Design of a Digital Integrated Circuit Test System

With the widespread application of digital integrated circuits, test systems are becoming more and more important. In the networked integrated circuit reliability test and test system project, it is necessary to test some military digital integrated circuit chips with a wide voltage range, but the voltage range that can be measured by the common small and medium-sized test systems on the market cannot meet the requirements, and the large test system is expensive. This article introduces a digital integrated circuit test system developed for this project, which can measure voltage range up to ±32V, is easy to use, and has low cost.

Test system structure and working principle
The system needs to perform functional tests and DC parameter tests on integrated circuits. Functional tests apply set test vectors to the input of integrated circuits, detect and compare the test vectors output by them, and thus verify whether the logical function of the device is normal. DC parameter tests verify the electrical parameters of integrated circuits in the form of voltage or current, and high test accuracy must be guaranteed.

In order to make the system structure flexible and easy to upgrade, a bus-based modular structure is adopted, as shown in Figure 1. The system consists of a channel board, a digital power supply board (DPS board), a precision measurement unit board (PMU board), a test interface board, a single-chip system board (CPU board) and a bus board. Each board is connected and exchanges data through the bus board. The DPS board provides power and voltage reference to the test system and provides operating voltage to the device under test (DUT). The function of the test interface board is to provide a test interface to the DUT and power on the device.

During the functional test, the computer sends the pre-generated test vectors to the MCU system. The MCU controls the channel board to convert the signal level to the level required for the test, and applies the converted timing waveform to the input pin of the device under test (DUT). Then the output of the DUT is detected, and the test results are transmitted to the MCU through the bus for judgment and processing. The DC parameter test process is to apply DC parameter test conditions to the DUT and realize the precise measurement of the DUT DC parameters through the PMU.

Channel board The
channel board has two functions. One is to synthesize the test code into the final test signal and apply it to the DUT. The other function is to analyze and compare the return signal of the DUT and return the comparison result to the single-chip computer system through the bus. The structural design of the channel board is shown in Figure 2. The control bus sets and controls the address of the DUT pin through the decoding and logic control unit, and the pin drive and control unit drives and controls the relay array to complete the input and output functions of the DUT pin data. VIH (VIL) is the high (low) drive level required for the test set by the DPS board. The bus sends the test vector pre-generated by the program, the level conversion and drive unit converts the test vector into a test timing waveform with a set level, and the pin drive and control unit controls the relay array to apply the waveform to the input pin of the DUT. The pin level comparison unit detects the output pin signal level, performs a logical comparison with the expected output data, and transmits the comparison result back to the lower computer. During the DC parameter test, the relay control unit connects the DUT on the test interface board to the PMU, and uses the PMU module to achieve precise measurement of voltage or current. The level conversion part of the channel board is designed as shown in Figure 3. After the circuit is stable, when there is no signal input, V1 is slightly higher than V2, and the output is VIH; when the TTL input is low level, since the capacitor voltage cannot change suddenly, V1 is lower than V2, the comparator flips, 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 charging and discharging of the capacitor, the output level cannot be maintained at a low level for a long time, and selecting a large enough capacitor can meet the test needs of this system.

[page]

Precision measurement unit
The precision measurement unit (PMU) is the basic unit of the system for precise measurement of DC parameters. The system uses 12-bit A/D and D/A converters, grading and Kelvin connection to achieve high-precision measurement. PMU can realize two working modes: pressure measurement (FVMI) and current measurement (FIMV). The principle diagram of pressure measurement in PMU is shown in Figure 3. Vin is used as input, and the device applies voltage Vp to DUT through the test interface board. The test current I can be obtained by testing Vout. According to the circuit diagram, it can be calculated:

Thus, according to formula (1), by controlling Vin, a set voltage Vp can be applied to the device under test, 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, the PMU can detect the load characteristics and static power consumption of the device by testing the high/low level of the output, the leakage current of the input, the output short-circuit current, and the static power consumption current.

In order to make the PMU have a sufficiently wide test range and test accuracy, A3 uses the high-voltage operational amplifier OPA445 with a FET input stage, which is connected as a follower, so that the current flowing into A3 is extremely small, ensuring the accuracy of the current test, and its high-voltage characteristics ensure the test range of the PMU.

Software part
The function of the software part is to control the test system with a computer and provide users with a friendly and easy-to-operate interface. The lower computer software is written in C51 program, and the main program flow chart is shown in Figure 4. The upper computer is written in VC#.net. The main work of the lower computer software is to set the system voltage and test conditions according to the test parameters transmitted by the upper computer, load the test vector to send the input waveform to the DUT pin, and then test the output waveform data, send it to the upper computer and store it in the database.

The actual application of users proves that the system is cost-effective and the test is accurate.