Multi-channel TRNG based on Scalable Cascaded Full Feedback Ring Oscillator

True random number generator (TRNG) is a key component in ensuring hardware security, and with the development of technologies such as high-speed communications, there is a higher demand for its generation rate. In this work, an ultra-high throughput rate TRNG based on a scalable cascaded full feedback ring oscillator (CFFRO) as the entropy source circuit is presented and implemented on Xilinx Artix-7, Kintex-7, and zynq UltraScale+ FPGAs devices. Unlike previous works, the proposed CFFRO is designed to be constructed as multiple parallel internal ROs, which, in turn, are sequentially cascaded and coupled to each other to disrupt the frequency spectrum of each ring oscillator and enhance the output uncertainty. Each internal ring oscillator in CFFRO can be used as an output for random numbers, creating multi-channel TRNG with parallel outputs and single-channel TRNG with multi-bit serial outputs. Measurements of the sequences extracted by both random number output schemes of TRNG show good randomness in the NIST SP800-22 suits and high entropy values in both the NIST SP 800-90B and AIS-31 testing suits, and the Dieharder suite verified the robustness under voltage and temperature variations. Moreover, due to the good extensibility of CFFRO, TRNGs with 2–8 channel counts are implemented in this work. At a sampling frequency of 400 MHz, the random sequences generated by 2–8 channel TRNGs can pass the tests.