Important electrical indicators in DC production testing of OLED displays (Part 2)-EEWORLD

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Testing a display consisting of an array of pixels requires automated signal routing to switch power to the pixels under test. A GPIB-controlled switch system, such as the 7002, can control the internal 2D relay switch scanner card. The block diagram in Figure 1 shows how two multiplex scanner cards can be connected to a display under test to form a 40×40 array. In this example, only one Model 2400 SourceMeter was used, and a Model 7015-C 1×40 two-pole solid-state relay multiplexer card was also used. The 7015-C is a solid-state relay switch with a switching time of less than 500 microseconds to ensure maximum test throughput. When using the Model 2400 SourceMeter, the bias current of each scanner card is much less than 1nA, allowing leakage current measurements to be accurate to 10-8-10-9A. In a test system using only one source meter, all relays connected to rows and columns on the scan card only need to be single-pole, connecting the "high" or "low" end to the display rows and columns.

Figure 3.jpg

Figure 1. Connection diagram using two 7015-C scanner cards, a 40×40 sample display, and a 2400 source meter.

Figure 4.jpg

Figure 2. Connection diagram for using two 7015-C Scanner Cards and a 40×80 sample display, a) using two Model 2400 SMUs and b) using four Model 2400 SMUs.

Building a test system with two or four SMUs instead of one ensures higher throughput and more efficient use of switch resources. Figures 2a and 2b show two and four Model 2400 SMUs connected to a display through a 7015-C 1×40 multiplexer card. When two or four SMUs are used, both the “high” and “low” sides of the relays are connected to the columns of the display. This configuration allows two or four pixels to be tested simultaneously during each test cycle. Each 7015-C card contains four groups of “A”, “B”, “C”, and “D”; or it contains four independent, two-pole 1×10 multiplexer cards. When two source meters are used, the four groups of "high" inputs are connected together and connected to source meter No. 1; the four groups of "low" inputs are also connected together and connected to source meter No. 2. For a system using four source meters, the "high" inputs of groups A and B need to be connected together, and the "low" inputs of groups A and B need to be connected together. Then connect the two 1×20 splitters to source meters No. 1 and 2. The same connection is used for groups C, D, and source meters No. 3 and 4. The number

of scan cards required for an application depends on the size of the display, that is, the number of pixel rows and pixel columns. With the 7015-C card, one scan card is required for every 80 columns and one scan card is required for every 40 rows. The 7002
switch board is specified to accommodate 10 cards; if more than 10 scan cards are required, an additional 7002 switch board can be added to the system.

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