Bonanza Mine: an Ultra-Low-Voltage Energy-Efficient Bitcoin Mining ASIC

Bitcoin is the leading blockchain-based cryptocurrency used to facilitate peer-to-peer transactions without relying on a centralized clearing house [1]. The conjoined process of transaction validation and currency minting, known as mining, employs the compute-intensive SHA256 double hash as proof-of-work. The one-way property of SHA256 necessitates a brute-force search by sweeping a 32b random input value called nonce. The 232 nonce space search results in energy-intensive pool operations distributed on high-throughput mining systems, executing parallel nonce searches with candidate Merkle roots. Energy-efficient custom ASICs are required for cost-effective mining, where energy costs dominate operational expenses, and the number of hash engines integrated on a single die govern platform cost and peak mining throughput [2]. In this paper, we present BonanzaMine, an energy-efficient mining ASIC fabricated in 7nm CMOS (Fig. 21.3.7), featuring: (i) bitcoin-optimized look-ahead message digest datapath resulting in 33% Cdyn reduction compared to conventional SHA256 digest datapath; (ii) a half-frequency scheduler datapath, reducing sequential and clock power by 33%; (iii) 3-phase latch-based design with stretchable non-overlapping clocks, eliminating min-delay paths; (iv) robust ultra-low-voltage operation at 355mV using board-level voltage-stacking; and (v) mining throughput of 137GHash/s at an energy efficiency of 55J/THash.