Joseph Barkate

Fast, simultaneous optimization of power amplifier input power and load impedance for power-added efficiency and adjacent-channel power ratio using the power smith tube

Reconfigurable adaptive amplifiers are expected to be a critical component of future adaptive and cognitive radar transmitters. This paper details an algorithm to simultaneously optimize input power and load reflection coefficient of a power amplifier device to obtain the largest power-added efficiency (PAE) possible under a predefined constraint on adjacent-channel power ratio (ACPR). The vector-based search relies on estimation of the PAE and ACPR gradients in the three-dimensional power Smith tube. Accurate convergence to the optimum impedance in the Smith chart is demonstrated in simulation and measurement search experiments requiring between 20 and 60 experimental queries. This paper presents a fast search to jointly optimize the input power level and load impedance. This method is feasible for future implementation in real-time reconfigurable power amplifiers.

Optimization of power-amplifier load impedance and waveform bandwidth for real-time reconfigurable radar

To create a reconfigurable radar transmitter, the power amplifier circuitry and waveform must be able to adjust in real time to changing operating frequencies and spectral requirements. For range radars, better range resolution can be accomplished by using waveforms of higher bandwidth. In this case it is desirable to maximize the chirp waveform bandwidth while maintaining spectral compliance and meeting power-added efficiency requirements. Based on the concept of the Smith Tube (presented in a recent conference article), this article describes a new intelligent, vector-based search for the load impedance and waveform bandwidth. The search provides the largest possible bandwidth while maintaining the power-added efficiency and adjacent-channel power ratio within specified requirements. The algorithm is demonstrated in measurement with multiple starting impedances and bandwidth search ranges, and consistently accurate and useful results are obtained. Multiple iterations of the two-part search can be performed for increased precision if the time needed to take additional measurements can be tolerated.

The Power Smith Tube: Joint optimization of power amplifier input power and load impedance for power-added efficiency and adjacent-channel power ratio

A new visualization tool for design is introduced: the Power Smith Tube. It provides aid in designing for optimum power-added efficiency (PAE) while meeting adjacent-channel power ratio (ACPR) requirements. The Power Smith Tube is a three-dimensional cylindrical extension of the Smith Chart with input power as the vertical axis. As such, this Smith Tube allows the visualization of design metrics, such as PAE and ACPR, as a function of both input power and load impedance. Performance of load-pull measurements or simulations at multiple values of input power provides data for the design. Design examples using the Power Smith Tube based on both simulation and measurement data are presented to demonstrate selection of load impedance and input power providing the highest PAE under ACPR constraints.

The bias smith tube: Simultaneous optimization of bias voltage and load impedance in power amplifier design

Multiple factors must be considered in power-amplifier design for wireless communications and radar, including bias voltage, input power, and load impedance. The Bias Smith Tube is presented as a three-dimensional extension of the Smith Chart with bias voltage as the vertical axis. It allows simultaneous visualization of nonlinear output characteristic behaviors over transistor bias voltage and load reflection coefficient. Simulated and measured three-dimensional surfaces of constant power-added efficiency (PAE), adjacent channel power ratio (ACPR), and delivered power are shown in the Bias Smith Tube, and a design approach is illustrated that finds the combination of load impedance and bias voltage providing maximum PAE under ACPR and/or delivered power constraints.

Circuit optimization algorithms for real-time spectrum sharing between radar and communications

The ability of radar and communication applications to share the radio spectrum will require the use of innovative agile circuit techniques for radar and communications. Reconfigurable circuits can provide real-time adjustment of operating frequency and spectral output, while maintaining system performance and maximizing power efficiency. This paper discusses recent developments in circuit optimization techniques for power efficiency and spectral performance. Optimization of a single parameter (load reflection coefficient) for multiple criteria is first addressed, followed by multiple-parameter, multiple-criteria optimizations. The use of the recently innovated Smith Tube to optimize additional parameters, such as input power and bias voltage, simultaneously with the load impedance is discussed. Optimization examples and a forward look to fast, emerging multidimensional circuit optimization techniques are provided.

Fast, momentum-aided optimization of transmitter amplifier load impedance and input power for cognitive radio using the power smith tube

A fast search including momentum is used to quickly and simultaneously optimize power-amplifier load impedance and input power for the highest power-added efficiency while maintaining adjacent-channel power ratio within compliance limits. This search makes use of the recently developed Power Smith Tube, and is expected to be useful in real-time reconfigurable communications and radar transmitters, as well as for fast computer and measurement aided design of power amplifiers. Simulation and measurement results are shown to demonstrate the improved accuracy provided by adding momentum to the search.

A simplex optimization technique for real-time, reconfigurable transmitter power amplifiers

The increased practice of dynamic spectrum allocation requires radar and communication systems that are able to change operating frequency and other performance criteria while maintaining performance metrics such as power efficiency and spectral compliance. This paper presents a simplex algorithm designed to allow frequency-agile circuits to quickly tune for maximum power-added efficiency. Simulation and measurement algorithm tests show that the algorithm produces consistent results from multiple starting points, and that the results show good agreement with traditional load-pull. This algorithm is expected to be useful in providing fast reconfiguration of transmitter power amplifiers.

Fast radar power amplifier optimization for bandwidth, efficiency, and spectral confinement using the Smith Tube

The Smith Tube, a three-dimensional cylindrical extension of the Smith Chart, provides a mechanism to simultaneously optimize power amplifier circuit and waveform parameters for radar transmitters. A direct, vector-based search algorithm is presented to find the optimum combination of bandwidth and load impedance for a power amplifier to maximize the waveform bandwidth while meeting requirements on the power-added efficiency and the adjacent-channel power ratio. For this optimization, waveform bandwidth is represented on the vertical axis of the Smith Tube, with the complex load reflection coefficient represented in the horizontal plane. Excellent correspondence is obtained in measurement testing of the algorithm from multiple starting combinations of load reflection coefficient and bandwidth. The results of this work are expected to be useful in real-time optimization of power amplifiers for radar and communications. The algorithm is expected to be useful in optimizing the range resolution of radar transmissions.

Designing power amplifiers for spectral compliance using spectral mask load-pull measurements

This paper demonstrates power amplifier design using load-pull measurements to determine spectral mask compliance as a function of load impedance. In most cases demonstrated in the open literature, the spectral spreading of the device is indirectly assessed by a metric such as the adjacent-channel power ratio or third-order intermodulation product. In the present paper, a spectral mask compliance metric is introduced that is less than or equal to zero for compliant spectra and positive for noncompliant spectra. The paper first examines the load-pull measurement for the spectral mask compliance metric, including the use of averaging to smooth the contours. Direct, dual-objective design of power amplifiers for spectral mask compliance and efficiency is then demonstrated by choosing the load impedance that provides the highest measured power-added efficiency while maintaining spectral compliance. With the device terminated in the chosen optimum impedance, measurement of the output spectrum and comparison with a spectral mask are performed to demonstrate spectral compliance at the selected design impedance.

Enabling the Internet of Things: Reconfigurable power amplifier techniques using intelligent algorithms and the smith tube

Future Internet of Things (IoT) devices will need to maintain high power efficiency while being able to reconfigure for changing performance requirements and operating frequencies. The design of quickly reconfigurable power amplifiers able to maintain high efficiency and meet spectral requirements will be critical to success. This paper discusses fast optimization techniques that will be useful in real-time optimization of transmitter power amplifiers: (1) a vector-based algorithm to find the load impedance giving the highest power-added efficiency (PAE) while keeping the adjacent-channel power ratio (ACPR) below a prespecified minimum, (2) the use of a spectral mask directly in the load-pull optimization in place of the ACPR, and (3) the extension of the Smith Chart to a three-dimensional, cylindrical “Smith Tube” for optimization involving an additional parameter: the waveform bandwidth. This paper builds a framework for design and the real-time optimization of reconfigurable, efficient, and spectrally compliant IoT power amplifiers.