Multilevel Supply-Modulated Chireix Outphasing With Continuous Input Modulation

Abstract

This work presents a dynamic characterization of a multi-level Chireix outphasing (ML-CO) power amplifier (PA) with modulated signals. The ML-CO technique combines the advantages of envelope tracking and outphasing architectures by limiting the supply modulation to discrete levels with an efficient power-DAC modulator and using outphasing for fine amplitude control. We describe an experimental test bench that supplies the required phase-and time-aligned modulated signals for outphasing and supply modulation simultaneously. Pulsed characterization is used to design a multi-level memory-less polynomial DPD. The linearized ML-CO GaN X-band MMIC PA is demonstrated with fixed input drive levels for 9.3-dB PAPR, 1.4-MHz and 11.3-dB PAPR, 10-MHz LTE signals with a 9.7 GHz carrier. For both signals, the average total power consumption is reduced by a factor of two when supply modulation is used. An investigation of control signal generation strategies is presented, including combinations of discrete supply and continuous input modulation. A simple exponential function tracks the optimal efficiency trajectory of the ML-CO PA, enabling overall efficiency improvements within 9 and 27 percentage points. This control strategy is applied to radar pulses with amplitude shaping and frequency chirp, with efficiency improvement of up to 11.8 percentage points compared to constant-supply operation, with 29 dB improvement in spectral confinement.

Multilevel outphasing power amplifier system with a transmission-line power combiner

“…Multilevel outphasing [78,79] is an expansion of the outphasing concept, intended to address the issue of back-off efficiency. As the generic block diagram in Figure 2.4 shows, the structure is otherwise similar, but a coarse-resolution amplitude signal A is used to control the output amplitude of each PA. 4 two common methods of implementing the amplitude levels: altering the PA supply voltage [80][81][82], and altering the number of active parallel PA units [83][84][85]. The output signal is expressed as…”

Supply Modulation Behavior of a Doherty Power Amplifier

“…Although SM is typically applied to single-ended PAs as overviewed in e.g. [3], it has been successfully demonstrated with other efficiency enhancement techniques including Chireix outphasing [4], load-modulated balanced [5], [6] and Doherty PAs [7]- [11]. Operating the main PA (MPA) and auxiliary PA (APA) in a DPA with different static supply voltages to extend the efficient range is shown in [7].…”

UHF Class E/F2 Outphasing Transmitter for 12 dB PAPR Signals

“…Individually, they achieve limited efficiency enhancement at deep power back-off (PBO). Nonetheless, it is possible to increase the power control range where the PA operates efficiently by means of multiway or combined solutions [2], [3]. As a drawback, both circuit complexity and cost increase significantly, demanding more than two active devices.…”