Linear Operation of Switch-Mode Outphasing Power Amplifiers

Radio transceivers are playing an increasingly important role in modern society. The ”connected” lifestyle has been enabled by modern wireless communications. The demand that has been placed on current wireless and cellular infrastructure requires increased spectral efficiency however this has come at the cost of power efficiency. This work investigates methods of improving wireless transceiver efficiency by enabling more efficient power amplifier architectures, specifically examining the role of switch-mode power amplifiers in macro cell scenarios. Our research focuses on the mechanisms within outphasing power amplifiers which prevent linear amplification. From the analysis it was clear that high power non-linear effects are correctable with currently available techniques however non-linear effects around the zero crossing point are not. As a result signal processing techniques for suppressing and avoiding non-linear operation in low power regions are explored. A novel method of digital pre-distortion is presented, and conventional techniques for linearisation are adapted for the particular needs of the outphasing power amplifier. More unconventional signal processing techniques are presented to aid linearisation of the outphasing power amplifier, both zero crossing and bandwidth expansion reduction methods are designed to avoid operation in nonlinear regions of the amplifiers. In combination with digital pre-distortion the techniques will improve linearisation efforts on outphasing systems with dynamic range and bandwidth constraints respectively. Our collaboration with NXP provided access to a digital outphasing power amplifier, enabling empirical analysis of non-linear behaviour and comparative analysis of behavioural modelling and linearisation efforts. The collaboration resulted in a bench mark for linear wideband operation of a digital outphasing power amplifier. The complimentary linearisation techniques, bandwidth expansion reduction and zero crossing reduction have been evaluated in both simulated and practical outphasing test benches. Initial results are promising and indicate that the benefits they provide are not limited to the outphasing amplifier architecture alone. Overall this thesis presents innovative analysis of the distortion mechanisms of the outphasing power amplifier, highlighting the sensitivity of the system to environmental effects. Practical and novel linearisation techniques are presented, with a focus on enabling wide band operation for modern communications standards

Cartesian Pre-distortion using a Sigma Delta Modulator for Multi-Standard RF Power Amplifiers

The system implements a pre-distortion algorithm for a non-linear PA by placing a pseudo static forward model of a PA in the feedback path of a Sigma Delta Modulator. Performing the predistortion in this way reduces the computation overhead incurred in calculating pre-distorter weights for a given power amplifier. In this paper a Cartesian LUT is used to represent the PA model, allowing the system to compensate for PA non-linearity caused by multiple signal standards. The system was tested using 3 modulation standards and showed improvement of up to 28dB while the PA model remained constant

Utilizing Sparse-Aware Volterra for Power Amplifier Behavioral Modeling

This paper presents a method for reducing the number of weights in a time series behavioral model for a power amplifier. The least-absolute shrinkage and selection operator (Lasso) algorithm is used to reduce the kernel size, preserving the important kernels, while eliminating the less important kernels. The algorithm is evaluated on a behavioral model for a class AB amplifier, the algorithm reduces the number of weights by greater than 70% without degrading model performance by a significant amount

Digital Quadrature Mixing of Lowpass Sigma-Delta Modulators for Switch-mode Power Amplifiers

In this paper a phase compensation technique for the digital upconversion of a quadrature signal for amplification with switch mode power amplifiers is proposed. When a digital signal generator is used to generate the complex envelope signal care must be taken to compensate for the phase skew between the two paths. If phase compensation is not implemented an image caused by up converting the complex envelope of the modulation signal is created. By compensating for phase skew between the I and Q signal paths it is possible to remove this image signal and enable the transmission of multi carrier signals. As a direct result of this technique there is a reduction in the filtering effort at the output of the power amplifier to meet spectral mask requirements

A Prospective, Controlled Trial of a Pharmacy-Driven Alert System to Increase Thromboprophylaxis rates in Medical Inpatients

Background: Although venous thromboembolism is an important cause of morbidity and mortality within the hospital, a significant proportion of at-risk inpatients do not receive measures known to reduce the risk of deep vein thrombosis and pulmonary embolism. Objective: To determine whether a pharmacy driven alert system would, compared to usual care, be associated with a higher rate of adequate VTE prevention measures among at-risk inpatients on a general internal medicine service. Design: Prospective, controlled trial. Setting: A university-based teaching hospital. Patients: Adults admitted (Monday through Friday) to the general internal medicine inpatient service from 6/19/06-9/21/06. Intervention: Pharmacist assessment of venous thromboembolism risk; pharmacist-driven alert to treating physician. Measurements: Proportion of at-risk patients receiving adequate thromboprophylaxis within 36 hours of admission. Results: Overall, 140 patients were at sufficient risk for VTE to be included. In the usual care group, prophylactic measures were ordered for 49 (61%) of the 80 patients at moderate to high risk. In the pharmacist-alert group, 44 (73%) of the 60 moderate to high VTE risk patients received adequate thromboprophylaxis (p = 0.15). Conclusions: Although we did not observe a statistically significant difference between the experimental groups, our results are consistent with previous reports suggesting that alert systems (whether computerized or human) can increase the proportion of hospitalized patients who receive adequate measures to prevent VTE

A Low Complexity NARX Structure using Indirect Learning Architecture for Digital Pre-Distortion

In this paper, we demonstrate a nonlinear autoregressive with exogenous input (NARX) DPD technique which is more compact, less computationally intensive and less susceptible to errors caused by noise in the PA output compared to an equivalent memory polynomial based DPD. Experimental validation is performed with a 20 MHz LTE signal for a GaN Doherty power amplifier

Cross-Memory Polynomial Modeling for RF Circuits

A new behavioral model is proposed which can provide similar accuracy to the memory polynomial model (MPM) but is shown to have a more efficient architecture for digital hardware implementation. These features have been achieved by the proposed formulation, in which the nonlinear weights of the memory terms are a function of only the present input sample. The new approach is evaluated and compared with the conventional MPM using a Wideband Code Division Multiple Access (WCDMA) signal applied to two different amplifier circuits

Fast Outflows in Hot Dust-obscured Galaxies Detected with Keck/NIRES

We present rest-frame optical spectroscopic observations of 24 Hot Dust-Obscured Galaxies (Hot DOGs) at redshifts 1.7–4.6 with KECK/NIRES. Our targets are selected, based on their extreme red colors, to be the highest-luminosity sources from the WISE infrared survey. In 20 sources with well-detected emission, we fit the key [O iii], Hβ, Hα, [N ii], and [S ii] diagnostic lines to constrain physical conditions. Of the 17 targets with a clear detection of the [O iii]λ5007 Å emission line, 15 display broad blueshifted and asymmetric line profiles, with widths ranging from 1000 to 8000 km s⁻¹ and blueshifts up to 3000 km s⁻¹. These kinematics provide strong evidence for the presence of massive ionized outflows of up to 8000 M_ ⊙ yr⁻¹, with a median of 150 M_ ⊙ yr⁻¹. As many as eight sources show optical emission line ratios consistent with vigorous star formation. Balmer-line star formation rates, uncorrected for reddening, range from 30 to 1300 M_ ⊙ yr⁻¹, with a median of 50 M_ ⊙ yr⁻¹. Estimates of the SFR from Spectral Energy Distribution fitting of mid- and far-infrared photometry suggest significantly higher values. We estimate the central black hole masses to be of order 10⁸⁻¹⁰ M_ ⊙, assuming the present-day M_(BH)-σ_★ relation. The bolometric luminosities and the estimated masses of the central black holes of these galaxies suggest that many of the active galactic nucleus-dominated Hot DOGs are accreting at or above their Eddington limit. The combination of ongoing star formation, massive outflows, and high Eddington ratios suggest Hot DOGs are a transitional phase in galaxy evolution

Fast Outflows in Hot Dust-obscured Galaxies Detected with Keck/NIRES

We present rest-frame optical spectroscopic observations of 24 Hot Dust-Obscured Galaxies (Hot DOGs) at redshifts 1.7–4.6 with KECK/NIRES. Our targets are selected, based on their extreme red colors, to be the highest-luminosity sources from the WISE infrared survey. In 20 sources with well-detected emission, we fit the key [O iii], Hβ, Hα, [N ii], and [S ii] diagnostic lines to constrain physical conditions. Of the 17 targets with a clear detection of the [O iii]λ5007 Å emission line, 15 display broad blueshifted and asymmetric line profiles, with widths ranging from 1000 to 8000 km s⁻¹ and blueshifts up to 3000 km s⁻¹. These kinematics provide strong evidence for the presence of massive ionized outflows of up to 8000 M_ ⊙ yr⁻¹, with a median of 150 M_ ⊙ yr⁻¹. As many as eight sources show optical emission line ratios consistent with vigorous star formation. Balmer-line star formation rates, uncorrected for reddening, range from 30 to 1300 M_ ⊙ yr⁻¹, with a median of 50 M_ ⊙ yr⁻¹. Estimates of the SFR from Spectral Energy Distribution fitting of mid- and far-infrared photometry suggest significantly higher values. We estimate the central black hole masses to be of order 10⁸⁻¹⁰ M_ ⊙, assuming the present-day M_(BH)-σ_★ relation. The bolometric luminosities and the estimated masses of the central black holes of these galaxies suggest that many of the active galactic nucleus-dominated Hot DOGs are accreting at or above their Eddington limit. The combination of ongoing star formation, massive outflows, and high Eddington ratios suggest Hot DOGs are a transitional phase in galaxy evolution