This letter presents a high-speed closed-loop capacitive-input voltage controlled oscillators (VCO)-based continuous-time delta sigma modulator (CTDSM) using a novel fully differential VCO topology whose parasitic pole is inherently located at a very high frequency, regardless of the number of inverters in the ring VCO. The mitigation of the parasitic pole is achieved by splitting the VCO's input transconductor into a set of distributed input transistors. Capacitive input and capacitive DAC result in a very low thermal noise front end, besides ensuring that there is no additional pole caused due to the VCO's input capacitance. A single pair of pseudo-resistors is used for providing dc negative feedback in the CTDSM. The prototype first-order 63-stage VCO-based CTDSM is fabricated in 40-nm CMOS and occupies a core area of 0.02 mm2 while achieving 63.1-dB dynamic range in 480 kHz-20.48 MHz bandwidth at 1 GS/s. This is the first work to mitigate the parasitic pole in a fully differential VCO, without relying on any additional active circuits. To the authors' best knowledge, this is also the first work to demonstrate the capacitive input in a high-speed CTDSM, without using chopping.
Abstract Silicon and oxygen are potential light elements in Earth's core because their stronger affinity to metal observed with increasing temperature posits that significant amounts of both can be incorporated into the core. It was proposed that an Fe–Si–O liquid alloy could expel SiO2 at the core-mantle boundary during secular cooling, leaving the core with either silicon or oxygen, not both. This was recently challenged in a study showing no exsolution but immiscibility in the Fe–Si–O system. Here we investigate the liquidus field of Fe–Si and Fe–O binaries and Fe–Si–O ternaries at core-mantle boundary pressures and temperatures using ab initio molecular dynamics. We find that the liquids remain well mixed with ternary properties identical to mixing of binary properties. Two-phase simulations of solid SiO2 and liquid Fe show dissolution at temperatures above 4100 K, suggesting that SiO2 crystallization as well as liquid immiscibility in Fe–Si–O is unlikely to occur in Earth's core.
In order to analyze the creep behavior of shale rocks, nanoindentation, a common and widely used method was employed in this study. During the experiments, an abnormal displacement behavior was observed in the holding stage which has rarely been reported. It was observed that the displacement increases with holding time followed by a decrease. Further analysis of the results showed that the reduction in the displacement could be due to elastic recovery during the holding period. The dynamic mechanical properties such as storage modulus and hardness were found to first decrease and then increase after the holding time exceeds a certain value which is inferred to elastic recovery. These findings indicate that at the beginning of the holding period, creep behavior would dominate the process while as the holding time proceed, the elastic recovery plays a more important role. Finally, we proposed a new model which includes elastic recovery to quantify the changes in displacement, storage modulus and hardness as a function of holding time.