InP HBT integrated circuit technology with selectively implanted subcollector and regrown device layers

We describe a quasi-planar HBT process using a patterned implanted subcollector with a regrown MBE device layer. Using this process, we have demonstrated discrete SHBT with f/sub t/>250 GHz and DHBT with f/sub t/>230 GHz. The process eliminates the need to trade base resistance for extrinsic base/collector capacitance. Base/collector capacitance was reduced by a factor of 2 over the standard mesa device with a full overlap between the heavily doped base and subcollector regions. The low proportion of extrinsic base/collector capacitance enables further vertical scaling of the collector even in deep submicrometer emitters, thus allowing for higher current density operation. Demonstration ring oscillators fabricated with this process had excellent uniformity and yield with gate delay as low as 7 ps and power dissipation of 6 mW/CML gate. At lower bias current, the power delay product was as low as 20 fJ. To our knowledge, this is the first demonstration of high-performance HBTs and integrated circuits using a patterned implant on InP.     

A new technique for shaped beam synthesis of equispaced arrays

Use is made of an existing technique to synthesize a sum pattern whose sidelobe peaks fit a prescribed envelope in a specified segment of the visible region. In terms of a polynomial representation of the pattern, certain roots are then displaced radially off the unit circle to achieve null-filling. The result is a shaped beam with low, equal-percentage ripple, and sidelobe heights in the nonshaped region that are individually controlled. The procedure is illustrated for a linear array, designed to produce acsc^{2}theta costhetapattern.     

Adaptive inverse filters for stereophonic sound reproduction

A general theoretical basis for the design of adaptive digital filters used for the equalization of the response of multichannel sound reproduction systems is described. The approach is applied to the two-channel case and then extended to deal with arbitrary numbers of channels. The intention is to equalize not only the response of the loudspeakers and the listening room but also the crosstalk transmission from right loudspeaker to left ear and vice versa. The formulation is a generalization of the Atal-Schroeder crosstalk canceler. However, the use of a least-squares approach to the digital filter design and of appropriate modeling delays potentially allows the effective equalization of nonminimum phase components in the transmission path. A stochastic gradient algorithm which facilitates the adaptation of the digital filters to the optimal solution, thereby providing the possibility of designing the filters in situ, is presented. Some experimental results for the two-channel case are given     

Design of a 3-D fully depleted SOI computational RAM

We introduce a three-dimensional (3-D) processor-in-memory integrated circuit design that provides progressively increasing processing power as the number of stacked dies increases, while incurring no extra design effort or mask sets. Innovative techniques for processor/memory redundancy and fast global bus evaluation are described. The architecture can be augmented with a nearest-neighbor physical 3-D communications network that can substantially reduce interconnect lengths and relieve routing congestion. The test chip, with 128 Kb of memory and 512 processing elements (PEs) on two fully depleted silicon-on-insulator (SOI) dies, can achieve a peak of 170 billion-bit-operations per second at 400 MHz.     

A mixed MAP/MLSE receiver for convolutional coded signalstransmitted over a fading channel

This paper addresses the problem of estimating a rapidly fading convolutionally coded signal such as might be found in a wireless telephony or data network. We model both the channel gain and the convolutionally coded signal as Markov processes and, thus, the noisy received signal as a hidden Markov process (HMP). Two now-classical methods for estimating finite-state hidden Markov processes are the Viterbi (1967) algorithm and the a posteriori probability (APP) filter. A hybrid recursive estimation procedure is derived whereby one hidden process (the encoder state in our application) is estimated using a Viterbi-type (i.e., sequence based) cost and the other (the fading process) using an APP-based cost such as maximum a posteriori probability. The paper presents the new algorithm as applied specifically to this problem but also formulates the problem in a more general setting. The algorithm is derived in this general setting using reference probability methods. Using simulations, performance of the optimal scheme is compared with a number of suboptimal techniques-decision-directed Kalman and HMP predictors and Kalman filter and HMP filter per-survivor processing techniques     

Atomistic Origin of the Enhanced Crystallization Speed and n‐Type Conductivity in Bi‐doped Ge‐Sb‐Te Phase‐Change Materials

Phase‐change alloys are the functional materials at the heart of an emerging digital‐storage technology. The GeTe‐Sb₂Te₃ pseudo‐binary systems, in particular the composition Ge₂Sb₂Te₅ (GST), are one of a handful of materials which meet the unique requirements of a stable amorphous phase, rapid amorphous‐to‐crystalline phase transition, and significant contrasts in optical and electrical properties between material states. The properties of GST can be optimized by doping with p‐block elements, of which Bi has interesting effects on the crystallization kinetics and electrical properties. A comprehensive simulational study of Bi‐doped GST is carried out, looking at trends in behavior and properties as a function of dopant concentration. The results reveal how Bi integrates into the host matrix, and provide insight into its enhancement of the crystallization speed. A straightforward explanation is proposed for the reversal of the charge‐carrier sign beyond a critical doping threshold. The effect of Bi on the optical properties of GST is also investigated. The microscopic insight from this study may assist in the future selection of dopants to optimize the phase‐change properties of GST, and also of other PCMs, and the general methods employed in this work should be applicable to the study of related materials, for example, doped chalcogenide glasses.     

Tapered transmission lines with a controlled ripple response

A synthesis procedure is presented which generalizes Klopfenstein's Dolph-Chebyshev design of a tapered transmission line to give a response with all lobe heights in the passband individually specified. This iterative technique permits the design of tapered transmission line sections with frequency responses of a wide variety. A rippled response can also be produced, with the peak and trough of each ripple cycle separately prescribed. A mixed response, part lobelike and part rippled, is also feasible. The computer program used in this technique is simple to write and economical to run. Experience has shown that the convergence is rapid, and that practical specifications lead to physically realizable tapers     

Resonant length of longitudinal slots and validity of circuit representation: Theory and experiment

Pertinent theory for the design of longitudinal slot arrays is reviewed and its dependence on the dominant mode scattering off a single slot is pinpointed. The critical need to know resonant length versus slot offset is emphasized and the desirability of determining this information theoretically rather than experimentally is argued. Then method of moments solutions are used to calculate resonant length versus slot offset for given waveguide dimensions and frequency. These theoretical results are compared to new, carefully obtained experimental data. Agreement is found to be so good, it is concluded that one can dispense with the costly gathering of experimental input data when designing longitudinal slot arrays fed by standard rectangular waveguide. A critical look is taken at the validity of representing the longitudinal slot as a shunt element on an equivalent transmission line. This assumption is found to be more and more questionable as thebdimension is reduced. For quarter-height guide, an alternate design procedure is suggested as being more accurate.     

Algorithm for multichannel LMS adaptive filtering

A modification of the LMS algorithm is presented in which the coefficients of an array of FIR filters, whose outputs are linearly coupled to an array of sensors, are adapted to minimise the mean-square sum of the error signals from these sensors. The application of the algorithm to the control of distributed parameter systems is discussed.     

Circadian rhythms and photoperiodic time measurement in mammals

Many mammalian species display seasonal breeding patterns correlated with annual cycles of change in the physiology and morphology of the reproductive system. Such annual reproductive cycles are often photoperiodically controlled (i.e, the annual change in day length determines when reproductive activity begins and when it ends within the annual cycle). Photoperiodic control of seasonally appropriate changes in reproductive activity is dependent on an endogenous time measuring process. Among mammals the physiological basis of photoperiodic time measurement has been studied most extensively in the golden hamster. Studies with this species indicate that photoperiodic time measurement is executed by the circadian system. The time measuring process depends on a circadian oscillation of responsiveness to light with properties similar to those of the hypothetical rhythm originally proposed by Bünning to explain photoperiodic phenomena in plants. The available evidence strongly suggests the participation of the pineal gland and the suprachiasmatic nucleus (SCN) in the photoperiodic regulation of mammalian reproductive cycles. However, little is known regarding concrete physiological mechanisms, and the extent to which the SCN and the pineal gland may participate in the time measuring process per se remains to be determined.