S.C. Cripps

Bio: S.C. Cripps is an academic researcher. The author has contributed to research in topics: Amplifier & Byte. The author has an hindex of 1, co-authored 1 publications receiving 2054 citations.

RF Power Amplifiers for Wireless Communications

Abstract: Linear PA Design. Conventional High-Efficiency Amplifier Modes. Class AB PAs at GHz Frequencies. Practical Design of Class AB PAs. Overdrive and the Class F Mode. Switching Mode Amplifiers for RF Applications. Switching PA Modes at GHz Frequencies. Signals, Modulation Systems, and PA Nonlinearities. Efficiency Enhancement Techniques. Power Amplifier Bias Circuit Design. Power Amplifier Architecture. PA Linearization Techniques.

Mitigation of Load Mismatch Effects Using an Orthogonal Load Modulated Balanced Amplifier

Abstract: This article presents an orthogonal load-modulated balanced amplifier designed to mitigate the effects of the load mismatch on the power-added efficiency and output power of the amplifier. This is achieved by electronically adjusting the ratio between the two input signals of the power amplifier (PA) (in phase and amplitude) and the reactive termination at the output nominally isolated port. The mode of operation of the PA is described using a theoretical analysis that highlights the role of the different tuning parameters and is confirmed by simulations using a simplified transistor model. The design and characterization under load mismatch of a prototype PA, working in the 1.6–3.2 GHz band are described and the experimental results compared to those of an analogous balanced PA, where it is shown that the orthogonal balanced amplifier is able to increase substantially the mismatch region on which a given target performance is achieved.

A Load-Modulated Balanced Amplifier: From First Invention to Recent Development

Abstract: The RF power amplifier (PA) is a unit in wireless transmitters that strengthens the signal to combat losses in transmission by converting dc electric power to the added RF output power. Over the past decades, with the rapid development of wireless communications, high-efficiency PA design has become one of the most popular topics in both academic research and industrial development as the PA consumes a high portion of the transmitter energy, and thus its power efficiency directly impacts the system performance. In addition, because the PA is the main source of distortion generated by the transmitter, linearity is another concern in PA design, particularly in wideband systems [1].

Still A-Masing [Microwave Bytes]

Abstract: Publication lead times being what they are, I now find myself hurriedly rewriting my introduction to this offering, having originally submitted a jaunty little opening paragraph in which I made some comments about Queen Elizabeth’s Platinum Jubilee. Then, having gone through the statutory process of copy editing and just about ready to roll the presses, Her Majesty passed away. Given that coverage of such “current affairs” is in any case well outside my remit I will revert, with due reverence, to my original copy.

Near-Field Microwave Microscopy for 3D Surface Assessment of Manufactured Structures

Abstract: Using near-field scanning microwave microscopy as a contact and non-contacting investigative tool for 3D surface metrology with three differing measurement modes, it has been possible to analyse structures that may be difficult for existing metrology systems. The system utilizes the small change in capacitance between a coaxial resonant probe (at around 2 GHz) ending in an open circuit tip, and the sample surface. This is measured in the frequency domain by the shift in the resonance frequency of the voltage transmission coefficient |S21|. It is also possible to investigate various materials (metallics, plastics etc.) owing to their differing dielectric properties. The probe has been tested on a computer-controlled 3D stage but is suitable for incorporation into a commercial co-ordinate measurement machine (CMM) to enhance its capability to inspect the inside surfaces of structures, e.g., threads in small bores.

How much energy is needed to run a wireless network

Abstract: In order to quantify the energy efficiency of a wireless network, the power consumption of the entire system needs to be captured. In this article, the necessary extensions with respect to existing performance evaluation frameworks are discussed. The most important addenda of the proposed energy efficiency evaluation framework (E3F) are a sophisticated power model for various base station types, as well as large-scale long-term traffic models. The BS power model maps the RF output power radiated at the antenna elements to the total supply power of a BS site. The proposed traffic model emulates the spatial distribution of the traffic demands over large geographical regions, including urban and rural areas, as well as temporal variations between peak and off-peak hours. Finally, the E3F is applied to quantify the energy efficiency of the downlink of a 3GPP LTE radio access network.

Power amplifiers and transmitters for RF and microwave

Abstract: The generation of RF/microwave power is required not only in wireless communications, but also in applications such as jamming, imaging, RF heating, and miniature dc/dc converters. Each application has its own unique requirements for frequency, bandwidth, load, power, efficiency, linearity, and cost. RF power is generated by a wide variety of techniques, implementations, and active devices. Power amplifiers are incorporated into transmitters in a similarly wide variety of architectures, including linear, Kalm, envelope tracking, outphasing, and Doherty. Linearity can be improved through techniques such as feedback, feedforward, and predistortion.

A robust digital baseband predistorter constructed using memory polynomials

Abstract: Power amplifiers (PAs) are inherently nonlinear devices and are used in virtually all communications systems. Digital baseband predistortion is a highly cost-effective way to linearize PAs, but most existing architectures assume that the PA has a memoryless nonlinearity. For wider bandwidth applications such as wideband code-division multiple access (WCDMA) or wideband orthogonal frequency-division multiplexing (W-OFDM), PA memory effects can no longer be ignored, and memoryless predistortion has limited effectiveness. In this paper, instead of focusing on a particular PA model and building a corresponding predistorter, we focus directly on the predistorter structure. In particular, we propose a memory polynomial model for the predistorter and implement it using an indirect learning architecture. Linearization performance is demonstrated on a three-carrier WCDMA signal.

A Review of GaN on SiC High Electron-Mobility Power Transistors and MMICs

Abstract: Gallium-nitride power transistor (GaN HEMT) and integrated circuit technologies have matured dramatically over the last few years, and many hundreds of thousands of devices have been manufactured and fielded in applications ranging from pulsed radars and counter-IED jammers to CATV modules and fourth-generation infrastructure base-stations. GaN HEMT devices, exhibiting high power densities coupled with high breakdown voltages, have opened up the possibilities for highly efficient power amplifiers (PAs) exploiting the principles of waveform engineered designs. This paper summarizes the unique advantages of GaN HEMTs compared to other power transistor technologies, with examples of where such features have been exploited. Since RF power densities of GaN HEMTs are many times higher than other technologies, much attention has also been given to thermal management-examples of both commercial “off-the-shelf” packaging as well as custom heat-sinks are described. The very desirable feature of having accurate large-signal models for both discrete transistors and monolithic microwave integrated circuit foundry are emphasized with a number of circuit design examples. GaN HEMT technology has been a major enabler for both very broadband high-PAs and very high-efficiency designs. This paper describes examples of broadband amplifiers, as well as several of the main areas of high-efficiency amplifier design-notably Class-D, Class-E, Class-F, and Class-J approaches, Doherty PAs, envelope-tracking techniques, and Chireix outphasing.

Nonlinear Microwave and RF Circuits

Abstract: Preface. Introduction, Fundamental Concepts, and Definitions. Solid-State Device Modeling. Harmonic-Balance analysis. Volterra-Series and Power-Series Analysis. Balanced Circuits. Diode Mixers. Diode Frequency Multipliers. Small-Signal Amplifiers. Power Amplifiers. Active Frequency Multipliers. Active Mixers. Oscillators. Index.