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Broadband Doherty Power Amplifier Based on Asymmetric Load Matching Networks

This brief presents asymmetric load matching networks for broadband Doherty power amplifiers (DPAs). The output combiner consists of two λ/4 impedance transformers with optimized characteristic impedance values in order to provide a load modulation at a high output power level; the bandwidth limitation for efficiency at the back-off power level can be then mitigated. For a proper load modulation with the proposed output combiner, asymmetric load matching networks between the carrier and peaking amplifiers are proposed. The input and output matching networks were designed using balanced open stubs, which are more insensitive to frequency than unbalanced open stubs. For the load matching networks, two-section matching networks were adopted. The designed and implemented broadband DPA showed a fractional bandwidth of 23.5% (from 750 to 950 MHz). It also showed measured efficiency values of higher than 55.4% at the peak power level and 51.5% at the 6-dB back-off power level, respectively. For the operational frequency range, a peak output power value of higher than 48 dBm and a gain of 14-15.8 dB were achieved.

Adaptive TX Leakage Canceler for the UHF RFID Reader Front End Using a Direct Leaky Coupling Method

This paper presents a new adaptive leakage canceler based on a direct leaky coupling method for an RF front-end circuit of an ultrahigh-frequency radio-frequency identication (UHF RFID) reader. For better receiver sensitivity, the leakage signal from a transmitter (TX) to a receiver (RX) should be suppressed. Compared with conventional methods, the proposed TX leakage canceler has a much simpler circuit configuration due to the direct leaky coupling circuit (LCC) and the phase shifter on the RX path. The LCC includes a variable resistor, a variable capacitor, and an inductor, which allow us to control the magnitude and the phase of the coupled TX signal. The phase shifter that is located on the RX path even before the low-noise amplifier controls the phase of the TX leakage signal. For the worldwide RFID bands that spans from 840 to 960 MHz, the canceler must be adaptively controlled by using a microcontroller and control circuits. For the experimental verification, an RF front-end circuit with the proposed adaptive TX leakage canceler was designed and implemented for the UHF RFID reader. The implemented RF front-end block occupies only 54 ×54 mm2, except for the control block. From 840 to 960 MHz, the adaptively controlled RF front-end circuit exhibited significant cancelation characteristics for the TX-RX leakage signals. This results in more than twice longer reading distances for the commercial RFID tags compared with the cases without the adaptive canceler.

Ultrabroadband Linear Power Amplifier Using a Frequency-Selective Analog Predistorter

This brief presents an ultrabroadband (2- to 600-MHz band) linear power amplifier using a compact frequency-selective analog predistorter, which includes a capacitor having an optimized capacitance and a biased Schottky diode connected in series. It is shunted at the input of the main amplifier and has a frequency-selective third-order intermodulation generation capability using its optimized capacitance. A two-stage push-pull power amplifier, which has an ultrabroadband operation range from 2 to 600 MHz, was implemented and linearized using the proposed analog predistorter. It exhibited high 1-dB compression point (P1 dB) and power-added efficiency characteristics of over 43 dBm and 32% at each P1 dB for the entire operating band, respectively. At an average output power level of 36 dBm for the two-tone signal input, which has a tone spacing of 1 MHz, its third-order intermodulation distortion over the entire band is no higher than -39.1 dBc after linearization, as compared with -34.2 dBc before linearization.

High-Efficiency Power Amplifier Using an Active Second-Harmonic Injection Technique Under Optimized Third-Harmonic Termination

This brief presents an active second-harmonic injection technique to improve the efficiency and bandwidth for high-efficiency power amplifiers (PAs). An optimum third-harmonic termination condition was examined for higher efficiency after the second-harmonic injection using a multiharmonic load-pull simulation. It was determined that the optimum third-harmonic termination is the same as that of the inverse class-F PA. Based on this result, a high-efficiency PA with an optimized third-harmonic termination for the second-harmonic injection was designed for a center frequency of 1 GHz as a main amplifier. The overall system requires an auxiliary second-harmonic amplifier and a diplexer between the main and auxiliary PAs. The PA with an optimized third-harmonic termination for the second-harmonic injection was implemented using a 10-W GaN high-electron-mobility transistor for both the main and auxiliary power stages. Compared with the PA without second-harmonic injection, the bandwidth with a power-added efficiency of more than 80% is extended from 60 (960-1020 MHz) to 180 MHz (880-1060 MHz) after the second-harmonic injection.

CMOS Power Amplifier Integrated Circuit With Dual-Mode Supply Modulator for Mobile Terminals

A CMOS power amplifier integrated circuit with an optimized dual-mode supply modulator is presented. The dual-mode supply modulator, based on a hybrid buck converter consisting of a wideband linear amplifier and a highly efficient switching amplifier, provides two operation modes: envelope tracking (ET) for high average output power and average power tracking (APT) for low output power. For the APT mode, the linear amplifier is switched off and the switching amplifier operates as a normal buck converter to supply DC voltage to the power amplifier according to the average output power. The optimum switch sizes of the switching amplifier were analyzed and applied for each operation mode for higher efficiency. An integrated circuit with a power amplifier and the dual-mode supply modulator was designed and fabricated using a 0.18-μm CMOS process for LTE applications at a frequency of 0.78 GHz. For the 16-QAM uplink LTE signal, the measured efficiency with an ET mode is as high as 45.4%, which is 7.0% higher than that from the stand-alone power amplifier at an average output power of 24 dBm. An efficiency of 14.1% was achieved with an APT mode at an average output power of 9 dBm. This is 3.2% higher than that with the ET mode.

Doherty power amplifier using a compact load network for bandwidth extension

This paper presents a Doherty power amplifier (DPA) with a compact load network for an extended bandwidth compared to the conventional DPA. The compact load network takes less area since it has just one load matching network after the quarter-wave transmission line and no offset-lines. For the verification, both conventional and compact DPAs are designed and built using GaN HEMT for the band from 650 to 800 MHz. They were evaluated using the down-link 16-QAM FDD LTE signal that has a PAPR of 9.96 dB and a signal bandwidth of 5 MHz. At an average output power of 34 dBm, which is approximately 9 dB back-off from the 1 dB compression point, the proposed compact DPA exhibited a power-added efficiency (PAE) level of more than 40% and an adjacent channel leakage power ratio (ACLR) level of lower than -25 dBc over the frequency band of from 650 to 800 MHz, while the conventional DPA showed a PAE level of more than 26.6% and an ACLR level lower than -23 dBc. In addition, the proposed compact DPA has a reduced circuit size by 40.9% compared to the conventional one.

Efficiency Enhancement for the 3.5 GHz Balanced Power Amplifier Using Dynamic Bias Switching

This paper presents an efficiency enhancement for the balanced power amplifier using DBS(Dynamic Bias Switching) method which dynamically provides the power amplifier with two bias voltage levels according to the input envelope signal. In order to apply the dynamic biases to each side of the balanced power amplifier, two switching stages are adopted. Using an OFDM signal with a bandwidth of 20 MHz and a PAR(Peak to Average Ratio) of 8.5 dB, 6 % of PAE(Power-Added Efficiency) is improved at an output power of 42.5 dBm.

Design of High-Power and High-Efficiency Broadband Amplifier Using 1:4 Transmission Line Transformer

This paper presents a design of a 100 W high-efficiency power amplifier, whose operational frequency band expands from 30 to 512 MHz, using negative feedback network, push-pull structure, broadband RF choke, and transmission line transformer for balun configuration. The push-pull amplifier has been tuned for higher output power using a shunt capacitor as a matching component at its load especially for high-frequency region. The implemented power amplifier exhibited a very flat power gain of throughout the operating frequency band and very high power-added efficiency(PAE) of greater than 40% at an output power of 100 W. It also showed second- and third-harmonic distortion levels of below -34 dBc and -12 dBc, respectively, through the entire operating frequency band.

Design of High-Efficiency Current Mode Class-D Power Amplifier Using a Transmission-Line Transformer and Harmonic Filter at 13.56 MHz

This paper presents a high-efficiency current mode class-D(CMCD) power amplifier for the 13.56 MHz band using a Guanella`s 1:1 transmission-line transformer and filtering circuits at the output network. The second and third s are filtered out in the load network of the class-D amplifier. The implemented CMCD power amplifier exhibited a power gain of 13.4 dB and a high power-added efficiency(PAE) of 84.6 % at an output power of 44.4 dBm using the 13.56 MHz CW input signal. The second and third distortion levels were -50.3 dBc and -46.4 dBc at the same output power level, respectively.

Highly Efficient 13.56 MHz, 300 Watt Class E Power Transmitter

This paper presents a design of high-efficiency and high-power class E power transmitter. The transmitter is composed of 300 Watt class E power amplifier and AC-DC converter. The AC-DC converter converts 220 V and 60 Hz AC to a 290 V DC. The generated DC voltage is directly applied to a bias of the class E power amplifier. Because the converter does not have DC-DC converter unit, it has very high conversion efficiency of about 98.03 %. To minimize the loss at the output of the power amplifier, high-Q inductor was implemented and deployed to the output resonant circuit. As a result, the 13.56 MHz class E power amplifier has a high power-added efficiency of 84.2 % at the peak output power of 323.6 W. The overall efficiency of class E power transmitter, including the AC-DC converter, is as high as 82.87 %.