Systematic analysis and cancellation of kickback noise in a dynamic latched comparator

A dynamic latched comparator can suffer from three non-idealities: offset voltage, random noise and kickback noise. Specifically in an analog-to-digital converter (ADC) the kickback noise of a comparator can noticeably affect the settling time and accuracy of the decision. This work offers an analytical treatment of kickback noise generation, and proposes a synchronized kickback noise cancellation technique, which is achieved via placing clocked NMOS-PMOS capacitors at the proper nodes to cancel out effectively those unwanted charges (electrons or holes) under different operating regions of the MOS devices. The technique is clock-rate insensitive and particularly suitable for the SAR-type ADC as it will not alter the charge stored in the capacitor array. Optimized in 65-nm CMOS the kickback noise is <±0.3 mV in 30× Monte–Carlo simulations at both 50- and 500-MHz clock rates. For 10-bit resolution in a full scale of 1 V_pp, the kickback noise of the proposed comparator comparing with the conventional one is improved by 48×, from 6.27 to 0.13 LSB.     

Widely tunable polarization-independent all-optical wavelengthconverter using a semiconductor optical amplifier

We report a polarization-independent widely tunable four-wave mixing wavelength converter using polarization diversity and broad-band orthogonal pumps in a single semiconductor optical amplifier. The conversion efficiency is nearly constant (less than 3-dB variation) over a 36-nm range with less than 0.34 dB polarization sensitivity. The power penalty at 10^-9 bit error rate for a 10-Gb/s signal is less than 0.9 dB     

The predictive ability of Bromilow's timecost model

Bromilow's log-log time-cost (BTC) model is tested and refitted with a new set of data for Australian construction projects completed between 1991 and 1998. It is shown that, as anticipated by earlier research, different parameter estimates are needed for different project types, with smaller industrial projects taking less time to complete than the smaller educational and residential projects. This results in the development of two separate models, one for industrial projects and one for non-industrial projects. No changes in parameter estimates are needed for projects with different client sectors, contractor selection methods and contractual arrangements. Alternatives to the log-log model failed to produce any improved fit. Finally, the results are compared with previous work to indicate the extent of changes in time-cost relationships in Australian construction projects over the last 40 years. This indicates a clear improvement in construction speed over the period. Furthermore, the ‘public’ sector group in particular has exhibited a greater variation (up to 132%) over the years.     

Broadband microstrip patch antenna

The characteristics of a rectangular microstrip antenna with an L-shaped probe are investigated. A foam layer with a thickness of around 10% of the wavelength is used as the supporting substrate. An impedance bandwidth of 35% and an average gain of 7.5 dBi can be achieved. The radiation pattern is stable across the passband     

Defect and error tolerance in the presence of massive numbers of defects

As scaling approaches the physical limits of devices, we will continue to see increasing levels of process variations, noise, and defect densities. Many applications today can tolerate certain levels of errors resulting from such factors. We introduce a new approach for error tolerance resulting in chips containing only error acceptable for such applications.     

Structural, Dielectric, and Thermal Properties of Strontium Barium Niobate-Doped Fused Silica Nanocomposites

Ferroelectric strontium barium niobate (SBN)-doped Na₂O–B₂O₃–SiO₂ (NBS) glass nanocomposites were prepared by dispersing sol–gel-derived SBN powder into fused NBS glass. Their structures were characterized by X-ray diffractometry and Raman spectroscopy. The dielectric constants were measured as functions of frequency and temperature using an impedance analyzer. The ferroelectric-to-paraelectric-phase transition was studied by differential scanning calorimetric analysis. Our results revealed that the embedded SBN has lower phase transition temperature and phase transition heat than those of SBN bulk materials. Their activation energy, however, is larger than that of SBN ultra-fine powders. Pure tetragonal-phase SBN nanocomposites can be obtained at annealing temperatures of 750°–1000°C. Their dielectric constants are ∼32–46 and ∼20–25 at low frequencies and radio frequencies, respectively, and the loss tangent is <0.1 at room temperature in the radio frequencies range. Our studies suggested that additional reduction in the loss properties must be made before these systems can be considered for application as microwave dielectric materials.     

Development of a magnetron-enhanced plasma process for tungstenetchback with response-surface methodology

A two-step etchback process to form tungsten plugs in submicron contacts and vias has been developed. the process uses an Applied Materials Inc., P5000 WCVD magnetron-enhanced, single-wafer system with an experimental design and response-surface methodology. Tungsten is first etched with an Ar/SF₆ mixture until excited N₂ molecules from the underlying TiN adhesion layer are detected in the plasma. Residual TiN is then etched for a fixed time with an Ar/Cl ₂ plasma. Both steps employ a rotating 0.5-Hz magnetic field. Although the use of the magnetic field has no pronounced effect on the etch rate of either film, it provides broad regions of high etch uniformity. In addition, the DC-bias voltage measured as part of the TiN study decreases with increasing magnetic field strength without reducing the etch rate of the film     

CD28-independent, TRAF2-dependent costimulation of resting T cells by 4-1BB ligand

4-1BB ligand (4-1BBL) is a member of the tumor necrosis factor (TNF) family expressed on activated antigen-presenting cells. Its receptor, 4-1BB, is a member of the TNF receptor family expressed on activated CD4 and CD8 T cells. We have produced a soluble form of 4-1BBL using the baculovirus expression system. When coimmobilized on plastic with anti-CD3, soluble 4-1BBL induces interleukin (IL)-2 production by resting CD28+ or CD28- T cells, indicating that 4-1BBL can function independently of other cell surface molecules, including CD28, in costimulation of resting T cell activation. At low concentrations of anti-CD3, 4-1BBL is inferior to anti-CD28 in T cell activation. However, when 4-1BB ligand is provided together with strong TCR signals, then 4-1BBL and anti-CD28 are equally potent in stimulation of IL-2 production by resting T cells. We find that TNF receptor-associated factor (TRAF)1 or TRAF2 associate with a glutathione S-transferase-4-1BB cytoplasmic domain fusion protein in vitro. In T cells, we find that association of TRAF1 and TRAF2 with 4-1BB requires 4-1BB cross-linking. In support of a functional role for TRAF2 in 4-1BB signaling, we find that resting T cells isolated from TRAF2-deficient mice or from mice expressing a dominant negative form of TRAF2 fail to augment IL-2 production in response to soluble 4-1BBL. Thus 4-1BB, via the TRAF2 molecule, can provide CD28-independent costimulatory signals to resting T cells.