Design considerations for a high-speed CMOS comparator

Design considerations for a high-speed CMOS comparator for application in highspeed analogue-to-digital conversion are presented. Extensive simulations show that the comparator designed accordingly operates well above 250MHz clock speed in standard 0.5µm CMOS technology. An accuracy of 5mV and average power consumption of 0.3mW on 3.3V power supply is observed using simulations when it operates at 250MHz.     

Grain refinement of Al-3.5FeNb-1.5C master alloy on pure Al and Al-9.8Si-3.4Cu alloy

The refinement potential of Al-3.5 Fe Nb-1.5 C master alloy on pure aluminium and Al-9.8 Si-3.4 Cu alloy has been investigated. Different amounts of Al-3.5 Fe Nb-1.5 C master alloy were added to estimate the optimal addition level. It was found that the addition of Al-3.5 Fe Nb-1.5 C grain refiner can promote significantly the refinement of grains in the pure aluminium, particularly at 0.1 wt.%, with the mean primary aluminium α-grain size reducing to 187±3 μm from about 1-3 mm. Similarly, the microstructural study of the Al-9.8 Si-3.4 Cu alloy die casting at different weight percentages(viz. 0.0 wt.%, 0.1 wt.% and 1.0 wt.%) of Al-3.5 Fe Nb-1.5 C master alloy shows that the Al-3.5 Fe Nb-1.5 C master alloy as a grain refiner is also acceptable for Al-Si cast alloys when the silicon content is more than 4 wt.%. As a result of inoculation with Al-3.5 Fe Nb-1.5 C master alloy, the average grain size of α-Al is reduced to 22±3 μm from about 71±3 μm and grain refining efficiency is not characterized by any visible poisoning effect, which is the major limitation in the grain refinement of Al-Si cast alloys by applying Al-Ti-B ternary master alloys. Mechanical properties such as ultimate tensile strength and yield strength are significantly improved by 9.6% and 9.7%, respectively.     

Effect of Mould Coatings and Pouring Temperature on the Fluidity of Different Thin Cross-Sections of A206 Alloy by Sand Casting

Thin-wall castings of the A206 alloy can pose a manufacturing problem associated with mould filling which results in fluidity defect. The mould coating generates a smooth surface, and reduces the friction between the melt and mould contact, thus reducing the heat-transfer coefficient, which in turn leads to enhancement of fluidity and mechanical properties. The fluidity of A206 alloy was observed in various cross-sections of the thin channels at three altered pouring temperatures i.e. 700, 750 and 780 °C for uncoated and coated green sand moulds. The Graphite and Soapstone powder coatings were used as sand mould coatings in the present investigation. It was found that the fluidity of aforesaid alloy was significantly increased with the Soapstone powder mould coating at pouring temperature of 750 °C. The characterization of the coating materials was performed by the X-ray diffraction analysis and scanning electron microscope test with EDAX.     

Reduced-sample-rate sigma–delta modulation using recursive deconvolution

A reduced-sample-rate sigma–delta modulation method using a recursive deconvolution technique for application in digital-to-analogue conversion is proposed and analysed. The method allows the sigma–delta modulators to operate at a sampling rate which is lower than the output bitstream rate by an integer factor. With the proposed in-loop mapping algorithm to map an m-bit sample to qb-bit samples, the total system inherits the advantages of a multilevel quantization conventional ΣΔ modulator in the digital part with regard to suppression of tones, improved stability and low power, while its output remains single-bit. The effectiveness of the technique is illustrated using simulations for second-and third-order modulators. © by John Wiley & Sons, Ltd.     

A Study on Hot Tearing Susceptibility of Al–Cu,Al–Mg,and Al–Zn alloys

The present investigation deals with the hot tearing susceptibility of A206, A518, and A713 alloys. The hot tearing tests of the mentioned alloys were conducted at three different pouring temperatures using sand mold casting. Metallic cores designed to facilitate constrained radial contraction of the aforementioned alloys were used for casting. Macroscopic cracks were found in all the samples except in A518 alloy. It was observed that pouring temperatural and grain size have significant effect on crack susceptibility. Among the investigated alloys, A713 was found to be extremely prone to hot tearing. The microstructure characteristics of the alloys were studied using optical and scanning electron microscopy. Relationships between the pouring temperature, grain size and crack lengths of the alloys were also established.     

An open-loop venetian blind control to avoid direct sunlight and enhance daylight utilization

Shading devices, such as venetian blinds, are widely used to eliminate glare and maintain a comfortable working environment for occupants. This paper proposes an open-loop control of blind height and slat angle based on an analytic model of solar position, and geometry of venetian blinds and the windows. The algorithm enables completely blocking direct sunlight from entering the room beyond a certain user specified interior distance from the window while enhancing daylight utilization. We derive closed-form solutions for blind height and angle which are easily implemented in practice. Moreover, the proposed blind control algorithm is simulated with favorable performance. The algorithm has also been implemented and verified in real-time test-beds.     

Optimization of green sand mould system using Taguchi based grey relational analysis

The strength of the mould cavity in sand casting is very much significant to attain high-quality castings. Optimization of green sand process parameters plays a vital role in minimizing casting defects. In the present research work, the effect of process parameters such as AFS grain fineness number, water, molasses, bentonite, fly ash, and ramming, and their levels on the resultant mould properties were investigated and optimized using Taguchi based grey relational analysis. The Taguchi L18 orthogonal array and analysis of variance(ANOVA) were used. The quality characteristics viz., green compression strength, permeability, bulk density, mould hardness and shatter index of green sand mould were optimized using grey relational grade, based on the experiments designed using Taguchi's Design of Experiments. ANOVA analysis indicated that water content is the most influential parameter followed by bentonite, and degree of ramming that contributes to the quality characteristics. The results are confirmed by calculating confidence intervals, which lies within the interval limits. Finally, microstructure observations and X-ray diffraction analysis have been performed for the optimal sand parametric combination. Results show that presence of maximum amount of SiO_2, which might be the reason for enhancement of the physical properties of the sand.     

Use of comb filters for efficient VLSI implementation of reducedclock frequency noise shapers

The use of comb filters as an elegant means of reduced clock frequency noise-shaping without excessive hardware overhead is presented. The significance of the method is illustrated using second order noise-shaping characteristics. A 256 times oversampled and noise-shaped bit-stream sequence is obtained by running a second order noise shaper at a clock frequency four times lower than that of the bit-stream sampling rate, in association with an in-loop multi-bit to four single bit transformation at a tolerable hardware overhead