A Variable-Clock-Cycle-Path VLSI Design of Binary Arithmetic Decoder for H.265/HEVC

The next-generation 8K ultra-high-definition video format involves an extremely high bit rate, which imposes a high throughput requirement on the entropy decoder component of a video decoder. Context adaptive binary arithmetic coding (CABAC) is the entropy coding tool in the latest video coding standards including H.265/High Efficiency Video Coding and H.264/Advanced Video Coding. Due to critical data dependencies at the algorithm level, a CABAC decoder is difficult to be accelerated by simply leveraging parallelism and pipelining. This letter presents a new very-large-scale integration arithmetic decoder, which is the most critical bottleneck in CABAC decoding. Our design features a variable-clock-cycle-path architecture that exploits the differences in critical path delay and in probability of occurrence between various types of binary symbols (bins). The proposed design also incorporates a novel data-forwarding technique (rLPS forwarding) and a fast path-selection technique (coarse bin type decision), and is enhanced with the capability of processing additional bypass bins. As a result, its maximum throughput achieves 1010 Mbins/s in 90-nm CMOS, when decoding 0.96 bin per clock cycle at a maximum clock rate of 1053 MHz, which outperforms previous works by 19.1%.