A Sparse Coding Neural Network ASIC With On-Chip Learning for Feature Extraction and Encoding

Hardware-based computer vision accelerators will be an essential part of future mobile devices to meet the low power and real-time processing requirement. To realize a high energy efficiency and high throughput, the accelerator architecture can be massively parallelized and tailored to vision processing, which is an advantage over software-based solutions and general-purpose hardware. In this work, we present an ASIC that is designed to learn and extract features from images and videos. The ASIC contains 256 leaky integrate-and-fire neurons connected in a scalable two-layer network of 8 × 8 grids linked in a 4-stage ring. Sparse neuron activation and the relatively small grid keep the spike collision probability low to save access arbitration. The weight memory is divided into core memory and auxiliary memory, such that the auxiliary memory is only powered on for learning to save inference power. High-throughput inference is accomplished by the parallel operation of neurons. Efficient learning is implemented by passing parameter update messages, which is further simplified by an approximation technique. A 3.06 mm² 65 nm CMOS ASIC test chip is designed to achieve a maximum inference throughput of 1.24 Gpixel/s at 1.0 V and 310 MHz, and on-chip learning can be completed in seconds. To improve the power consumption and energy efficiency, core memory supply voltage can be reduced to 440 mV to take advantage of the error resilience of the algorithm, reducing the inference power to 6.67 mW for a 140 Mpixel/s throughput at 35 MHz.