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Photoconductive semiconductor switch (PCSS) allowing side illumination was fabricated on high purity semi-insulating (HPSI) 4H-SiC. A 532-nm pulsed laser with variable optical energy was used to trigger the PCSS. The performance of the PCSS was characterized under the two different load conditions, 50- $\Omega $ load and 0.05- $\Omega $ , with a current viewing resistor (CVR). The PCSS exhibited significantly different output characteristics for the two different loads. The equivalent resistance of the PCSS with the 50- $\Omega $ load, which was calculated from the output voltage and current, was inversely proportional to the optical energy, but the one with a 0.05- $\Omega $ load exhibited saturation behavior with the optical energy. While the times at peak output with the 50- $\Omega $ load were similar at various optical energies, the times at peak output with the 0.05- $\Omega $ load were dependent on the optical energy. Output current oscillation was also observed after the PCSS was turned off in the case of 0.05- $\Omega $ load condition. The different output characteristics for the different load resistances were analyzed using the transient response of the equivalent circuits. The PCSS exhibited a minimum on-state resistance of $0.27~\Omega $ with the optical energy of 8 mJ and a maximum output current of 657 A at the bias voltage of 4.8 kV. The operating voltage of the PCSS was limited by surface flashover, which caused an additional output pulse following the first output pulse.

High purity semi-insulating (HPSI) 4H-silicon carbide (SiC) was used to fabricate lateral and vertical photoconductive semiconductor switches (PCSSs). The lateral PCSSs were illuminated from the frontside (fPCSS) or the backside (bPCSS). The side-illuminated vertical PCSS (vPCSS) was designed to increase the light-matter interaction volume. A 532-nm pulsed laser with adjustable energy was utilized to excite the PCSSs. The turn-on time was found to be highly dependent on the optical illumination energy, and the full-width at half-maximum of the PCSSs output waveforms was related to the peak output voltage. The output electrical pulse from the vPCSS exhibited a shorter turn-on time and a larger pulsewidth than the two types of lateral PCSSs. The vPCSS outperformed the fPCSS and bPCSS in terms of minimum $\mathrm{\scriptscriptstyle ON}$ -state resistance and output pulse amplitude under the same optical illumination energy. The vPCSS, which utilizes a large effective contact area to collect photogenerated carriers, also had higher photon absorption efficiency by arranging the optical path at a right angle to the carrier transport. The vPCSS exhibited a minimum $\mathrm{\scriptscriptstyle ON}$ -state resistance of 0.34 $\Omega $ at optical illumination energy of 8 mJ. [ABSTRACT FROM AUTHOR]

Variable valve actuation plays an important role in modern engine design. Fuel economy, emissions, and power output can be improved through appropriately varying valve lift and timing. One means of independently and continuously adjusting these valve profile parameters is with an electro-hydraulic valve system (EHVS). However, with an EHVS, it is very difficult to achieve the same level of accurate position control that a mechanical cam provides. In particular, the response time delay and the nonlinear dynamics of the hydraulic system can lead to error in valve position control. The paper first describes the identification method used to obtain a mathematical model of the EHVS. Based on the model, two linear feedback controllers are developed and compared. To further improve the tracking performance, a repetitive feed-forward controller is added to augment the feedback controller and the root mean square tracking error is improved to under 40 \mum. Stability and steady-state tracking error variance analyses complete the mathematical framework of this work. [ABSTRACT FROM PUBLISHER]

Homogeneous charge compression ignition (HCCI) is one of the most promising piston-engine concepts for the future, providing significantly improved efficiency and emissions characteristics relative to current technologies. This paper presents a framework for controlling an HCCI engine with exhaust recompression and direct injection of fuel into the cylinder. A physical model is used to describe the HCCI process, with the model states being closely linked to the thermodynamic state of the cylinder constituents. Separability between the effects of the control inputs on the desired outputs provides an opportunity to develop a simple linear control scheme, where the fuel is used to control the work output and the valve timings are used to control the phasing of combustion. The controller is tested on both a single and multi-cylinder HCCI engine, demonstrating the value of a physical model-based control approach that allows an easy porting of the control structure from one engine to another. Experimental results show good tracking of both the work output and combustion phasing over a wide operating region on both engines. In addition, the controller is able to balance out differences between cylinders on the multi-cylinder engine testbed, and reduce the cycle-to-cycle variability of combustion. [ABSTRACT FROM PUBLISHER]

Systems-on-a-chip (SOCs) with many complex intellectual property cores require a large volume of data for manufacturing test. The computing power of the embedded processor in a SOC can be used to test the cores within the chip boundary, reducing the test time and memory requirements. This paper discusses techniques that use the computing power of the embedded processor in a more. sophisticated way. The processor can generate and reuse random numbers to construct test patterns and selectively apply only those patterns that contribute to the fault coverage, significantly reducing the pattern generation time, the total number of test applications and, hence, the test time. It can also apply deterministic test patterns that have been compressed using the characteristics of the random patterns as well as those of the deterministic patterns themselves, which leads to high compression of test data. We compare three fast run-length coding schemes which are easily implemented and effective for test-data compression. We also demonstrate the effectiveness of the proposed approach by applying it to some benchmark circuits and by comparing it with other available techniques. [ABSTRACT FROM AUTHOR]

GaAs photoconductive semiconductor switches (PCSSs) with comb electrodes were fabricated on semi-insulating GaAs. A pulsed 1064-nm laser with a 700-ps (FWHM) pulse width and optical energy of $134 \; \mu $ J was used to trigger 2-mm-gap PCSSs with comb lengths ranging from 0 to $750 \; \mu $ m. The effect of the comb electrodes on the output characteristics was investigated by comparing the performance parameters of sample devices with different comb lengths. Devices with a longer comb exhibited higher peak output voltage and better immunity against surface flashover. A PCSS specimen with a 750- $\mu $ m comb exhibited a higher peak output voltage by 3.53 times compared to a PCSS without a comb at bias voltages lower than 1 kV. Moreover, the PCSS with the 750- $\mu $ m comb electrode successfully generated a pulse with a peak voltage of 1.34 kV, while the peak voltage generated by a PCSS without a comb was limited to 0.74 kV.