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Through the Lens of Color: An Interview with Gareth Doherty, Author of Paradoxes of Green: Landscapes of a City-State
No full textThis interview by Mark Tirpak with Gareth Doherty of Harvard University Graduate School of Design, focuses on his Paradoxes of Green: Landscapes of a City-State (University of California Press, 2017). With Paradoxes of Green (2017) and via the interview, Doherty recounts some of the findings of his ethnographic fieldwork in the Kingdom of Bahrain and describes tensions arising from differing conceptions of what ‘green’ means or signifies within this growing and predominantly arid region. An argument that Doherty makes in Paradoxes of Green (2017) is that color and form are interlinked, and that color deserves deeper consideration by policy-makers and other formal shapers of cities. The interview draws from Paradoxes of Green (2017) to discuss some of Doherty’s findings as well as his latest work on the intersections between landscape architecture and anthropology.Version of Recor
A Wideband Two-Way Digital Doherty Transmitter in 40nm CMOS
No full textA 40nm CMOS wideband digital Cartesian push-pull inverted Doherty operating in class-E is presented. Wideband Doherty operation is achieved over a 1.9-to-3GHz frequency band, using an off-chip power combining network. The fully digital transmitter (DTX) provides 25.3dBm peak power with a drain/DTX line-up efficiency (DE/SE) of 58.7%/44.9%, respectively, at 2.4GHz. When operated with a 160MHz 256-QAM OFDM signal, it achieves 46.1%/32.7% average DE/SE, with an ACLR and EVM better than −40.6dBc and −33.9dB, respectively, using a simple memory-less digital pre-distortion (DPD).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
Through the Lens of Color: An Interview with Gareth Doherty, Author of Paradoxes of Green: Landscapes of a City-State
No full textThis interview by Mark Tirpak with Gareth Doherty of Harvard University Graduate School of Design, focuses on his Paradoxes of Green: Landscapes of a City-State (University of California Press, 2017). With Paradoxes of Green (2017) and via the interview, Doherty recounts some of the findings of his ethnographic fieldwork in the Kingdom of Bahrain and describes tensions arising from differing conceptions of what ‘green’ means or signifies within this growing and predominantly arid region. An argument that Doherty makes in Paradoxes of Green (2017) is that color and form are interlinked, and that color deserves deeper consideration by policy-makers and other formal shapers of cities. The interview draws from Paradoxes of Green (2017) to discuss some of Doherty’s findings as well as his latest work on the intersections between landscape architecture and anthropology
Financial Innovation in the Management of Catastrophe Risk
No full textCatastrophic events such as hurricane and earthquakes are the dominant source of risk for many property casualty insurers. Primary insurers usually limit the scale and geographic scope of their operations in order to focus on core competencies such as marketing, underwriting and loss control. But his often leaves them without sufficient geographic spread to diversify catastrophe risk. The traditional hedge for the primary insurer is reinsurance. Specialist reinsurers achieve a spacial spread of risk and can therefore bear catastrophe risk that is undiversifiable to the primary. But the transaction costs associated with reinsurance, and therefore premiums, are high. High premiums, coupled with the fact that catastrophe losses exhibit little correlation with capital market indices, has attracted considerable activity in Wall Street in searching for new instruments that securitize catastrophe risk. Indeed many players are now talking of catastrophe risk being a new “asset class” and new instruments such as catastrophe options and catastrophe bonds are starting to appear. The rationale for these new instruments is usually developed as follows. Recent catastrophe events such as Hurricane Andrew and the Northridge earthquake have imposed costs on the insurance industry of an order of magnitude not thought possible only a decade ago. More sophisticated modeling now presents potential losses to the industry of 200 billion. Two such events, or one such event combined with continued mass tort claims (e.g. successful plaintiff claims in tobacco litigation) could cripple the whole industry. However, losses of this size would hardly cause a ripple in capital markets. The U.S. capital market currently currently consists of securities representing some $13 trillion of investor wealth and the loss scenarios cited above amount to less than one standard deviation of daily trading volume. Presentations by merchant bankers, reinsurance brokers and others have echoed this potential for diversifying catastrophe risk within the capital market. The high transactions costs of reinsurance offers potential for hedging instruments to be offered to primary insurers that are both competitive with current reinsurance and which offer investors high rates of return. Moreover, since catastrophe risk is uncorrelated with market indices, the benchmark for such investments is just the risk free rate. Pricing new instruments requires that the expected loss be estimated with some. Until recently, insurers and reinsurers had a comparative advantage in information on catastrophic events. But in the past decade a number of modeling firms have developed models that combine seismic and meteorological information with data on the construction, siting, and value of individual buildings. These models can be used to simulate the economic effects of many thousands of storms and earthquakes. Although such models are used by the insurance firms and reinsurers, mainly for loss estimation and re-balancing their exposure, the same models are now available to other companies and investors. The arrival of the modelers and their models is eroding the comparative information advantage of insurers and reinsurers and opening the door to new players. Insurers will retain their comparative advantage over, say, merchant banks in related insurance services such as marketing, underwriting and loss settlement facilities. But the stage has been set for an unbundling of insurance products with insurers retaining marketing underwriting and settlement services and risk bearing by-passing the reinsurance industry and being provided more directly from the capital market. But the combination of high transaction costs for reinsurance and the vast capacity of the capital market for diversification, is not sufficient to ensure the success of these new instruments. The costs associated with reinsurance do not necessarily reflect monopoly rent. Relationships between primary insurers and reinsurers involve moral hazard; the relationship relaxes the incentive for the insurer to underwrite carefully or to settle claims efficiently. Consequently, the reinsurer will monitor the primary. Moreover, long term relationships are often formed to counter such expropriation. The apparently high transaction costs of reinsurance may simply reflect the resolution of moral hazard. If new instruments such as catastrophe options and bonds are to compete successfully with reinsurance, they must be able resolve incentive conflicts between the primary insurer and the ultimate risk bearer. Indeed, if moral hazard is not resolved, using past insurance loss data to estimate the potential returns for purchasers of catastrophe bonds, etc, is spurious. The purpose of this paper is to examine and categorize new catastrophe hedging instruments. These instruments will then be compared with traditional risk management strategies adopted by primary insurers in order to compare their relative efficiency at resolving incentive conflicts. Each instrument offers a different combination of credit risk, basis risk and moral hazard. For example, catastrophe reinsurance is subject to significant credit risk and moral hazard, but does not encounter significant basis risk. I will argue that the differential performance of the traditional and new instruments offers primary insurers with a richer portfolio of risk management strategies, though no strategy is dominant in its performance on all three criteria.
Wideband Digital Intensive Doherty Concepts
No full textMany applications require wide bandwidth transmitters, but unfortunately, they usually have way less than 50% average drain efficiency for their modulated signals. This low efficiency is a significant drawback in all wireless applications, both for battery power devices and base stations. The Doherty radio frequency (RF) power amplifier architecture is widely used to enhance the average efficiency for modulated signals in base stations. Its popularity is due to its relatively cheap and simple hardware and its suitability to handle high-power wideband modulated signals. However, even Doherty amplifiers often have less than 50% average efficiency and are restricted in their RF bandwidth.This thesis reviews recent research on the Doherty power amplifier (DPA) topology and discusses possible power and bandwidth efficiency improvements. In the second part of the thesis, another topology is introduced, which also provides Doherty-like behavior. That topology is called a Pseudo Doherty Load Modulated Balanced Amplifier (PD-LMBA). The performance of PD-LMBA is compared with “conventional” DPAs. Circuit design examples of DPA and PD-LMBA are given. The thesis concludes with a PD-LMBA prototype design, which appears to be very promising in its wideband performance.Electrical Engineering | Microelectronic
Helping children think: Gaze aversion and teaching
No full textLooking away from an interlocutor's face during demanding cognitive activity can help adults answer challenging arithmetic and verbal-reasoning questions (Glenberg, Schroeder, & Robertson, 1998). However, such `gaze aversion' (GA) is poorly applied by 5-year-old school children (Doherty-Sneddon, Bruce, Bonner, Longbotham, & Doyle, 2002). In Experiment 1 we trained ten 5-year-old children to use GA while thinking about answers to questions. This trained group performed significantly better on challenging questions compared with 10 controls given no GA training. In Experiment 2 we found significant and monotonic age-related increments in spontaneous use of GA across three cohorts of ten 5-year-old school children (mean ages: 5;02, 5;06 and 5;08). Teaching and encouraging GA during challenging cognitive activity promises to be invaluable in promoting learning, particularly during early primary years
A Highly Linear Wideband Polar Class-E CMOS Digital Doherty Power Amplifier
No full textThis article presents the first application of a digital-intensive intrinsically linear digitally controlled class-E technique in a Doherty configuration. By careful nonlinear segmentation and multiphase RF-clocking along with overdrive-voltage control and automatic duty-cycle correction, it is shown that even the nonlinearities related to Doherty operation can be fully handled by the underlying design such that digital predistorion (DPD) can be, in principle, omitted. The nonlinearity behavior of the whole digital Doherty power amplifier (PA) is analyzed, and closed-form equations are given to predict the AM-AM and AM-phase modulation (PM) curves. In addition, time/phase mismatch between the peak and main branches and the AM and PM signals is accurately compensated. In order to achieve the maximum intrinsic linearity, two separate chips with the same architecture, but different design parameters, are fabricated as the main and peak amplifiers in 40-nm bulk CMOS. To achieve a large RF bandwidth and high passive combiner efficiency, a differential low-loss, wideband Marchand balun-based Doherty power combiner, implemented using reentrant coupled lines with independent second-harmonic control is proposed, and together with the matching network is fabricated on a two-layer PCB. The measured peak/6-dB power backoff P OUT, drain efficiency/power-added efficiency at 2.4 GHz are 17.5 dBm/12.2 dBm, 57%/52% and 36%/25% with VDD main/peak = 0.6 V/0.7 V. Measured results without using DPD show -41-dBc adjacent channel power ratio (ACPR) and -36-dB error vector magnitude (EVM) for a 16-MHz OFDM signal at 2.5 GHz. By using DPD, the measured ACPR and EVM of a 16-MHz/32-MHz OFDM signals are -52 dBc/-48 dBc and -50 dB/-48 dB, respectively.Accepted author manuscriptElectronic
A 39 W Fully Digital Wideband Inverted Doherty Transmitter
No full textA high-power fully-digital Doherty transmitter (DDTX) is proposed. It features two segmented LDMOS output switch banks implemented in a custom V T -down-shifted LDMOS technology. A 40 nm CMOS controller digitally activates the individual LDMOS gate segments of the output stage at RF speed. An inverted Doherty power combiner is proposed that features non-short circuited 2 nd harmonic conditions for the main and peak switch banks to boost the RF bandwidth. To guarantee smooth output power and efficiency vs. frequency, a 2 nd harmonic trap is introduced in the power combiner, yielding an RF bandwidth of > 400 MHz. The realized demonstrator can achieve over 39 W peak output power. Its highest drain and system efficiencies, respectively 60 % and 57 %, were found at 34.2 W of output power, while in power back-off its peak drain and system efficiencies are 52 % and 48 % respectively. Over a 25 dB output range, the system efficiency is within 4 percent points of the drain efficiency.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
A Millimeter-Wave CMOS Series-Doherty Power Amplifier With Post-Silicon Inter-Stage Passive Validation
No full textThis article presents a wideband series-Doherty power amplifier (SDPA) for millimeter-wave (mm-wave) fifth-generation (5G) applications. It features a compact two-step impedance inverting-based series-Doherty power combiner that provides broadband close-to-perfect power back-off (PBO) efficiency enhancement. The amplitude-to-amplitude (AM-AM)/amplitude-to-phase (AM-PM) performance of the load-modulated Doherty power amplifier for broadband operation is analyzed. We also devise a post-silicon inter-stage passive validation (PSIV) approach to evaluate the mm-wave chip prototype utilizing the embedded voltage root mean square detectors. The proposed SDPA is realized in a 40-nm bulk CMOS, and it delivers 20.4 dBm PSAT with 39.1%/34% PAE at 0-/6-dB PBO. Over a 23.5-30 GHz band, its PAE is >24% at 6-dB PBO. At 27 GHz, applying a '2 GHz 16-quadratic-amplitude modulation (QAM) orthogonal frequency-division multiplexing (OFDM)' signal, the proposed SDPA generates 10.2 dBm average power with 18.9% average PAE. The average error vector magnitude is better than -24.5 dB without digital predistortion for a '400-MHz 64-QAM OFDM' signal while generating an average output power of 8.8 dBm with 15% PAE. The AM-AM/AM-PM of the realized SDPA is investigated by employing a '50-MHz 64-QAM OFDM' signal, validating our analysis and showing that the linearity limitation of DPAs is systematic and predictable. Utilizing the proposed PSIV approach, the frequency response of the input/inter-stage passive circuits is measured, indicating an excellent agreement with 3-D electromagnetic (EM) simulation results.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
Recent Developments of Dual-Band Doherty Power Amplifiers for Upcoming Mobile Communications Systems
No full textPower amplifiers in modern and future communications should be able to handle different modulation standards at different frequency bands, and in addition, to be compatible with the previous generations. This paper reviews the recent design techniques that have been used to operate dual-band amplifiers and in particular the Doherty amplifiers. Special attention is focused on the design methodologies used for power splitters, phase compensation networks, impedance inverter networks and impedance transformer networks of such power amplifier. The most important materials of the dual-band Doherty amplifier are highlighted and surveyed. The main problems and challenges covering dual-band design concepts are presented and discussed. In addition, improvement techniques to enhance such operations are also exploited. The study shows that the transistor parasitic has a great impact in the design of a dual-band amplifier, and reduction of the transforming ratio of the inverter simplifies the dual-band design. The offset line can be functionally replaced by a Π-network in dual-band design rather than T-network
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