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In multiple device tests, such as those that involve burn-in, multiple parts are measured simultaneously over a specified period. A continuous current flow is usually mandatory to drive the DUTs, but multiple light detectors may be multiplexed to a current meter through a switching system. The appropriate choices for switching system and meter will be dictated by the dynamic range of the currents of interest.

在多器件测试情况下，例如涉及老化的测试，我们要在规定的时间内同时测量多个部件。驱动DUT通常需要连续的电流，但是多个光学探测器可以通过开关系统[1]复用一个电流计。用户可以根据所测电流的动态量程选择合适的开关系统[2]和电流计[3]。

Various switch options are applicable to testing multiple LEDs. For example, the Model 3706 System Switch/Multimeter has six switch module slots, so it can handle up to 576 multiplexed channels or 2688 matrix cross-points. Like Series 2600A instruments, it includes an on-board TSP and a TSP-Link® inter-unit communication/triggering bus, which allows integrating these instruments into a system quickly and easily. This integration allows tight synchronization of operations between the instruments and lets them operate from a single test script. Figure 3 illustrates a three-LED device test system with one photodiode (PD) channel.

多LED器件测试可以选择多种类型的开关。例如，3706型开关/万用表[4]具有6个开关模块插槽，因此它最多可支持576个复用通道或者2688个矩阵交叉点。与2600A系列[5]仪器类似，它也内置了板载TSP和TSP-Link®设备间通信/触发总线，利用这套总线可以快速而方便地将这些仪器集成到一个系统中。这种集成支持紧密同步的仪器间操作，并且能够让它们在一个测试脚本的控制下进行操作。图3给出了具有一个光电二极管（PD）通道的三LED器件测试系统结构。

Figure 3. Block diagram with scalable Model 2602A SourceMeter channels for an LED array test system.

2602A通道A、2602A通道B、2602A通道A、2602A通道B、TSP-Link

图3. 采用可扩展2602A数字源表通道构建LED阵列测试系统的模块图

Minimizing LED Testing Error

Common sources of measurement error in LED production testing include lead resistance, leakage current, electrostatic interference, and light interference, but junction self-heating is one of the most significant error sources. The two tests susceptible to junction heating are the forward voltage and leakage current tests. As the junction heats, the voltage will drop or, more importantly, the leakage current will increase during the constant voltage test. Therefore, it is important to shorten the test time as much as possible without sacrificing measurement accuracy or stability.

[1] 开关系统：http://www.keithley.com.cn/products/semiconductor/semiswitchsys

[2] 2790开关系统：http://www.keithley.com.cn/products/localizedproducts/dmm/2790

[3] 如何使用库仑计测量弱电流及优点：http://www.keithley.com.cn/llm/a/15.html

 [4] 3706型开关：http://www.keithley.com.cn/products/localizedproducts/switching/3706

[5] 2600A系列仪器：http://www.keithley.com.cn/products/semiconductor/sourcemeasureunits/series2600sys/?mn=2612A