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In this article, a continuous-mode inverse class GF (CCGF−1) power amplifier is introduced based on a new closed-form expression for the drain current. This analytical expression is utilized to exploit second source harmonic impedance manipulation in order to expand the design space of the output matching circuit resistively. This approach allows to diminish the complexity of the design of the load matching network at the fundamental and harmonic frequencies and to achieve wider bandwidth while simultaneously improving drain efficiency across the new optimum admittance points. Using the nonlinear model of a commercially available 10-W gallium nitride (GaN) device, load—pull and source–pull techniques are used to design a wideband CCGF−1. The designed amplifier is fabricated using the selected transistor in low-temperature co-fired ceramic (LTCC) technology. Measurement results show that, over the frequency band between 3.05 and 3.85 GHz, a drain efficiency of more than 70%, 11–12.4-dB gain, and 39.9–41.4-dBm output power at 3-dB gain compression have been achieved. Although not designed for linearity, the fabricated amplifier shows an adjacent channel power ratio better than 26 dBc under a 20-MHz long-term evolution (LTE) signal having a 10.45-dB peak-to-average power ratio. [ABSTRACT FROM AUTHOR]

In this paper, a new low-power and blocker-tolerant receiver architecture, the generalized N-phase quadrature phase shift frequency selective (QPS-FS), is proposed and analyzed that is suitable for radio frequency (RF) energy harvesting networks. A complete comparative analysis of the N-phase QPS-FS receiver with conventional N-path passive mixer (P-M) receiver is also provided. The QPS-FS receiver utilizes the impedance translation concept to improve the receiver selectivity but eliminates the need of an active multiphase clock generation circuit used in the conventional N-path P-M receivers. It uses a single clock signal source at the desired signal carrier frequency and a phase shift network in the RF path of the receiver for frequency downconversion and quadrature (I/Q) demodulation. The QPS-FS receiver requires a slower clock signal source, the frequency of which is equal to the desired band RF signal carrier frequency ($f_{c})$ as opposed to at least N/2 times $f_{c}$ for the conventional N-path P-M receivers. Consequently, the lower frequency clock source requirement extends the frequency coverage of the receiver by a factor of at least N/2 for a given clock source with a fixed maximum frequency. Reduction of the operating frequency and elimination of the active multiphase clock generation circuit would also eventually reduce the overall power consumption for the whole receiver system as confirmed through measurements. A wideband receiver calibration approach provides less than 2% of error vector magnitudes between the transmitted and received constellation points for various modulated signals having bandwidths up to 4 MHz. [ABSTRACT FROM AUTHOR]

The behavior of a power amplifier (PA) is substantially affected by the output mismatch and mutual coupling in modern compact transmitters. To date, different works in the literature address the problem of coupling and mismatch separately, which are limited in terms of performance with a higher level of mismatch and mutual coupling. This paper identifies the reflection at the PA–antenna interface to be an effective parameter to unify the problem of mismatch and mutual coupling. Thus, a reflection-aware PA modeling and linearization method is proposed to compensate the adverse effect of mismatch and/or mutual coupling. The performance of the proposed method is investigated with a class AB and a Doherty PA under wide range of output mismatch and/or mutual coupling conditions with a 20-MHz WCDMA signal. The proposed method shows robust performance with an average adjacent channel power ratio better than 45 dBc. Such robust linearization performance under diverse output mismatch and mutual coupling conditions is highly desirable for modern and future communication systems that are subject to undergo rapid fluctuations under antenna matching and cross-coupling conditions. [ABSTRACT FROM AUTHOR]

This paper derives a novel continuum of Doherty power amplifier (PA) solutions with enhanced load modulation over an extended RF bandwidth. It is analytically shown that Doherty PAs with efficiency peaks at maximum power and at an arbitrary back-off level can be achieved with numerous configurations of output power combiner. Generalized governing equations for carrier and peaking transistor current ratios, voltage profiles, and biasing conditions are derived in order to assess the performance of any Doherty amplifier configuration. The generalization demonstrates the impact of the selection of the output combiner on PA performance and highlights the tradeoffs between the different solutions. A wideband Doherty PA was designed based on the proposed methodology and implemented using packaged gallium nitride transistors. Over the frequency band of 0.55–1.10 GHz, the Doherty PA exhibited drain efficiency in excess of 40% and 56% at 6-dB output power back-off (OPBO) and peak power, respectively. The Doherty PA was successfully linearized when driven with modulated stimulus and achieved average drain efficiency above 40% at 7.1-dB OPBO. [ABSTRACT FROM PUBLISHER]

This letter presents a new antenna topology to implement the load modulation in the Doherty transmitter, which resulted in enhancing the bandwidth compared to previous works. The active load modulation is realized by using a monopole array antenna, which serves as both Doherty combiner and wave radiator. The load impedances of amplifiers can be dynamically tuned through the mutual coupling of the array elements. Detailed design equations and procedures are developed. For verification, a Doherty transmitter operating at 1.95–2.10 GHz has been designed and fabricated using GaN HEMT transistors. The prototype transmitter exhibited a power-added efficiency of 53% at peak power level and maintained an efficiency of 43% at 6.8-dB backoff, over the frequency band of 1.95–2.10 GHz. [ABSTRACT FROM AUTHOR]

A novel design space of load modulated (LM) continuous Class-B/J power amplifiers (PAs) is proposed, and a detailed mathematical analysis is presented. The combination of LM technique and continuous mode is introduced to enhance the wideband performance of LM PAs. An inversely proportional relationship between ZL and C\mathrm {out} is derived, which indicates that the nonlinear C\mathrm {out} can affect the optimal load impedances at output power backoff (OPBO) and the design parameter \beta should be appropriately adjusted. The measured results of a PA prototype show that the PAE is 39%–45% under LM when OPBO = 5 dB across 1.6–2.4 GHz. Compared with the same PA with fixed V_{\mathrm {var}} , the proposed PA with optimum V_{\mathrm {var}}$ at 2 GHz achieves a PAE improvement with 11% when OPBO = 5 dB. [ABSTRACT FROM PUBLISHER]

In this paper, a new Doherty amplifier architecture along with an analytical based design methodology is proposed. The proposed architecture uses novel three-port network as the output matching/combining network (OMCN). The three-port OMCN performs the power combining for any arbitrary output power ratios from the two transistors of the Doherty amplifier. It also performs the impedance matching from any arbitrary complex load impedance to the optimum impedances for both transistors at peak output power. Commonly in Doherty amplifiers, an optimum performance at peak power and a sub-optimum performance at power back-off are often obtained. Using the proposed output network, optimum performance can be reached at power back-off, as well as at peak power. Another three-port network is proposed for input matching/dividing network (IMDN) at the input of the proposed Doherty amplifier. The three-port IMDN is designed to perform the power division with any arbitrary division ratio, adjust the arbitrary phase difference between the input signals to the two transistors, and provide the impedance matching from any arbitrary complex source impedance to the optimal source impedances for the two transistors. To verify the provided theory, two prototype amplifiers are designed and tested. A 12-W amplifier is designed for a 50-\Omega source and load impedances at 1 GHz. Another 12-W amplifier is designed at 1 GHz for complex source and load impedances. Both amplifiers have efficiency of higher than 50% at 7-dB output power range. [ABSTRACT FROM PUBLISHER]

This paper presents the broadband class-C mode of operation, termed the “continuous class-C”, which is an extension of a standard class-C design but with the optimum fundamental and second harmonic terminations now forming a continuous arrangement of load impedances on the Smith chart. With the generic drain current waveform depending on the amplifier conduction angle, and by using the well-established continuous class-B (class-J) voltage waveforms, a set of closed-form equations for the fundamental and second harmonic impedances are derived. These provide a wide impedance design space to realize broadband class-C power amplifiers (PAs) with the constant output power, gain and efficiency over a significant bandwidth. The continuous class-C mode is subdivided into low- and high-power modes for which load impedance, output power and drain efficiency ratios are found and compared to those of the continuous class-B. New design spaces are graphically shown for both class-C modes. The proposed continuous class-C concepts are validated experimentally with on-wafer load pull measurements of an integrated 8×50 μm, ~ 1 W, 20 V GaN MMIC transistor. The proposed theory is also applied in simulations of power amplifiers operating in continuous class-B and continuous class-C modes. [ABSTRACT FROM AUTHOR]

An architecture and design procedure for transformer-less load-modulated power amplifiers (PAs) having high efficiency at power back-off is presented. This architecture utilizes a comparable load modulation concept as in the Doherty PA; however, contrary to the Doherty PA, it neither requires an output impedance transformer, nor offset lines, which are the main limiting factors in designing wideband Doherty amplifiers. In this architecture, the proper load modulation at the transistor drain levels is directly dependant on the design of the main and peaking amplifiers' matching networks. It is shown that the design of the output impedance of the peaking amplifier as a frequency-varying susceptance rather than as a quasi-open circuit impedance (as in Doherty amplifiers) helps in achieving better wideband performance. Based on the analytical results, a step-by-step procedure is proposed for designing wideband load-modulated PAs having high efficiency over a wide power back-off region. Based on the proposed architecture and its design procedure, a 10-W PA is designed and prototyped in the 1.96–2.46-GHz band exhibiting a power-added efficiency of more than 40% at a 6-dB power back-off. In comparison with a symmetrical Doherty amplifier design using the same device, the proposed architecture exhibits a 250% enhancement in its fractional bandwidth. [ABSTRACT FROM PUBLISHER]

This paper proposes a new method for extending the bandwidth of Doherty power amplifiers (PAs) in the digital domain. The bandwidth enhancement is achieved through a frequency-selective pre-compensation mechanism that is derived to prevent the efficiency degradation that naturally occurs as the frequency of operation deviates from the center frequency. A methodical analysis of the frequency response of the conventional Doherty PA and that of the proposed Doherty PA is carried out to point out the limitations of the former and demonstrate the capability of the latter in recovering the bandwidth. Over the frequency range spanning from 1.96 to 2.46 GHz, the measured drain efficiency at 6–7-dB output power back-off is higher than 40% for the proposed Doherty PA. Such efficiency performance is achievable only from 2.04 to 2.22 GHz using the conventional Doherty PA. Hence, the bandwidth is enhanced from 180 to 500 MHz, which corresponds to an increase by a factor of 2.8 (i.e., almost triple). By applying the proposed methodology, a Doherty PA that is originally designed at the center frequency of 2.14 GHz for downlink wideband code division multiple access became operative at 1.98-GHz uplink wideband code division multiple access (UL-WCDMA), 2.22-GHz long-term evolution (LTE), and 2.34-GHz worldwide interoperability for microwave access (WiMAX) bands. The average drain efficiencies for UL-WCDMA, LTE, and WiMAX applications, were 40.1%, 44.2%, and 41.4%, respectively, using the proposed Doherty PA, and 37%, 37.3%, and 35.2%, respectively, using the conventional Doherty PA. [ABSTRACT FROM PUBLISHER]

An analytical design methodology of outphasing amplification systems is proposed using new simplified analytical expressions for the instantaneous efficiency and the input/output voltages of Chireix outphasing combiners. These expressions are derived first for ideal voltage sources with nonzero internal impedance and later for ideal Class-B amplifiers where dc current variation is incorporated. They take into account the impedance mismatch between the amplifiers and the lossless combining structure and account explicitly for the all of the combiner's electrical parameters. We show that the maximum achievable instantaneous combining efficiency can be controlled in position and in value through the judicious choice of the combiner's stub length and transmission-line characteristic impedance. We further show that, when this choice is combined with the amplified signal's distribution, the average combining efficiency can be precisely controlled and easily maximized. Various validations of the proposed expressions are performed by comparison with experimental and simulation results for various combiners as well as for a complete linear amplification with nonlinear components amplifier. Excellent agreement between simulations and measurements is obtained in all cases considered. [ABSTRACT FROM PUBLISHER]

A design methodology for a concurrent dual-band Doherty power amplifier (PA) with frequency-dependent backoff power ranges is presented in this paper. Based on a dual-band T-shaped network and a coupled line network, different dual-band components needed in Doherty PA topology, including a 3-dB branch-line coupler, an offset line, and a quarter-wavelength transformer, are developed. Two prototypes with balanced and imbalanced backoff power range modes are implemented to verify the feasibility. Continuous wave signal test results show that the proposed dual-band PA successfully achieves a power-added efficiency of 33% and 30% at the 6-dB backoff point from the saturated output power at 880 and 1960 MHz, respectively. To meet linearity requirements, the PA nonlinear behavior is characterized by using digital multitone signals, which categorize the distortions of a concurrent dual-band PA into intermodulation and cross-modulation. Finally, a 2-D digital predistortion technique is used to compensate for the nonlinearity of PA in dual bands. Two two-tone signals are applied to the dual bands for linearization, and the experimental results show that this technique achieves improvements of better than 19.1 and 24.6 dB for the intermodulation and cross-modulation in the dual bands, respectively. [ABSTRACT FROM AUTHOR]

An original source- and load-pull topology based on a passive technique is presented in this paper. The proposed system consists of passive tuners and loop structures. The use of a passive loop structure in cascade with a passive tuner allows for synthesis of reflection coefficients in the order of 0.97 magnitudes at the device under test's access plane. The measurement and characterization results of a 1W GaAs MESFET device show an improvement of 0.9 dB in the gain and 6% in the power-added efficiency when the proposed impedance synthesis techniques are used. [ABSTRACT FROM PUBLISHER]

This letter proposes a new design technique for quad-band Doherty power amplifier (DPA) based on the T-section coupled lines network (TCLN). The TCLN allows for the design of a quad-band impedance inverter at three arbitrary frequencies and one associated frequency offering more flexibility in the design of quad-band DPAs than the state of the art. The ratio of the largest operating frequency to the smallest operating frequency is found in the range 1.95 to 7, as the ratio of the other two operating frequencies is located in the range of 1.3 to 2.76. A quad-band DPA is implemented with TCLN, operating at 0.73, 1.65, 2.67, and 3.57GHz. The measured results agree with the anticipation perfectly. [ABSTRACT FROM PUBLISHER]