CN100405072C

CN100405072C - LED screen dead pixel detection method and circuit therefor

Info

Publication number: CN100405072C
Application number: CNB2004100705742A
Authority: CN
Inventors: 梁宁
Original assignee: Konka Group Co Ltd
Current assignee: Konka Group Co Ltd
Priority date: 2004-08-10
Filing date: 2004-08-10
Publication date: 2008-07-23
Anticipated expiration: 2024-08-10
Also published as: CN1734276A

Abstract

The present invention relates to an LED screen dead pixel detection method and a circuit thereof. A unidirectional cascade detection signal line is arranged between displaying units to ensure that the dead pixel detection is accurately positioned to a single LED. The dead pixel detection circuit comprises a frequency detection circuit, a detection resistor, a PMOS field effect transistor, a difference operation amplifier, a comparator, a reference power supply, a diode and an actuator, wherein the output end of the frequency detection circuit is connected with the grid electrode of the PMOS field effect transistor. The detection resistor is connected between the source drain electrodes of the PMOS field effect transistor, and both ends of the detection resistor are connected with the difference operation amplifier. The output end of the difference operation amplifier is connected with the positive input end of the comparator, and the inverse input end of the comparator is connected with the reference power supply. The inverse output end of the comparator is connected with the diode, and the other end of the diode is connected with the detection signal line.

Description

A kind of LED screen dead pixel detection method and used circuit thereof

Technical field

The invention belongs to LED screen display technique field, particularly LED display bad some detection technique and used circuit thereof.

Background technology

There is millions of LED in a light emitting diode (LED) display screen, these LED directly are connected with chip for driving, chip for driving generally adopts string and conversion chip, and connect with cascade system, if it is a string that full frame chip for driving is cascaded into, data transmission is so slowly, so that the solution of can't working is that screen is divided into a plurality of display units, data are serial transfers in the unit, then are parallel transfer between the unit.For indoor screen, several often row of display unit or several row, for outdoor screen, for the ease of installing, the general body structure that adopts, as shown in Figure 1, a casing is exactly a display unit, desirable 16 * 16 (totally 256 points) of pixel count in the unit, 32 * 16 (totally 512 points) 64 * 48 (totally 3072 points) etc., a LED screen generally is made up of dozens or even hundreds of display unit.

Will carry out " bad point " after the LED screen is installed for the first time and detect, the LED screen after use a period of time also needs to go bad some detection, and so-called bad point is exactly the LED that barrier can not be luminous for some reason, and fault comprises that LED damages and the LED rosin joint.At present, the detection of the bad point of LED screen is a gordian technique, and particularly outdoor screen should disposablely as far as possible detect all bad points exactly, otherwise erecting frame is just found bad point after removing, and must rebuild erecting frame and repair bad point, and erected cost will increase.

At present, most LED product, bad point detects and can only navigate to the chip for driving level, promptly can only navigate to the some LED among the LED (being generally 16) that chip for driving drives.

Summary of the invention

The present invention aims to provide a kind of LED screen dead pixel detection method and used circuit thereof, and its bad point of LED screen of eliminating prior art in fact detects the limitation and the shortcoming that can only navigate to the chip for driving level.

Therefore, an object of the present invention is to provide a kind of LED screen dead pixel detection method, wherein only need to increase the signal lines of a unidirectional cascade, can guarantee bad point detect accurately navigate to single led.

Another object of the present invention provides the circuit that the bad point of a kind of LED of being used for screen detects, and makes it to carry out the bad point of LED screen and detects.

Other advantages of the present invention, purpose and characteristics are partly set forth in the following description, are conspicuous for having studied those of ordinary skills hereinafter.Can realize and obtain purpose of the present invention and other advantages by the structure that particularly points out in instructions and its claim and the accompanying drawing.

Realize purpose of the present invention, such as here enforcement and comprehensive description, a kind of LED screen dead pixel detection method is provided, comprising:

In each display unit of LED screen, provide bad-point detecting circuit;

Between display unit, adopt the series cascade type of drive that view data, data clock and field sync signal are provided;

It is characterized in that:

The signal lines of a unidirectional cascade is set between display unit;

Wherein send view data and data clock when detecting beginning, when the cycle of field sync signal be normal demonstration 2 times shield bad point according to the level detection LED of data clock and signal lines.

According to the present invention, the capacity of display of LED screen is M * N, M 〉=1 wherein, and N 〉=1, M, N are integer.

According to the present invention, the bad point of LED screen situation comprises that LED damages and the LED rosin joint.

According to the present invention, can utilize the Internet network to send the view data that detects usefulness, by Internet the testing result waveform is beamed back main control computer again, can realize the strange land detection.

The present invention also provides a kind of LED of being used for screen circuit that bad point detects, and comprising:

Frequency detection circuit, detection resistance, PMOS field effect transistor, differential operational amplifier, comparer, reference power supply, diode and driver, wherein

Field sync signal connects the frequency detection circuit input end, the grid of the output termination PMOS field effect transistor of frequency detection circuit.

Joint detection resistance between the source-drain electrode of PMOS field effect transistor, the two ends of detecting resistance connect differential operational amplifier;

The output terminal of differential operational amplifier is connected to the positive input of comparer;

The reverse input end of comparer connects reference power supply, and output terminal is connected to diode;

The other end of diode is connected to signal lines.

From the detailed description of the present invention below in conjunction with accompanying drawing, above and other purposes of the present invention, characteristics will be more obvious.

Description of drawings

Fig. 1 illustrates the LED display of being made up of a large amount of display units;

Fig. 2 illustrates the numbering of display unit;

Fig. 3 illustrates the cascade between display unit and the signal of bad-point detecting circuit;

Fig. 4 illustrates the field sync signal under normal displaying mode and the detecting pattern;

Fig. 5 illustrates DCLK and the DETECT signal that the cascade between display unit transmits;

Fig. 6 illustrates the output waveform of DCLK and DETECT signal and gives an example;

Fig. 7 illustrates the bad-point detecting circuit when LED divides into groups in the display unit.

Embodiment

Present embodiment is that 640 * 480 LED display is an example with the capacity of display, but is not limited to this situation, and for example can adopt the capacity of display is the LED display of M * N, M 〉=1 wherein, and N 〉=1, M, N are integer.In the capacity of display is 640 * 480 LED display, suppose to adopt 32 * 16 display unit, then full framely form, as shown in Figure 2 by 20 * 30=600 display unit.

View data RGB, data clock DCLK and field sync signal VSYNC etc. adopt the series cascade type of drive between 600 display units, press numeric order transmission among Fig. 2, as shown in Figure 3.

Below sketch the bad some detection process of LED display.

When LED display was in normal displaying mode, VSYNC was a positive pulse signal, and field frequency is 50Hz or 60Hz, as shown in Figure 4.When VSYNC is low level corresponding to the demonstration phase, promptly LED screen show luminous, when VSYNC is high level corresponding to blanking interval.

When LED display is in detecting pattern, when the cycle of field sync signal VSYNC is normal displaying mode 2 times, after detecting beginning, the bad point that each display unit carries out this unit successively by Fig. 2 sequence number detects, utilize ad hoc single cascade signal lines DETECT, display unit reads detection signal, and detection signal judges whether to exist bad point according to this from last (promptly No. 600).Notice that the DETECT input end of first display unit is by 1k Ω resistance eutral grounding (as shown in Figure 5), make that DETECT is 0V when being in normal displaying mode, its logic level is ' 0 '.

As shown in Figure 3, the bad-point detecting circuit in all display units is identical, is made up of frequency detection circuit 1, detection resistance 2, PMOS field effect transistor 3, differential operational amplifier 4, comparer 5, reference power supply 6, diode 7 and driver 8.

32 * 16 display unit comprises 512 pixels, and every pixel is made up of red, green, blue three-color LED, and like this, every display unit has 512 * 3 LED to need to detect, and full frame 600 display units have 600 * 512 * 3=921600 LED to need to detect.Adopt constant-current driven chip (as TB62706) driving LED, the electric current that flows through LED when LED is luminous is constant, can be set in 5～90mA scope, generally get tens mA, each display unit is by independently 5V Switching Power Supply power supply, output current reaches tens～tens amperes, by power supply cabling, PCB layout, the LED total current is provided by the output branch road of PMOS pipe and detection resistance, but not the LED electric current is provided by other branch road, the PMOS pipe can adopt many in parallel uses, and to improve output current and to reduce PMOS pipe conducting resistance, total conducting resistance requires to reach m Ω level.

When being in normal displaying mode, frequency detection circuit is output as 0V, the conducting of PMOS field effect transistor, and the 5V power supply has the ability to provide big electric current to LED.Otherwise when being in detecting pattern, frequency detection circuit is output as 5V, and the PMOS field effect transistor is ended, owing to detect the metering function of resistance 2, the 5V power supply can only provide the electric current of tens mA to LED, detects resistance 2 values 10 Ω.

Detect beginning, main control computer sends and to make full frame every luminous view data and data clock DCLK of LED one by one, DCLK time clock number equals full frame LED number, promptly 921600, detect beginning at the 1st rising edge place of DCLK, when detected LED is luminous, tens mA current flowing resistances 2 are arranged, and produce the pressure reduction of hundreds of mV, amplify through differential operational amplifier 4, and convert single-ended signal to, be input to the normal phase input end of comparer 5, this signal is greater than reference voltage 6, and making comparer 5 output terminals is 5V, making DETECT by diode 7 is 4.3V, and its logic level is ' 1 '.When detected LED because of self damage or rosin joint when not luminous, there is not pressure difference signal (or very little pressure reduction) on the resistance 2, the output voltage that makes operational amplifier 4 is less than reference voltage, comparer 5 output terminals are 0V, diode 7 ends, DETECT is pulled down to 0V by the 1k Ω resistance among Fig. 5, and its logic level is ' 0 '.The logic level of DCLK signal and DETECT is sent to the output terminal of last display unit (No. 600 display units) by cascade, detects this output end signal and can judge whether to exist bad point, as shown in Figure 6.

With full frame 921600 LED ordering, main control computer can be known the LED sequence number that current detection arrives by to the DCLK counting, obviously, can accurately locate LED by the LED sequence number, determines that it belongs to which number display unit and the position in display unit.From last display unit promptly No. 600 display units extract DCLK and DETECT signal, when detecting a certain sequence number LED, be ' 0 ' if detect DETECT, illustrate that this sequence number LED is a bad point, as shown in Figure 6.

In order to reduce the load of PMOS pipe 2, LED in each display unit can be divided into groups, every group has relevant detection resistance, PMOS pipe and calculus of differences discharger, pass through PCB layout, make every group of LED provide electric current by on the same group PMOS pipe, each is organized the differential operational amplifier output terminal and inserts the normal phase input end of comparer 4 through diode, and this normal phase input end is by a 1k Ω resistance eutral grounding, each organizes a shared frequency detection circuit, as shown in Figure 7.

If the view data that will detect usefulness sends to the LED display in strange land by the Internet net, the testing result waveform is beamed back main control computer by the Internet net again, can accurately orient out of order LED by analysis waveform.

Claims

1. LED screen dead pixel detection method comprises:

In each display unit of LED screen, provide bad-point detecting circuit;

It is characterized in that:

The signal lines of a unidirectional cascade is set between display unit;

Wherein when detecting beginning, send view data and data clock, and the cycle that makes field sync signal 2 times during, shield bad point according to the level detection LED of data clock and signal lines for normal the demonstration.

2. method according to claim 1, wherein the capacity of display of LED screen is M * N, M 〉=1 wherein, N 〉=1, M, N are integer.

3. method according to claim 1, wherein the bad point of LED screen situation comprises that LED damages and the LED rosin joint.

4. method according to claim 1 wherein utilizes the Internet network to send the view data that detects usefulness, beams back the testing result waveform by Internet again.

5. one kind is used for the circuit that the bad point of LED screen detects, and comprising:

Field sync signal connects the frequency detection circuit input end, the grid of the output termination PMOS field effect transistor of frequency detection circuit;

The PMOS field effect transistor links to each other with the positive pole of LED with the output branch road that detects resistance, is the LED power supply;

The other end of diode is connected to signal lines;

Be connected with driver on the signal lines, the detection signal level that each display unit is exported passes to the signal lines of next display unit by driver.