Down with noise [active noise control]

Annoying noise in the passenger cabins of propeller aircraft, the rumble in air-conditioning systems, and the sounds disrupting headset communication are being reduced these days by active noise control, thanks to advances in digital signal processing. The technique relies on the principle of destructive interference between two sound fields, one field is generated by the original or primary sound source, the other by a secondary sound source setup to interfere with, and cancel, that unwanted primary sound. The primary source may be an engine and the secondary source, a loudspeaker with an electronically controlled output. Destructive interference is at its most efficient when the two sound fields can be accurately aligned in space over an acoustic wavelength. It works best on low frequency sounds, whose acoustic wavelengths are large compared to the zone in which the noise is cancelled     

Radio sociology [noise investigation]

The article discusses the use of radio telemetry in wildlife research. An aircraft was used to locate a migrating, radio-tagged, sharp-shinned hawk. A 222 MHz four-element Yagi receiving antenna was clamped to the entrance step on the right side of the aircraft, so that it pointed in the direction normal to the direction of flight. The idea was to climb to an appropriate altitude, and fly in large circles to scan a substantial area for the missing bird. While the antenna beam swept across a small town a rush of noise-like sound was heard. This resulted in an investigation of the relationship between a town's radiation (radio noise) signature and its other attributes, such as economic type, population, geographic concentration, etc     

Truncation noise in fixed-point SFGs [digital filters]

A new model for predicting truncation error variance in fixed-point filter implementations is introduced. The proposed model is shown to be more accurate than existing models, particularly for some direct hardware implementations. In addition, some comments are made on the applicability of existing error models     

Balancing act [noise based sensory enhancement technology]

Research teams at Afferent Corp. and at Boston University have been collaborating to develop and test a new class of neurotherapy devices that have the promise of directly improving mechanical sensory function to help prevent falls in the elderly and foot injuries and amputations in people with diabetes. These devices are based on the discovery that certain forms of electrical or mechanical stimulation applied to mechanoreceptors increase their ability to detect sensory information. Results show that the best type of stimulation signal is not a finely tuned frequency but rather white noise. When presented with this stimulus over an extended period, the sensory neurons were unable to adapt to it. These findings reinforce the growing body of research that establishes the connection between sensory activity and the ability of the nervous system to repair itself following injury.     

Shake, rattle and control [noise abatement]

In a world where noise pollution is a growing problem, generating yet more noise can provide the solution. Here, the author explains this apparent paradox, achieved through the use of active noise control techniques     

Roundoff noise minimization using delta-operator realizations[digital filters]

The authors examine the advantages of using delta operator state space realizations rather than shift operator realizations of transfer functions in terms of minimizing roundoff noise gain. They give several conditions under which the optimal roundoff noise gain for delta operator realizations is smaller than the optimal gain for shift operator realizations. They then illustrate that even sparse (and hence nonoptimal) delta operator realizations can have smaller roundoff noise gain than the optimal shift operator realizations     

Comment on "Scattering by a bi-isotropic body" [and reply]

The author comments on a paper by Monzon (IEEE Trans. Antennas Propagat., vol.43, p.1288-96, Nov. 1995). The author comments that Monzon gave no indication as to whether the nonreciprocal variety of bi-anisotropic media can or do exist. The present comment notes that there is no reason to suggest that these can or do exist. A reply is presented by Monzon where he feels that the situation regarding these materials is not yet settled.     

Microscopic noise modeling and macroscopic noise models: how good aconnection? [FETs]

Based on the active line concept, a novel approach for the calculation of the high frequency noise performance of field effect transistors (FET) is proposed. By using a simple analytical theory, the FET small signal equivalent circuit as well as the macroscopic noise sources and their correlation are calculated for different two-port terminations. Values of the usual dimensionless noise parameters P, R, C, gate noise temperature T_g and drain noise temperature T _d are then given and discussed. By comparison with a more realistic numerical modeling of the noise performance, the validity of the analytical noise model is discussed. The validity of Pospieszalski's noise model and its relations with Pucel's one is emphasized     

Aaargh! I just loooove flicker noise [Open Column]

The author discusses his love-hate relationship with flicker noise and the fact that there is still a lot we don't know about it and might want to find out. For one, it is still not agreed what the best mathematical model is, and he has not yet found a mathematical model that both includes the non-stationarity of 1/f noise and is also useful for designers. On the to-do list are also better ways to calculate and simulate it; things like auto-zeroing, correlated double sampling and other switched circuits are really cumbersome to analyze and to simulate in IC design tools (if it can be done at all). We also should creatively use Klumperink's and Bloom's switching ideas to reduce the effect of flicker noise in many different ways. The fourth missing element is teaching; flicker noise is so omni-present and important, but he has yet to find a university graduate who knows more about it than that it's there (and in most cases not even this). These are all things that could be contributed by the members of the IEEE CAS society     

"What I did last summer" [internship]

Internships offer engineering students a unique window into the real-world workplace and can help students make better career decisions. In the current employment landscape, that on-the-job experience can also prove invaluable. The National Association for Colleges and Employers (NACE, Bethlehem, Pa.) reports a 36.4 percent drop in hiring of recent college grads, who in many cases are competing for fewer openings with more experienced unemployed workers. But doing real engineering as interns can make all the difference when prospective employers are sifting through endless resumes in search of qualified candidates. This article briefly discusses the issues to consider when looking for an internship     

1.5-nm gate oxide CMOS on [110] surface-oriented Si substrate

The dc and RF analog characteristics of ultrathin gate oxide CMOS on [110] surface-oriented Si substrates were investigated for the first time. The transconductance of p-MOSFETs on [110] substrates is 1.9 times greater than that on [100] substrates even in gate oxides in the direct-tunneling regime. An extremely high cutoff frequency of 110 GHz was obtained in 0.11 /spl mu/m gate length p-MOSFETs with 1.5 nm gate oxides. This is the highest value ever obtained for p-channel Si MOSFETs at room temperature. Further, it was demonstrated that more than 100 GHz of cutoff frequency is realized both for n- and p-MOSFETs. Thus, using [110] substrates results in a better balance for n- and p-MOS performances. The SiO/sub 2/ film and SiO/sub 2//Si interface qualities on [110] substrates were also investigated. In this experiment, it was found that direct-tunneling gate leakage current and initial 1/f noise of MOSFETs on [110] substrates are larger than those on [100] substrates. The reliability regarding Negative Bias Temperature Instability (NBTI) for p-MOSFETs on [110] substrates was also inferior to that for [100] MOSFETs. However, with a high-k insulator or improvement of the SiO/sub 2/ film quality, high mobility of p-MOSFETs on [110] substrates will have a potential not only for digital applications but also for new RF analog circuits under low supply voltage.     

Fountain of knowledge [analysis engine]

This article presents WebFountain, a system that can convert the anarchy of online data - Web pages, e-mail, chat rooms, and more - into a format that can be analyzed to identify commercially valuable information. By leveraging the vast reserves of untapped information online, WebFountain can let companies make smarter business decisions while creating an open platform that encourages more machine understanding research to leave the laboratory.     

Characterization of microstrip lines near a substrate edge anddesign formulas of edge-compensated microstrip lines [MMICs]

The proximity effects of microstrip lines near a substrate's edge present a problem for effectively designing high-packing-density MMICs (monolithic microwave integrated circuits). Proximity effects of this type are analyzed using the rectangular boundary division method. It is assumed that the cross-sectional dimensions of transmission lines in the MMICs are small compared with the wavelengths to allow the use of the quasi-TEM-wave approximation. Then, the concept of edge-compensated microstrip lines to keep the characteristic impedance constant near a substrate edge is introduced to circumvent the proximity effects and to expand the interconnection flexibility of microstrip lines on MMIC substrates. The practical design parameters of edge-compensated 50-Ω microstrip lines are given in the form of numerical data and simple polynomials for CASD (computer-aided design) work with a curve-fitting procedure. Results of capacitance measurements are compared with this theory with errors of about 1% resulting     

"Anti" up the aperture [antiguided VCSEL structures]

Coupled vertical cavity surface-emitting laser (VCSEL) arrays are an attractive means to increase the coherent output power of VCSELs. Single-mode VCSELs, with output powers greater than 10 mW, would be useful as telecommunication transmitters /spl lambda/=1.3-1.55 /spl mu/m) or sources for optical interconnects. Commercially available single-mode VCSELs, even at shorter wavelengths /spl lambda/=0.85 /spl mu/m), are generally limited to a few milliwatts of output power. The conventional VCSEL structure incorporates a built-in positive-index waveguide, designed to support a single fundamental mode. Promising results in the 3-5 mW range (/spl lambda/=0.85 /spl mu/m) have been obtained from wet-oxidized, positive-index-guided VCSELs with small emission apertures (less than 3.5 /spl mu/m-dia). The small aperture size leads to a high electrical resistance and high current density, which can impact device reliability. By contrast, antiguided VCSEL structures have shown promise for achieving larger aperture single-mode operation. To obtain high single-mode powers with a larger emitting aperture, the use of a negative-index guide (antiguide) is beneficial. This paper discusses antiguided structures and some of their advantages when incorporated in 2-D VCSEL array structures.     

Wavelet analysis [for signal processing]

As every engineering student knows, any signal can be portrayed as an overlay of sinusoidal waveforms of assorted frequencies. But while classical analysis copes superbly with naturally occurring sinusoidal behavior-the kind seen in speech signals-it is ill-suited to representing signals with discontinuities, such as the edges of features in images. Latterly, another powerful concept has swept applied mathematics and engineering research: wavelet analysis. In contrast to a Fourier sinusoid, which oscillates forever, a wavelet is localized in time-it lasts for only a few cycles. Like Fourier analysis, however, wavelet analysis uses an algorithm to decompose a signal into simpler elements. Here, the authors describe how localized waveforms are powerful building blocks for signal analysis and rapid prototyping-and how they are now available in software toolkits     

Communications [technology analysis and forecast]

Several spectacular changes in the communications scene over the past few years will have a still stronger impact in 1997. Most obviously, the World Wide Web has been expanding. Showing a nice mixture of optimism and concern, the telecommunications establishment is mulling how best to exploit the Web commercially while deploying such packet-switched networks as the integrated services digital network (ISDN) and such subscriber access technologies as asymmetric digital subscriber line (ADSL) to keep the telecom infrastructure from being overwhelmed. Amid the competitive pressures generated by deregulation, telecom companies have more incentive than ever to squeeze as much performance as possible out of their existing infrastructure. Hence the attraction of local-access technologies like ADSL for boosting the capacity of installed copper subscriber loops, and long-haul technologies like wavelength division multiplexing (WDM) for boosting the capacity of installed optical fiber. Wireless local-area networks (LANs) are benefiting from spread-spectrum technology, just as cellular telephony is. Also planned is provision of satellite-based, global mobile voice and datacom services to pocketsized, hand-held devices     

Avalanche noise characteristics of thin GaAs structures withdistributed carrier generation [APDs]

It is known that both pure electron and pure hole injection into thin GaAs multiplication regions gives rise to avalanche multiplication with noise lower than predicted by the local noise model. In this paper, it is shown that the noise from multiplication initiated by carriers generated throughout a 0.1 μm avalanche region is also lower than predicted by the local model but higher than that obtained with pure injection of either carrier type. This behavior is due to the effects of nonlocal ionization brought about by the dead space; the minimum distance a carrier has to travel in the electric field to initiate an ionization event