Hipernetch: High-Performance FPGA Network Switch

We present Hipernetch, a novel FPGA-based design for performing high-bandwidth network switching. FPGAs have recently become more popular in data centers due to their promising capabilities for a wide range of applications. With the recent surge in transceiver bandwidth, they could further benefit the implementation and refinement of network switches used in data centers. Hipernetch replaces the crossbar with a “combined parallel round-robin arbiter”. Unlike a crossbar, the combined parallel round-robin arbiter is easy to pipeline, and does not require centralised iterative scheduling algorithms that try to fit too many steps in a single or a few FPGA cycles. The result is a network switch implementation on FPGAs operating at a high frequency and with a low port-to-port latency. Our proposed Hipernetch architecture additionally provides a competitive switching performance approaching output-queued crossbar switches. Our implemented Hipernetch designs exhibit a throughput that exceeds 100 Gbps per port for switches of up to 16 ports, reaching an aggregate throughput of around 1.7 Tbps.

Spontaneous Mind-Wandering Tendencies Linked to Cognitive Flexibility in Young Adults

Despite that previous studies have investigated mind wandering using task-switching paradigms, the association between the tendency to mind wander and cognitive flexibility remains largely unexplored. The present study investigated the relationship between self-reported spontaneous mind-wandering tendencies and task-switching performance in young adults. Seventy-nine university students performed a forced task-switching and a voluntary task-switching paradigm and then completed a battery of questionnaires. The results showed that compared to participants with lower spontaneous mind-wandering tendencies, participants with higher spontaneous mind-wandering tendencies demonstrated better performance (evidenced by smaller switch cost reaction times) in the forced task-switching paradigm despite indicating more mind wandering during task performance. Performance on the voluntary task-switching paradigm, on the other hand, did not differ between the two groups. The findings in the forced task-switching paradigm indicate a link between mind wandering and cognitive flexibility, thus providing initial evidence in favor of a role for switching in mind wandering.

Time-based task expectancy: perceptual task indicator expectancy or expectancy of post-perceptual task components?

The temporal predictability of upcoming events plays a crucial role in the adjustment of anticipatory cognitive control in multitasking. Previous research has demonstrated that task switching performance improved if tasks were validly predictable by a pre-target interval. Hence, far, the underlying cognitive processes of time-based task expectancy in task switching have not been clearly defined. The present study investigated whether the effect of time-based expectancy is due to expectancy of post-perceptual task components or rather due to facilitation of perceptual visual processing of the coloured task indicator. Participants performed two numeric judgment tasks (parity vs. magnitude), which were each indicated by two different colours. Each task was either more or less frequently preceded by one of two intervals (500 ms or 1500 ms). Tasks were indicated either by colours that were each more frequently (or in Exp. 1 also less frequently) paired with the interval or by colours that were equally frequent for each interval. Participants only responded faster when colour and task were predictable by time (expected colour), not when the task alone was predictable (neutral colour). Hence, our results speak in favour of perceptual time-based task indicator expectancy being the underlying cognitive mechanism of time-based expectancy in the task switching paradigm.

Status and Trends of Power Devices

Advances in power semiconductor technology have improved the efficiency, size, weight, and cost of power electronic systems. Power integrated circuits have been developed for the use of power converters for portable, automotive and aerospace applications. New materials (SiC and GaN) have been introduced for advanced applications. They increase the output power density per area or per volume, reduce the consumption of natural resources, and increase the efficiency of electric systems. Especially the effects of SiC devices are dramatic. The paper reviews the state of these devices in terms of higher voltages, higher power density, and better switching performance.

A Novel MOS-Channel Diode Embedded in a SiC Superjunction MOSFET for Enhanced Switching Performance and Superior Short Circuit Ruggedness

In this study, a novel MOS-channel diode embedded in a SiC superjunction MOSFET (MCD SJ-MOSFET) is proposed and analyzed by means of numerical TCAD simulations. Owing to the electric field shielding effect of the P+ body and the P-pillar, the channel diode oxide thickness (tco) of MCD can be set to very thin while achieving a low maximum oxide electric field (EMOX) under 3 MV/cm. Therefore, the turn-on voltage (VF) of the proposed structure was 1.43 V, deactivating the parasitic PIN body diode. Compared with the SJ-MOSFET, the reverse recovery time (trr) and the reverse recovery charge (Qrr) were improved by 43% and 59%, respectively. Although there is a slight increase in specific on-resistance (RON), the MCD SJ-MOSFET shows very low input capacitance (CISS) and gate to drain capacitance (CGD) due to the reduced active gate. Therefore, significantly improved figures of merit RON × CGD by a factor of 4.3 are achieved compared to SJ-MOSFET. As a result, the proposed structure reduced the switching time as well as the switching energy loss (ESW). Moreover, electro-thermal simulation results show that the MCD SJ-MOSFET has a short circuit withstand time (tSC) more than twice that of the SJ-MOSFET at various DC bus voltages (400 and 600 V).