Design of a Test System for Digital Integrated Circuits

Summary:The working principle and composition of a test system for digital integrated circuits are introduced. The hardware and software design scheme of the system is presented. The system is based on a custom bus structure and can test a wide range of levels.

　　Key word:Digital integrated circuit test function test channel board precision measurement unit

With the wide application of digital integrated circuits, test systems become more and more important. In the reliability test and test system project of networked integrated circuits, it is necessary to test some military digital integrated circuit chips with wide level range. The common small and medium-sized test systems in the market can not reach the required level range, while large test systems are expensive. This paper introduces a digital integrated circuit test system developed for this project. The test level can reach (+) 32V, which is easy to use and low in cost.

　　Test System Structure and Working Principle

The system requires functional testing of integrated circuits and testing of DC parameters. Functional testing verifies the logic function of the device by applying set test vectors to the input of the integrated circuit, detecting and comparing the test vectors of its output. DC parameter test is to verify the electrical parameters of integrated circuits in the form of voltage or current, to ensure a higher test.

In order to make the system structure flexible and easy to upgrade, a bus-based modular structure is used, which is shown in Figure 1. The system consists of a channel board, a numerical control power board (DPS board), a precise measurement unit board (PMU board), a test interface board, a single-chip computer system board (CPU board) and a bus board. Each card connects and exchanges data through the bus board. The DPS board provides power supply and voltage reference for the test system and operating voltage for the DUT. The function of test interface board is to provide test interface for DUT and power up the device.

During the function test, the computer sends the pre-generated test vectors to the single-chip computer system. The single-chip computer controls the channel board to convert the signal level to the level required for the test, and applies the converted time series waveform to the input pin of the device to be tested (DUT), then detects the output of DUT, and passes the test result to the single-chip computer through the bus for judgment and processing. DC parameter testing process is to apply DC parameter testing conditions to DUT, and to achieve precise measurement of DUT DC parameters through PMU.

　　Channel board

Channel board has two functions: one is to apply the final test signal of test code synthesis to DUT, the other is to analyze and compare the return signals of DUT, and return the comparison results to single-chip computer system through bus. The structure design of the channel plate is shown in Figure 2. The control bus sets and controls the address of the DUT pin by decoding and logic control unit, and the pin drive and control unit drive and control the relay array to complete the input and output functions of the DUT pin data. VIH (VIL) is a high (low) drive level required for testing generated by DPS board settings. The bus sends test vectors pre-generated by the program, and the level conversion and drive unit converts the test vectors to test sequence waveforms at set levels. The pin drive and control unit control relay array apply the waveforms to the input pins of the DUT. The pin level comparison unit detects the signal level of the output pin, and logically compares the result with the expected output data and returns the comparison to the lower computer. During DC parameter testing, the relay control unit connects the DTU on the test interface board to the PMU, and uses the PMU module to precisely measure the voltage or current. The level conversion section of the channel board is designed as shown in Figure 3. After the circuit is stabilized, when there is no signal input, V1 is slightly higher than V2, and the output is VIH. When the TTL input is at low level, the V1 is lower than V2 because the capacitance voltage cannot change abruptly, the comparator is flipped and the output is VIL. When the TTL input is high level, similarly, V1 is slightly higher than V2, and the output is VIH. Due to the capacity charging and discharging, the output level cannot be kept at a low level for a long time. Selecting a large enough capacity can meet the test needs of the system.

　　Precision measurement unit

Precision Measurement Unit (PMU) is the basic unit for precise measurement of DC parameters. The system uses 12-bit A/D and D/A converters, grading and Kelvin connection to achieve high measurement. PMU can work in two ways: pressure flow measurement (FVMI) and flow pressure measurement (FIMV). The schematic diagram of pressure flow measurement in PMU is shown in Figure 3. Vin is used as input, the device applied voltage Vp is applied to DUT by the test interface panel, and the test current I can be obtained by testing Vout. Based on the circuit diagram, it can be calculated that, according to formula (1), the set voltage Vp can be applied to the device under test by controlling Vin, and according to formula (2), the current I flowing through the pin of the device under test can be calculated by testing Vout.

In DC parameter testing, PMU can detect load characteristics and static power consumption of components by testing output high/low level, input leakage current, output short circuit current and static power consumption current.

In order to make the PMU have a sufficiently wide test range and test, A3 uses a high voltage operational amplifier OPA445 with FET input level, which is connected with a follower, so that the current flowing into A3 is minimal, which ensures current test, and its high voltage characteristics ensure the test range of PMU.

　　Software section

The function of the software part is to use the computer to control the test system and to provide a friendly and easy-to-operate interface for users. The lower computer software is written in C51 program, and the main program flowchart is shown in Figure 4. The upper computer is written with VC#.net. The main work of the lower computer software is to set the system voltage and test conditions according to the measured parameters transmitted by the upper computer, load the test vector and send the input waveform to the DUT pin, then test the output waveform data, send it to the upper computer and store it in the database. User's practical application proves that the system has high performance-price ratio and accurate test.

　　Reference

[1].PMUdatasheethttp://www.dzsc.com/datasheet/PMU_1198106.html.
[2].TTLdatasheethttp://www.dzsc.com/datasheet/TTL_1174409.html.
[3].OPA445 Datasheethttp://www.dzsc.com/datasheet/OPA445_1056277.html.
[4]. Chen Hui Digital Integrated Circuit Test System 2 OPA445 Data Manual Burr Brown Company

Source:Xiang Xueqin