| Due to the great progress with Light Emitting Devices (LED), as a result the instrument for the measurement of LED's parameters should be improved simultaneously. The current-voltage (I/V) characteristic of devices is a basic and main one among all the parameters of LED, it also is important to reveal the operating mechanism of devices and evaluate the device performance. And accompanied with the improvement of the device efficiency, the weak current-low operating voltage characteristic is helpful to analyze the mechanism of the carriers generation and carrier migration. At the same time, because of the utilization of microprocessor and computer, the measurement instruments and systems is becoming to automation, standardization and can be connected to Internet for data exchange or share. In the thesis, an automatic measure system for I/V characteristics of LED is introduced, this system can measure the weak-current with high accuracy and can be operated conveniently and quickly. The whole system compose of a programmable voltage source, a programmable weak-current measure device, computer with the measure and control software. Computer can communicate with the programmable voltage source and the programmable weak-current measure device through the standard RS-232 interface, the measure and control software can send the relative instructions to control the voltage source and the creak-current measure device, according to the requirement of I/V characteristic, then an output voltage is stressed on the LED from the voltage source, at the same time this system acquire the original data of the LED's current, after the data is processed by computer software, finally this system get the I/V result, and the data can be displayed in a figure or be outputted as a text file. The programmable Voltage Source is made of microprocessor 89c51, voltage reference AD780, D/A converter AD669, scale and output current expanding circuit, RS-232 interface circuit and other affiliated circuits, in which, the scale and output current expanding circuit include operational amplifier OPA445 and some relays with optocouplers as isolators. While measuring, the computer software send instructions about measure and some parameters to microprocessor through RS-232, then the microprocessor connect different voltage reference to D/A converter, let the D/A converter and scale/output current expanding circuit output a voltage to the object device (LED). The main performance of the programmable Voltage Source is as following: four scales is 1~100mV, 0~1V, 0~10V and 0~50V respectively; the resolution of each scale is 1μV, 10μV, 0.1mV and 1mV; the accuracy of each scale is 2%R±10d, 0.1%R±5d, 0.02%R±5d and ±0.02%R±5d; the minimum voltage step is 2μV, 15μV, 0.15mV and 0.75mV. When an operating voltage is applied on the LED, the programmable weak-current measure device can measure the original data on current and upload these original data to computer. The measurable current is divided into five scales in this programmable weak-current measure device: 100pA, 100nA, 10μA, 1mA and 100mA, their resolution of each scale is 1fA, 1pA, 100pA, 10nA and 1μA, their accuracy of each scale is 1%R±10d, 0.2%R±5d, 0.1%R±5d, 0.1%R±5d and 0.1%R±5d, respectively. The hardware of this weak-current measure device is made of microprocessor 89C51, weak-current amplifier and gain automatic-exchange circuit, A/D converter AD7710, RS-232 interface circuit and other affiliated circuits. After microprocessor measured the original data of current using the measurement model, then upload them to computer. There is an automatic text software (ATS) in the computer, and this ATS can process the original data to acquire accurate current data when the random noise and jam signal exist, finally get the device I/V curve. ATS is built by software Testpoint from CEC company, the measure language of ATS is the Standard Commands for Programmable...
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