摘要
Abstract
Computing-In-Memory(CIM)based on Spin Transfer Torque Magnetic Random Access Memory(STT-MRAM)is expected to be an effective way to overcome the"memory wall"bottleneck.This paper proposes a high-energy-efficient CIM design scheme for STT-MRAM in the time domain:a custom series-connected memory cell structure,through the series connection of transistors and complementary MTJ design,forms a magnetic resistance chain of multiple rows of memory cells in the computing mode,and combines a time-domain conversion circuit to convert the resistance value into a pulse delay signal.Further,a complementary series array architec-ture is designed,generating differential time signals through the separate storage of positive and negative weights to support signed num-ber calculations.In terms of quantization circuit design,a Successive Approximation Register(SAR)Time-to-Digital Converter(TDC)is proposed,which adopts a structure combining a voltage-adjustable delay chain and a flip-flop.To achieve multi-bit multiply-accumu-late operations,a signed number weight encoding scheme and a digital post-processing architecture are proposed.Through encoding weight mapping and digital shift-accumulate algorithms,the 8-bit input and 8-bit weight multiply-accumulate operation is decomposed into low 5-bit time-domain calculation and high-bit digital-domain calculation,outputting a 21-bit full-precision result.Based on the 28 nm CMOS process,the layout design and post-simulation were completed.At 0.9 V voltage,a 9-bit multiply-accumulate operation with a resolution margin of 270 ps was achieved,with an energy consumption of only 16 fJ per operation.The designed 5-bit SAR-TDC achieves high linearity conversion from time to digital.A 9 Kb time-domain CIM macrocell with an area of 0.026 mm2 was designed,in-cluding a memory cell array,SAR-TDC module,computing circuit,and read-write control circuit.The macrocell can achieve energy ef-ficiencies of 26.4 TOPS/W and 42.8 TOPS/W when performing convolutional layer and fully connected layer calculations,respectively,while achieving 8-bit precision calculation and an area efficiency of 0.523 TOPS/mm2.关键词
磁性随机存储器/存内计算/时间域计算/逐次逼近型TDCKey words
magnetic random access memory/computing-in-memory/time-domain computing/successive approximation register time-to-digital converter分类
信息技术与安全科学
