IMS 2017

A Fully Polar Transmitter for Efficient Software-Defined Radios

While polar modulation is a transmitter technique that is known to maximize energy efficiency, it also has no circuit linearity and traditionally is unable to produce signals that contain envelope zeros such as QAM and LTE. This polar transmitter solves this weakness and is modulation agnostic across the decade-wide tuning bandwidth of 200 – 2500 MHz. In particular, a conventional Nyquist filtered 256QAM signal is generated with error vector magnitude (EVM) less than 1.5% across the frequency range, and is below 1% across the bottom decade of frequency – without use of digital predistortion (DPD) linearization.  Peak output power is 2.5 watts.

ICC 2017

Polar Modulation Based Reduction of Communications Energy Consumption

Analysis of the energy consumed by the mobile communication infrastructure shows that it draws gigawatts of power. Further analysis of the individual components drawing this power shows that the largest consumption occurs in the infrastructure (base station) power amplifier (PA), along with its associated radio transceiver (XCVR) and digital signal processing (DSP). Meaningful reduction of this power draw therefore requires achieving significant reduction in this power drawn in each base station, though with the further requirement that network service levels are not degraded. This forces recognition that the important metric for base station output signal quality is its modulation accuracy, independent from whether the circuitry implementing that signal is linear or not. This work shows that suppressing transmitter circuit linearity by using switching circuit techniques is successful at maintaining output signal accuracy while improving transmitter operating efficiency for LTE base stations from near 12% to more than 40%.

CCIC 2017

Energy Efficiency Maxima for Wireless Communications: 5G, IoT, and Massive MIMO

Any power amplifier (PA) is a peak-power limited circuit. It must be designed to provide whatever the signal maximum peak envelope power (PEP) may ever be. In contrast, communication coverage and range are based on signal root-mean-square (rms) power, usually called the average signal power. To the extent that the PEP exceeds this average power there exists a peak-power to average power ratio (PAPR) that is greater than 1. The average output power reduction from signal PAPR therefore reduces available communication range from a particular sized PA. Large PAPR values cause several important economic and realization problems, including: a) the communication range available from a particular PA is proportionally reduced, b) the PA needed to provide a required communication range must be proportionally larger, c) the maximum output power from the PA is not available to the channel for communication range and coverage, and so on. Signal PAPR is therefore economically expensive, and high values must be accepted only when a value to the communication system justifies its cost.

WCNC 2017

Fundamentals for Energy-Efficient Massive MIMO

Massive MIMO uses antenna arrays with more than 100 elements to direct transmitted energy, and receiver sensitivity, individually toward multiple intended users [1]. This large number of elements requires an individual and independent transmitter within each, in order to have complete flexibility in definition and control of each beam. This large number of transmitters places additional constraints on acceptable energy efficiency due to the complicated flow of dissipated power and its corresponding temperature rises. Any successful field implementation of massive MIMO must understand the energy efficiency of the array, both at each individual element [2] and in combination, to not only properly function but also to keep the hardware well within safe operating limits.

Texas Microwave 2016

A 300MHz to 1200MHz Saturated Broadband Amplifier in GaN for 2W Applications

For power amplifiers to be maximally efficient, it is necessary to operate them in a switch mode which minimizes time in the high power dissipation regions of the transistor characteristic [1, 2, 3]. Typical switch mode amplifiers are narrow band due to matching circuit characteristics. With the advent of GaN based transistors, it is now possible to design moderate power broadband amplifiers without matching circuits [4]. This is primarily due to the large breakdown voltage in GaN [5] which allows a designer to operate transistors directly with a 50 ohm load impedance.

RWW 2017

Signal Design and Figure of Merit for Green Communication Links

To achieve maximum energy efficiency in transmitters, it is known that circuit linearity must not only be compromised, it must actually be suppressed [1]. To take full advantage of the available energy efficiency in any power amplifier (PA), it is also necessary to use signals that allow PA operation at that efficiency [2]. In particular, signals that contain envelope zero crossings force PA circuit linearity and place a lower ceiling on the actually achievable energy efficiency that can be far below that available from the PA transistor [3].

EDI-CON 2016

Maximizing Wireless Communications Energy Efficiency

Any power amplifier (PA) is a peak-power limited circuit. It must be designed to provide whatever the signal maximum peak envelope power (PEP) may ever be. In contrast, communication coverage is based on signal root-mean-square (rms) power, usually called the average signal power. To the extent that the PEP exceeds this average power there exists a peak power to average power ratio (PAPR) that is greater than 1. Large PAPR values cause several important economic and realization problems, including: a) the communication range available from a particular PA is proportionally reduced, b) the PA needed to provide a required communication range must be proportionally larger, c) the maximum output power from the PA is not available to be used in the channel, and so on. Signal PAPR is therefore economically expensive, and must be accepted only when a value to the communication system justifies its cost.

ARFTG

Importance and Measurement of Phase-Stiffness in RF Switching Amplifiers

Immunity of RF power amplifiers (PA) to reverse signal injection and changes in load reflection coefficients due to antenna mutual coupling in active phased arrays is essential for maintaining signal integrity and controllable radiation patterns. In conventional active phased-array radar, the amplifiers are protected from any reverse signal injection from the antenna by including isolators and/or circulators between the PA and the antenna [1-3].

MILCOM 2015

Decade Bandwidth Agile GaN Power Amplifier Exceeding 50% Efficiency

When meeting design requirements for maximum energy efficiency in transmitters, it is known that circuit linearity must not only be compromised, it must actually be suppressed. In these maximally nonlinear operation modes the usual measures of circuit gain cannot remain in their common indiscriminate use, but rather must be evaluated separately for their unique information. By intentionally performing maximal-efficiency circuit design, additional requirements are identified that additionally provide wideband operation. Such amplifiers are also inherently compatible with wideband phased-array systems because of their suppressed linearity. All of these traits directly benefit desired reductions in size, weight, and power (SWaP) for field, airborne, and spaceborne communications and radar systems.