Xuan Anh Nghiem

Design of Concurrent Multiband Doherty Power Amplifiers for Wireless Applications

This paper presents the design of concurrent multiband Doherty power amplifiers (MB-DPA) based on a newly developed multiband impedance inverter network (MB-IIN). The design concept can theoretically be applied to a large number of frequency bands. To support the design of MB-DPAs, a detailed realization of the MB-IIN is introduced for the first time. For verifying the proposed MB-IIN design technique, tri-band and quad-band DPAs for 950, 1500, 2140, and 2650 MHz are designed, implemented, and characterized. Measurement results show good performance in terms of efficiency, linearity, and especially the pronounced Doherty behavior in all targeted bands, demonstrating the prospective applications of the developed MB-IIN in the design of concurrent multiband Doherty power amplifiers for wireless communications.

Novel design of a concurrent tri-band GaN-HEMT Doherty power amplifier

In this paper, a novel design approach of a concurrent tri-band Doherty power amplifier (DPA) for the frequency bands at 1.49 GHz, 2.14 GHz and 2.64 GHz is presented. To the best of our knowledge, this is the first time that a concurrent tri-band DPA has been successfully designed and implemented. The design concept can be extended to cover a large number of frequency bands. In order to make a tri-band DPA feasible, all passive structures involving the DPA, especially the tri-band Impedance Inverter Network (IIN), must be designed such that they fulfil the tri-band operation requirements. A tri-band approach is validated in hybrid technology using a 10 W and a 25 W GaN-HEMTs for the carrier and peaking PA, respectively. The measured results show peak drain efficiencies of 61 %, 58.1 % and 46.1 % and the corresponding 6 dB output power back-off (OBO) efficiencies of 50.3 %, 39.45 % and 28.3% and the output power of 45.2 dBm, 43 dBm and 41.5 dBm for the first, second and third band, respectively.

Broadband Sequential Power Amplifier With Doherty-Type Active Load Modulation

This paper presents the concept and the detailed analysis of a sequential power amplifier with Doherty-type active load modulation (SPA-D). By introducing a Doherty-type output combiner into the conventional sequential power amplifier (PA), highly efficient amplification over broadband and wide dynamic range for the reconfigurable output power back-off can be achieved. The proposed amplifier mimics both the sequential and the Doherty PAs by exploiting the active load modulation region that has not been considered in the design of Doherty amplifiers. A broadband SPA-D prototype having 8-dB output back-off power (OBO) is designed and implemented. The experimental results exhibit drain efficiencies of 50%-75% at 7-10-dB OBO and 57%-70% at peak power with Doherty-like behavior over 700-MHz bandwidth centered at 2.35 GHz. The ability to easily reconfigure the breakpoint is experimentally verified, providing a convenient means for optimizing the amplifier efficiency according to various wireless standards. In addition, by using a memoryless digital predistortion, the spectrum emission mask required for long-term evolution down link can be fulfilled, making it well suited for applications in modern wireless transmitters.

Design of a broadband three-way sequential Doherty power amplifier for modern wireless communications

This paper presents the design and implementation of a broadband 3-way sequential-based Doherty power amplifier (DPA). This design approach can also be extended for a broadband N-way DPA architecture. A 12 - 23.5 W 3-way DPA has been designed, implemented and characterised to verify the proposed technique. The measured drain efficiency of 55 - 69 % over 500 MHz at 12 - 14 dB output power backoff (OBO) and 60 - 75 % over 600 MHz at saturation is achieved. Single-tone measurement at 2.1 GHz exhibits a drain efficiency of 63 %, 62.5 % and 75 % at 13.6 dB, 6 dB and 0 dB OBO, respectively. Also at this frequency, linearised measurement with a 10 MHz-LTE signal having a crest factor of 8.2 dB shows an average drain efficiency of 59 % and adjacent channel leakage ratio (ACLR) better than -45.5/ - 45.7 dBc at an average output power of 34.5 dBm. To the best knowledge of the authors, this is the first broadband 3-way sequential Doherty power amplifier with such high performance reported so far.

Novel design of a 10 dB back-off broadband sequential Doherty power amplifier for wireless applications

This paper presents the design and experimental results of a broadband sequential Doherty power amplifier (S-DPA). This new type of DPA allows large back-off (BO), highly efficient and broadband DPAs to be realised. A 10 W/10 dB BO S-DPA is designed to verify the design concept. Measurement results show obvious Doherty behaviour with 8 - 11 dB output power back-off over a 1.85 - 2.4 GHz frequency range. A drain efficiency of 65% over 300 MHz at BO and ≥ 58% over 500 MHz bandwidth at saturation is obtained. To show the state-of-the-art of the S-DPA, the drain efficiency at 2.0 GHz is selected with 74.5 % at saturation and 67.3% at 10 dB BO. Linearised measurement with a 10 MHz LTE signal having a crest factor of 7.5 dB at 2.1 GHz exhibits an average drain efficiency of 53% and an adjacent channel leakage ratio (ACLR) of -44.2/ - 48.7 dBc at an average output power of 32.7 dBm. To the best of the authors knowledge, this is the first wideband, 10 dB BO DPA with such high efficiency reported so far.

Design of a concurrent quad-band GaN-HEMT Doherty power amplifier for wireless applications

This paper presents the design and measurement results of a quad-band Doherty power amplifier (DPA) for concurrent operation in the 900 MHz, 1.5 GHz, 2.1 GHz and 2.6 GHz frequency bands. In principle, a quad-band DPA requires that all passive structures involving the DPA, but especially the impedance inverter network (IIN), be either broad-or multiband to cover the desired number of frequency bands. In this work, a newly developed multiband IIN is introduced, enabling the realisation of multiband symmetric and asymmetric DPAs. The design concept can theoretically be applied for a large number of frequency bands. The approach has been validated in hybrid technology using a 10 W and 25 W GaN-HEMT as carrier and peaking devices, respectively. The measured results show peak drain efficiencies of 58.12 %, 60.52 %, 52.74 %, and 43.3 %, associated with output powers of greater than 41.75 dBm in all four bands. The corresponding drain efficiencies at 6 dB output power back-off are measured to be 48 %, 56 %, 47 % and 31.8 % for the first, second, third, and fourth band, respectively. To the best of our knowledge, this is the first time a quad-band concurrent DPA has been successfully designed and implemented.

Design of a 57 % bandwidth microwave rectifier for powering application

This paper proposes a novel implementation of a high frequency rectifier, which is realised using the simplified real frequency technique. The optimum impedances presented at the diode package plane are found from source-pull simulation over a broad frequency range. The implemented broadband rectifiers show good performance in terms of efficiency and bandwidth. Using a HSMS 2820 Schottky diode device, greater than 50 % efficiency has been measured from 1.25 GHz to 2.25 GHz. Furthermore, greater than 60 % efficiency with 14 dB (from 12 dBm to 26 dBm) input power dynamic range is achieved at 1.8 GHz. Peak efficiency of 77 % is obtained at the input power of 23 dBm. The high efficiency over such a large bandwidth is believed to be the best reported to data in open literature at these frequencies.

Improvement on linearity with iterative calibration technique for multilevel LINC transmitters

This paper proposes an iterative calibration technique to enhance the linearity for multilevel LINC transmitters. With this approach, the precision of characterising AM/AM and AM/PM behaviours for discrete levels can be improved, which results in better adjacent channel leakage ratio (ACLR) and error vector magnitude (EVM) performance. An ML-LINC transmitter is built with two PAs in GaN technology, which delivers 40.8 dBm output power with 68% drain efficiency at 2.05 GHz. Up to 5 dB ACLR improvement can be observed by iterative calibration using S1/S2 for a 5 MHz LTE signals. The configuration with 16 levels can give satisfying linearity performance to meet the standard specification, while keep the complexity reasonable. Measurement results show an ACLR of -46 dBc, EVM of 1.9% (QPSK) and 4.2% (64-QAM) at average output power of 35.7 dBm with 51.1% drain efficiency for a 10 MHz LTE signals with a PAPR of 7.9 dB. The performance of the built ML-LINC tranmitter is compared to the state-of-the-art. Both the linearity and drain efficiency are quite competitive.

A practical approach for RF circuit size reduction

In this paper, a practical approach to circuit miniaturisation using periodically loaded transmission lines (TL) is presented. A full investigation of T- and π-shaped unit cells that constitutes periodic structures (PS) has been conducted, leading to a straightforward method for miniaturizing passive RF/Microwave circuits and components. For the completion of the design method, the normalised 3 dB cutoff frequency of the unit cells has been thoroughly studied, providing a guideline for optimum structure parameters that meet the required bandwidth while ensuring a reasonable size reduction ratio. For demonstration, a broadband power divider/combiner with a frequency band of 1.0 - 3.0 GHz has been implemented, showing very good performance with a size reduction of about 47 % compared to the conventional design.

Iterative characterisation approach using realistic excitation signals for linearisation of transmitters

This paper presents a new approach to improve the accuracy of power amplifier or transmitter characterisation. Compared to traditional characterisation, an iterative characterisation approach using realistic excitation signals is introduced. Based upon this approach, more accurate nonlinear behaviour for AM/AM and AM/PM can be measured. A memoryless piecewise digital predistortion (DPD) model using iterative characterisation is built to linearise a power amplifier (PA). The linearity improvement by using the iterative characterisation approach is verified in measurements with LTE excitation signals on a PA at 2.05 GHz. For a 10 MHz 64-QAM LTE signal with a PAPR of 8.1 dB measured ACLR1 could be reduced with two additional steps from -41.6 dBc to -47.6 dBc. At the same time measured EVM was better than 4.2% for an average drain efficiency of 51%. Only few steps are required with the proposed linearisation approach to improve the linearity of components without extra complexity to the DPD.