Amplitude quantization is one of the main sources of spurious noise frequencies in Direct Digital Frequency Synthesizers (DDFSs), which affect their application to many wireless telecommu- nication systems. In this pa...Amplitude quantization is one of the main sources of spurious noise frequencies in Direct Digital Frequency Synthesizers (DDFSs), which affect their application to many wireless telecommu- nication systems. In this paper, two different kinds of spurious signals due to amplitude quantization in DDFSs are exactly formulated in the time domain and detailedly compared in the frequency do- main, and the effects of the DDFS parameter variations on the spurious performance are thoroughly studied. Then the spectral properties and power levels of the amplitude-quantization spurs in the absence of phase-accumulator truncation are emphatically analyzed by waveform estimation and computer simulation, and several important conclusions are derived which can provide theoretical support for parameter choice and spurious performance evaluation in the application of DDFSs.展开更多
The gravitational collapse of a massless scalar field with a self-interaction term λφ~4 in anti-de Sitter space is investigated.We numerically investigate the effect of the self-interaction term on the critical ampl...The gravitational collapse of a massless scalar field with a self-interaction term λφ~4 in anti-de Sitter space is investigated.We numerically investigate the effect of the self-interaction term on the critical amplitudes,forming time of apparent horizon,stable island,and energy transformation.The results show that a positiveλsuppresses the formation of black hole,while a negativeλenhances the process.We define two susceptibilities to characterize the effect of the self-interaction on the black hole formation,and find that near the critical amplitude,there exists a universal scaling relation with the critical exponentα≈0.74 for the time of black hole formation.展开更多
基金Supported by National High-Technology Research and Development Plan of China (Grant No.2006AA01Z452)
文摘Amplitude quantization is one of the main sources of spurious noise frequencies in Direct Digital Frequency Synthesizers (DDFSs), which affect their application to many wireless telecommu- nication systems. In this paper, two different kinds of spurious signals due to amplitude quantization in DDFSs are exactly formulated in the time domain and detailedly compared in the frequency do- main, and the effects of the DDFS parameter variations on the spurious performance are thoroughly studied. Then the spectral properties and power levels of the amplitude-quantization spurs in the absence of phase-accumulator truncation are emphatically analyzed by waveform estimation and computer simulation, and several important conclusions are derived which can provide theoretical support for parameter choice and spurious performance evaluation in the application of DDFSs.
基金Supported by the National Natural Science Foundation of China under Grant Nos.11375247 and 11435006
文摘The gravitational collapse of a massless scalar field with a self-interaction term λφ~4 in anti-de Sitter space is investigated.We numerically investigate the effect of the self-interaction term on the critical amplitudes,forming time of apparent horizon,stable island,and energy transformation.The results show that a positiveλsuppresses the formation of black hole,while a negativeλenhances the process.We define two susceptibilities to characterize the effect of the self-interaction on the black hole formation,and find that near the critical amplitude,there exists a universal scaling relation with the critical exponentα≈0.74 for the time of black hole formation.
