Before the emergence of ultra-wideband (UWB) radios, widely used wireless communications were based on sinusoidal carriers, and impulse technologies were employed only in specific applications (e.g. radar). In 2002, the Federal Communication Commission (FCC) allowed unlicensed operation between 3.1–10.6 GHz for UWB communication, using a wideband signal format with a low EIRP level (−41.3dBm/MHz). UWB communication systems then emerged as an alternative to narrowband systems and significant effort in this area has been invested at the regulatory, commercial, and research levels.

IEEE Transactions on Microwave Theory and Techniques and Antennas and Propagation Announce a Joint Special Issue on Ultra-Wideband (UWB) Technology

Total bandwidth of existing wireless communication technologies covers a wide frequency range of over one octave. But most existing power amplifier configurations cannot meet this requirement while at the same time maintaining a high efficiency. Therefore, a new structure that can achieve multioctave bandwidth is proposed in this paper together with the design methodology. The difficulty in realizing a bandwidth larger than one octave lies in the overlapping of fundamental and harmonic frequencies. Regarding this problem, the continuous class-F mode is extended to allow a resistive second harmonic impedance, rather than the pure reactive one. With the relaxed design requirements and overlapping design space of fundamental and second harmonic frequencies, harmonic tuning and fundamental frequency matching networks can be designed separately. More importantly, broadband matching for fundamental frequencies can be implemented simply by considering only three fundamental frequency points using the multiple frequencies matching method. To verify the validity of the proposed methodology, a multioctave power amplifier was designed, fabricated, and measured. Measured results verify a wide bandwidth of 128.5% from 0.5 to 2.3 GHz. Over this frequency range, drain efficiency was larger than 60% with output power greater than 39.2 dBm and large signal gain larger than 11.7 dB.

Design of Ultrawideband High-Efficiency Extended Continuous Class-F Power Amplifier

In this paper, a broadband continuous-mode Doherty power amplifier (CM-DPA) is realized taking advantage of the noninfinity output impedances of peaking stage Specifically, the carrier PA of the designed DPA operates in a continuous class-J mode when the peaking PA is in the OFF-state, where the output impedance of the peaking PA has some influences on the carrier PA When the peaking transistor is in the OFF-state, the load impedance variation of the carrier transistor versus noninfinity peaking impedance is presented in this contribution The proposed method surmounts the back-off drain efficiency deterioration of DPAs at two side working bands through elaborately processing the noninfinity peaking impedance This paper also presents a method to derive the required OFF-state output impedance of the peaking stage by the carrier PA in a symmetrical broadband DPA A broadband CM-DPA working over 16–27 GHz (bandwidth of 51%) is designed and fabricated for interpreting our theories The simulated load trajectory of the carrier transistor is in line with the design space of continuous class-J mode Under continuous wave excitation, experimental results show the drain efficiencies of 465%–635% at 6-dB output back-off power levels and 56%–753% at peaking power levels The maximum output power of this DPA is 438–452 dBm with a gain of 94–115 dB across the whole working band Furthermore, a 20-MHz LTE modulated signal with a peak-to-average power ratio of 74 dB is also applied to the fabricated CM-DPA at 22 GHz At an average output power of 375 dBm, measurement results show the adjacent channel power ratios of −302 and −501 dBc before and after digital predistortion, respectively

Broadband Continuous-Mode Doherty Power Amplifiers With Noninfinity Peaking Impedance

The unique material properties of GaN, wide bandgap, high thermal conductivity, high breakdown voltage, high electron mobility and the device properties of GaN HEMT (High Electron Mobility Transistor) namely low parasitic capacitance, low turn on resistance and high cut off frequencies make it a good choice to use in a power amplifier. During this era of wire- less communication with complex modulation schemes having high peak to average power ratio, maintaining the efficiency and linearity of power amplifier is a tough task. In this paper an extensive review of GaN HEMT based power amplifier is presented. First of all, GaN technology is described and compared with other semiconductor technologies. The different classes of power amplifier like class B, C, D, E, F and J with GaN is discussed. Efficiency and linearity enhancement techniques like envelope tracking, Doherty power amplifier and digital predistortion used in applications with high PAPR waveforms is described. The advantages of GaN MMIC (Microwave Monolithic Integrated Circuit) are reviewed. Finally different thermal management solutions used for GaN power amplifier to cope with its self heating phenomenon are explained.

A review of GaN HEMT broadband power amplifiers

This paper presents a broadband three-stage Doherty power amplifier (DPA) using impedance compensation for bandwidth extension. Different from the conventional design, an impedance-compensating load combiner is proposed to broaden the bandwidth of the three-stage DPA by employing the output impedances of the peaking amplifiers. Considering the load impedance of the peaking branch as an independent design variable, the Doherty load modulations are analyzed in theory, pointing out the optimized solution for the load combiner. To achieve the impedance compensation, the peaking output matching networks are deliberately designed with the dual-impedance matching topology. Experimental results show that a three-stage DPA is realized from 1.6 to 2.6 GHz (48% fractional bandwidth) with a measured efficiency of 50%–53% at 9.5-dB back-off and a saturated output power around 45.5 dBm. When stimulated by the 20- and 40-MHz modulated signals at an average output power of around 36.5 dBm, the proposed DPA can achieve the adjacent channel leakage ratio of −50 dBc over the whole frequency band after linearization, with an average efficiency of higher than 50%.

Improved Three-Stage Doherty Amplifier Design With Impedance Compensation in Load Combiner for Broadband Applications

This paper proposes a design approach for a broadband and high-efficiency continuous inverse Class-F ( ${\text {CCF}}^{-1}$ ) power amplifier (PA) based on a modified elliptic low-pass filtering (LPF) matching network (MN). From theoretical and practical perspectives, the importance of a swift impedance transition from the higher end of the fundamental frequency band to the lower end of the second harmonic band is discussed, when designing a broadband single-mode PA. After being compared with widely used Chebyshev LPF MNs, a modified elliptic LPF MN, which provides a sharp roll-off, is utilized to provide the required rapid transition. A step-by-step design procedure of the proposed modified elliptic LPF MN is presented. Experimental results show that a high-efficiency ${\text {CCF}}^{-1}$ PA is realized from 1.35 to 2.5 GHz (fractional bandwidth = 60%) with measured drain efficiency of 68%–82% and output power of 41.1–42.5 dBm. When stimulated by a 20-MHz LTE signal with an average output power of approximately 34.5 dBm, the proposed PA, combined with digital pre-distortion, achieved adjacent channel leakage ratios (ACLRs) below $-{\text {45 dBc}}$ , with average efficiency (AE) ranging from 37% to 45.8%. Similar performance is measured when the proposed PA is driven by a dual-band dual-mode modulated signal with a 100-MHz instantaneous bandwidth at a center frequency of 2.14 GHz.

/pdf/highly-efficient-broadband-continuous-inverse-class-f-power-d78wdh1h9m.pdf

Highly Efficient Broadband Continuous Inverse Class-F Power Amplifier Design Using Modified Elliptic Low-Pass Filtering Matching Network

This paper presents a high-efficiency gallium nitride Doherty power amplifier (DPA) using an integrated compensating reactance (CR) for broadband operation. With an additional quarter-wavelength transmission line integrated in the peaking amplifier output, a CR is generated to compensate the load impedance of the carrier amplifier in the low-power region and thus enhance the back-off efficiency over a wide frequency range without affecting the Doherty load modulation at saturation. For this purpose, a peaking output matching network (OMN) is employed to convert the output impedance of the peaking device into quasi-short circuit when it is off and achieve proper impedance matching when it is on. A two-point matching technique using the transmission ( $ABCD$ ) matrix is employed to design such desired OMN. Measurement results show that the DPA has a 6-dB back-off efficiency of 50%–55% and a saturated efficiency of 57%–71% over the frequency band of 1.7–2.8 GHz (49% fractional bandwidth). When driven by a 20-MHz long term evolution modulated signal at 6.5-dB back-off power, the DPA can achieve an average efficiency of more than 50% with high linearity after linearization over the design frequency band.

/pdf/a-broadband-high-efficiency-doherty-power-amplifier-with-4on09xf291.pdf

A Broadband High-Efficiency Doherty Power Amplifier With Integrated Compensating Reactance

To reduce power consumption of wireless transmitters, the transmission power level of RF power amplifiers (PAs) may dynamically change according to real-time data traffic. This leads that the existing digital predistortion (DPD) techniques cannot be directly employed because they are mainly suitable for eliminating distortion induced by the PAs operated at a relatively stable condition, e.g., at a constant average power level. To resolve this problem, a power adaptive DPD is proposed in this paper. By accurately modeling the behavior change pattern of the PA with the input power adjustments and embedding it into the DPD model, the proposed DPD system is able to adjust its coefficients to adapt to the behavior variation of the PA induced by the power adjustments without real-time recalibration. A low-complexity online coefficients updating method is also proposed to track the behavior change of the PA caused by other factors, such as bias shifting or temperature variation, during real-time operation. Measurements with a high power LDMOS Doherty PA have been used to validate the proposed approach. Results show that the proposed DPD and its coefficients updating approach can produce excellent performance with very low complexity compared to the conventional approaches.

/pdf/power-adaptive-digital-predistortion-for-wideband-rf-power-3vl98ywkw3.pdf

Power Adaptive Digital Predistortion for Wideband RF Power Amplifiers With Dynamic Power Transmission

In this paper, a generalized dual-basis envelope-dependent sideband (GDES) distortion model structure is proposed to compensate the distortion induced by transmitter leakage in concurrent multi-band transceivers with non-contiguous carrier aggregation. This model has a generalized structure that is constructed via first generating a nonlinear basis function that maps the inputs to the target frequency band where the distortion is to be cancelled, and then multiplying with a second basis function that generates envelope-dependent nonlinearities. By combining these two bases, the model keeps in a relatively compact form that can be flexibly implemented in digital circuits such as field programmable gate array (FPGA). Experimental results demonstrated that excellent suppression performance can be achieved with very low implementation complexity by employing the proposed model.

/pdf/digital-compensation-for-transmitter-leakage-in-non-4nn2gce6ar.pdf

Digital Compensation for Transmitter Leakage in Non-Contiguous Carrier Aggregation Applications With FPGA Implementation

In this paper, an output-controllable digital predistortion (DPD) technique is proposed to partially inverse the nonlinear behavior of RF power amplifiers (PAs). Compared to the existing DPD, the proposed method changes the goal that the PA output must be exactly the same as the original input to a new one that the PA output can be arbitrarily controlled according to user's demand. The proposed approach largely expands the capability of DPD and thus provides more flexibility for system designers to effectively use DPD to manipulate the PA output in order to handle more application scenarios and objectively conduct further system optimization. Various application cases have been tested. The experimental results demonstrate that the proposed approach has great potential in future wireless communication system design.

/pdf/output-controllable-partial-inverse-digital-predistortion-16sb8qx4to.pdf

Yan Guo

Papers

Highly Efficient Broadband Continuous Inverse Class-F Power Amplifier Design Using Modified Elliptic Low-Pass Filtering Matching Network

A Broadband High-Efficiency Doherty Power Amplifier With Integrated Compensating Reactance

Power Adaptive Digital Predistortion for Wideband RF Power Amplifiers With Dynamic Power Transmission

Digital Compensation for Transmitter Leakage in Non-Contiguous Carrier Aggregation Applications With FPGA Implementation

Output-Controllable Partial Inverse Digital Predistortion for RF Power Amplifiers