Rise time

About: Rise time is a research topic. Over the lifetime, 4748 publications have been published within this topic receiving 47512 citations.

A superconducting sampler for Josephson logic circuits

Abstract: A method is described for automating a technique which is used to sample transition duration (rise time) in superconducting logic circuits. The method is based on measuring the time at which a biased Josephson junction switches under the influence of an applied signal. The system transition duration is limited primarily by time jitter which is estimated to be 7 ps. Transition durations of as little as 9 ps have been observed.

Design of Archimedes Spiral Antenna to Optimize for Partial Discharge Detection of Inverter Fed Motor Insulation

Abstract: The partial discharge (PD) in inverter-fed motors generated from high frequency and short rise time impulsive voltage are more complex than traditional sinusoidal voltage operated motors due to the noise initiated from fast switching power electronics devices. Available PD sensors and related technology for DC and sinusoidal voltage cannot be used at repetitive impulsive voltage conditions. This work aims to report the design of antenna with optimized geometry and satisfied parameters to detect PD for impulsive voltage. The antenna is verified and the influence of both impulse voltage parameters and test configuration on PD features are discussed. The envelope detection technique after the filter in the frequency domain was proposed to reduce the complexity and cost of PD test hardware under impulsive voltages with fast rise times. The frequency domain energy of PD from motor insulation is mainly distributed in the range of 0.6-1.8 GHz. By increasing the amplitude and frequency of input impulsive voltage, the range of PD energy spectrum is enlarged to (1.5-1.8 GHz) and by decreasing input amplitude the PD signal strength decays abruptly. Moreover, the high-frequency distribution of PD energy attenuates more severely with the distance and the electromagnetic energy of PD decays nonlinearly with the increase of propagation distance. Therefore, under the premise of satisfying the safety test, selecting the test distance below 15 cm can ensure that the test results have a high signal-to-noise ratio and signal integrity. The experience reported in this study could provide suggestions for off-line PD measurements for inverter-fed motor insulation evaluations for manufacturers.

A Fast Response, Three-Electrode Liquid Crystal Device

Abstract: A new, three-electrode, hybrid-aligned nematic (HAN) liquid crystal (LC) device for fast response applications is described. The three-electrode configuration generates electric field horizontally and vertically which alternately turn the LC cell on and off. The fast response is realized with both the turn-on and turn-off processes driven by an electric field. The transmission and response time of such a LC device as a function of the rubbing angle were studied. A total response time (rise time plus fall time) of less than 2 ms was obtained for a non-optimized HAN LC cell with a cell gap of 6 µm. Such a device is promising for video and other applications where fast response is required.

Electrical aging of stator insulation of low voltage rotating machines supplied by inverters

Abstract: Nowadays, the use of inverters for speed variation of low voltage motors has become more and more common. The most common technology for this kind of apparatus uses pulse width modulation (PWM). It is characterized by a square voltage shape with short rise and fall times. In order to insure the quality of turn to ground insulation submitted to these constraints, a study on the aging of polyethylene terephthalate (Mylar/sup TM/) has been undertaken. Influence of rise and fall times, frequency and voltage magnitude has been investigated for time duration up to 1000 hours. To realize a good voltage application, samples were previously metalized. Two different behaviors according to the rise time and magnitude are observed. For long rise and fall times, changes in the capacity values are obtained although, for smaller rise or fall times, a degradation of the metalized electrode appears. A surface charge generation process is discussed to explain this phenomena.

High-brightness and high-speed vertical cavity surface-emitting laser arrays

Abstract: High-power vertical-cavity surface-emitting laser (VCSEL) arrays, which can serve as the light source in modern lidar and three-dimensional optical sensing systems, have recently attracted a lot of attention. In these types of systems, the time-of-flight (ToF) technique, based on the round-trip time of short optical pulses is usually adopted. Further enhancement of the ranging distance and depth resolution in these ToF driven systems by the incorporation of a VCSEL array with a high available power, high brightness (narrow divergence angle), and fast response time is highly desirable. However, a large number of light emission apertures (several hundreds) in the VCSEL array is usually necessary to raise the output power level to several watts. This leads to a large parasitic capacitance and the RC-limited bandwidth may become the dominant limiting factor of the speed of the high-power VCSEL array. In this work, Zn-diffusion and oxide-relief apertures are used to manipulate the optical modes and reduce the parasitic capacitance, respectively, in a unit device for a 940 nm VCSEL array. The demonstrated VCSEL array has a quasi-single-mode output, high available power (4 W; 1% duty cycle), narrow divergence angle (${\sim}{14}^\circ $∼14∘ at ${{1/e}^2}$1/e2) under maximum output power, and a fast rise time ($ {\lt} {100}\;{\rm ps}$<100ps). These results open up new possibilities for further enhancing the performance of ToF sensing systems at the 940 nm wavelength.