138 research outputs found
An Auto-Zero-Stabilized Voltage Buffer With a Quiet Chopping Scheme and Constant Sub-pA Input Current
No full textThis article describes an auto-zero stabilized voltage buffer that achieves low offset and low noise with sub-pA input current. A high gain stabilization loop is used to periodically cancel the buffer’s offset. The loop itself is periodically disconnected from the buffer and auto-zeroed, during which its bandwidth is reduced to reduce the associated noise folding. However, this also reduces its offset correction range, and so to avoid overloading, its initial offset is digitally trimmed. To break up the correlation between the residual low-frequency (LF) noise of the auto-zero and stabilization phases, the loop is periodically chopped, which significantly reduces the buffer’s LF noise. Finally, the duty-cycle of the two phases is optimized to bring the buffer’s LF noise density close to 2–√ times its white noise density (14 nV/ Hz−−−√ ), which is the fundamental limit of an AZ amplifier. The buffer also achieves a constant and low input current (0.8 pA), as well as a state-of-the-art offset (0.4 μV ).Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
A Chopper-Stabilized Amplifier with a Relaxed Fill-In Technique and 22.6pA Input Current
No full textIn chopper amplifiers, the interaction between the input signal and the chopper clock can cause intermodulation distortion (IMD). This is mainly due to finite amplifier bandwidth, which causes signal-dependent output spikes at the chopping transitions. Such chopper-induced IMD can be mitigated by the fill-in technique, which involves ping-ponging between the outputs of two identical OTAs chopped in quadrature, thus generating a spike-free output. In this letter, a relaxed implementation is proposed in which the output of a fill-in OTA is only briefly used to avoid the spikes of a chopped main OTA. As a result, the fill-in OTA does not need to be chopped, and so it can be duty-cycled to save power. Furthermore, the chopper ripple caused by the main OTA can now be suppressed by a single low-noise ripple-reduction loop, rather than the two AZ loops required in a previous ping-pong implementation of the fill-in technique. Compared to the latter, the proposed amplifier achieves similar IMD performance (-125.7 dB), a 25× lower input current (22.6 pA), and a flat noise floor (12 nV/ Hz).Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
31.4 A Chopper-Stabilized Amplifier with -107dB IMD and 28dB Suppression of Chopper-Induced IMD
No full textAmplifiers often employ chopping to achieve low offset and low-frequency noise. However, the interaction between the input signal and the chopper clock can cause chopper-induced intermodulation distortion (IMD) [1] -[5]. This is especially problematic for input frequencies (Fin) near even multiples of the chopping frequency (FCH), as the resulting IMD tones fold-back to low frequencies and so cannot be filtered out. In [2] -[4], spread-spectrum clocks are used to convert such tones into noise-like signals. However, this increases the noise floor and does not address the underlying problem. This paper shows that chopper-induced IMD is mainly due to amplifier delay, which results in large chopping spikes. A novel fill-in technique is proposed that mitigates these spikes, and so reduces the chopper-induced IMD. In a prototype chopper-stabilized amplifier, it reduces the chopper-induced IMD by 28dB, resulting in an IMD of -126dB for input frequencies near 4FCH (=80kHz). Similarly, it improves the chopped amplifier's two-tone IMD (79 and 80kHz) from -97dB to -107dB, thus maintaining the same IMD as the un-chopped amplifier.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
A Fill-In Technique for Robust IMD Suppression in Chopper Amplifiers
No full textIn chopper amplifiers, the interaction between the input signal and the chopper clock can give rise to intermodulation distortion (IMD). This chopper-induced IMD is mainly due to amplifier delay, which causes large pulses at the output of the amplifier's output chopper. This article proposes the use of a so-called fill-in technique to eliminate these pulses, and thus the resulting IMD, by multiplexing the outputs of two identical amplifiers that are chopped in quadrature. A prototype chopper-stabilized amplifier was implemented in a 180-nm CMOS process. Measurements show that the fill-in technique suppresses chopper-induced IMD by 28 dB, resulting in an IMD of -126 dB for input frequencies near 4 FCH (=80 kHz). It also improves the amplifier's two-tone IMD (with 79 and 80 kHz inputs) from -97 to -107 dB, which is the same as that obtained without chopping.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
The life and works of James Miller, 1704-1744, with particular reference to the satiric content of his poetry and plays.
No full textPhDJames Miller was born the son of a Dorset rector in 1704. He
was himself ordained, but acquired no benefice until just before his
early death, probably because of a scathing portrayal of the Bishop
of London in one of his verse satires. At Oxford he wrote a vivacious
comedy of humours, set in the University. Its production in 1730
began his dramatic career, at a time when the number of London
theatres had just doubled, and new dramatic forms were being invented.
In 1731 his poem Harlequin-Horace, a witty inversion of
the Ars Poetica, attacked pantomime and opera, but also painted a
lively portrait of the entire theatrical world, in the tradition of
the Dunciad.
After collaborating in a translation of Moliere's works Miller
wrote two plays based on this author. Of all his dramatic works
these were the most successful with his contemporaries, and were
followed by a modernisation of Much Ado, and a ballad-opera adapted
from an afterpiece by Jean-Baptiste Rousseau, and rendered highly
topical. Miller made similar use of a recent French comedy showing
a Red Indian's reactions to civilisation, a satiric "fable" by Walsh
and Voltaire's Mahomet. A large quantity of original material was
incorporated into most of these, and this is generally satirical in
nature. The Indian is made to voice almost egalitarian sentiments.
An afterpiece, "The Camp Visitants", satirised military inaction
in the war, and was apparently banned. The manuscripts of the six
plays produced after the Licensing Act bear the examiner's deletions,
and illustrate the nature of the censorship at this time.
Miller's greatest strength is probably his flexible, vigorously
colloquial dialogue. His political satire is mostly contained in
the poetry, which attacks Walpole's administration with increasing
vehemence through the seventeen-thirties, until its fall. In 1740
two poems that used Pope in symbolic contrast to Walpole caused a
sensation. In both poetry and plays Miller is also a social satirist,
who lays unusually strong emphasis on false taste and the deterioration
of culture
From Nonlinear Integrated Optics to Microresonator Frequency Combs
No full textPerhaps one of the most spectacular current applications of nonlinear integrated optics, a field
which was pioneered by George Stegeman more than thirty years ago [1], is that of nonlinear
microresonator based optical frequency comb light sources. Optical frequency comb sources are
characterized by a spectrum comprising many equally spaced components [2], and have a wide
range of scientific and technological applications. Although commercial comb generators are based
on mode-locked lasers and fiber supercontinuum generation, nonlinear integrated optics provides a
low-cost and chip-scale alternative, based on a low-power cw laser coupled into a high-Q
microresonator [3]. So far microresonator frequency combs have exploited the third order “Kerr”
nonlinearity, which permits to generate successive comb lines with a spacing equal to the resonator
free-spectral range via cascaded four-wave mixing [4-5]. Modeling of microresonator frequency
combs can be greatly simplified by a single partial differential equation approach [4-6], analogous
to the case of other coherently driven Kerr spatially diffractive [7] or temporally dispersive [8-9]
nonlinear cavities. In order to lower the threshold power and extend the spectral range of frequency
comb generation, for example into the visible or mid-infrared, while still using near-infrared cw
laser pumps, quadratic nonlinear cavities can be exploited [10]. These quadratic microresonator
frequency comb sources operate close to the phase-matching condition for the underlying quadratic
processes, and not in the cascading regime that reduces the dynamics to the Kerr case [11]. Quite
remarkably, a single time domain partial differential equation with an effective delayed third-order
nonlinearity was derived to describe with excellent accuracy the dynamics of quadratic frequency
comb generation [12-13]. In situations where multiple processes are present, and the frequency
combs generated around the interacting waves over multiple octaves overlap, we carried out
numerical modeling based on a single envelope equation approach [14].
References
[1] G.I. Stegeman, E.M. Wright, N. Finlayson, R. Zanoni, and C.T. Seaton, J. Lightwave Technology 6, 953 (1988).
[2] T. Udem, R. Holzwarth, and T. W. Hänsch, Nature 416, 233 (2002).
[3] P. Del’Haye, A. Schliesser, O. Arcizet, T. Wilken, R. Holzwarth, and T. J. Kippenberg, Nature 450, 1214 (2007).
[4] S. Coen, H. G. Randle, T. Sylvestre, and M. Erkintalo, Opt. Lett. 38, 37 (2013).
[5] T. Hansson, D. Modotto, and S. Wabnitz, Phys. Rev. A 88, 023819 (2013).
[6] T. Hansson, D. Modotto, and S.Wabnitz, Opt. Comm. 312, 134 (2014).
[7] L. A. Lugiato and R. Lefever, Phys. Rev. Lett. 58, 2209 (1987).
[8] M. Haelterman, S. Trillo, and S. Wabnitz, Opt. Commun. 91, 401 (1992).
[9] F. Leo, S. Coen, P. Kockaert, S.-P. Gorza, P. Emplit, and M. Haelterman, Nature Photon. 4, 471 (2010).
[10] I. Ricciardi, S. Mosca, M. Parisi, P. Maddaloni, L. Santamaria, P. De Natale, and M. De Rosa, Phys. Rev. A 91,
063839 (2015).
[11] G. I. Stegeman, D. J. Hagan, and L. Torner, Optical and Quantum Electronics 28, 1691 (1996).
[12] F. Leo, T. Hansson, I. Ricciardi, M. De Rosa, S. Coen, S. Wabnitz, and M. Erkintalo, Phys. Rev. Lett. 116, 033901
(2016).
[13] F. Leo, T. Hansson, I. Ricciardi, M. De Rosa, S. Coen, S. Wabnitz, and M. Erkintalo, Phys. Rev. A 93 (2016).
[14] T. Hansson, F. Leo, M. Erkintalo, J. Anthony, S. Coen, I. Ricciardi, M. De Rosa, and S. Wabnitz, J. Opt. Soc. Am.
B 33, 1207 (2016)
Etude de la relation existant, chez Aedes aegypti L., entre la durée d'exposition à un insecticide et la mortalité résultante [Dipt. Nematocera]
No full textUsing the W.H.O. test kit for adult mosquitoes, the author studies the exposure period-mortality relationship.
Young unfed females of Ae. aegypti and W.H.O. dieldrin and malathion impregnated papers are used, with exposure periods of 7m. 30s. up to 8 hours.
The recorded mortality is proportional to the exposure period logarithm. Characteristic lethal concentrations are inversely proportional to exposure period along the equation c.t = K.
So insecticide susceptibility in adult mosquitoes, Phlebotomus, tsetse flies, Stomoxys and Drosophila can be expressed either by characteristic lethal concentration, or by characteristic lethal exposure period.L'auteur étudie, à l'aide de la trousse O.M.S. pour la détermination de la sensibilité aux insecticides des moustiques adultes, la relation existant entre la durée d'exposition à l'insecticide et la mortalité.
Il utilise des femelles jeunes à jeun d'Ae. aegypti et les papiers O.M.S. imprégnés de dieldrine et de malathion, avec des temps d'exposition allant de 7m 30s à 8 heures.
La mortalité observée est proportionnelle au logarithme de la durée d'exposition. Les concentrations létales caractéristiques sont inversement proportionnelles au temps d'exposition selon une fonction du type c.t = constante.
Pour les moustiques adultes, les phlébotomes, les glossines, les stomoxes et les drosophiles, la sensibilité aux insecticides peut donc aussi bien être exprimée sous forme de temps d'exposition létal que sous forme de concentration létale.Hamon J. Etude de la relation existant, chez Aedes aegypti L., entre la durée d'exposition à un insecticide et la mortalité résultante [Dipt. Nematocera]. In: Bulletin de la Société entomologique de France, volume 68 (9-10), Novembre-décembre 1963. pp. 225-232
Etude de la relation existant, chez Aedes aegypti L., entre la durée d'exposition à un insecticide et la mortalité résultante [Dipt. Nematocera]
No full textUsing the W.H.O. test kit for adult mosquitoes, the author studies the exposure period-mortality relationship.
Young unfed females of Ae. aegypti and W.H.O. dieldrin and malathion impregnated papers are used, with exposure periods of 7m. 30s. up to 8 hours.
The recorded mortality is proportional to the exposure period logarithm. Characteristic lethal concentrations are inversely proportional to exposure period along the equation c.t = K.
So insecticide susceptibility in adult mosquitoes, Phlebotomus, tsetse flies, Stomoxys and Drosophila can be expressed either by characteristic lethal concentration, or by characteristic lethal exposure period.L'auteur étudie, à l'aide de la trousse O.M.S. pour la détermination de la sensibilité aux insecticides des moustiques adultes, la relation existant entre la durée d'exposition à l'insecticide et la mortalité.
Il utilise des femelles jeunes à jeun d'Ae. aegypti et les papiers O.M.S. imprégnés de dieldrine et de malathion, avec des temps d'exposition allant de 7m 30s à 8 heures.
La mortalité observée est proportionnelle au logarithme de la durée d'exposition. Les concentrations létales caractéristiques sont inversement proportionnelles au temps d'exposition selon une fonction du type c.t = constante.
Pour les moustiques adultes, les phlébotomes, les glossines, les stomoxes et les drosophiles, la sensibilité aux insecticides peut donc aussi bien être exprimée sous forme de temps d'exposition létal que sous forme de concentration létale.Hamon J. Etude de la relation existant, chez Aedes aegypti L., entre la durée d'exposition à un insecticide et la mortalité résultante [Dipt. Nematocera]. In: Bulletin de la Société entomologique de France, volume 68 (9-10), Novembre-décembre 1963. pp. 225-232
Sustainable Development of the Nile River at Greater Khartoum
No full textSudan is the largest country in Africa, but there is poverty and a lack of infrastructure, skills and opportunity despite its substantial natural resources. The capital of Sudan is Khartoum City,
located at the confluence of the Blue and White Nile Rivers. Unfortunately development on Nile
River Front is limited due to the risk of flooding and erosion. There is a danger that rapid
economic development may take place in this unique area without sustainable development
planning. This research project aims to develop strategies to protect the Nile River banks by
suitable stabilization methods so that development can take place safely.
Data has been collected about hydrology, morphology, geotechnical factors, soil classifications, river pattern systems, driving forces, and the main problems restricting sustainable development and engineering works for the Nile River. In addition the following have been reviewed: historical background, existing land uses, current environmental situations, and the economic and social conditions of the study areas. Research identified Cairo, Egypt as a similar case study, where data collected by the author included historical background, current situations, strategic visions and development plan for Nile River Shores. Further information was collected about sustainable development from a general literature review.
From these collected data a set of guidelines and indicators for sustainable development was
established related to environmental, economic and social factors. Based on those guidelines and
indicators, methods of stabilization of the banks for each shore were specified and a proposed
development plan was established. Methods of stabilization of banks and the development plan
were refined and evaluated to establish a final version of the development plan: Sustainable
Development of the Nile River Front (SDNRF) at Greater Khartoum. From refinement and evaluations, barriers and constraints for implementation were specified with their suggested
solutions. Finally, conclusions and recommendations related to the SDNRF Manual about
development and regulations were established
Frances Ellen Colenso, 1849-1887 : her life and times in relation to the Victorian stereotype of the middle class English woman
No full textIncludes bibliographical referencesThe stereotype of the Victorian middle class woman, which generally characterised her as a passive, ornamental, helpless and dependent creature, has been one of the most popular caricatures of the nineteenth century. Recent research into this hitherto largely ignored social class has begun to re-adjust this image. The stereotyped distressed gentlewoman who emigrated to Australia and New Zealand for instance has recently been critically examined, but so far the female emigrant and settler in colonial South Africa has been ignored. It is only since the early 1970s that academic research into feminism began to appear. The influence of the women's liberation movement and of the increasing interest in social history, while stimulating research into Victorian women in England and her colonies, has only penetrated historical research within South Africa in the last decade
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