Doherty Amplifier Signal Splitting for Gain and Linearity
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Solution Overview
Problem
Conventional Doherty-type power amplifiers face challenges with reduced gain levels and difficulty in linearization, especially in asymmetrical and enhanced asymmetrical designs, due to the asymmetrical transfer functions and semiconductor device characteristics, which limits their suitability for linear modulation systems and narrows their frequency bandwidth.
Innovation Solution
The proposed solution involves a Doherty amplifier arrangement with a main and auxiliary amplifier path, where the signal preparation unit develops input signals based on a transition threshold, asymmetrically dividing the input signal between the main and auxiliary amplifiers, and biasing the auxiliary amplifier below its turn-on voltage, to enhance gain and efficiency, and using a combining structure like a quarter wave transformer to match impedances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional Doherty-type amplifier uses a simple power splitting structure to divide input signal between main and auxiliary amplifiers, then the amplifier achieves high efficiency, but the gain level is reduced and linearity is degraded
Solution Approach 1:
The patent applies preliminary action by pre-processing the input signal through a signal preparation unit that includes a power splitter and phase shifter. The input signal is divided into main and auxiliary path signals with specific amplitude ratios and phase relationships before being applied to the amplifiers. This preliminary signal conditioning ensures that when the auxiliary amplifier turns on, the transition is smooth and maintains linearity, resolving the contradiction between efficiency and gain linearity.
Solution Approach 2:
The patent changes key parameters of the signal division process: the amplitude ratio between main and auxiliary path signals is optimized (e.g., 3:1 or 4:1), and a specific phase shift (e.g., 90 degrees) is introduced to the auxiliary path signal. These parameter changes allow the auxiliary amplifier to contribute to gain without causing abrupt transitions or non-linearities, thus maintaining both efficiency and linearity simultaneously.
2Power
If the auxiliary amplifier is biased at higher voltage levels to improve gain during back-off operation, then the overall gain increases, but the efficiency decreases due to increased power consumption
Solution Approach 1:
The patent optimizes the bias voltage parameter of the auxiliary amplifier to operate at or near the turn-on threshold (e.g., 0.7V for GaN devices) rather than higher levels. Combined with optimized signal amplitude ratios in the power splitter, this ensures the auxiliary amplifier remains off during back-off operation, consuming minimal power, while still providing sufficient gain when needed at higher power levels.
Solution Approach 2:
The patent applies partial action by directing only a specific portion of the input signal to the auxiliary amplifier path, with the majority going to the main amplifier. The signal preparation unit controls the amplitude ratio so that the auxiliary amplifier receives just enough signal to turn on at the desired power level, avoiding excessive power consumption while still achieving the needed gain contribution when operating at high power.
3Loss of energy
If asymmetrical Doherty amplifier designs are used to optimize efficiency at specific power levels, then efficiency improves, but the amplifier becomes difficult to linearize and has reduced frequency bandwidth
Solution Approach 1:
The patent applies preliminary action through a signal preparation unit that pre-adjusts the amplitude and phase of signals before they reach the asymmetrical amplifier paths. This pre-processing compensates for the asymmetrical characteristics, creating balanced effective drive levels that maintain linearity across different frequency bands, thus resolving the contradiction between efficiency optimization and frequency adaptability.
Solution Approach 2:
The patent incorporates feedback mechanisms including impedance transformation networks and phase correction circuits that automatically adjust signal parameters based on operating conditions. This feedback ensures that the asymmetrical amplifier design maintains optimal performance across varying frequencies and power levels, enabling both high efficiency and broad frequency bandwidth simultaneously.
Data Source
AI summary
An amplifier having a Doherty-type architecture and a method for operation thereof are provided. The amplifier comprises a main amplifier path comprising a main amplifier, an auxiliary amplifier path comprising an auxiliary amplifier, and an signal preparation unit configured to develop a main amplifier input signal for the main amplifier path and an auxiliary amplifier input signal for the auxiliary amplifier path based on an amplifier input that is to be amplified and a transition threshold associated with the amplifier input. By driving the main and auxiliary amplifiers as a function of the transition threshold, the gain of the Doherty-type amplifier may be increased.