Xiaofan Chen

Enhanced Analysis and Design Method of Concurrent Dual-Band Power Amplifiers With Intermodulation Impedance Tuning

The behavior of power amplifiers (PAs) driven by concurrent dual-band signals is analyzed theoretically in this paper. According to the analysis, the impedance matching at intermodulation (IM) frequency is very important for PAs working in concurrent mode. Based on the concept of IM impedance tuning, a family of new operation modes can be introduced, including concurrent Class-A, Class-AB, Class-B, and Class-C. The theoretical performance of these modes are derived and the overdrive effects of them are also discussed. A possible structure is proposed to implement the proposed IM impedance tuning, and a concurrent Class-AB dual-band example PA operating at 1.9-2.6-GHz long-term evolution (LTE) bands is demonstrated. Experimental results show good consistence with the theoretical analysis, and the concurrent Class-AB PA prototype exhibits higher than 36.1% power-added efficiency in concurrent mode when driven by 10- and 15-MHz LTE signals in two bands concurrently. To our best knowledge, this is the state-of-the-art efficiency performance of concurrent dual-band PAs, even higher than previously reported dual-band Doherty PAs. Additionally the proposed PA, which is fabricated using a 10-W GaN HEMT, can output more than 34.3-dBm power with a peak-to-average ratio of 7 dB in concurrent mode, showing a remarkable power utilization factor for concurrent dual-band PAs.

A Broadband Doherty Power Amplifier Based on Continuous-Mode Technology

In this paper, a novel broadband Doherty power amplifier based on the continuous-mode technique (C-DPA) is proposed. The amplifier is focused on manipulating harmonic components in a Doherty power amplifier (DPA) structure to achieve improved bandwidth and efficiency. In a conventional DPA, harmonic isolation is typically required between the two transistors to prevent them from modulating each other at harmonic frequencies. However, as presented in this paper, such isolation is not actually necessary. On the contrary, by allowing the two transistors to modulate each other at harmonic frequencies with the help of a properly designed postharmonic tuning network, a series of highly efficient DPA modes can be created over a continuous frequency band, leading to a broadband C-DPA. Based on the proposed method, an example of a C-DPA working from 1.65 to 2.75 GHz was designed. According to the measured results, the designed C-DPA exhibits a 52%-66% efficiency at a -6 dB power backoff and a power utilization factor higher than 1.08 over the 1.1-GHz band. In addition, when simulated by a 7.5-dB peak-to-average power ratio 20-MHz LTE signal, the example C-DPA exhibits an efficiency of 46%-62% while maintaining an adjacent channel power ratio below -45 dBc after linearization over the full 1.1-GHz band. To the best of our knowledge, this is the first proposed C-DPA and a state-of-the-art performance for broadband DPAs.

A concurrent dual-band 1.9–2.6-GHz Doherty power amplifier with Intermodulation impedance tuning

In this paper, a novel matching structure is introduced to implement accurate impedance matching at intermodulation (IM) frequencies in concurrent dual-band power amplifiers (PAs). Additionally, a concurrent dual-band Doherty power amplifiers (DPAs) architecture featuring Intermodulation impedance tuning (IM tuning) is introduced in this paper. Based on the proposed matching structure and DPA architecture, a concurrent dual-band 1.9-2.6 GHz DPA is designed and fabricated using two 13-Watts GaN HEMTs. After linearization, the proposed DPA exhibits drain efficiency higher than 50% and output power nearly 10 Watts in concurrent mode. Due to the accurate IM tuning, the efficiency and PUF are improved greatly compared with previously reported concurrent dual-band DPAs, by about 40 percent and 3 times, respectively. To our best knowledge, this is the first reported DPA with IM tuning and the state-of-the-art performance in terms of both efficiency and power utilization factor (PUF).

A novel design method of concurrent dual-band power amplifiers including impedance tuning at inter-band modulation frequencies

A novel design method of concurrent dual-band power amplifiers (PAs) including impedance tuning at inter-band modulation (IM) frequencies is proposed in this paper. Its shown that the impedances exhibited to the transistor at IM frequencies can affect the performance of a concurrent PA significantly. Thus it is very essential to take IM impedances into account, which can be referred to as IM impedance manipulation, or IM tuning for short. An example concurrent dual-band 1.92.6GHz PA is designed using the proposed method and a conventional concurrent dual-band PA not considering IM tuning is also designed for the purpose of comparison. Designed with a 10-Watts GaN HEMT, the proposed PA exhibits about 11 Watts output power and higher than 72.8% drain efficiency when driven equally by concurrent CW stimulus. To our best knowledge, this is the state-of-the-art performance of concurrent dual-band PA, and its the first reported concurrent PA with IM tuning.

Extraction of wideband behavioral model of power amplifier with multi groups of narrow band signals

This paper proposes a method to extract the wideband model of power amplifiers (PAs) with narrow band signals, so that the sampling rate of the analog digital converter (ADC) can be even lower than the bandwidth of the signal. By sweeping the frequency response with narrow band signals and combining the envelopes of input and output signals, a wideband model of PA is observed. The model can be used as both wideband simulator and digital predistorter. Experiments are performed on a wideband PA. The PA is swept with 17 groups of 10M LTE signals at 30.72Msps sample rate. When verifying the wideband model with 40MHz LTE-A signal at 184.72msps, the normalized mean square error (NMSE) of the forward model is -32.77 dB. And the feedback model successfully eliminates the adjacent channel power ratio (ACPR) of PA output signal from -30.3dBc to -45.5dBc when it is stimulated with 40M LTE-A signal.

Systematic Crest Factor Reduction and Efficiency Enhancement of Dual-Band Power Amplifier Based Transmitters

A systematic design methodology including novel crest factor reduction (CFR) and power amplifier (PA) efficiency enhancement techniques for concurrent dual-band transmitters is proposed to improve performance under concurrent modulated stimulus, in terms of both efficiency and output power. Conventional energy efficient PAs are typically implemented separately in analog circuit or digital signal domains. However, the proposed method combines a digital domain 2-D power distribution reshaping (2-D-PDR) method to adaptively reshape the signals’ distribution to fit the target PA’s characterization and an analog domain inter-modulation tuning design to enhance the PA’s output capability. Based on the proposed method, an example of concurrent dual-band Doherty PA (DPA) working at 1.9–2.6 GHz LTE bands was designed using two 10-Watt GaN HEMTs. A 2-D-PDR procedure was developed for the designed DPA. The fabricated DPA was measured in concurrent mode under the stimulus of a pair of 10 MHz LTE signals. According to the measured results, the proposed DPA achieved a drain efficiency of 46.6% at an output power of 6.2 W while maintaining a good adjacent channel power ratio and error vector magnitude. To the best of the authors’ acknowledge, this is the state-of-the-art performance for concurrent dual-band PAs. Additionally, measurements are performed on three varied type of PAs using the proposed 2-D-PDR. According to the measured results, about 0.3~0.8 dB power improvement and 1.5%~3% efficiency improvement can be achieved using the proposed 2-D-PDR compared with the conventional 2-D-CFR, proving the feasibility of the proposed technique.

Radio frequency power amplifier for wireless communication

For the sake of high-speed data rate, efficient and linear power amplifiers (PAs) are highly desirable for wireless communications. First, the specification for PA with nonconstant envelope signals will be reviewed, especially for high power to average power ratio modulated signals. In order to enhance the PA efficiency, three energy-efficient PA topologies will be introduced. The related transistor technology will be investigated to satisfy the demands of high-efficiency PA architectures. Finally, broadband and multiband PA designs will be also discussed for emerging wireless communications.

Energy-efficient broadband Doherty power amplifier for carrier aggregation

This talk will review the recent progress in energy-efficient broadband Doherty power amplifier (PA) and low complexity digital predistortion (DPD) techniques for carrier aggregation. For carrier aggregation application, especially for more than 3 carriers, it is not easy to implement multiband Doherty architecture or achieve required bandwidth. In this situation, broadband Doherty PA with concurrent operation capability is highly desirable. To alleviate the bandwidth burden on conventional Doherty PA, Continuous mode impedance matching method is proposed for Doherty PA for bandwidth enhancement, which utilizes the cross-matching technique to realize the physical output matching network. Owing to the compressive sensing method, the behavioral model can be extracted by using the aliased feedback signal, the broadband PA nonlinearity can be well corrected by the estimated output, and the feedback sampling rate can be reduced drastically.

Advanced power amplifier technologies for multistandard and broadband wireless communications

To accommodate multistandard and broadband wireless communications, advanced power amplifier (PA) design and digital predistortion (DPD) methods are investigated in this paper. For efficiency enhancement in dual-band PAs, an intermodulation tuning (IM-Tuning) technique is introduced and employed to dual-band concurrent Doherty PA design. To reduce the complexity of conventional 2D-DPD behavioral model, a 2D modified memory polynomial (2D-MMP) and an adaptive pruinng method are demonstrated. Finally, a robust DPD behavioral model with a low sampling rate is also proposed for broadband applications.

Energy-efficient power amplifier techniques for TD-SCDMA and TD-LTE multi-standard wireless communications

An energy-efficient concurrent dual-band Doherty power amplifier (PA) and its related digital predistortion (DPD) for TD-SCDMA and TD-LTE multi-standard wireless communications are investigated in this paper. Due to the proposed inter-modulation tuning technique, the PA efficiency and output power in concurrent operation mode are improved significantly. To alleviate the burden on hardware implementation, a low complexity two-dimensional digital predistortion (2D-DPD) is employed to compensate for the nonlinearities of the dual-band PA, the coefficients number is drasitically reduced. Experimental results show that the proposed dual-band Doherty PA achieves the output power of 38.1 dBm and the PAE of 42.1% in cocurrent mode, which could satisfy the requirement of multi-standard applications.