Abstract:
A method and system for LED calibration is provided for a plurality of LED modules cascaded in a series. Each LED module includes a plurality of LEDs, a driver and a controller. The control signal from a calibration host is transmitted to all the modules to light all LEDs in the LED module. Through the controller of the LED module, the calibration data transmitted from the calibration host is stored in the memory inside the driver so that all the LEDs will emit light according to the calibration. The present invention improves the uniformity of the light emission and improves the module maintenance convenience.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to a method and system for LED calibration, and more specifically to a method and system with a controller and memory for calibrating serially connected LED modules. 
   BACKGROUND OF THE INVENTION 
   In recent years, LEDs are widely used to replace the conventional tungsten light bulbs in many lighting and signing applications because of the high luminance efficiency. However, as the current LED manufacturing process uses the semiconductor epitaxial process, the opto-characteristics of the LEDs vary greatly from batches to batches. Therefore, it is necessary to calibrate the manufactured LEDs. The current calibration method is to use a complex control circuit to obtain and store the optimal calibration data for each LED in the memory so as to calibrate the image signal in real-time and improve the lighting uniformity of the LEDs. 
     FIG. 1  shows a schematic view of a conventional LED calibration system. As shown in  FIG. 1 , a calibration host  20  outputs calibration control signal CCT, image enabling signal CCPG and image capturing control signal CCPT to LED module  10 , image pattern generator  30  and image capturing device  40 , respectively. According to CCT, LED module  10  enters either calibration mode or normal display mode. Image pattern generator  30 , based on CCPG, generates image pattern signal PGS. Image capturing device  40 , based on CCPT, performs image capturing on light LT emitted from LED module  10 , and generates image capturing data IDT for calibration host  20 . Calibration host  20  receives and processes IDT to generate calibration data for LED module  10 , and LED module  10  stores the calibration data. 
   LED module  10  includes a controller  12 , a driver  14 , a memory  16  and a plurality of LED arrays  18 , where each LED array  18  further includes a plurality of LEDs. When LED module  10  enters the calibration mode, controller  12  receives PGS to generate driver control signal DRVCTL for driver  14 . After receiving DRVCTL, driver  14  generates drive signal DRV to drive the LEDs of LED array  18  to emit light LT of required brightness and color. At the same time, controller  12  receives CCT from image capturing device  40 , and stores calibration data CCDT of CCT in memory  16  so that controller  12  can make all the LEDS generate uniform light by capturing CCDT in memory  16  to calibrate DRVCTL when LED module  10  enters the normal display mode. 
   The shortcomings of the conventional technology are the difficulty to install the above complex calibration device in the small-sized LED lighting device with the limited circuit board area and the increasing number of the LEDs, and the additional cost of the calibration device incurred to counteract the market competiveness. 
   Another shortcoming of the conventional technology is that the calibration data of all the LEDs are stored in a single memory of the module. If a few LED malfunction, it is necessary to perform calibration and obtain all the LEDs&#39; calibration data of the new module after the replacement of the malfunctioned LEDs. However, for outdoor LED display, this approach increases the maintenance cost and sometimes even the entire LED module needs to be replaced. 
   Therefore, it is imperative to devise an easy-to-maintain and simply-structured LED module and a more efficient LED calibration method and system so improve the calibration of LED modules without increasing the manufacturing cost. 
   SUMMARY OF THE INVENTION 
   The primary object of the present invention is to provide a system for LED calibration, including serially connecting a plurality of LED modules, with each module having a plurality of LEDs, a driver and a controller. By transmitting the control signals output from calibration host to all the modules to light the LEDs of each module, the present invention also uses the controllers inside the modules to store the calibration data transmitted from the calibration host into the memory inside the driver so that the emitted light of the LEDs are calibrated to improve the lighting uniformity of the LEDs and keeping the module maintenance easy. 
   Another object of the present invention is to provide a system for LED calibration, where the drivers of the LED modules have built-in memory for storing LED calibration data and to simplify the circuit routing and circuit design of the LED modules. 
   Yet another object of the present invention is to provide a system for LED calibration, using the communication protocol established between the calibration host and the LED modules so that the LED modules are controlled by calibration host to enter either calibration mode or normal display mode. 
   Yet another object of the present invention is to provide a method for LED calibration, using the communication protocol established between the calibration host and the LED modules so that the LED modules are controlled by calibration host to enter either calibration mode or normal display mode, and the calibration host transmits control instructions and data in different modes so that the serially connected LED modules can obtain all the LED calibration data in a single calibration and store the LED calibration data of each LED module in the memory of the LED module. 
   Yet another object of the present invention is to provide a method for LED calibration, using the communication protocol established between the calibration host and the LED modules so that the controller of each LED module can capture the correct data from the data transmitted by the calibration host and stores the data in the memory for calibrating the LED opto-characteristics in normal display mode. 
   Therefore, through the system and method for LED calibration of the present invention, the aforementioned shortcomings of conventional LED calibration technology can be solved while reducing the hardware manufacturing cost and providing high efficiency maintenance. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention can be understood in more detail by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein: 
       FIG. 1  shows a schematic view of a conventional LED calibration system; 
       FIG. 2  shows a schematic view of a first embodiment of an LED calibration system of the present invention; 
       FIG. 3  shows a schematic view of a second embodiment of an LED calibration system of the present invention; and 
       FIG. 4  shows a flowchart of an LED calibration method of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2  shows a schematic view of the first embodiment of the LED calibration system of the present invention. The LED calibration system of the present invention includes a plurality of LED modules. The present embodiment includes three LED modules  60 A,  60 B,  60 C, with each module including a controller  62 , a plurality of drivers  64 , a memory  66  and an LED array  68 , where LED array  68  includes a plurality of LEDs (not shown). For simplicity,  FIG. 2  shows only a driver  64 . However, the driver of embodiment of the present invention includes the single-channel driver for driving a single LED and a multi-channel driver for driving a plurality of LEDs. 
   The LED calibration system of the present invention further includes a calibration host  20  and an image capturing device  40 . Calibration host  20  controls the entire calibration process and outputs image capturing control signal CCPT to image capturing device  40  so that image capturing device  40  detects light LT emitted by LED modules  60 A,  60 B,  60 C, and generates image capturing data (IDT). Calibration host  20  processes IDT to generate calibration data, which is sent through instruction data input signal CD to LED module for storage. 
   Driver  64  has an instruction data input end and an instruction data output end (not shown), and the plurality of drivers  64  in the LED modules are cascaded together by instruction data input end and instruction data output end. That is, the instruction data output end of the previous driver is connected to the instruction data input end of the next driver so that all the drivers can receive the data transmitted by calibration host  20 . 
   Controller  62  of the LED module includes a signal input end of a self-test enabling TP and a signal input end of an instruction data input signal CD, where controller  62  will enter the self-test mode and send the default image signal automatically to the driver when self-test enabling TP is high so that the driver will light the LEDs and display the default image to provide self-test capability to the LED module. If self-test enabling TP is low, controller  62  will enter either calibration mode or normal display mode, based on instruction data input signal CD. In the present embodiment, self-test enabling TP is grounded for performing calibration. 
   The format of instruction data input signal CD includes an instruction byte and a plurality of data bytes. The instruction byte is configured as calibration mode and normal display mode, such as, h00 in instruction byte indicating the calibration mode and h01 in instruction byte indicating the normal display mode. Of course, the configuration of the instruction byte is not limited to the above exemplary. In addition, the number of the data bytes can be optimized according to the system requirement. For example, for the LED module with N single-channel drivers, N data bytes can be allocated. For the LED module with N dual-channel drivers, 2N data bytes can be allocated for lighting LEDs or for transmitting LED calibration data. 
   In calibration mode, controller  62  first transmits the data bytes of instruction data input signal CD directly to the instruction data input end of driver  64  of LED module  60 A. The instruction data output end of driver  64  is connected to the instruction data input end of the next driver  64 , and so on, for lighting all LEDs of LED module  60 A. At the same time, the instruction data output end of the last driver  64  of LED module  60 A is instruction data output signal CDX of LED module  60 A, as shown in  FIG. 2 , and is connected to instruction data input signal CD of next LED module  60 B, and so on. Because the data in the data bytes are the calibration image of calibration host  20 , calibration host  20  then receives image capturing data IDT from image capturing device  40 , and generates the data bytes to indicate the LED calibration data. Therefore, controller  62  will store the data into memory  66  to complete the calibration process. 
   When in normal display mode, controller  62  will use the externally input data bytes with the calibration data captured from the memory to perform calibration computation to generate the calibration driving control signal for driver  64  so that driver  64  can light the LEDs and display the uniform light LT. The calibration computation can be addition or multiplication, depending on the manner in which calibration host  20  uses to obtain the calibration data when in calibration mode. 
   It is worth noting that the CD format of the present embodiment and the calibration computation are only exemplary, and the scope of the present invention is not limited to the above embodiment. In other words, any CD format able to transmit mode selection information and image data information are all within the scope of the present invention. Also, any calibration computation able to match the manner with which calibration host  20  uses to generate calibration data is also within the scope of the present invention. 
     FIG. 3  shows a schematic view of a second embodiment of an LED calibration system of the present invention. In this embodiment, driver  65  of the LED calibration system includes a built-in memory  66  so as to simplify the circuit design and layout of LED module  60 . In addition, memory  66  can also be included inside controller  62  to achieve the same simplification of the circuit design and layout of LED module  60 . Memory  66  of the first and second embodiments can be EEPROM. 
     FIG. 4  shows an LED calibration method of the present invention, controlled by controller  62 . After the host is switched on in step S 10 , step S 12  is for the memory to obtain the data and transmit to the driver. Step S 14  is to determine whether it is in self-test mode. When self-test enabling TP of controller  62  is high, LED module enters the self-test mode and then proceeds to step S 16  to transmit the default image data to the driver so that LEDs display the default image and returns to step S 14 . If self-test enabling TP is low in step S 14 , proceed to step S 18 . Step S 18  is to use the instruction byte of CD instruction data input signal to determine whether the mode is the normal display mode. If in normal display mode, proceed to step S 20  to capture memory data and transmit to the driver for image calibration to make LEDs display the calibrated image; otherwise, proceed to step S 22  to capture the data bytes of CD as calibration data and proceed to step S 24 . Step S 24  is to store the calibration data to the memory and return to step S 14  and repeat the above operations. 
   Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.