Development Of OLED Test System

OLED is the abbreviation of Organic Light Emitting Diode. As a displaydevice, OLED have the advantage of self-luminous, thin and light, highbrightness, wide viewing angle, low power and rapid response, etc. As alight source, OLED has the advantage of light-emitting softly, diffusedsurface light source, easier to achieve white light, which can be madeinto any shape and so on. So, OLED research gets more and more popularin recent years. In the research process, you need to measure variousparameters on the OLED device, and compare the related data to guidepractice.In CHINA, most of OLED measurement systems are in the method ofbuilding-block, they respectively purchase power supply, light intensitymeasuring equipment, and spectral measurement equipment, etc, fromdifferent manufacturers, and then collect those devices together to forma measurement system. It is very inconvenient. And it is a real challengefor OLED-related professional researchers, who need to not only read someoperating manuals which are different industry they are in, but also mayneed to write some program out of their majors. It is a very large obstacleof research working.In this article, according to the problems of the current OLEDmeasurement system and the measuring requirement of the OLED, we havedeveloped a set intelligent OLED measurement system, combining with thepower electronics technology, optical technology, microcontrollerapplication technology, software engineering and sensor technology, etc.This article focuses on discussion about the hardware design of the testsystem, and introduces the software briefly. The new measurement systemwe developed would realize the intelligent and multifunctional of OLEDmeasurements, simplify the operation process, and improve the workingefficiency. This article focuses on the hardware aspects of the OLED measurementsystem. The hardware mainly includes two parts, i.e. the master controllerand the slave controller. According to their different functions the slavecontroller can be divided into multi-functional measurement unit, colormeasurement unit and lifetime measurement unit. The master controller hasa core of C8051F340, connected to the computer through the USB interface,through two different UART interface connected to the slave controllerand the next node of the master controller. We take RS-485as electricalcommunications protocol between the master controller and the next nobleof the master controller. The master controller offers power supply tothe slave controller, and integrates the temperature controller of thesamples. The C8051F340in the master controller also needs to monitor theoperation of the entire system to make the appropriate response based onthe different events, at the same time communicates to the commands fromthe computer to the slave controller, and passes the relevant data fromthe slave controller to the computer. Multi-functional measurement unithas a core of C8051F350, the use of the H-bridge circuit achieves thediversification of the OLED drive, which can optimize the application ofOLED. The multi-functional measurement unit by adding filters in frontof the BPW34S photocell to achieve high accuracy measurement of theintensity of visible light, which can characterize the light-emitting ofan OLED. Color measurement unit has a core of C8051F001, its OLED-driverare identical to the multi-function measurement unit. Just the opticalsensor uses a simple TCS3200color sensor to measure the light color ofOLED. The infrared response is relatively strong due to the TCS3200internal are actually silicon photodiodes, but the sensor itself is noinfrared suppression filter, so the color measurement unit uses infraredsuppression filter to prevent any possible infrared interference colormeasurement. The lifetime measurement unit is a simplified version of themulti-functional unit, most hardware are identical to multi-functionalmeasurement unit, but OLED drive power has been changed from the linear power supply into a switching power supply in order to improve efficiency,furthermore the expensive filters in front of the silicon photocell arecancelled. Because, in the processing of lifetime measurement, theaccurate value of the OLED light intensity is not essential, we just needto measure the relative changes of light intensity, then accuratelymeasure or estimate the luminescence lifetime of OLED devices. All thethree different functions of the slave controller can control the sampletemperature, the temperature control actuator uses H-bridge to controlthe semiconductor cooling piece, and achieve function switching of thecooling and heating. The slave controller uses a PID algorithm to controlthe sample temperature. The temperature sensor uses TMP275, a digitalinterface and high-precision temperature sensor.For the measurement system, both the master controller and slavecontroller software are written in C-language, it uses the KEILdevelopment environment, achieve the test process automation. The mastercontroller software plays the role of monitoring the system status andcommand and data transmission. The slave controller software controls alltest parameters, complete the measuring process, and data collection.The PC software is written in Visual Basic, it calls the NI MeasurementStudio controls library and USBXpress of dynamic link libraries tosimplify the design of the curve display and USB interface part of theprogram. The PC software can set parameters for all controlled units, andsave the measured sampled data to the appropriate file. In the measurementprocess, the users only need to set the interested parameters, the filename and path, then can start the sample measurements. All measuringprocess are done automatically, greatly improves the efficiency of themeasurement.