John Dooley

Reconfigurable Class S power amplifiers at RF and microwave frequencies

When a delta-sigma modulator (DSM) is placed before a class D switching stage the combination can be used to amplify time varying envelope signals. However a bandpass DSM is commonly employed and is required to have a sampling frequency approximately four times the carrier frequency. At RF or microwave frequencies proprietary hardware was previously needed to implement the DSM. However, it is shown here in simulation and from experimental measurement that a suitable DSM for class S power amplifiers can be implemented at RF and microwave frequencies using mid-range FPGA technology.

Improved Coding-Efficiency Two-Level Source Encoder for RF Switch-Mode Power Amplifiers

A ΣΔ-driven RF switch-mode power amplifier is inherently linear only when it has a two-level output. At the same time, a two-level output generates the largest amount of quantization noise. This brief analyzes the effect of nonequal level spacing in a three-level ΣΔ output and provides a method for shaping the corresponding error noise to regions outside the band of interest. Subsequently, the nonlinearity-shaping property is utilized to obtain an improved two-level drive signal based on three-level ΣΔ modulation. The new binary drive signal is proven to have better adjacent channel leakage ratio and higher coding efficiency than a conventional two-level ΣΔ modulator. In the investigated case, measured coding efficiency improves from 8.9% of the conventional two-level modulator to 21% of the modified two-level modulator.

A Reconfigurable Platform to Drive High Frequency Class S Power Amplifiers Using Multi-gigabit Transceivers

In this research work we present a reconfigurable platform that implements all the digital processing and RF carrier generation for the class S power amplifier proposed by the Institute of Microelectronics and Wireless Systems. This amplifier is a combination of a lowpass or bandpass sigma-delta modulation stage in series with a frequency shifting stage and a switch mode amplifier followed by a band pass filter. The reconfigurable platform is parameterizable, scalable and it has been optimized for reconfigurable devices. It takes advantage from the multi-gigabit serial links embedded into the new FPGAs to synthesize binary RF signals, and from the parameterizable soft cores that the FPGA vendor provides. The implementation results for a stand-alone and for a tiny Wishbone compatible system-on-programmable-chip versions are presented. The design is validated with data measured in the simulation and in the prototype.

Behavioral Modeling of Outphasing Amplification Systems

This paper presents a comparison of existing and novel behavioral models targeted at the outphasing power amplifier (PA) architecture. A comprehensive comparison of ten modeling strategies is presented in the results. Novel techniques for outphasing PAs, such as vector switched and dual path time series, are also presented for the first time. Investigation of such techniques was driven by the analysis of outphasing operation at minimum output powers, demonstrating the generation of frequency-dependent amplitude and phase deviations, which can be difficult to characterize. The increased robustness was achieved at the cost of additional complexity; for practical implementation, time series coefficient reduction techniques were also evaluated. The results of all modeling approaches are experimentally validated for the wideband operation of an NXP 19-W GaN digital outphasing amplifier module. Considering computational complexity and accuracy for system-level modeling across all presented options, a subset of existing and new models is identified as best suited for modeling outphasing PAs.

Linearization of an Outphasing Amplifier for Wide-band Multi-carrier Signals

A novel method using self-organizing maps to determine the optimum ranges to partition the vector switched Volterra series is presented. Analyzing characteristics of the input signal it is possible to separate different regions of operation. Partitioning of the correction algorithm provides the ability to target regions of different non-linear behavior with separate coefficients. This work is validated with experimentally measured results and shows an adjacent channel power ratio (ACPR) of -49/-50 dBc achieved for a four carrier Wideband Code-Division Multiple Access (WCDMA) signal using a 19 watt digital outphasing amplifier from NXP.

New CCTV approaches for environmental enforcement in Ireland

According to a survey carried out in Ireland among the environment departments of all Local Authorities, closed-circuit television (CCTV) systems are the most widely used technology for monitoring and prosecuting illegal environmental activities. Despite the fact that new technologies have been proposed in recent years, CCTV remains the preferred option. However, commercial CCTV systems are not specifically designed to tackle environmental enforcement issues. From the survey analysis the main limitations of commercial CCTV equipment deployed to date for environmental enforcement are: night time monitoring, monitoring of high risk or hostile areas, and battery powered CCTV systems for short term or remote deployments. The objective for the research was to identify solutions to the CCTV issues raised in the survey. It focused on the adaptation, installation and testing of commercial CCTV equipment for environmental enforcement scenarios. For each scenario several technologies with different configurations were evaluated. Equipment employed in this work included: digital video cameras, infra red illuminators, analogue cameras with long range optical zoom and low power consumption cameras. The effectiveness of each solution was assessed on its ability to detect and record with accuracy individuals, or vehicle licence plates, and the offences committed in a cost effective manner. In conclusion, this research provided solutions for the three CCTV challenges raised in the survey by Irish Local Authorities. Consequently, new approaches to environmental monitoring are available to Local Authorities for future environmental enforcement in Ireland.

Behavioral modeling approach for array of amplifiers in active antenna array system

Memory polynomial behavioral models are widely used to model nonlinear distortion mechanisms in a single RF power amplifier. However, when a number of power amplifiers are used in parallel, as in the case of active antenna arrays, the total number of parameters will increase significantly. Hence, new strategies are required to model and linearize these systems efficiently. In this paper a novel efficient modeling approach for these array systems is presented and experimentally verified by applying the method to the measured data of an array of amplifiers. The experimental results prove the efficiency of the approach.

Design of signal modulator for RF polar transmitter

This paper presents new approach to signal modulation for high efficiency polar transmitter. The new modulator is derived by analyzing complex to polar transforming equations. Once spectral behavior of an envelope and phase signals are known, new architecture offering lower complexity in an analog domain and more flexibility for reconfiguration than a conventional modulator is derived. Concept of the modulator is verified in the course of step-by step simulations with a 5MHz BW input signal at a carrier frequency fC = 2.14GHz. Also, a drain efficiency of a Class E PA driven by the modulator is discussed, and optimal solution for sampling rate is proposed.

Reconfigurable high frequency class S power amplifier demonstrator

This paper presents an end-to-end high frequency class S power amplifier. A description of the full testbench and some important points on generation of RF outputs from FPGA devices and current mode class D design are given. Experimental measurements are provided for the prototype PA consisting of a signal generator, analog to digital converter, driver circuit, current mode class D switching stage and bandpass filter. Theory and experimentally measured results for this prototype are presented for a multi tone signal centred at 930 MHz and with a total output power of 24.7dBm.

Digital quadrature mixing of lowpass sigma-delta modulators for switch-mode power amplifiers

In this paper a phase compensation technique for the digital up conversion 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.