Trends and differences of the temperature effect on mismatch in different CMOS technology nodes

Statistical drain-current differences between pairs of supposedly identical transistors, usually known as matching, represent a crucial aspect of analog and mixed-signal circuits. Although matching has been a subject of study for more than two decades, how the temperature affects it is still scarcely discussed in the open literature [1,2]. In previous work, we discussed temperature effects on matching properties for a low-power CMOS 65-nm platform [1]. Measurements have been performed over a temperature range of 0 ◦C to 125 ◦C under several operating conditions. We discussed the temperature impact on relative current mismatch in the deep subthreshold region and the behavior of relative ION mismatch for individual pairs over temperature. Both subjects are important in modern circuit designs since the subthreshold region is often employed in ultra low-power circuits, while a drift in the individual pair mismatch can create problems in trimmed circuits. In this paper we expand the original study by considering a wide span of technology nodes (140 nm to 45 nm). A broader range of device architectures and gate lengths is crucial for a better understanding of the physics behind the mismatch-temperature relation and propose consistent compact model solutions. The relative drain current mismatch is analyzed using fluctuation sweeps. In figures 1 and 2 an example of this comparison is shown. The device architecture has a big impact on the matching already at room temperature, for example in the case of NMOS for C45 (Fig. 1) the presence of the halos worsens the matching [3]. It is therefore interesting to see how such changes affect the temperature dependence. In this respect, trends of the threshold voltage mismatch and the relative current factor mismatch will be also shown. In conclusion, this paper provides reliable information for circuit designers and system architects on the issue of the influence of temperature on mismatch based on a large set of measurements spanning different technology nodes

New light curves and ephemeris for the close eclipsing binary V963 PER

We have obtained CCD photometry in 2010-11 of V963 Per (=GSC3355 0394), which is a recently identified close binary star with unequal eclipse depths. The seven new eclipse timings yield an improved ephemeris, but we caution that secondary eclipse can be affected by variation of the light curve. This variation seems to be on a monthly timescale at the few percent level.Comment: 6 pages, 3 figure

V532 oph is a new R coronae borealis star

V532 Oph has been found to be a member of the rare, hydrogen-deficient R Coronae Borealis (RCB) stars from new photometric and spectroscopic data reported in this article. The light curve of V532 Oph shows the sudden, deep, irregularly spaced declines characteristic of RCB stars. Its optical spectrum is typical of a warm (Teff ∼ 7000 K) RCB star, showing weak or absent hydrogen lines, C2 Swan bands, and no evidence for 13C. In addition, the star shows small pulsations typical of an RCB star and an infrared excess due to circumstellar dust. It also appears to be significantly reddened by foreground dust. The distance to V532 Oph is estimated to be 5.5-8.7 kpc. These new data show that this star was misclassified as an eclipsing binary in the General Catalog of Variable Stars. The new data presented here for V532 Oph reveal the power of high-quality, high-cadence, all-sky photometric surveys, such as ASAS-3, to identify new RCB candidates on the basis of light-curve data alone, now that they have been collecting data for durations sufficiently long to reveal multiple declines. Despite their small numbers, RCB stars may be of great importance in understanding the late stages of stellar evolution. In particular, their measured isotopic abundances imply that many, if not most, RCB stars are produced by WD mergers, which may be the low-mass counterparts of the more massive mergers thought to produce type Ia supernovae. Therefore, establishing the population of RCB stars in the Galaxy will help constrain the frequency of these WD mergers. © 2009. The Astronomical Society of the Pacific. All rights reserved

All conformally flat pure radiation metrics

The complete class of conformally flat, pure radiation metrics is given, generalising the metric recently given by Wils.Comment: 7 pages, plain Te

Photometry of GSC 762-110, a new triple-mode radially pulsating star

Stars pulsating in three radial modes are very rare; only three examples are known in the Galaxy. These stars are very useful since their periods may be measured very precisely, and this will constrain the global stellar parameters and the models of the star's interior. The purpose of this paper is to present a new example of the class of triple-mode radial pulsators. A search for candidate multi-mode pulsators was carried out in public survey data. Time-series photometry of one of the candidates, GSC 762-110, was performed. GSC 762-110 was found to be a triple-mode radial pulsator, with a fundamental period of 0.1945d and period ratios of 0.7641 and 0.8012. In addition two non-radial modes were found, for which the amplitude has diminished considerably over the last few years.Comment: Accepted for publication in Astronomy & Astrophysic

V371 Per - A Thick-Disk, Short-Period F/1O Cepheid

V371 Per was found to be a double-mode Cepheid with a fundamental mode period of 1.738 days, the shortest among Galactic beat Cepheids, and an unusually high period ratio of 0.731, while the other Galactic beat Cepheids have period ratios between 0.697 and 0.713. The latter suggests that the star has a metallicity [Fe/H] between -1 and -0.7. The derived distance from the Galactic Plane places it in the Thick Disk or the Halo, while all other Galactic beat Cepheids belong to the Thin Disk. There are indications from historical data that both the fundamental and first overtone periods have lengthened.Comment: Accepted for publication in MNRA

Analysis of RR Lyrae Stars in the Northern Sky Variability Survey

We use data from the Northern Sky Variability Survey (NSVS), obtained from the first generation Robotic Optical Transient Search Experiment (ROTSE-I), to identify and study RR Lyrae variable stars in the solar neighborhood. We initially identified 1197 RRab (RR0) candidate stars brighter than the ROTSE median magnitude V = 14. Periods, amplitudes, and mean V magnitudes are determined for a subset of 1188 RRab stars with well defined light curves. Metallicities are determined for 589 stars by the Fourier parameter method and by the relationship between period, amplitude, and [Fe/H]. We comment upon the difficulties of clearly classifying RRc (RR1) variables in the NSVS dataset. Distances to the RRab stars are calculated using an adopted luminosity-metallicity relation with corrections for interstellar extinction. The 589 RRab stars in our final sample are used to study the properties of the RRab population within 5 kpc of the Sun. The Bailey diagram of period versus amplitude shows that the largest component of this sample belongs to Oosterhoff type I. Metal-rich ([Fe/H] > -1) RRab stars appear to be associated with the Galactic disk. Our metal-rich RRab sample may include a thin disk as well as a thick disk population, although the uncertainties are too large to establish this. There is some evidence among the metal-rich RRab stars for a decline in scale height with increasing [Fe/H], as was found by Layden (1995). The distribution of RRab stars with -1 < [Fe/H] < -1.25 indicates that within this metallicity range the RRab stars are a mixture of stars belonging to halo and disk populations.Comment: 68 pages, 26 figures, 9 tables, accepted to A

Discovery of a Very Young Field L Dwarf, 2MASS J01415823-4633574

While following up L dwarf candidates selected photometrically from the Two Micron All Sky Survey, we uncovered an unusual object designated 2MASS J01415823-4633574. Its optical spectrum exhibits very strong bands of vanadium oxide but abnormally weak absorptions by titanium oxide, potassium, and sodium. Morphologically such spectroscopic characteristics fall intermediate between old, field early-L dwarfs (log(g)~5) and very late M giants (log(g)~0), leading us to favor low gravity as the explanation for the unique spectral signatures of this L dwarf. Such a low gravity can be explained only if this L dwarf is much lower in mass than a typical old field L dwarf of similar temperature and is still contracting to its final radius. These conditions imply a very young age. Further evidence of youth is found in the near-infrared spectrum, including a triangular-shaped H-band continuum reminiscent of young brown dwarf candidates discovered in the Orion Nebula Cluster. Using the above information along with comparisons to brown dwarf atmospheric and interior models, our current best estimate is that this L dwarf has an age of 1-50 Myr and a mass of 6-25 M_Jupiter. The location of 2MASS 0141-4633 on the sky coupled with a distance estimate of ~35 pc and the above age estimate suggests that this object may be a brown dwarf member of either the 30-Myr-old Tucana/Horologium Association or the ~12-Myr-old beta Pic Moving Group.Comment: Accepted for publication in the 10 March 2006 issue (volume 639) of the Astrophysical Journa