A 17.5-fJ/bit Energy-Efficient Analog SRAM for Mixed-Signal Processing

An energy-efficient analog SRAM (A-SRAM) is proposed to eliminate redundant analog-to-digital (A/D) and digital-to-analog (D/A) conversion in mixed-signal systems, such as neuromorphic chips and neural networks. D/A conversion is integrated into the SRAM readout by charge sharing of the proposed split bitline (BL). Also, A/D conversion is integrated into the SRAM write operation with the successive approximation method in the proposed input-output block. Also, a configurable SRAM bitcell array is proposed to allocate the converted digital data without unfilled bitcells. The multirow access decoder selects multiple bitcells in a single column and configures the bitcell array by controlling the BL switches to split BLs. The proposed A-SRAM is implemented using the 65-nm CMOS technology. It achieves 17.5-fJ/bit energy-efficiency and 21-Gbit/s throughput for the analog readout, which are 64% and 1.3 times better than those of the conventional SRAM followed by a digital-to-analog converter (DAC). Also, the area is reduced by 91% compared with the conventional SRAM with analog-to-digital converter (ADC) and DAC.