Program Design Of TCAM Memory Bist

With the rapid development of the chip industry,memory is widely used in chips,and a large amount of stored content has brought huge challenges to fast retrieval.The method of using software to search will bring huge memory occupancy problems and limit the development of network equipment.Therefore,a method of using hardware search has emerged.The tristate content addressable memory is improved from the traditional content addressable memory,and the advantage of TCAM(Ternary Content Addressable Memory)compared to CAM(Content Addressable Memory)is that it cannot only implement retrieval functions,but also perform fuzzy matching,and the application scenarios are more extensive,but it also brings more complex transistor structures,which puts forward higher requirements for the DFT of the chip.On the one hand,it is very difficult and impractical for the limited I/O ports to directly access the TCAM unit for testing.On the other hand,with the development of Moore's Law,the rapid progress of IC design and manufacturing process,the density of transistors on the chip the growth of multiples has also led to an increasing possibility of failures on the chip.TCAM is essentially a type of memory with retrieval function,therefore,you can consider using the memory built-in self-test technology for testing.The principle of MBIST technology is to insert a test circuit into the original functional circuit.The test vector is automatically generated by the inserted test circuit and input into the functional circuit.The test circuit will capture the response generated by the functional circuit and compare the results,and analyze the functional circuit based on the response.Whether there is a failure,the purpose of automatic testing inside the chip is achieved.It is only necessary to input the instruction to start the test and capture the information of the test state from the outside,which greatly reduces the requirements for external equipment.This thesis focuses on this research goal of TCAM Memory Bist circuit program design,introduces the development process and research status of TCAM and MBIST technology,clarifies the problems faced by TCAM testing,and shows the necessity and rationality of MBIST's application in TCAM testing.Then,according to the similar characteristics of the TCAM storage structure and the SRAM structure,combined with the transistor failure model,the TCAM failure analysis is performed to determine the type of failure that may exist in the TCAM.The main work of this thesis is to design a special test algorithm for testing the TCAM storage structure based on the SRAM test algorithm,and design a comparison algorithm for the TCAM matching structure for testing,that is,design a two-step algorithm for the overall TCAM Tested and designed the MBIST circuit to realize the algorithm and verification results,and achieve the purpose of automatic test on the TCAM in the chip.Then a kind of bypass logic of Memory Bist is designed to reduce the adverse effect of the insertion of the test circuit on other subsequent tests.Finally,the design circuit is simulated and analyzed.The simulation results show that the MBIST circuit designed in this thesis successfully achieves the purpose of testing the TCAM,and the bypass logic ensures that the normal function of the chip is not affected after the MBIST circuit is inserted.Although the MBIST circuit will increase the chip area,it has the advantages of wide test coverage and high-test efficiency,so it is a necessary research direction for the memory test field.