Combination Modulator for Transmitter Efficiency
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Solution Overview
Problem
Existing communications transmitters face limitations in energy efficiency and bandwidth expansion when using either quadrature-modulator-based or polar modulation transmitters, particularly due to the need for output power back-off and challenges at low output power levels.
Innovation Solution
A communications transmitter that combines quadrature and polar modulation domains, with a configurable baseband processor and amplifier stages operating in linear, envelope tracking, or switch modes, depending on output power levels and modulation schemes, to optimize energy efficiency and prevent bandwidth expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If quadrature-modulator-based transmitters are used to achieve complex modulation schemes, then spectral efficiency is improved, but energy efficiency deteriorates due to the need for output power back-off to maintain linearity
Solution Approach 1:
The transmitter is divided into two independent domains: a polar modulation domain that handles phase modulation with constant envelope, and a power amplification domain that handles amplitude modulation. This segmentation allows each domain to operate optimally without the tradeoff present in conventional quadrature modulators, where the PA must operate in linear region sacrificing efficiency.
Solution Approach 2:
The invention transitions from the traditional quadrature domain (I-Q plane) to the polar domain (amplitude-phase plane). By changing the modulation domain from rectangular coordinates to polar coordinates, the system can separately control phase and amplitude, enabling the PA to operate in nonlinear efficient region while still achieving complex modulation schemes through the combination of constant-envelope phase modulation and subsequent amplitude modulation.
2Use of energy by moving object
If polar modulation transmitters are used to improve energy efficiency, then the power amplifier can operate as nonlinear PA, but bandwidth expansion occurs due to abrupt phase changes
Solution Approach 1:
The system performs preliminary phase modulation to generate a constant-envelope phase-modulated carrier signal before amplitude modulation. By establishing the phase-modulated signal first with proper filtering and conditioning, the system prepares the signal in advance to avoid bandwidth expansion issues during subsequent amplitude modulation stages.
Solution Approach 2:
The invention dynamically adjusts the modulation approach based on signal characteristics and operating conditions. The system can switch between pure polar modulation and hybrid approaches, and dynamically control the amplitude modulation depth to prevent excessive bandwidth expansion while maintaining energy efficiency benefits.
3Use of energy by moving object
If polar modulation is used at low output power levels, then energy efficiency is improved, but the power amplifier becomes incapable of operating as a switch
Solution Approach 1:
The system changes operating parameters based on output power level. At low power levels, the amplitude modulation depth is reduced or the PA is operated in a different mode (e.g., Class AB instead of Class D/E switch mode) to maintain reliable operation. The invention adapts the PA operating class and modulation depth as parameters to maintain both efficiency and reliability across the full power range.
Solution Approach 2:
An intermediary amplitude modulation stage is introduced between the constant-envelope phase modulation and the final power amplification. This intermediary stage allows the PA to always receive a constant-envelope signal for reliable switch-mode operation, while the amplitude information is superimposed in a controlled manner that maintains PA reliability even at low output power levels.
Data Source
AI summary
A communications transmitter includes a combination modulator and a baseband processor configured to generate amplitude, angle, in-phase and quadrature signals. The combination modulator is configured to modulate in the quadrature domain or the polar domain, depending on an output power level of the transmitter and/or the type of modulation scheme being used. When configured to modulate in the quadrature domain, the baseband processor is configured to generate time-varying in-phase and quadrature modulating signals and time-invariant amplitude and angle signals for the combination modulator. When configured to modulate in the polar domain, the baseband processor is configured to generate time-varying amplitude and angle modulating signals and time-invariant in-phase and quadrature signals for the combination modulator. In another embodiment of the invention, the communications transmitter is configurable to operate in three different operational modes: linear, envelope tracking and switch modes. Which operational mode the communications transmitter is configured to transmit depends on the type of modulation scheme being used and/or the transmitter output power level.