A 3-bit load-pulling digital power amplifier

Abstract

A radio frequency (RF) 3-bit digital power amplifier (DPA) is described in this paper. It consists of three RF amplifiers connected at their outputs with a transmission line (TL) network. The three amplifiers are designed for different output powers (POUT). The TL network allows them to load-pull one other to achieve eight different amplitude states by alternatively enabling and disabling the amplifiers via their gate bias. A prototype was designed in the National Instruments' Microwave Office (MWO) for 500 MHz with the aid of a genetic algorithm to optimize the TL network for all seven active (on-) states. The optimizer efficiencies goals were based on data derived from load-pull simulation. The POUT goals were based on a 1 Vrms step-size. In simulation, ≥50% efficiency was achieved at all on-states with 29.7 dBm peak POUT. A practical prototype based on the simulation achieved an efficiency of ≥40% over all seven on-states. A peak POUT of 28.9 dBm was achieved, with the lowest state at 22.4 dBm.

Highly Efficient 3-Bit Digital Power Amplifier for OFDM Waveform Amplification

“…In (19), we can observe that the output voltage depends on the transmission coefficients, the reflection coefficients, and the three input voltages. The transmission coefficients and the reflection coefficients are related to the S-parameter response of the power combiner and the impedance connected to the power combiner.…”

“…Another architecture to improve the back-off efficiency is the power-mixer array in which multiple PAs with the same RF power are paralleled. However, this approach is unsuited for high-PAPR signals such as OFDM, whereas the PDF is radically different from a uniform distribution [19], [20], [23].…”

Highly Efficient 3-Bit Digital Power Amplifier for OFDM Waveform Amplification

“…In (19), we can observe that the output voltage depends on 324 the transmission coefficients, the reflection coefficients, and 325 the three input voltages. The transmission coefficients and the 326 reflection coefficients are related to the S-parameter response of the power combiner and the impedance connected to the power combiner.…”