CN215911167U - LED display system - Google Patents

Abstract

The LED display system has an LED display screen coupled to a driver circuit. The driving circuit includes a scrambling pulse width modulation generator, a register and a memory. The scrambled PWM generator receives image data from an external source and, after some compensation, is sent to the scrambled PWM generator for distribution according to a new set of rules including compensated image data K. The compensation image data K may be an empirical value or obtained from a formula using coefficients p and q, which may be obtained by calibration.

Description

LED display system

This application is a continuation of U.S. patent application No. 15/945,497 filed on 4/2018, the contents of which are incorporated herein by reference in their entirety.

Technical Field

The present invention relates generally to devices for driving displays. More particularly, the present invention relates to an apparatus for compensating image data to improve the refresh rate and brightness uniformity of an LED display.

Background

Modern LED (light emitting diode) displays require higher gray scales to achieve higher color depth and higher visual refresh rates to reduce flicker. For example, 16-bit gray scale for RGB LED pixels allows 16-bit levels of red, green, and blue LEDs (21) respectively⁶65536). Such RGB LED pixels are capable of displaying 65536 in total³And (4) color. One method commonly used to adjust the gray scale of an LED is pulse width modulation ("PWM"). Briefly, PWM generates a series of voltage pulses to drive an LED. When the pulse voltage is higher than the LED forward voltage, the LED is turned on. Thus, the pulse duration (i.e., pulse width) of the PWM signal determines the on/off time of the LED when the pulse amplitude exceeds a threshold. The percentage of the on-time to the sum of the on-time and the off-time (i.e., the pulse width modulation period) is the duty cycle, which determines the brightness of the led. The configuration and operation of an exemplary LED display system (including LED topology, circuitry, PWM engine, etc.) is described in detail in U.S. patent No. 8963811 issued on 24.2.2015 and U.S. patent application No. 15/901,712 filed 21.2.2.2018.

Another parameter of an LED display screen is the gray value, which is the brightness level of the LED display screen. In a 16-bit resolution LED display screen, the gray scale values range from 0 (full darkness) to 65535 (maximum brightness), corresponding to duty cycles from 0% to 100%. When the gray value is low, the brightness level of the LED is low. Conversely, when the gradation is high, the luminance level is also high. LED displays often suffer from performance problems at low gray scale values.

Another parameter of an LED display screen is its gray scale clock ("GCLK") frequency, which is related to the maximum number of GCLK cycles in a data frame and the refresh rate of the display. In addition, the frame rate refers to the number of times a video source inputs a full frame of new data to the display screen in one second. The refresh rate of an LED display screen is the number of times the LED display screen draws data per second. The refresh rate is equal to the frame rate multiplied by the number of segments.

One of the advantages of Pulse Width Modulation (PWM) is low power loss of the switching devices. When the switch is off, there is little current. When the switch is conducting, there is little voltage drop across the switch. Thus, the power loss in both cases is close to zero. On the other hand, Pulse Width Modulation (PWM) is defined by a duty ratio, a switching frequency, and a load characteristic. When the switching frequency is sufficiently high, the pulse sequence can be smoothed to recover the average analog waveform. However, when the switching frequency is low, the off-time of the light emitting diode will be noticeable and appear to the observer as flickering.

Scrambled pulse width modulation ("S-PWM") changes conventional pulse width modulation and enables higher visual refresh rates. To accomplish this, S-PWM scrambles the on-time in one PWM cycle into a number of shorter PWM pulses that drive each scan line in turn. In other words, the total gray value is scrambled into a plurality of pulse width modulation pulses within one pulse width modulation period. In conventional pulse width modulation schemes, there may be only one pulse width modulated pulse such that the light emitting diode is continuously illuminated for a period of time, while the light emitting diode is not illuminated for the remaining time. In contrast, S-PWM allows the LED to emit light in successive short pulses during the pulse width modulation period so that the light pulses are more evenly distributed during the pulse width modulation period, avoiding or reducing flicker.

The number of GCLK cycles of a pulse width modulation cycle is equal to the power of 2 control bits:

the GCLK cycle number is 2, and for example, 65536 GCLKs are used for 16-bit gray scale. Note that the number of GCLK in one PWM period is equal to the gray value at its maximum luminance, i.e., the maximum pulse width. In some S-PWM, the total number of GCLK can be divided into MSBs (most significant bits) and LSBs (least significant bits) of the gray scale period. Each PWM period is divided into segments (or sub-PWM periods) according to the following formula:

number of fragments 2 least significant digit

For a 60hz frame rate and a video source with a PWM period length of 8000 GCLK's, the PWM period can be divided into 32 segments (LSB 5) so that each segment has a pulse duration of 250 GCLK's. Thus, a total of 1600 GCLK gray values can be assigned to 32 segments, 50 GCLK per segment, potentially increasing the refresh rate by up to 32 times. However, when the PWM pulse duration (i.e., pulse width) in a segment is less than the time required to raise the LED voltage above the forward voltage, the LED will remain unlit. Us patent No. 9,390,647 provides a solution to extend the pulse duration by adding a fixed number of GCLKs over the pulse. However, such S-PWM schemes result in a significant increase in light energy output at low brightness levels, as explained elsewhere in the present disclosure. Other solutions may require another power supply to provide additional drive current to extend the pulse duration, which increases the complexity and cost of the LED display electrical system.

Therefore, new systems and methods are needed to improve the image quality of LED displays while eliminating the disadvantages of the prior art.

SUMMERY OF THE UTILITY MODEL

An embodiment of the LED display system of the present invention includes an LED display screen coupled to a driver circuit. The driving circuit includes a scrambling pulse width modulation generator (S-PWM generator), a register, and a memory. The S-PWM generator receives image data having a gray scale value of (X + K). X is a gray value of data from an external image source and K is a compensation value provided by the driving circuit.

According to one embodiment, the S-PWM generator assigns the gray value (X + K) into the segments according to the following rule:

when (X + K) is equal to or less than G₀*S₀When the temperature of the water is higher than the set temperature,

S＝ceil((X+K)/G₀),R＝mod(X+K,G₀) (1)

when (X + K) is greater than G₀*S₀When the temperature of the water is higher than the set temperature,

M＝floor((X+K)/S₀),L＝mod(X+K,S₀) (2)

in formulae (1) and (2), G₀Is the number of groups, S₀Is the number of preset segments stored in the drive circuit. S is the number of output segments, where the pulse width of S-1 segments is G₀GCLK, and the remaining segment has a pulse width R.

Further, L isThe number of segments with pulse width M +1 is received, respectively. The rest of S₀The L segments each receive a pulse width M. Note that the unit of the pulse width or the gray value is GCLK. For example, one pulse width M means that one pulse width has a time length of M GCLK.

Number of packets G₀This may be empirically predetermined or obtained by calibrating the flashing of the LED display screen. It may be stored in a memory in the driver circuit. The compensation value K is related to a first set of calibration data obtained at high brightness and a second set of calibration data obtained at low brightness of the LED display screen. For example, K ═ q — X (floor (p X) + q), where p is derived from the first set of calibration data and q is derived from the second set of calibration data.

In some embodiments, the array of Light Emitting Diodes (LEDs) in a LED display screen may be arranged in a common cathode configuration or a common anode configuration. The LED display screen may be a large wall display screen for indoor or outdoor use. The LED display screen can also be a miniature display screen of the handheld device.

The utility model also provides an operation method of the LED display system. The LED display screen is coupled to a driving circuit having a scrambled pwm generator. The image data X is sent to the drive circuit. The image data X is compensated by multiplying the calibration coefficient p in a multiplier. The image data is further compensated by adding another constant q in the adder. Thus, a total compensation value K is added to X so that the compensated image data has a value of (X + K).

The compensated image data (X + K) is then sent to the S-PWM generator. The S-PWM generator scrambles the compensated image data into a plurality of segments, generates short pulse width modulation pulses and sends the short pulse width modulation pulses to a power supply or a current source.

The utility model further provides an image data compensation method for the LED display system. The LED display screen is driven by a driving circuit with an S-PWM generator. The drive circuit is coupled to a video source. The image data input by the video source is X, and the compensated image data is floor (p X) + q. Either the p-value, or the q-value, or both, can be obtained by calibration. For example, the display screen may be uniformity calibrated at a high brightness level to determine the value of p and at a low brightness level to determine the value of q. Alternatively, the value of p or the value of q, or both, are predetermined empirical numbers.

The values of p, q, or both, may be determined independently for each individual LED in the LED display screen. Alternatively, q is constant for the same color LED in an LED display, p is constant for the same color LED in an LED display, or both.

Drawings

The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings.

Fig. 1 presents a schematic diagram of prior art S-PWM schemes a and B.

Fig. 2 shows the effect of the modified S-PWM scheme C.

Fig. 3 illustrates the operation of the prior art S-PWM scheme B.

Fig. 4 shows the operation of the improved S-PWM scheme C.

Fig. 5 shows a block diagram of an LED display system of the present invention.

Fig. 6 presents a flow chart of an iterative process for calibrating an LED array.

Detailed Description

Fig. 1-6 and the following description explain embodiments of the utility model only in a pictorial and text manner. It should be noted that from the following discussion, alternative embodiments of the structures and methods of the utility model herein are readily identified as viable alternatives that may be employed without departing from the principles of the claimed invention.

Reference will now be made in detail to several embodiments of the utility model, examples of which are illustrated in the accompanying drawings. It is noted that where feasible, similar or analogous reference numbers may be used in the figures and may indicate similar or analogous functions. The figures depict embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated in the accompanying drawings may be employed without departing from the principles of the utility model described in the accompanying claims.

The terms "coupled" and "connected," as used herein, unless otherwise specified, refer to an indirect or direct electrical connection. Thus, if a first device couples or connects to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection to other devices or connections.

In the present invention, the term "low brightness" (i.e., low gray scale) generally refers to the case where the input signal length is short, for example, shorter than 4 times the LED boosting time, or shorter than 3 times the LED boosting time. Conversely, the term "high brightness" (i.e., high gray scale) refers to a case where the input signal length is high, for example, more than 4 times the LED boosting time, or more than 6, 8, 10 times the LED boosting time.

Fig. 1 illustrates two existing S-PWM schemes. The top panel displays a gray value of 320 GCLK for one gray data input period, i.e., a total width of the PWM pulse is 320 GCLK for one gray data input period. In the S-PWM scheme A (shown in the middle panel of FIG. 1), 320 GCLK 'S are distributed in 32 segments (segment 0 through segment 31), each having 10 GCLK' S. In the S-PWM scheme B (shown in the lower panel of FIG. 1), an offset equal to N GCLK is added to each segment of PWM pulses to extend the PWM pulse width to N GCLK, resulting in (N +10) GCLK-wide pulses. In the S-PWM scheme B, the expanded PWM pulse width extends beyond the boost time to the forward voltage (Vf) of the LED, causing the LED to light up.

The utility model provides an innovative S-PWM scheme C. For illustrative purposes, X is the gray level value of the input image data within one gray level input period; k is a compensation value added to the input image data; s₀Is the number of segments; g₀Is the length of each segment.

In the S-PWM scheme C, when (X + K) is equal to or less than G₀*S₀When S is ceil ((X + K)/G)₀)，R＝mod(X+K,G₀). S is the number of output segments, where the pulse width of S-1 segments is G₀One GCLK, the pulse width of the remaining 1 segment is R, R is less than G₀Is a positive integer of (1). An output segment, as used herein, is a segment having a pulse width of at least 1 GCLK, and a segment without an output pulse is said to beIs a "dark segment". Thus, (S)₀-S) segments are dark segments.

In contrast, when (X + K) ═ G is greater₀*S₀When M is floor (X + K)/S₀，L＝mod(X+K,S₀). L is the number of segments with pulse width M +1, and the rest S₀The pulse width of the L segments is M.

The rule is applied to distribute 1-320 GCLK to 32 segments (S)₀32), assume that the number of packets is 8 GCLK (G)₀8), the distribution of the gray values is as shown in tables 1 and 2 below. Table 1 shows the distribution of gray values from 1 to 256 GCLK (e.g., gray value ≦ S)₀*G₀256), table 2 gives the distribution of gray values from 257 to 320 GCLK.

TABLE 1

TABLE 2

Table 1 shows that when the gradation value is less than or equal to S₀*G₀The available gray scale data is first put into a single segment until the pulse width modulation pulse width in the segment reaches G₀Then the remaining gray scale data is put into another PWM pulse width less than G₀In the section (2). Thus, the maximum pulse width modulation pulse width in each segment is G₀(i.e., eight in this example). Thus, at very low gray values, a single segment is preferentially filled until the segment has a pulse width G₀While the remaining segments do not receive signals and remain in the dark segment state. Please note that when the gray level is equal to G₀*S₀While the pulse width of each segment is G₀。

When the gray value is larger than G₀*S₀The distribution law changes. As shown in Table 2, for over G₀*S₀The number of GCLK, one time divided1 GCLK is allocated to each segment until all 32 segments are present (G)₀+1) GCLK. Then, exceed (G)₀+1)*S₀The redundant GCLK of (a) is assigned to each segment one GCLK at a time until all 32 segments have (G +2) GCLKs.

Therefore, in the present embodiment, when the gray-level value is greater than S₀*G₀The rule of assigning the gray values to the respective segments is the same as the conventional S-PWM scheme. However, when the gray scale value is low, i.e., less than S₀*G₀When the method is to have at least G₀The number of segments of pulse width is maximized.

Fig. 2 shows the effect of the inventive S-PWM scheme C. Panels A, B and C in fig. 2 show the output light energy (i.e., brightness) of a group of LEDs in response to an input data length (i.e., input pulse width). Panel a shows the behavior of the LEDs without any compensation. The LED will not light up until the input pulse width exceeds a threshold level. Once the LED is lit, the energy output value of the LED typically increases linearly, but at different rates. Panel B shows the result of a first compensation that improves the uniformity of the led brightness at high brightness. Panel C shows the result of an embodiment of the current invention, which provides a second compensation in addition to the first compensation. After the second compensation, when the input pulse width is narrow, the LED emits light.

Fig. 3 is a graph of the light energy output of the LEDs in S-PWM scheme B shown in the middle panel of fig. 1. In the bottom panel of FIG. 3, when the PWM pulses in each segment are (t-1) GCLK, the light energy output in one segment is e (t-1) and the total light energy output in 32 segments is 32 × e (t-1). When the pulse width in a segment is extended by 1 GCLK to t GCLK values, the total light energy output in the 32 segments is 32 xe (t), as shown in the top panel in fig. 3. Therefore, the difference in optical energy output caused by one GCLK is 32 × (e (t) -e (t-1)).

Fig. 4 shows the light energy output of the light emitting diode in the utility model S-PWM scheme C of the present invention. In the bottom panel of FIG. 4, the pulse width modulated pulses in segment 1 are t GCLK, while each of the remaining segments receives (t-1) GCLK and remains unlit. When the input pulse width modulation value is increased by one GLCK, this GCLK is assigned to segment 2. Adding a GLCK to segment 2 is sufficient to light the leds, as shown in the top panel in fig. 4. Therefore, the difference in light energy output caused by one GCLK is 1 × (e (t) -e (t-1)).

Since the S-PWM scheme B increases the pulse width modulation value in each of the 32 segments by the same GLCK number, the LED is either in an illuminated state in all segments or remains unlit in all segments, not allowing trimming at low brightness. In contrast, the S-PWM scheme C allows a limited increase in the PWM values of individual segments under certain conditions, so that the LEDs emit light at least in some segments, even at very low brightness levels. Thus, the S-PWM scheme B results in a significant increase in light energy output, while the S-PWM scheme C allows for fine tuning of the light energy output.

In some embodiments of the utility model, the compensation value K is obtained by calibration. For example, calibration is performed by taking a picture and adjusting the brightness of individual LEDs in an LED display screen. This calibration is usually performed at high brightness. The purpose is to achieve uniformity of display screen brightness. In such a calibration, each LED in the LED display screen receives the same image data-the same X value. A first picture of the LED display screen is taken showing the change in LED brightness. The first data is added to the image data and sent to the LEDs. A second photograph is taken. And adjusting the input image data, and taking a picture until the brightness uniformity reaches a preset standard. This time, the compensation value K corresponding to the LED display screen is set.

In some embodiments, each LED pixel is an RGBLED pixel comprising a red light emitting diode, a blue light emitting diode, and a green light emitting diode, each LED receiving its respective input image data X_iAnd obtaining the coefficient p_iAnd i is r, g or b. Obtaining the coefficient p by calibrating each individual LED_iAnd then stored in a structure, such as a look-up table, in a memory, such as a static random access memory. The memory may be built on the same chip with the driver circuit or on a different chip coupled to the driver circuit chip. When needed, such as when the LED is powered on, the coefficients are retrieved to beThe calibration data is preloaded into registers in the driver circuit.

In another embodiment, the calibration is performed under high brightness conditions to obtain a first set of coefficients p_iAnd calibrated under low brightness conditions to obtain a second set of coefficients q_i. In some embodiments, the performance characteristic at low brightness is flickering of the LED display screen, which can be monitored by visual inspection. Assume that, under low brightness conditions, a single LED receives input image data Xi and assigns a coefficient q after a calibration process_i. Or, q_iMay be stored in a memory in the driver circuit. Thus, the coefficient p_i,q_iOr both may be assigned to each individual LED.

For a 1920x1080 pixel color LED display screen, there may be up to six calibration data matrices-P_r、P_b、P_g、Q_r、Q_bAnd Q_gEach matrix is 1920x1080 in size. The elements in these matrices are p_imnOr q_imnWhere i ═ r, g, or b, m is the row number and n is the column number of the color pixels in the LED array.

P, p as used herein_iAnd p_imnMay be used interchangeably. Each of them is a coefficient assigned to one LED of the LED array, and p refers to a general coefficient assigned to one LED, p_iEmphasizing the color of the LED, p_imnIndicating the color and location of the LED. The coefficient p may vary from led to led. Alternatively, the same coefficient p may be applied to all LEDs of the same color in the LED array. Likewise, q_i,And q is_imnMay be used in the same manner. Furthermore, p_iOr p_imnIs designated as coefficient matrix P, and q, q_iOr q is_imnIs designated as coefficient matrix Q.

One of the calibration methods in the present invention is an open loop process that uses two or more images of the LED array to derive the coefficients p and q. First, calibration is performed at a high brightness level. The LED array has a uniform input data set for each red, green or blue color. For example, when pwm _ R is 65535, pwmWhen G is 0 and pwm B is 0, the red LED in the LED array is turned on. A camera is used to take an image of the LED array. The image is then processed to derive the brightness of each red led to obtain the intensity matrix a. The illumination efficiency of each red led is proportional to the corresponding matrix element. The red LEDs in m rows and n columns have A_rmnAnd the average intensity of all red LEDs in the LED array is the mean value (a). Corresponding coefficient p_imnThis can be derived from the following equation:

p_imnarmn/mean (A) (3)

The same process is repeated when the input to the LED array is green or blue. Thus, red, green and blue each have a corresponding coefficient p_imn. The coefficient matrix P being coefficients P_imnOf the matrix of (a).

The second step of the calibration process may be performed at a low brightness level. Likewise, for each red, green or blue color, a uniform data set is sent to all of the same color but lower intensity LEDs in the LED array. For example, the data set (pwm _ R200, pwm _ G0, pwm _ B0) lights all red LEDs in the array with low brightness. An image of the LED array is taken and an intensity matrix B is extracted from the image. Likewise, each of the red, green and blue colors is calibrated to obtain the corresponding matrix B.

Suppose the high brightness input data is X_HThe low brightness input data is X_L. The following equation can be obtained:

B_imn＝(X_L–q_imn)*p_imn*X_L/X_H (4)

and q is_imn＝X_L-B_imn*X_H/X_L/p_imn (5)

q_imnIs the coefficient obtained for a colored LED at low intensity. Coefficient matrix q_imnDesignated as matrix Q.

The above calculations assume that the imaging efficiency is the same at high and low brightness levels, which may not be as accurate as possible. The term "imaging" as used hereinEfficiency "refers to the ratio between the brightness extracted from the image of the light emitting diode and the actual brightness of the light emitting diode. To address this issue, in some embodiments, q is obtained using two different but lower brightness LED array images_imn. At the input data are respectively X₁And X₂Two images are taken at two different low brightness levels from which two intensity matrices B1 and B2 are derived. In this case, q can be obtained by solving two linear equations for each color LED_imnAs follows:

B1i_mn＝(X₁-q_imn)*p_imn (6)

B2_imn＝(X₂-q_imn)*p_imn (7)

q_imn＝X₁-B1_imn(X₁-X₂)/(B1_imn-B2_imn) (8)。

another typical calibration method is a closed loop or iterative process that uses an imaging system to adjust the coefficient q of each LED to achieve a uniform brightness. The process uses an adjustment loop in which the value of q is modified to reduce the variation in the measured image until the displayed image is at or below a predetermined level. The details of this embodiment are described below with reference to fig. 6.

As shown in fig. 6, in S1, using the same procedure as described above, the coefficient matrix P is obtained from the image taken at a high luminance level according to equation (3). In S2, the coefficient matrix Q is assigned with either an initial value or a numerical value calculated in S8. In S3, a data matrix X' is applied to the LED array.

X’＝(X+Q)*P (9)

The matrix X is a uniform matrix. Thus, Q adjusts the matrix X. A uniform matrix as used herein is a matrix in which all elements have the same value.

After the adjustment, in S4, an image is captured and the intensity matrix B is extracted using the image. According to equation (8), in S5, the difference between the matrix B and the uniform matrix is calculated as an error matrix E.

E ═ B-mean (B) (10)

In equation (10), the average value (B) is a matrix of the average intensity values of the LEDs in the LED array, which is a uniform matrix.

In S6, the error matrix E is compared with a predetermined threshold value. If E is equal to or less than the threshold, Q is output as a result of the calibration. The threshold may be a fraction of the mean (B), e.g., 1% of the mean (B) or 0.5% of the mean (B). Each element Q in the matrix Q is a coefficient obtained at low luminance or an equivalent thereof. If E is greater than the threshold, the process continues to S7.

The compensation matrix C is calculated using the error matrix E in S7.

C＝-k*E (11)

k is a constant less than the illumination efficiency of the LED array, i.e. 50% of the average illumination efficiency of the LED array.

In S8, the compensation matrix C is added to the matrix Q to obtain an adjusted Q_new。

Q_newQ + C ═ Q-k ═ E ═ Q-k (B-mean (B)) (12)

Will Q_newQ in S2 is assigned to calculate a new input data matrix X' for the LED array and a new iteration is started.

When the observed intensity of an LED pixel in an array is high, the corresponding element in the error matrix E of the LED array will also be large. For this reason, a more significant compensation value C is required for the LED pixel for this pixel (C ═ k × E). Thus, the input is to the pixel q_newIs small (Q) in new data_newQ + C), resulting in lower output brightness. Further adjustments to Q are made using the new output intensity matrix B and the smaller k value. Therefore, each iteration requires modification of the input data to ensure that the brighter LED pixels have smaller input values, so that the output image becomes more uniform. The iteration continues until the change in the image reaches a predetermined level or without any further significant reduction. The resulting Q matrix provides Q values for calculating the compensation value k.

In some embodiments, for example, the light emitted by the LEDs is uniformAnd uniform, it may not be necessary to apply a different q for each individual led. Conversely, all LEDs of the same color in an LED array may use a set of calibration data at low brightness, high brightness, or both. That is, at low brightness, all red LEDs use the same q_rAll blue LEDs use the same q_bAll green LEDs using the same q_gThus, q will be_imn(three matrices q)_r、q_bAnd q is_gEach matrix size is 1920 × 1080) down to three digits. Whatever q is used for low brightness_r、q_bAnd q is_gValue, at high brightness, all red LEDs can use the same p_rAll blue LEDs using the same p_bAll green LEDs using the same p_gThus p will be_imnThree matrices p_r、p_bAnd p_gThe size of each matrix is 1920x1080) down to three numbers. This simplification reduces the size of the memory required to store the calibration data. In these embodiments, the values of q and p may be selected empirically or obtained by calibration.

q and p are both used to determine the compensation value K in order to achieve an optimal compensation of the light emitting diode over the entire range of brightness levels.

In another embodiment of the utility model, the number of packets G₀Number of sum stages S₀May be determined empirically or obtained by calibration. S₀And G₀Stored in the driving circuit of the led display panel, for example, in a register. During calibration, an initial G is set in the driver circuit₀Value (e.g. 8) and/or initial S₀Values (e.g., 32) for LED displays operating at different brightness levels, particularly low brightness levels, to test performance characteristics such as flicker and brightness uniformity. G₀And S₀Adjustments may be made until the performance meets or exceeds a predetermined criterion.

Note pi, qi, G₀And S₀The values of (A) may be obtained by calibration of the LED array, or may not require calibrationThe determination is then directly predetermined, for example empirically.

Fig. 5 is a block diagram of an exemplary LED display system of the present invention. The video source sends video data (8, 10, or 12 bits) to an LED display system having an LED display screen with an LED array and LED drive circuitry. The video data is gamma corrected and converted to 16-bit data in a color depth converter. The 16-bit data stream enters a multiplier where a first set of calibration data is combined into the data stream. The first set of calibration data is obtained under high brightness conditions, i.e. high brightness calibration. Suppose the input data is X_iHigh luminance calibration multiplies input data by a calibration factor p_i. For example, the output data of the multiplier is equal to a Floor function: floor (p)_i*X_i). This calibration adjusts the 16-bit data to obtain pixel efficiency. The first compensation shown in panel B of fig. 2 is an exemplary result of this high brightness calibration.

The data from the multiplier enters an adder where a second set of calibration data q is stored_iThe addition is performed. The second set of calibration data is obtained under low brightness conditions, i.e., low brightness calibration. Suppose the calibration data will be q_iA GCLK is added to N₁Output data N of adder₂Is equal to (N)₁+q_i) Or (floor (p)_i*X)+q_i). Therefore, the compensation value K_iDetermined by both the high brightness calibration and the low brightness calibration, corresponds to the curve shown in panel C of fig. 2.

The calibrated image data (X + K) is sent to the S-PWM engine, which receives the preset number of segments S from the register₀And a predetermined number of packets G₀And generates a digital PWM signal. The digital PWM signal is sent to a plurality of power supplies. These power supplies in turn drive a scanning type LED display screen, which may be a common anode configuration or a common cathode configuration.

In a common anode configuration, the LED display screen has an array of RGB LED pixels arranged in rows and columns. The LED array has a plurality of common anode nodes. Each of the plurality of common anode nodes operatively connects the anodes of the same color LED pixels in a row to a respective scan switch. The cathodes of the LED pixels in the same column are connected to a power supply.

In a common cathode configuration, the LED array has a plurality of common cathode nodes. Each of the plurality of common cathode nodes operatively connects the cathodes of the LED pixels in a row to a respective scan switch. The anodes of the LEDs of the same color in a column of LED pixels are connected to a current source.

Many modifications and other embodiments of the utility models set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. For example, the driver circuit may be used to drive an array of LEDs in a common cathode or common anode configuration. The elements in the LED array may be single color LEDs or RGB units or any other form of LEDs. The driver circuit can be scaled up or down to drive various sizes of LED arrays. Multiple driver circuits may be employed to drive multiple LED arrays in an LED display system. The components of the driver circuit may be integrated on a single chip or may be integrated on multiple chips or on a printed circuit board. Further, the display screen may be any suitable display, including a large outdoor display panel or a small miniature display screen for a cell phone. Such variations are within the scope of the utility model. It is to be understood that the utility model is not to be limited to the specific embodiments disclosed and that modifications and embodiments are intended to be included within the scope of the appended claims.

Claims (4)

1. An LED display system, comprising:

an LED display screen with an LED array;

and a driving circuit for driving the LED display screen,

wherein the driving circuit includes a scrambling pulse width modulation generator, a register, and a memory, wherein the scrambling pulse width modulation generator receives the compensated image data having a gray value of X + K, X being a gray value of data from an external image source, K being a compensation value generated by the driving circuit,

wherein the scrambling pulse width modulation generator allocates the gray value X + K into a plurality of segments according to the following set of rules:

when X + K is equal to or less than G₀*S₀When S is ceil ((X + K)/G)₀) And R ═ mod (X + K, G)₀) Wherein G is₀Is the number of groups, S₀Is a preset number of segments stored in the drive circuit, S is the number of output segments, where the pulse width of S-1 segments is G₀GCLK, and the pulse width of the remaining segment is R; and is

When X + K is greater than G₀*S₀When M is floor ((X + K)/S)₀) And L ═ mod (X + K, S0), where L is the number of segments receiving pulse width M +1, respectively, and the remaining S₀L segments each receive a pulse width M, and

wherein the compensation value K is a predetermined value or K ═ (floor (p X) + q) -X is obtained by calibrating the luminance uniformity of the LED array, where p and q are constants obtained by calibrating the luminance uniformity of the LED array; p is a matrix element in a coefficient matrix P derived from one image of an LED array at a high brightness level, each matrix element P corresponding to one LED in the LED array, Q is a matrix element in a coefficient matrix Q derived from two images of two LED arrays at low brightness levels, each matrix element Q corresponding to one LED in the LED array.

2. The LED display system of claim 1, wherein the number of groupings is predetermined or obtained by measuring the flashing of the LED display screen.

3. The LED display system of claim 1, wherein the LED display screen comprises an LED array of RGB LED pixels, wherein the LED array has a plurality of common anode nodes, each of the plurality of common anode nodes operatively connecting the anode of the same color LED in a row to a respective scan switch, and the cathode of the LED pixel in the same column operatively connected to a power supply.

4. The LED display system of claim 1, wherein the LED display screen comprises an LED array of RGB LED pixels, wherein the LED array has a plurality of common cathode nodes, each of the plurality of common cathode nodes operatively connecting a cathode of an LED pixel in a row to a respective scan switch, and an anode of an LED of the same color in a column of LED pixels operatively connected to a current source.

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