A rubidium-beam microwave clock, optically pumped by a distributed feedback diode laser, is experimentally investigated. The clock is composed of a physical package, optical systems, and electric servo loops. The phys...A rubidium-beam microwave clock, optically pumped by a distributed feedback diode laser, is experimentally investigated. The clock is composed of a physical package, optical systems, and electric servo loops. The physical package realizes the microwave interrogation of a rubidium-atomic beam. The optical systems, equipped with two 780-nm distributed feedback laser diodes, yield light for pumping and detecting. The servo loops control the frequency of a local oscillator with respect to the microwave spectrum. With the experimental systems, the microwave spectrum, which has an amplitude of 4 n A and a line width of 700 Hz, is obtained. Preliminary tests show that the clock short-term frequency stability is 7 × 10^-11 at 1 s, and 3 × 10^-12 at 1000 s. These experimental results demonstrate the feasibility of the scheme for a manufactured clock.展开更多
This paper describes a field programming gate array (FPGA) based low level radio frequency (LLRF) prototype for the SSRF storage ring RF system: This prototype includes the local oscillator (LO), analog front e...This paper describes a field programming gate array (FPGA) based low level radio frequency (LLRF) prototype for the SSRF storage ring RF system: This prototype includes the local oscillator (LO), analog front end, digital front end, RF out, clock distributing, digital signal processing and communication functions. All feedback algorithms are performed in FPGA. The long term of the test prototype with high power shows that the variations of the RF amplitude and the phase in the accelerating cavity are less than 1% and 1° respectively, and the variation of the cavity resonance frequency is controlled within 4-10 Hz.展开更多
Comparing the city-size distribution at the urban agglomeration(UA) scale is important for understanding the processes of urban development. However, comparative studies of city-size distribution among China's thre...Comparing the city-size distribution at the urban agglomeration(UA) scale is important for understanding the processes of urban development. However, comparative studies of city-size distribution among China's three largest UAs, the Beijing-Tianjin-Hebei agglomeration(BTHA), the Yangtze River Delta agglomeration(YRDA), and the Pearl River Delta agglomeration(PRDA), remain inadequate due to the limitation of data availability. Therefore, using urban data derived from time-series nighttime light data, the common characteristics and distinctive features of city-size distribution among the three UAs from 1992 to 2015 were compared by the Pareto regression and the rank clock method. We identified two common features. First, the city-size distribution became more even. The Pareto exponents increased by 0.17, 0.12, and 0.01 in the YRDA, BTHA, and PRDA, respectively. Second, the average ranks of small cities ascended, being 0.55, 0.08 and 0.04 in the three UAs, respectively. However, the average ranks of large and medium cities in the three UAs experienced different trajectories, which are closely related to the similarities and differences in the driving forces for the development of UAs. Place-based measures are encouraged to promote a coordinated development among cities of differing sizes in the three UAs.展开更多
With the rapid development of deep submicron (DSM) VLSI circuit designs, many issues such as time closure and power consumption are making the physical designs more and more challenging. In this review paper we provid...With the rapid development of deep submicron (DSM) VLSI circuit designs, many issues such as time closure and power consumption are making the physical designs more and more challenging. In this review paper we provide readers with some recent progress of the VLSI physical designs. The recent developments of floorplanning and placement, interconnect effects, modeling and delay, buffer insertion and wire sizing, circuit order reduction, power grid analysis, parasitic extraction, and clock signal distribution are briefly reviewed.展开更多
We propose a hierarchical interconnection network with two-phase bufferless resonant clock distribution, which mixes the advantages of mesh and tree architectures.The problems of skew reduction and variation-tolerance...We propose a hierarchical interconnection network with two-phase bufferless resonant clock distribution, which mixes the advantages of mesh and tree architectures.The problems of skew reduction and variation-tolerance in the mixed interconnection network are studied through a pipelined multiplier under a TSMC 65 nm standard CMOS process.The post-simulation results show that the hierarchical architecture reduces more than 75% and 65%of clock skew compared with pure mesh and pure H-tree networks,respectively.The maximum skew in the proposed clock distribution is less than 7 ps under imbalanced loading and PVT variations,which is no more than 1%of the clock cycle of about 760 ps.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.11174015)
文摘A rubidium-beam microwave clock, optically pumped by a distributed feedback diode laser, is experimentally investigated. The clock is composed of a physical package, optical systems, and electric servo loops. The physical package realizes the microwave interrogation of a rubidium-atomic beam. The optical systems, equipped with two 780-nm distributed feedback laser diodes, yield light for pumping and detecting. The servo loops control the frequency of a local oscillator with respect to the microwave spectrum. With the experimental systems, the microwave spectrum, which has an amplitude of 4 n A and a line width of 700 Hz, is obtained. Preliminary tests show that the clock short-term frequency stability is 7 × 10^-11 at 1 s, and 3 × 10^-12 at 1000 s. These experimental results demonstrate the feasibility of the scheme for a manufactured clock.
文摘This paper describes a field programming gate array (FPGA) based low level radio frequency (LLRF) prototype for the SSRF storage ring RF system: This prototype includes the local oscillator (LO), analog front end, digital front end, RF out, clock distributing, digital signal processing and communication functions. All feedback algorithms are performed in FPGA. The long term of the test prototype with high power shows that the variations of the RF amplitude and the phase in the accelerating cavity are less than 1% and 1° respectively, and the variation of the cavity resonance frequency is controlled within 4-10 Hz.
基金National Natural Science Foundation of China,No.41621061,No.41501092 Talents Training Program from the Beijing Municipal Commission of Education No.201500002012G058
文摘Comparing the city-size distribution at the urban agglomeration(UA) scale is important for understanding the processes of urban development. However, comparative studies of city-size distribution among China's three largest UAs, the Beijing-Tianjin-Hebei agglomeration(BTHA), the Yangtze River Delta agglomeration(YRDA), and the Pearl River Delta agglomeration(PRDA), remain inadequate due to the limitation of data availability. Therefore, using urban data derived from time-series nighttime light data, the common characteristics and distinctive features of city-size distribution among the three UAs from 1992 to 2015 were compared by the Pareto regression and the rank clock method. We identified two common features. First, the city-size distribution became more even. The Pareto exponents increased by 0.17, 0.12, and 0.01 in the YRDA, BTHA, and PRDA, respectively. Second, the average ranks of small cities ascended, being 0.55, 0.08 and 0.04 in the three UAs, respectively. However, the average ranks of large and medium cities in the three UAs experienced different trajectories, which are closely related to the similarities and differences in the driving forces for the development of UAs. Place-based measures are encouraged to promote a coordinated development among cities of differing sizes in the three UAs.
文摘With the rapid development of deep submicron (DSM) VLSI circuit designs, many issues such as time closure and power consumption are making the physical designs more and more challenging. In this review paper we provide readers with some recent progress of the VLSI physical designs. The recent developments of floorplanning and placement, interconnect effects, modeling and delay, buffer insertion and wire sizing, circuit order reduction, power grid analysis, parasitic extraction, and clock signal distribution are briefly reviewed.
基金Project supported by the National Science and Technology Major Project of the Ministry of Science and Technology of China(No. 2009ZX01034-001-001-006)the National Natural Science Foundation of China(No.60906014)
文摘We propose a hierarchical interconnection network with two-phase bufferless resonant clock distribution, which mixes the advantages of mesh and tree architectures.The problems of skew reduction and variation-tolerance in the mixed interconnection network are studied through a pipelined multiplier under a TSMC 65 nm standard CMOS process.The post-simulation results show that the hierarchical architecture reduces more than 75% and 65%of clock skew compared with pure mesh and pure H-tree networks,respectively.The maximum skew in the proposed clock distribution is less than 7 ps under imbalanced loading and PVT variations,which is no more than 1%of the clock cycle of about 760 ps.