The observation information of the voltage test is the logic output value of the circuit under test. This method obtains the logical output value of the corresponding circuit by inputting different test vectors to the circuit, and then compares the collected logical output value of the circuit with the expected logical output value of the circuit corresponding to the input vector to achieve the purpose of detecting whether the circuit can achieve the expected logical function in the actual operating environment. This method is simple but not suitable for large-scale integrated circuits with more redundancy.
If the defect occurs in the redundant part, it cannot be detected. Moreover, when the circuit scale is large, the test vector set will also multiply, which will directly lead to problems such as difficult generation of test vectors and low diagnostic efficiency. In addition, if the fault only affects the circuit performance rather than the circuit logic function, the voltage diagnosis cannot be detected. Since the logic value of the voltage output by the integrated circuit is not necessarily related to all nodes in the circuit, the voltage test cannot detect the non functional failure of the integrated circuit.
Therefore, in the early 1980s, the diagnosis technology based on the power supply current of integrated circuits was proposed. The power supply current is usually directly or indirectly related to all nodes in the circuit, so the current based diagnosis method can cover more circuit faults. However, the current diagnosis technology is not proposed to replace the voltage test, but to supplement it to improve the detection rate and coverage rate of fault diagnosis. Current diagnosis technology is divided into static current diagnosis and dynamic current diagnosis. The core of quiescent current diagnosis technology is to compare the power supply current of the circuit under test with the preset threshold value to determine whether the circuit under test has fault.
It can be seen that the selection of threshold is the key to determine the detection rate of this method. The early quiescent current diagnosis technology adopted a fixed threshold, but the fixed threshold can not adapt to the development of integrated circuit chips to deep submicron.
Therefore, later generations have made continuous improvement in the static current detection method, and successively proposed differential static current detection technology, current ratio diagnosis method, static current detection technology based on clustering technology, etc. Dynamic current diagnosis technology came out in the 1990s. The dynamic current can directly reflect the switching frequency of the internal voltage of the circuit during the state transition. The detection technology based on dynamic current can detect the faults that cannot be detected by the previous two methods, and further expand the fault coverage.
With the development and maturity of intelligent technology, integrated circuit chip fault detection technology is also moving towards the intelligent trend.