, and is not limited herein.

The precharge speed compensation module corrects the charge speed of the precharge voltage of the lamp beads based on the precharge speed compensation coefficient of the lamp beads. By correcting the charging speed, the charging speed can reach the corresponding pre-charging voltage (potential) quickly, so that the display effect of the lamp beads is improved. For example, the precharge voltages V1, V2, V4 may be corrected from 0 to the corresponding potential rapidly by the precharge speed compensation coefficient. However, the precharge voltages V4, V5, V6 have potential jumps, but since the potential jumps are relatively small, correction based on the precharge speed compensation coefficient is unnecessary.

Based on the formula q=cv=it, t=cv/i, where V is the voltage of the constant current driving channel of the driving chip, which can be regarded as a fixed value. Thus, the adjustment of t can be achieved theoretically by adjusting i and C. Based on this, the precharge speed compensation module (not shown) may include at least one of a first current control unit that controls a charge current level of the precharge circuit based on the precharge speed compensation coefficient and a first capacitance control unit that controls a charge capacitance level within the precharge circuit based on the precharge speed compensation coefficient. The larger the current is, the faster the precharge speed is, and the duration of precharge to a certain potential is short; conversely, the smaller the current, the slower the precharge speed, and the longer the precharge time to a certain potential. The larger the charge capacitance value, the faster the precharge speed, and vice versa.

In implementation, the first current control unit may change the bias current magnitude IB in the precharge circuit or the mirror ratio of the current mirror based on the precharge speed compensation coefficient to achieve control of the charge current magnitude of the precharge circuit. The first capacitance control unit may control the number of charge capacitances or capacitance capacities of the charge capacitances in the precharge circuit based on the precharge speed compensation coefficient to achieve control of the magnitudes of the charge capacitances. The specific implementation of the first current control unit and the first capacitance control unit may vary based on the specific circuitry of the precharge circuit, and the invention is not limited herein.

The precharge time compensation module corrects the duration time of at least one precharge voltage of the lamp beads based on the precharge time compensation coefficient of the lamp beads so as to improve the display effect of the lamp beads. For example, the precharge duration of one or more of the precharge voltages V1, V2, V4, V5, V6 described above may be corrected using a precharge time compensation coefficient. The precharge time compensation module may be implemented based on a related timing circuit, i.e., the timing of a certain precharge voltage is controlled by a precharge time compensation factor, such as to lengthen or shorten its duration. The related circuits for controlling the duration of the precharge voltage are referred to in the prior art and will not be described in detail herein.

Further, the compensation coefficient of the driving current comprises at least one of a current compensation coefficient, a constant-current opening speed compensation coefficient and a constant-current closing speed compensation coefficient of the driving current; as shown in fig. 7, the current compensation circuit includes a current compensation module and a constant current speed compensation module.

The current compensation module corrects the driving current of the lamp bead based on the current compensation coefficient of the lamp bead.

In the embodiment of the present invention, the driving current is also referred to as a constant current driving current. The constant current switching tube of the driving chip is controlled to be turned on, the constant current driving module outputs driving current to the lamp beads based on PWM signals, and the lamp beads are displayed; and controlling the constant current switching tube to be closed, and stopping constant current output, so that the lamp beads are not displayed. The same driving current generated by the driving chip can be corrected by using the current compensation coefficient of the lamp beads, if the driving current is large, the lamp beads can be brighter, and the driving current finally flowing through the lamp beads is slightly different due to the fact that the current compensation coefficients of the lamp beads are different, so that the luminous efficiency difference caused by different values of the LED lamp beads VF can be optimized, and the lamp beads can have the same display brightness when in the same gray scale display.

In one embodiment, the current compensation module includes a third selector, a fourth selector, an intermediate resistor, and a variable current source.

The third selector is connected with the first end of the intermediate resistor, the fourth selector is connected with the second end of the intermediate resistor, and the variable current source provides variable current for the intermediate resistor according to the current compensation coefficient of the lamp bead; the third selector selects the first end of the intermediate resistor as an input end or an output end based on the input second selection signal, and the fourth selector selects the second end of the intermediate resistor as an output end or an input end based on the corresponding input second selection signal; the input end is connected with the voltage VDI, and the voltage VDO output by the output end is the bias voltage of the constant current driving channel of the driving chip.

In an embodiment, the variable current source provides a variable current to the intermediate resistor in accordance with a current compensation coefficient. The number of the variable current sources can be one or two, and when the number of the variable current sources is two, the first variable current source and the second variable current source are respectively connected with two ends of the intermediate resistor. When the resistance of the intermediate resistor is sufficiently large, the variable current source is composed of one variable current source. That is, when the resistance value of the intermediate resistor is greater than or equal to the built-in resistors of the third and fourth selectors, the variable current source may be composed of one variable current source, and the intermediate resistor is connected to both ends of the variable current source.

Alternatively, the third selector and the fourth selector may be the same data selector.

Taking the current compensation module shown in fig. 8 as an example, the working principle of the current compensation module is described in the present invention.

The positive input of the third selector MUX3 is connected to the negative input of the fourth selector MUX4, with a corresponding voltage VDI. The negative input of the third selector MUX3 is connected to the positive input of the fourth selector MUX4 and the corresponding voltage is VDO.

The output end of the third selector MUX3 and the output end of the fourth selector MUX4 are respectively connected with the first end N1 and the second end N2 of the intermediate resistor Rc. The first variable current source i1 and the second variable current source i2 are respectively connected to the first end N1 and the second end N2 of the intermediate resistor Rc.

According to the second selection signal i_cal [ T ], the third selector MUX3 is configured to select the first terminal N1 of the intermediate resistor Rc as an input terminal or an output terminal, and the fourth selector MUX4 correspondingly selects the second terminal of the intermediate resistor Rc as an output terminal or an input terminal. Two variable current sources i1, i2 are used to provide a second synchronous current in accordance with the current compensation coefficient.

When i_cal [ T ] =1, vdo=vdi-ic_cal [ T-1:0 ]. Rc, Δi≡ -ic_cal [ T-1:0 ]. Rc ×gdsnm_cm.

When i_cal [ T ] =0, vdo=vdi+ic_cal [ T-1:0 ]. Rc, Δi≡ic_cal [ T-1:0 ]. Rc ×gdsnm_cm.

Wherein, I_CAL [ T ] is a second selection signal, I_CAL [ T-1:0] is a current compensation coefficient, ic_CAL [ T-1:0] is a second synchronous current provided by a first variable current source I1 and a second variable current source I2 according to the current compensation coefficient, rc is the resistance of an intermediate resistor, gdsNM_CM is the drain-source conductance of an N-channel MOS tube in a third selector and a fourth selector, and DeltaI is a compensation current between an input end and an output end.

That is, in the current compensation module, the positive and negative of the compensation current are determined by the second selection signal, and the magnitude of the current value of the compensation current is determined by the current compensation coefficient, so that the bias voltage VDO of the constant current driving channel is changed, and the magnitude of the driving current output from the constant current driving channel is changed. The second synchronous current flows through the intermediate resistor, and the voltage division generated by the intermediate resistor is ic_I_CAL [ T-1:0 ]. Rc.

When the second selection signal is 1, the first end N1 of the intermediate resistor is taken as an input end, and the voltage is VDI; the second terminal N2 of the intermediate resistor is used as an output terminal and the voltage is VDO. I.e. the voltage VDO at the output is the input voltage VDI minus the divided voltage of the intermediate resistor. Accordingly, the resulting compensation current Δi is negative.

When the second selection signal is 0, the first end N1 of the intermediate resistor is taken as an output end, and the voltage is VDO; the second terminal N2 of the intermediate resistor is used as an input terminal and the voltage is VDI. I.e. the voltage VDO at the output is obtained by adding the voltage division of the intermediate resistor to the voltage VDI at the input. Accordingly, the resulting compensation current Δi is positive.

And the constant current speed compensation module corrects the opening speed of the constant current switching tube for controlling the output of the driving current based on the constant current opening speed compensation coefficient. And the constant-current speed compensation module corrects the closing speed of the constant-current switching tube based on the constant-current closing speed compensation coefficient.

The correction principle of the constant current speed compensation module in the embodiment of the invention is similar to that of the precharge speed compensation module, and the principle is not repeated here. The constant current speed compensation module may include at least one of a second current control unit and a second capacitance control unit, the second current control unit controls the gate current of the constant current switching tube based on a constant current on speed compensation coefficient or a constant current off speed compensation coefficient, and the second capacitance control unit controls the charging capacitance for controlling the constant current switching tube to be turned on or off based on the constant current on speed compensation coefficient or the constant current off speed compensation coefficient. In implementation, the capacitance controlled by the second capacitance control unit may be a capacitance in the operational amplifier AMP2 connected to the gate of the constant current switching transistor, such as a miller correction capacitance for loop stabilization. Of course, in practice, the capacitor may be another type of capacitor, which is not limited herein.

The circuit principles of the precharge compensation circuit and the current compensation circuit are described in detail above in connection with the specific embodiments, respectively, and next, how the precharge compensation circuit and/or the current compensation circuit performs display correction for each lamp bead of the row based on the respective compensation coefficients will be described.

In one embodiment, the VF detection compensation circuit further includes a memory and M sets of N-bit latch circuits, referring to fig. 9,M, the N-bit latch circuits are in one-to-one correspondence with M constant current driving channels of the driving chip, and each set of latch circuits is connected to a precharge compensation circuit and a current compensation circuit in the corresponding constant current driving channel. In various embodiments of the present invention, the constant current drive channel should not be simply understood as a physical pin (the physical pin is denoted herein as a constant current drive channel pin end), but may be understood as a constant current drive channel circuit, such as the circuit shown in fig. 12, in which the precharge compensation circuit and the current compensation circuit may be located.

Each set of latch circuits includes: a first latch and a second latch;

in the ith display row, the first latch in the M groups of N-bit latch circuits latches the compensation coefficients of the lamp beads in the ith (i+1) th row read from the memory; in the ith display row and in the (i+1) th display row, a latch II in the M groups of N-bit latch circuits latches the compensation coefficients of the ith row and the (1) th row lamp beads output by the latch I and then sends the latched compensation coefficients into a precharge compensation circuit or a current compensation circuit so as to carry out display correction on the ith row and the (1) th row lamp beads.

The key idea of this embodiment is to buffer the compensation coefficient of the next row of beads in advance in the current display row, and buffer the compensation coefficient of the next row of beads again in the display row when the next row of beads starts to perform display correction.

Each group of LATCH circuits can comprise a LATCH I and a LATCH II based on a ping-pong structure, wherein the LATCH I in the M groups of N-bit LATCH circuits latches corresponding compensation coefficients based on LATCH signals LATCH-EN [ (M-1): 0], the LATCH signals LATCH-EN [ (M-1): 0] correspond to M constant current driving channels, for example, the LATCH signals of the constant current driving channels 0 are LATCH-EN [0], and the LATCH signals of the constant current driving channels 1 are LATCH-EN [1]. The second latch in the M groups of N-bit latch circuits is connected to the same line feed signal ROW, and outputs the latched compensation coefficient of the current ROW lamp bead corresponding to the line feed signal ROW to the precharge compensation circuit or the current compensation circuit, for example, when the precharge circuit shown in fig. 3 is started, the compensation coefficient of the current ROW lamp bead is output to the precharge compensation circuit, and further, according to the type of the current corresponding compensation coefficient, the compensation coefficient can be output to one or more of a precharge voltage compensation module, a precharge speed compensation module and a precharge time compensation module in the precharge compensation circuit; when the constant current driving circuit shown in fig. 3 is turned on, the compensation coefficient of the current lamp bead is output to the current compensation circuit, and further can be output to at least one of the current compensation module and the constant current speed compensation module in the constant current driving circuit according to the type corresponding to the compensation coefficient.

Wherein, the first latch and the second latch are N bits, which correspond to the size of the compensation coefficient CAL [ (N-1): 0]. The LATCH circuit corresponding to the constant current driving channel 0 shown in fig. 10 includes N latches i and N latches ii connected in one-to-one correspondence, the N latches i are connected to the same LATCH signal LATCH-EN 0, and the N latches i are sequentially latched based on the LATCH signal LATCH-EN 0, and the compensation coefficients vf_cal [ (N-1) ] to vf_cal 0 are correspondingly latched. N latches II are connected into a line-changing signal ROW, the compensation coefficient transmitted by the latches I is latched and then output by OUT [ (N-1): 0], namely, as shown in figure 10, the N latches respectively output OUT [ (N-1) ] to OUT [0].

Taking the voltage compensation coefficient of the precharge voltage as an example, the driving configuration enables the correction function of the precharge voltage compensation module. The correction sequence is shown in FIG. 11, the driving chip is 16 constant current driving channels, D0-D15, and the voltage compensation coefficient of each lamp bead is VF_CAL 5:0, and the total is 6 bits.

In the ith display row, a LATCH in the 16-bit LATCH circuit latches the respective compensation coefficients VF_CAL [5:0] of the (i+1) th row of lamp beads based on LATCH signals LATCH-EN [15:0]. The first LATCH in the LATCH circuit corresponding to the constant current drive channel 0 latches the compensation coefficients VF_CAL [5], VF_CAL [4], VF_CAL [3], VF_CAL [2], VF_CAL [1], and VF_CAL [0] in order based on the LATCH signal LATCH-EN [0]. When the rising edge of the ROW-changing signal ROW of the lamp beads in the (i+1) th ROW arrives, namely after the latches II receive the ROW-changing signal ROW, the lamp beads indicate that the lamp beads are in the (i+1) th display ROW currently, and each latch II latches the compensation coefficient output by the corresponding latch I and then sends the compensation coefficient to the precharge voltage compensation module. The compensation coefficient of each row i+1 lamp bead finally latched by the latch II in the 16 groups of latching circuits is expressed as VF_CAL_CH [15:0], and corresponds to 16 constant current driving channels D [15:0].

In another embodiment, the VF detection compensation circuit further includes a memory connected to a plurality of constant current drive channels, each constant current drive channel including a precharge compensation circuit or a current compensation circuit;

in the ith display row, the compensation coefficients of the ith row of lamp beads read from the memory are respectively sent to the precharge compensation circuits or the current compensation circuits in the constant current driving channels so as to carry out display correction on the ith row of lamp beads. The implementation mode is generally applicable to special circuits, if the compensation coefficient of each lamp bead is 6bit data, and the driving chip is provided with 16 constant current driving channels, the total is 96bit data, the compensation coefficient of the ith row of lamp beads is read from the memory according to the addresses of the lamp beads and then is respectively sent into the precharge compensation circuits in the 16 constant current driving channels, and then the display correction of the ith row of lamp beads is realized.

The invention focus of the present application is described in detail above, and the implementation of the VF detection circuit and the processing circuit will be described next.

Because the embodiment of the invention is suitable for the LED display screen, the VF detection circuit can acquire the VF value of each lamp bead on the LED display screen, and the VF value can be realized by the following steps:

1) The system sets the channel current of the constant current driving channel as the actual working current IOUT (VF is related to the current magnitude, so the actual channel current magnitude needs to be set during detection) through register configuration;

2) Configuring vf_det_en=1, enabling the VF detection function;

3) Detecting VF values (also called VF quantized code values) of m rows of lamp beads corresponding to a constant-current driving channel 0;

a) Turning on channel output of row drive connected with row line of row 1 lamp beads;

b) Sending a PWM signal to channel0 to ensure that the current flowing through the lamp beads to be detected is IOUT;

c) After the output voltage of channel0 is stable, sampling and quantizing the output voltage by an ADC (analog-to-digital converter) built in a VF detection circuit, so that the detected VF voltage value is converted into binary data with specified precision, namely, the VF quantized code value is the binary data;

d) Storing the VF quantized code value corresponding to the lamp beads in the first row and the first column into a memory for waiting processing;

e) Sequentially turning on the output of row driving connected with row lines of the 2 nd to m th row lamp beads, and repeating the steps b to d until VF values of all row lamp beads corresponding to channel0 are detected, and storing the corresponding quantized code values into a memory;

4) And (3) sequentially detecting m rows of lamp beads corresponding to the constant current driving channels channel1 to (n-1), wherein the specific steps are similar to the step (3), until VF of the m rows and n columns of lamp beads is detected, and storing the corresponding quantized code values into a memory.

In the embodiment of the invention, the embodiment of the invention is not limited herein, and can be realized by referring to the related prior art, regarding how to realize the principle circuit for collecting the VF voltage value of the lamp bead after the output voltage of the constant current driving channel is stable. The VF detection circuit provided by the embodiment of the invention can acquire the VF voltage value after the output voltage of the constant current driving channel is stable, and the VF voltage value acquired in this way is more accurate.

After the VF value for each bead is obtained, the processing circuit processes the VF value.

In one embodiment, the compensation coefficients are respectively related to preset coefficients of various types, and the processing circuit may obtain each compensation coefficient of the lamp bead based on the following steps:

step 1, calculating to obtain a first average value based on the VF value of each lamp bead;

the processing circuit adds the VF values of all the lamp beads acquired by the VF detection circuit to obtain an average value as a first average value.

Step 2, screening out VF values with the deviation degree meeting preset conditions from the first mean value, and calculating to obtain a second mean value according to the screened VF values;

for example, if the VF value of a certain bead deviates from the first average by more than 50%, it may indicate that the bead is in a short-circuit or open-circuit state. The processing circuit selects VF values within 50% of the first mean value from the VF values of all the lamp beads, and calculates an average value as a second mean value according to the VF values after screening.

And 3, calculating the difference value of the VF value of each lamp bead and the second average value, and determining and storing the pre-charging compensation coefficient and/or the driving current compensation coefficient of each lamp bead based on the difference value and the respective pre-set coefficients of the pre-charging and driving currents.

As described above, the pre-charge compensation coefficient further includes at least one of a pre-charge voltage compensation coefficient, a pre-charge speed compensation coefficient and a pre-charge time compensation coefficient, and the driving current compensation coefficient further includes at least one of a driving current compensation coefficient, a constant current on-speed compensation coefficient and a constant current off-speed compensation coefficient, so that the pre-set coefficient of the present invention can be set only for the pre-charge and the driving current, or can be set in a refined manner for the pre-charge voltage, the pre-charge speed and the pre-charge time under the pre-charge, or can be set in a refined manner for the driving current itself, the constant current on-speed and the constant current off-speed.

In one embodiment, the voltage compensation coefficient of the precharge voltage of the lamp beads may be vf_cal [ P:0] =Δvf×k1; the current compensation coefficient of the driving current of the lamp bead may be i_cal [ T:0] =avf×k2. Wherein ΔVF is the difference between the VF value of the lamp bead and the second average value, K1 is a first preset coefficient, K2 is a second preset coefficient, and K1 and K2 can be preset according to the display effect of actual needs.

After the compensation coefficient of at least one of the driving current and the precharge of each lamp bead is obtained, the compensation coefficient corresponding to each lamp bead can be stored, namely written into a memory, and the memory can be an SRAM (static random access memory) in a driving chip. In one implementation, the memory may be set for each type of compensation coefficient, for example, a memory is set for each of the voltage compensation coefficient, the precharge speed compensation coefficient, and the precharge time compensation coefficient for precharge, and a memory is set for each of the current compensation coefficient, the constant current on speed compensation coefficient, and the constant current off speed compensation coefficient for driving current.

In each memory, each lamp bead has a corresponding address, and the corresponding compensation coefficient of the lamp bead can be obtained by reading the address. For example, addresses 0 to 15 are addresses of the 1 st row of beads in sequence, and the compensation coefficient of the 1 st row of beads can be obtained by reading the addresses 0 to 15.

In another implementation, a memory may be used to store all the compensation coefficients for each bead, but the reading is more complex.

The invention also provides a driving chip which comprises the VF detection compensation circuit in the embodiment. Referring to fig. 12, fig. 12 is a schematic diagram illustrating a part of a driving chip according to an embodiment of the invention. The driving chip comprises the VF detection compensation circuit, a reference voltage generation circuit, a bias circuit, a current output circuit and a precharge generation circuit.

The reference voltage generation circuit is used for generating a reference current Iref and a reference voltage. Wherein, C0:L is L+1 bit wide control signal, which can control the reference current Iref and further control the output current range.

And a bias module for generating a first bias voltage VD, a second bias voltage VGI, and a bias current based on the reference voltage.

The precharge generation circuit is electrically connected with the reference voltage generation circuit and is used for outputting precharge voltage to the precharge compensation module of the VF detection compensation circuit. The output end of the precharge compensation module is connected to the constant current driving channel end. In this example, the reference voltage generating circuit and the precharge compensation module may be understood as a part of the foregoing precharge module.

The current output circuit is electrically connected with the bias circuit and is used for outputting corresponding output current based on the second bias voltage VGI and the bias current. One input end of the operational amplifier AMP2 is connected with the first bias voltage VD, the other input end of the operational amplifier AMP2 is connected with the voltage VDI, the output end of the operational amplifier AMP2 is connected with the grid electrode of the constant current switching tube NM_C1, the drain end of the constant current switching tube NM_C1 is connected with the pin end of the constant current driving channel, and the current compensation module is connected between the voltage VDI and the source end of NM_C1. OE [0:N ] represents a column driving line control signal of the LED array, and the operational amplifier AMP2 effectively controls the starting of the constant current switching tube NM_C1 based on the OE, so that the driving current corrected based on the current compensation coefficient I_CAL [ T-1:0] is output through the pin end of the constant current driving channel.

The specific circuit structures and descriptions of the reference voltage generating circuit, the bias circuit, the current output circuit, the precharge generating circuit, and the op AMP2 are referred to in the related art, and are not repeated herein.

Based on the above embodiment, the present invention further provides a display device, which may include the driving chip described above.

The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and any changes or substitutions easily contemplated by those skilled in the art within the scope of the present invention should be included in the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. The VF detection compensation circuit is characterized by comprising a VF detection circuit, a processing circuit, a precharge compensation circuit and/or a current compensation circuit;

2. The VF detection compensation circuit of claim 1, wherein,

the precharged compensation coefficient comprises at least one of a precharged voltage compensation coefficient, a precharged speed compensation coefficient and a precharged time compensation coefficient;

the precharge compensation circuit includes at least one of a precharge voltage compensation module, a precharge speed compensation module, and a precharge time compensation module; wherein:

the precharge time compensation module corrects a duration of a precharge voltage of a lamp bead based on the precharge time compensation coefficient of the lamp bead.

3. The VF detection compensation circuit of claim 1, wherein,

the compensation coefficient of the driving current comprises at least one of a current compensation coefficient of the driving current, a constant current opening speed compensation coefficient and a constant current closing speed compensation coefficient;

the constant current speed compensation module corrects the opening speed of the constant current switching tube controlling the output of the driving current based on the constant current opening speed compensation coefficient, and/or

And the constant-current speed compensation module corrects the closing speed of the constant-current switching tube based on the constant-current closing speed compensation coefficient.

4. The VF detection compensation circuit according to claim 2, wherein said precharge voltage compensation module comprises: the first selector, the second selector, a plurality of fixed resistors and a current source;

the first selector selects one resistor node of the plurality of fixed resistors as an input end of the precharge voltage based on a first selection signal, and the second selector selects the voltage at the one resistor node of the plurality of fixed resistors as a target precharge voltage output of the lamp bead based on a voltage compensation coefficient of the lamp bead.

5. The VF detection compensation circuit of claim 3, wherein said current compensation module comprises: a third selector, a fourth selector, an intermediate resistor, and a variable current source;

the input end is connected with the voltage VDI, and the voltage VDO output by the output end is bias voltage of a constant current driving channel of the driving chip.

6. The VF detection compensation circuit according to any one of claims 1-5, further comprising a memory and M sets of N-bit latch circuits, the M sets of N-bit latch circuits corresponding one-to-one to M constant current drive channels of a drive chip, each set of latch circuits connected to the precharge compensation circuit and or the current compensation circuit in the corresponding constant current drive channel;

Each set of latch circuits includes: a first latch and a second latch;

in the ith display row and in the (i+1) th display row, a second latch in the M groups of N-bit latch circuits latches the compensation coefficients of the ith row lamp beads output by the first latch and then sends the latched compensation coefficients into the precharge compensation circuit or the current compensation circuit so as to carry out display correction on the ith row lamp beads and the (i+1) th row lamp beads.

7. The VF detection compensation circuit according to claims 1-5, further comprising a memory connected to a plurality of constant current drive channels, each constant current drive channel comprising the precharge compensation circuit and or the current compensation circuit;

and in the ith display row, respectively sending the compensation coefficients of the ith row of lamp beads read from a memory into the precharge compensation circuits or the current compensation circuits in the constant current driving channels so as to carry out display correction on the ith row of lamp beads.

8. The VF detection compensation circuit of claim 1, wherein the processing circuit is configured to:

Calculating a first average value based on the VF value of each lamp bead;

screening out VF values, the deviation degree of which meets the preset condition, from the first mean value, and calculating to obtain a second mean value according to the screened VF values;

9. A driving chip comprising the VF detection compensation circuit according to any one of claims 1 to 8.

10. A display device comprising the driver chip as claimed in claim 9.