2.4 Gbps, 7 mW All-Digital PVT-Variation Tolerant True Random Number Generator for 45 nm CMOS High-Performance Microprocessors

Abstract

This paper describes an all-digital PVT-variation tolerant true-random number generator (TRNG), fabricated in 45 nm high-k/metal-gate CMOS, targeted for on-die entropy generation in high-performance microprocessors. The TRNG harvests differential thermal-noise at the diffusion nodes of a pre-charged cross-coupled inverter pair to resolve out of metastability, generating one random bit/cycle. A self-calibrating 2-step tuning mechanism using coarse-grained configurable inverters and fine-grained programmable clock delay generators, along with an entropy-tracking feedback loop provide tolerance to 20% PVT variation-induced device mismatches, enabling lowest-reported energy-consumption of 2.9 pJ/bit with a dense layout occupying 4004 μm2, while achieving: (i) 2.4 Gbps random bit throughput, 7 mW total power consumption with 0.7 mW leakage power component, measured at 1.1 V, 50°C, (ii) random bitstreams that passes all NIST RNG tests with raw entropy/bit measured up to 0.9999999993, (iii) good distribution of 1's with 4-bit entropy of 3.97996 and high-entropy pattern probability of 0.066 (iv) wide operating supply voltage range with robust sub-threshold voltage performance of 14 Mbps, 5.6 μW, measured at 280 mV, 50°C, (v) 12 fine-grained high-entropy settings for the TRNG to dither in during steady-state operation, (vi) <;3% error while using an analytical ergodic Markov chain model for predicting pattern probabilities and (vii) 200x higher throughput and 9x higher energy-efficiency than previously reported implementations. Design modifications for robust operation in 22 nm high-volume manufacturing in the presence of 3σ process variations demonstrate scalability of the all-digital design to future technologies.