Research On Radiation-hardened Coding Technology Of Memory

In the process of exploring space,SRAM memory in spaceborne systems is highly susceptible to single event effect.To solve this problem,people usually use error correction code circuits to reinforce the memory.With the shrinking of integrated circuit process size,the impact of single event effect has changed.The specific performance is the occurrence of multi-bit flip and the improvement of the sensitivity of the circuit to SET.In order to ensure the normal operation of the spaceborne system,it is of great significance to carry out further research on error correction coding.For the problem of multi-bit flipping,this paper proposes two new error correction codes.First,the NHVD code is proposed based on the HVD code.In the NHVD code,by proposing a new coding method,the number of generated parity bit is reduced from 50 to38,and by proposing a method for directly positioning the flip point,the number of iterations of the decoding operation is reduced from 36 to 15.The error correction capability of the NHVD code is consistent with the HVD code,which can correct the 3-bit random error of the data bit and detect odd bits error of the parity bit in one group.Then to improve the error correction ability of the parity bits,this paper proposes the NHVD-H code which uses the Hamming code and intra-code interleaving to reinforce the parity bit of the NHVD code.After reinforcement,it can achieve 3-bit correction and 5-bit detection for parity errors.This paper carries out circuit design and function verification for theNHVD-H code.First,the circuit design is completed,and the critical path delay is 9.62ns under the process of SMIC 130nm.Then,behavioral level simulation is performed using the modelsim,and the circuit successfully implements detection error correction for all 8000 data.Finally,board level verification is performed using the CycloneII development board.And through the online debugging of SignalTap?,the FPGA function is normal,which proves the reliability of the circuit.For the increase of circuit sensitivity to the SET,in this paper,the SET effect simulation and reinforcement design of the codec circuit of error correction code is carried out.The simulation results for the complete circuit show that a single pulse injection may cause multiple output changes,resulting in codec exception.It also show that the coding circuit is more sensitive to the SET effect than the decoding circuit,which is explained by the principle of logical shielding.The simulation results for the simplified circuit show that the pulse capture window increases with the increase of LET,and the pulse current can affect the output when LET is 5 MeV·cm²·mg^-1.The capture of the pulse at the output is proportional to the clock frequency,but independent of the logic chain length of the circuit.In order to improve the reliability of codec circuit,this paper reinforces the codec circuit.The simulation shows that the maximum pulse width that can be filtered out by the reinforced circuit is 0.82 ns,and it can filter out the generated pulse when the LET is 100MeV·cm²·mg^-1.In this paper,the proposed NHVD-H code and Hamming code circuit are added to the simplified spaceborne system and carried out simulation.The pulse injection of the SRAM shows that the NHVD-H code is running normally in the system.Compared with the Hamming code which can only correct one bit error,the NHVD-H code completely avoids system errors in the error of three or less bits.The pulse injection of the codec circuit shows that the reinforcement design of the circuit successfully prevents the influence of the particle bombardment on the codec circuit and improves the reliability of the error correction code.