Single Ring Oscillator Research Articles

A 2.5 pJ/bit PVT-Tolerant True Random Number Generator Based on Native-NMOS-Regulated Ring Oscillator

In this brief, an energy-efficient true random number generator (TRNG) is presented based on the jitter noise of a single ring oscillator (RO). By XORing two different oscillation stages of the RO, consecutive pulses can be generated due to the fixed intrinsic propagation delay and more importantly, the time-varying jitter-noise-caused variation to the above delay. By continuously quantizing the above pulses’ width using another high-frequency RO-based time-to-digital converter (TDC), the TDC’s least significant bits (LSBs) are dominated by the jitter noise, of which the magnitude can be largely increased through reducing the RO’s supply voltage with a native NMOS transistor. Based on a 40-nm standard CMOS process, the proposed TRNG design is fabricated and extensively characterized. By passing the widely-exploited test tools of National Institute of Standards and Technology (NIST) and autocorrelation function, the proposed TRNG’s randomness has been well validated. Moreover, the randomness evaluation is further extended to various process-voltage-temperature (PVT) conditions, and the measured Shannon entropy is always larger than 0.999995, showing excellent PVT tolerance. Finally, the proposed TRNG features a high energy efficiency of 2.5 pJ/bit at a throughput of 53 Mbps.

The optimized layout strategy of ring oscillator network for Trojan detection

The method of Trojan detection based on the RON (Ring Oscillator Network) has been widely proposed and has a good effect. However, the method needs to integrate a RON on the chip to sense the voltage drop generated by the Trojan. Currently, the number of ROs (Ring Oscillator) required for a RON has not been discussed, which has a large impact on the additional hardware overhead. Therefore, based on the RON for Trojan detection, we propose an optimized layout strategy that can effectively control the number of ROs integrated into the circuit. By measuring the sensing range that can be perceived by a single RO, the sensing radius of the RO is obtained; then, ROs are placed in the circuit in a way of regular hexagonal lattice to clarify the number of ROs required in the network. Determining the appropriate number of ROs not only reduces the hardware overhead required for on-chip integration, but also ensures the reliability of Trojan detection, ensuring seamless coverage of the circuit with as few ROs as possible.

Reducing the Impact of Local Load Variation on the DUT in a Process Detector Using a Supply Controlled Ring Oscillator

The extraction of threshold voltage ( $V_{TH}$ ) of a transistor using process detector is important for device and process characterization. This paper proposes a fully digital on-chip $V_{TH}$ detector using a supply controlled ring oscillator (RO) to extract local random variation of $V_{TH}$ . As a single RO is employed to extract $V_{TH}$ variation from an array of independently selectable device under tests (DUTs), the local load variation observed by each DUT is almost constant and makes the proposed detector insensitive to local load variation. The supply noise due to the oscillation of RO can be suppressed using a decoupling capacitor. The measurement results of 300 DUTs in a test chip, occupying a silicon area of $44 ~\mu \mathrm {m} \times 126 ~\mu \text{m}$ in 130 nm technology node demonstrates the efficacy of the proposed detector.

Low Phase Noise Wide Tuning Range N-Push Cyclic-Coupled Ring Oscillators

Cyclic-coupled ring oscillators (CCRO) provide several unique features over regular ring oscillators such as availability of multiple sets of phase-shifted outputs and reduced phase noise. Furthermore, when combined with N-push frequency multiplication low phase noise, wide tuning ranges and millimeter-wave (mm-wave) frequencies can be realized. In this work, we propose two N-push CCROs fabricated in a 90 nm digital CMOS process. First, a wideband N-Push/M-Push CCRO is presented which achieves an output frequency range of 3.16-12.8 GHz using a unit cell ring oscillator operating at 1-2.56 GHz. The measured phase noise at 1 MHz offset is -103.4 dBc/Hz and -101.6 dBc/Hz at 3.16 GHz and 12.8 GHz, respectively. Second, an mm-wave N-Push CCRO is presented. It generates an output frequency of 13-25 GHz with a low phase noise performance of -95 dBc/Hz at 1 MHz offset over the output frequency range. The proposed oscillators achieve superior phase noise performance as well as competitive figure-of-merit compared with the state-of-the-art ring oscillators. In addition, the operation of the CCRO and its phase noise is analyzed. We confirm, analytically and experimentally, that the phase noise of an M-stage CCRO improves by 10 M over that of a single ring oscillator. We also show that the phase noise improvement bandwidth is a function of the coupling strength.