A High-Throughput and Flexible CNN Accelerator Based on Mixed-Radix FFT Method

CNN acceleration algorithms, including Winograd, Fast Fourier Transform (FFT) and Number Theoretic transform (NTT), have demonstrated their potential in efficiently operating current Convolutional Neural Networks (CNNs). However, deploying FFT algorithm for CNN acceleration would introduce significant invalid elements, unnecessary computations and unacceptable transformation overhead. To address these issues, this paper proposes a series of improved methods along with an FFT-based architecture for efficient and simplified CNN acceleration. First, a novel mixed-radix FFT algorithm is proposed for the reduction of invalid elements. Moreover, Hermitian symmetry is utilized to further reduce the scale of FFT transformation and the number of multiplications. Furthermore, an efficient FFT-based CNN accelerator with a resource-efficient transformation component and a multiplication-reduced PE array is designed. Our proposed accelerator is implemented based on Xilinx XCVU440 with a running frequency of 238MHz, achieving actual performance of 2109-2797 GOPS and DSP efficiency of 1.37-1.82 GOPS/DSP. Compared to previous works based on Winograd, FFT and NTT, our proposed accelerator can realize up to $9.42\times $ speedup on actual performance and $1.11\times -6.41\times $ speedup on DSP efficiency.