Digital Controlled Oscillator
A monolithically integrated, digitally controlled oscillator is presented. It has an output frequency range from 18.9 Hz to ≫ 20 MHz, the long term stability of a quartz oscillator and a short term clock edge uncertainty with a standard deviation of 0.4 ns. The digital frequency control is fully linear with a resolution of 18.9 Hz. The only required external component is a reference quartz. The circuit operates from a single 5 V power supply and is fabricated in a 1.5 ¿m, double metal, single poly, CMOS process. The chip area is 4.1 mm2.
DTMF Generator based on Interleaved Oversampling
A circuit is described which uses one oversampling frequency synthesizer in an interleaved mode to generate dual-tone multi-frequency (DTMF) telephone dialling tones. The synthesizer is based on direct digital synthesis using phase accumulation. The Digital to analogue conversion is carried out using a first order sigma-delta (¿¿). This ¿¿ converter is also used in interleaved mode. The smoothing filter consists of a simple second order RC filter.
EFFECT OF SAMPLE PREPARATION ON WATER TREE RESISTANCE OF XLPE/SEBS BLENDS
The effects of an aromatic polymer, such as poly[styrene-b-(ethylene-co-butylene)b-styrene] (SEBS), and its preparation processes on water tree resistance, morphology, crystallinity, dielectric constant and dielectric loss tangent of crosslinked polyethylene (XLPE)/SEBS and XLPE/SEBS/ethylene vinyl acetate (EVA) blends were investigated. The XLPE/SEBS samples were characterized by means of differential scanning calorimetry, scanning electron microscopy, dielectric spectral analysis and the accelerated water treeing experiment. The results clearly showed that although SEBS was partially compatible with LDPE and it was dispersed evenly in XLPE matrix, the blends demonstrated excellent dielectric performances, such as dielectric constant and dissipation factor. The crystallinity of XLPE/SEBS blends was decreased with increase in SEBS content and it was further decreased with the addition of EVA. SEBS could effectively improve the water-tree resistance of XLPE and both SEBS and EVA were found to improve the water tree resistance of XLPE synergistically as expected. The differences in sample preparation processes could change the phase morphology and dielectric performance of the blends, and could also influence the dispersion of SEBS in XLPE matrix as well as the crystallinity of the blends. Different preparation processes led to different water tree resistance behaviours of the samples. The improvement of SEBS dispersion in XLPE matrix helped to improve the water tree resistance of XLPE.