Fundamentals of oscillator performance

The oscillator is arguably the most essential part of any communication system: it defines a channel frequency, or timing and synchronisation in a digital system. The phase noise of any oscillator has a fundamental lower limit. It limits the achievable efficiency of spectrum use and degrades the error rate in practical applications. Any low-noise oscillator can be described as a positive-feedback Q-multiplier circuit. Such a model shows that phase noise is minimised if the square of the effective circuit Q and the signal-to-noise ratio in the oscillator are maximised. This simple fact is true for all oscillators and it provides the basis for more efficient and lower noise designs     

Elastoplastic torsion theory for whisker crystals

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 127–134, March–April, 1991.     

Methodologies for characterizing traffic in wide area networks: Analysis and benchmarking

Since computer networks play an important role in distributed computing environments, an application's performance depends heavily on the quality of service provided by the communication networks. To ensure a high performance, the characteristics of wide area networks, WANs, must be well understood. This paper presents methodologies to characterize WAN traffic based on real measurements from Bellcore's backbone network that connects remote sites using dedicated T1 links. This paper also suggests some workload models that can be used for wide area network sizing and performance evaluation studies. It is found that the inter-site traffic pattern depends on the time of the day and the day of the week. Furthermore, the traffic between two sites is found to be reasonably symmetric, except for those sites designated as back-up sites. The coefficient of variation is used as a measure for the traffic burstiness and it is found to be 1·5 degree during working hours. The methods presented here are easy to use and cost-effective.     

RbCl:Li color center laser with laser diode pumping

CW operation of a RbCl:Li-F_A(II) laser has been obtained under pumping by a red laser diode. Pump power at threshold is 90 mW. Single frequency operation of the color center laser has been achieved. The intensity noise generated by two pump sources (laser diode and Kr-ion laser) is compared     

A modified method of characteristics incorporating streamline diffusion

A hybrid finite-element method, combining ideas from a modified method of characteristics and the streamline diffusion method, delivers accurate solutions to the advection–diffusion equation. An error analysis for the case of tensorial diffusion shows that the lowest-order version of the scheme, which allows one to use a symmetric linear solvers at each time step, possesses first-order accuracy in time and space. Numerical experiments demonstrate the scheme's ability to model advection-dominated transport of solute plumes without distorting sharp fronts. © 1995 John Wiley & Sons, Inc.     

Effect of exponentially graded base doping on the performance ofGaAs/AlGaAs heterojunction bipolar transistors

The authors have fabricated n-p-n GaAs/AlGaAs heterojunction bipolar transistors (HBTs) with base doping graded exponentially from 5×10¹⁹ cm^-3 at the emitter edge to 5×10¹⁸ cm^-3 at the collector edge. The built-in field due to the exponentially graded doping profile significantly reduces base transit time, despite bandgap narrowing associated with high base doping. Compared to devices with the same base thickness and uniform base doping of 1×10¹⁹ cm^-3 , the cutoff frequency is increased from 22 to 31 GHz and maximum frequency of oscillation is increased from 40 to 58 GHz. Exponentially graded base doping also results ill consistently higher common-emitter current gain than uniform base doping, even though the Gummel number is twice as high and the base resistance is reduced by 40%     

Cyclostationary crosstalk suppression by decision feedbackequalization on digital subscriber loops

Interference from digital signals in multipair cables has been shown to be cyclostationary under some conditions. This work evaluates the performance of a decision feedback equalizer (DFE) in the presence of cyclostationary interference (CI), intersymbol interference (ISI), and additive white noise (AWN). A comparison between a DFE with CI and one with stationary interference (SI) shows the ability of the DFE to substantially suppress CI. Fractionally spaced and symbol-rate DFE equalizers are also compared and the former is found to yield better performance, especially in the presence of CI. The use of a symbol-rate DFE using an adaptive timing technique that finds the receiver's best sampling phase is proposed for when the fractionally spaced DFE cannot be used because of its complexity. The results also demonstrate the potential benefits of synchronizing central office transmitter clocks, if a fractionally spaced DFE is used at the receiver     

Long-wavelength infrared photoinduced switching of a resonanttunneling diode using the intersubband transition

Voltage switching induced by long-wavelength infrared light from a CO₂ laser was observed using a double-barrier resonant tunneling diode (RTD) biased in the bistable region and the intersubband transition (IT) between the quantum confined states. Possible optoelectronic and all-optical switching applications involving hysteresis are proposed and discussed