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This paper investigates the source and implication of efficiency minima that is typically observed during the second-harmonic load–pull of transistor amplifiers. The study starts with the theoretical derivation of time-domain voltage and current waveforms as a function of conduction angle ( $\alpha$ ) at the second-harmonic efficiency minima, where the output power and drain efficiency (DE) are at minimum. Thereafter, this paper unfolds a systematic re-engineering approach that is developed to recover the performance degradation and to exploit the region of efficiency minima in favor of design and implementation of high-efficiency inverse class-F power amplifiers (PAs). Interestingly, the inferences drawn from the in-depth analysis are shown to provide a simplified first-pass design approach that guarantees inverse class-F PA operation without an a priori knowledge of device parasitic elements. Theoretical postulations and simulation results are experimentally validated using an on-wafer active harmonic load–pull and a prototype design using 1.95-mm NXP gallium nitride die at a frequency of 2.6 GHz. The designed PA delivers an output power of 40 dBm with DE of 76% and gain of 12 dB at 3-dB gain compression. The measurement results confirm the theoretical framework reported in this paper.

This paper presents an in-depth, systematic study of the impact of input and output harmonics in the design of high-efficiency power amplifiers (PAs). The study evaluates the performance of harmonically tuned amplifiers, tackling concurrently both input and output harmonics. The proposed theory starts with deriving an altered input voltage waveform under the impact of input nonlinearity. Intrinsic drain voltage and drain current components are formulated as a function of the conduction angle $\alpha $ considering both source and load terminations. Output power and drain efficiency are then computed as a function of input nonlinearity, $\alpha $ , and output loading conditions. The derived formulations allow to investigate the design sensitivity to input nonlinearity and its impact on fundamental design space. The impact of source harmonics is evaluated using harmonic source pull under different output loading conditions. Thereafter, PA design and implementation has been carried out using NXP 1.95 mm die to confirm the distinctive behavior of class GF and GF−1 amplifiers with respect to the input harmonic terminations. For practical validation, four different design cases with different second harmonic source impedances are investigated. At 2.6 GHz, drain efficiencies ranging between 76% and 83% were exhibited depending on the source and load harmonic tuning for each design case. Measurement results confirm the theoretical findings reported in this paper.

Nonlinearities in Radio Frequency Power Transistors can be attributed to mechanisms such as non-linear transconductances and nonlinear capacitances at the device terminals. In this paper, we extend the work in by Ladhani et al to include the impact of the nonlinear gate-source capacitance in a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and discuss its contribution (along with the gate baseband impedance) to the amplifier’s intermodulation distortion and linearizability. Measured results show that for a 140W (P1dB (1dB Compression Point)) Class AB LDMOS (Laterally Diffused Metal Oxide Semiconductor Field Effect Transistor) PA, an optimized gate baseband impedance provides 6dB improvement in corrected ACPR (Adjacent Channel Power Ratio) and 7dB improvement in corrected Alt-1 (First Adjacent Channel Power Ratio) at 7dB backoff from peak power using a 4-Carrier WCDMA (Wideband Code Division Multiple Access) signal.

This letter investigates the source of performance degradation and efficiency null that is traditionally observed during second-harmonic load pull of active power transistors. A theory that explains the performance degradation is presented, resulting in a simplified closed-form equation that predicts the location of performance null for different device peripheries and/or design frequencies. Thereafter, the intrinsic drain waveforms for null and maximum efficiency are analyzed to study potential causes for efficiency degradation. The theory is validated using active load-pull measurements of laterally diffused metal–oxide–semiconductor and gallium nitride active devices for different peripheries (0.5–4.8 mm) at various frequencies of operation (2, 2.6, and 3.5 GHz).

Massive MIMO systems for pre-5G and 5G applications have necessitated the development of low power (2-5W average) high efficiency PAs due to the need for multiple PA elements to form a 64, 128 or 256 element array base station system. Such requirements pose several challenges such as the need for high efficiency, linearizability with simple digital predistortion systems, low cost and small form factors. In this paper, we discuss a novel technique for the miniaturization of a fully-integrated, low-cost LDMOS Doherty Power amplifier using ABCD matrix equivalents for the matching networks. A small form factor 50-Ohm in-out Doherty PA is designed for the 2.5-2.7GHz band and its performance is discussed in the context of a low-complexity DPD system with very few coefficients. The PA achieves a PAE of 42% with a gain of 32dB and corrects to -55dBc with a 60MHz (3x20MHz) LTE signal.

A compact, pre-matched gallium-nitride (GaN) device is proposed to support high power, high efficiency, concurrent multiband amplifier applications. Novel in-package matching networks addressing both the input and output of high power GaN active devices are considered. As proof-of-concept, a symmetric Doherty power amplifier (PA) with 55.3 dBm (340 W) peak power is demonstrated to achieve 20% fractional RF bandwidth from 1.805 – 2.2 GHz with high efficiency and low baseband impedance. With digital-predistortion (DPD) compensation, the amplifier achieves 48% drain efficiency at average output power of 48.8 dBm, and ACPR better than -52 dBc during concurrent transmission of signals with 395 MHz instantaneous signal bandwidth (ISBW). The results represent the highest linearized efficiency reported for concurrent 3GPP Band 3 and Band 66 multiband scenarios for high power infrastructure PA applications.

RF Pre-Matching of High Power Transistors involves considerations of impedance matching, RF Bandwidth, phase characteristics as well as physical realization. Due to the increase in signal bandwidth requirements of next generation applications, it has become necessary to incorporate baseband impedance circuits to ensure the power transistor is capable of amplifying these signals with minimum distortion as well as correct within specifications using digital predistortion systems. In this paper we analyze the baseband response of a widely used pre matching topology for RF Power Transistors as well as propose and analyze modifications that allow for improved large signal bandwidth operation. The results show than an ACLR improvement of approximately 10dB resulted from the addition of an integrated bias network with damping resistance using the same DPD complexity.

This paper introduces the Class O2 power amplifier (PA) with high power-density and drain efficiency. A new waveform engineering-based design approach is proposed to realize a reliable high-efficiency PA operation while tuning both second and third harmonic impedances to open-circuit termination. The proposed theory derives the intrinsic current and voltage waveforms as a function of input second-harmonic tuning which is adopted to enable the realization of reliable Class O2 PA operation. A multi-harmonic vector load-pull system is used for the practical validation that is carried out using a 10-W gallium nitride (GaN) transistor. On load-pull, the Class O2 mode demonstrates a drain efficiency of 87% at an output power of 39.8 dBm with a gain of 10 dB at a frequency of 1.0 GHz.

This paper presents the impact of input non-linearity and its dependence to output loading conditions in the design of Gallium Nitride (GaN) based Power Amplifiers (PAs). The drain efficiency variation due to the input non-linearity for any arbitrary second harmonic loading condition is presented. The theory presents generalized current waveform equations as a function of conduction angle $\pmb{(\alpha)}$ and input harmonic non-linearity $(\gamma_{2})$ . Thereafter, to quantify the impact of source harmonics, a systematic methodology to evaluate the efficiency degradation is proposed. For practical validation, the active load pull (ALP) experiments are carried out using a 0.7 mm GaN die by NXP at 2.6 GHz. The drain efficiency variation as a function of second harmonic load reactance has been measured and reported at P3dB gain compression. While, class B, and class F shows 5–6% drain efficiency variation to second harmonic source pull, class $\mathbf{F}^{-1}$ , and class $\hat{\mathbf{J}}/\hat{\mathbf{J}}^{\ast}$ shows immunity to the input non-linearity with only 1–2 % drain efficiency variation.

The paper extends the concept of waveform shaping for back-off applications which can be applied to realize power amplification sub-blocks in load modulation based power amplifiers. The proposed theory starts with deriving the intrinsic current and voltage waveforms as a function of output power back-off factor. Thereafter, a design methodology is proposed to optimize the performance of power amplifier for back-off requirements within a limit of 3 dB gain compression. For experimental validation, the implementation is carried out using a 1.95 mm gallium nitride (GaN) die. The single-ended PA is designed to operate as a carrier PA in a 35 dBm average asymmetric Doherty configuration (44 dBm peak power). The PA exhibits a drain efficiency of 78% at an average output power of 35 dBm at a frequency of 2.6 GHz.

An integrated passive device (IPD) supporting both RF and baseband impedance matching is proposed that is directly suitable for high power, multiband amplifier applications. The impedance matching method and design techniques are discussed. As proof-of-concept, we present an LDMOS Doherty power amplifier (PA) with 400 W peak power using the proposed IPD to demonstrate 20% fractional RF bandwidth with low baseband impedance. Measurements of the Doherty PA with digital pre-distortion system indicate that the amplifier achieves over 40% drain efficiency at average P out of 48.5 dBm with over 15 dB of gain during concurrent transmission of 3GPP Band 3 & Band 66 from 1.805–2.2 GHz while meeting ACPR of −53 dBc. The results represent over 2 times improvement of instantaneous bandwidth capability over prior work and enables for the first time 395 MHz instantaneous bandwidth capability for high power downlink cellular infrastructure communication systems.

The expression of the steroidogenic acute regulatory protein (STAR) is regulated by PKA in response to trophic hormone stimulation through the second messenger cAMP. However, in steroidogenic cells, the concentrations of hormone necessary to maximally induce cAMP synthesis and PKA activity are often significantly higher than is necessary to achieve maximum steroidogenesis. One general mechanism believed to make PKA signaling more effective is the use of A-kinase anchoring proteins (AKAPs) to recruit PKA to discrete subcellular compartments, which coordinates and focuses PKA action with respect to its substrates. The characterization of AKAP121 has suggested that it enhances the posttranscriptional regulation of STAR by recruiting both Star mRNA and PKA to the mitochondria, thereby permitting more effective translation and phosphorylation of STAR. Testing this hypothesis revealed that cAMP-induced STAR expression and steroidogenesis closely followed AKAP121 abundance when this AKAP was silenced or overexpressed in MA-10 cells but that these changes were effected posttranscriptionally. Moreover, silencing AKAP121 expression in these cells specifically altered the localization of type II PKA regulatory subunit alpha (PKAR2A) at the mitochondria but did not affect its relative expression within the cell. Affinity purification experiments showed that PKAR2A preferentially associated with AKAP121, and cAMP analogs that activate type II PKA induced STAR phosphorylation more efficiently than analogs stimulating type I PKA. This suggests that AKAP121 and PKAR2A serve to enhance steroidogenesis by directing the synthesis and activation of STAR at the mitochondria in response to cAMP.

This novel design technique was developed for the input pre-match circuit of discrete base station power amplifiers utilizing multi-section low pass, band pass and high pass topologies by carefully selecting the pole locations to achieve state of the art performance for broadband operation over 20% fractional bandwidth. The techniques have been applied to a 28 V, 230 W LDMOS PA to cover the RF bandwidth from 1.8 GHz to 2.2 GHz with equivalent RF performance for power, gain and efficiency as the narrowband designs while maintaining user-friendly input and load impedances as well as minimal linear phase distortion. To our knowledge, this is the first 28 V LDMOS high power amplifier capable of covering the 20% fractional bandwidth at 2 GHz reported to date.

In this paper we demonstrate high gain, high efficiency, single and balanced Doherty power amplifiers (PAs) that have the ability to transmit signals which occupy the full frequency band from 1930MHz–1995MHz. The PAs have been designed using a new generation of Freescale LDMOS power transistors [1], in which the drain side video-bandwidth (VBW) has been enhanced. For the first time we will show the ability of the PA to handle wideband envelope signals (> 80MHz) with excellent nonlinearity correction using Digital Pre-distortion (DPD). Narrow band as well as wideband DPD measurement results will be presented for single and balanced Doherty PAs including driver stages. These RF Doherty PAs are targeted for use in next generation wideband wireless communication systems.

RF Power Transistors, by design, have an upper limit to the input-signal bandwidth that can be amplified without incurring excessive distortion. The interaction between components internal to the pre-matched RF Power Transistor and on the external circuit board creates resonances at frequencies that are of the order of the modulation bandwidth of the signal. In this paper, we demonstrate a technique to improve the ‘video-bandwidth’ (VBW) capability of RF Power transistors using high-k capacitors. The improvement is more than 2 times a standard device. Also, digital predistortion performance is demonstrated with excellent results for narrow band as well as wideband signals (>50MHz). This capability enables wideband RF Power Amplifier Design for next generation systems demanding wider bandwidth / faster data rates.

This paper presents techniques used in integration for high-power RF semiconductor products and their use in wireless infrastructure power amplifiers. Integrated single and multi-stage devices are discussed, as well as PA architecture comparisons and benefits for class AB, and high efficiency amplifiers. Manufacturing advantages and disadvantages of traditional discrete, versus various types of integrated semiconductor devices are compared for both ground-based and tower-mounted amplifier applications.

A 120 Watt LDMOS radio frequency integrated circuit (RFIC) targeting 1.8 GHz GSM, EDGE, and Evolved EDGE base station applications has been developed using state of the art design techniques and LDMOS technology. The amplifier was designed to cover the 1.8 GHz to 2 GHz GSM bands, and performs exceptionally well under both GSM and EDGE conditions. The two-stage, single-chip design exhibits 27 dB of gain and delivers 132 Watts of output power (1 dB compression; 27 Volt DC supply) with an associated PAE of 51%. Under EDGE modulation, at an average output power of 46 Watts, the EVM is less than 1.6 % and the spectral re-growth is −63 dBc and −78 dBc at 400, and 600 kHz offsets, respectively. This is the highest power, 1.8 to 2 GHz, two-stage RFIC in an over-molded plastic package, reported to date.

This paper presents a dual path 150W Silicon LDMOS 2-stage RF power amplifier designed for WCDMA at 2.2GHz. This device is capable of handling 2 times the UMTS band with flat RF performance. Under a 1 tone CW stimulus, this power amplifier delivers 150W with a power added efficiency of 47% and 29dB linear gain. A 2-stage compact Doherty amplifier constructed of an “in-package” 2 × 75W architecture is also presented, showing the versatility of this unique design. Using the device in a dual-path configuration, this Doherty circuit delivers an increase in drain efficiency of 9–12 points at 8 dB output backoff from P3dB compression, compared to a circuit using the device in a 150W, class-AB reference design.

The expression of the steroidogenic acute regulatory protein (STAR) is regulated by PKA in response to trophic hormone stimulation through the second messenger cAMP. However, in steroidogenic cells, the concentrations of hormone necessary to maximally induce cAMP synthesis and PKA activity are often significantly higher than is necessary to achieve maximum steroidogenesis. One general mechanism believed to make PKA signaling more effective is the use of A-kinase anchoring proteins (AKAPs) to recruit PKA to discrete subcellular compartments, which coordinates and focuses PKA action with respect to its substrates. The characterization of AKAP121 has suggested that it enhances the posttranscriptional regulation of STAR by recruiting both Star mRNA and PKA to the mitochondria, thereby permitting more effective translation and phosphorylation of STAR. Testing this hypothesis revealed that cAMP-induced STAR expression and steroidogenesis closely followed AKAP121 abundance when this AKAP was silenced or overexpressed in MA-10 cells but that these changes were effected posttranscriptionally. Moreover, silencing AKAP121 expression in these cells specifically altered the localization of type II PKA regulatory subunit alpha (PKAR2A) at the mitochondria but did not affect its relative expression within the cell. Affinity purification experiments showed that PKAR2A preferentially associated with AKAP121, and cAMP analogs that activate type II PKA induced STAR phosphorylation more efficiently than analogs stimulating type I PKA. This suggests that AKAP121 and PKAR2A serve to enhance steroidogenesis by directing the synthesis and activation of STAR at the mitochondria in response to cAMP.

In this paper we report a method of applying digitally modulated signals to an RF power transistor in a load-pull system. This methodology ensures that the transistor experiences realistic thermal conditions, as well as realistic electrical conditions during test. The measured data is then sliced at constant value of CCDF enabling meaningful performance comparisons to be made between devices and technologies.

Protein kinase A (PKA) anchoring proteins (AKAPs) tether PKA to various subcellular locations. AKAP121, which tethers PKAII to the outer mitochondrial membrane, includes a K homology (KH) RNA-binding motif. Purified AKAP121 KH domain binds the 3' untranslated regions (3'UTRs) of transcripts encoding the Fo-f subunit of mitochondrial ATP synthase and manganese superoxide dismutase (MnSOD). Binding requires a structural motif in the 3'UTR and is stimulated by PKA phosphorylation of the domain or a mutation that mimics this phosphorylation. AKAP121 expressed in HeLa cells promotes the translocation of MnSOD mRNA from cytosol to mitochondria and an increase in mitochondrial MnSOD. Both reactions are stimulated by cAMP. Thus, by focusing translation at the mitochondrial membrane, AKAP121 may facilitate import of mitochondrial proteins in response to cAMP stimulation.