Supply Modulated Power Amplifier Research Articles

A novel digital transceiver module structure for multi-functional active phased array systems

This paper proposes a transceiver (T/R) module structure for the multi-functional active phased array (APA) systems (including radar and wireless communication systems). The proposed structure uses a full digital interface and applies a GaN supply-modulated power amplifier (SMPA) to improve the power efficiency. In particular, the paper proposes a solution that combines the direct digital synthesis (DDS) with IQ modulation to perform flexibly the functions of phase shifting and amplitude level controlling of the transmitted signals with high resolution for antenna beamforming and scanning. The proposed solution not only eliminates RF attenuator and phase shifter that are commonly used in antenna beamforming but also flexibly configures system functions. The experimental results of designing and manufacturing DDS and IQ modulation parts demonstrate the ability of the proposed structure to generate several common signal types used in radar and communication systems as well as verifies the ability to control the phase and the amplitude level of the transmitted signal.

Joint Dual-Input Digital Predistortion of Supply-Modulated RF PA by Surrogate-Based Multi-Objective Optimization

A generalized dual-input digital predistortion (DPD) methodology for supply-modulated (SM) power amplifiers (PAs) is proposed. Contrary to classical approaches, the SM and the radio frequency (RF) signals are treated as separate digital inputs to be jointly predistorted. A multi-objective optimization (MOO) strategy allows to explore the inherent PA performance tradeoffs to jointly optimize the DPD coefficients for improved power-added efficiency (PAE) and higher RF output power, yet guaranteeing a prescribed linearity performance. To avoid dealing with an unbearably high number of experimental acquisitions, MOO is here made feasible by fast simulation of an empirical surrogate model of the PA, which is progressively refined from a reduced set of iterative acquisitions. The proposed technique enables the adoption of a dynamic supply shaping function, and it automatically accounts for the signals’ statistics. Eventually, the method outperforms classical SM approaches, yet using a DPD of the same order, as demonstrated by the experimental results on a gallium nitride (GaN) SM PA operating at 3.5 GHz in the presence of orthogonal-frequency-division-multiplexing (OFDM)-like high-peak-to-average power ratio (PAPR) modulated signals with 10- and 20-MHz bandwidths (BWs).

Saturated PAs for High Efficiency: Operation of Saturated Amplifiers Having the Optimum Voltage Waveform to Achieve Maximum Efficiency

High efficiency is a crucial design consideration. This is true not only for power amplifiers (PAs), but also for transmitters such as the Doherty PA and the supply-modulated PA, due to thermal management, reliability, and size [1]-[3] issues. Several PA topologies, e.g., class E, class F, and class F-1, have been proposed to achieve high efficiency [3]-[17]. In the class-E PA, a transistor acts as a switch, which has very low loss. The voltage of the class-E amplifier is supported through the charging and discharging of a transistor's output capacitor, which is parallel with the switch. Because this amplifier tunes all the harmonic components using the LC resonator, it delivers the highest efficiency among the proposed amplifiers. The capacitor's charging step, however, cannot be abrupt; above the theoretical maximum frequency fmax,E, the capacitor cannot be discharged quickly enough to support the ideal waveform [3], [4]. As a result, the efficiency of the class-E PA is significantly degraded at a frequency above fmax,E [3]-[6]. Also, the power density of the class-E amplifier is low because of the low content of the fundamental voltage component.

Minimum pulse reservation‐based switching frequency reduction for wideband supply modulated power amplifiers

A minimum pulse reservation method is proposed to reduce the switching frequencies of the supply modulated power amplifier (PA). It is achieved by expanding the minimum pulse length of the multi-level supply voltage. Also, by comparing the maximum voltage of the minimum pulse with the designed chopped voltage, the minimum pulse is reserved in an optimised way to maximise the PA efficiency. To validate the proposed technique, a four-level supply modulated PA is fabricated, which is excited by a wideband modulated signal, that is 40-MHz long-term evolution signal. Experimental results show that the proposed method can significantly reduce the switching frequencies and achieve higher efficiency than state-of-the-art bandwidth reduction methods, which is very promising for the wideband supply modulated PA design.

Highly Efficient 1.8-GHz Amplifier With 120-MHz Class-G Supply Modulation

A broadband and highly efficient class-G supply modulated power amplifier (PA) system with 120-MHz instantaneous modulation bandwidth operating in the 1.8-GHz band is presented in this paper. The core element is the fast class-G supply modulator which switches the supply voltage of the RF PA between three discrete levels with a minimum pulse duration of 2.5 ns. Two designs for the drain bias interface between PA and modulator are evaluated where the best results are achieved for an implementation based on a $\lambda $ /4-wavelength RF-choke. Measurement results are presented for a 120-MHz contiguous carrier aggregated signal using eleven subcarriers with modulation bandwidths ranging from 5 to 20 MHz for each subcarrier. In combination with digital predistortion, the system achieves 38.5% PAE with −40-dB EVM and −46-dB ACLR for the 120-MHz multicarrier signal with a peak-to-average power ratio of 10 dB at the PA output and 39-dBm average output power. The total efficiency enhancement achieved by the class-G modulation is 13% points.

A Three-Port Nonlinear Dynamic Behavioral Model for Supply-Modulated RF PAs

We propose a three-port nonlinear dynamic behavioral model for supply-modulated power amplifiers (PAs). The proposed model not only accounts for the radio frequency (RF) input-output relationship, but also for the interaction between a modulated voltage supply, the RF output power and the supply current. The model is based on a modified Volterra formulation which accounts for the dynamic deviations with respect to a quasi-static model. The frequency-domain kernels of the proposed model are directly extracted from measurements performed with a low-frequency-extended large-signal network analyzer on an RF hand-set PA. The model is validated under random multitone modulated RF input and supply. The presented technique allows for the independent control of the RF and the supply ports. As such, it allows a separate description of both the dynamic contribution of the RF modulated input and of the dynamic supply voltage. The proposed model shows an improvement with respect to a quasi-static approach in predicting the RF output, the supply current, as well as the power-added efficiency.

A LINC-based polar transmitter with reduced envelope bandwidth for wideband communications

This paper presents a polar transmitter with reduced envelope bandwidth and the linear amplifier with nonlinear components (LINC) technique is used to produce constant-envelope signals according to the remaining envelope information. This architecture relaxes the bandwidth requirement for the traditional envelope modulators. Only the low-frequency part of the envelope signal is amplified to provide power supply for the power amplifier (PA) stage. In the LINC path, the remaining envelope information is modulated into the phase signals, which are used as the radio frequency (RF) input to the nonlinear PA pair. At the RF output, the envelope information is retrieved from these two parts by the supply-modulated PA pair. The simulation results show that the envelope bandwidth is reduced to around one third of the original bandwidth by the proposed technique. For 2-level LINC structures, the combining efficiency of the proposed architecture is improved to more than twice as the one of LINC-only structure since the combining angles are reduced.