Digital IQ RF Transmitter with Pre-Distortion Power Amplification
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Solution Overview
Problem
Conventional RF transmitters face inefficiencies due to the use of linear power amplifiers and are limited by narrowband capabilities and high clock frequencies, which are not implementable in practical CMOS and subscriber communication units, necessitating an improved RF transmitter design that leverages digital signal processing to enhance power efficiency and scalability.
Innovation Solution
An RF transmitter with a digital signal processing module performing two-dimensional non-uniform mapping of complex input signals to in-phase and quadrature digital pre-distortion control words, driving switch-mode power cells to generate analogue RF signals, thereby compensating for non-linearity and extending the digital domain to the power amplifier module for improved efficiency and scalability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If linear power amplifiers are used in conventional RF transmitters, then the transmitters can operate with simple architecture, but the power efficiency becomes very low
Solution Approach 1:
The patent replaces the linear power amplifier (analog component) with a switch-mode power amplifier controlled by digital pre-distortion algorithms. This substitution transforms the analog power amplification stage into a digitally-controlled switch-mode system, achieving high power efficiency while maintaining architectural simplicity through digital domain processing.
2Loss of energy
If switch-mode power amplifiers are used to improve power efficiency, then power efficiency becomes very high, but the input-output relationship becomes highly non-linear
Solution Approach 1:
The patent applies digital pre-distortion to the input signal before it reaches the switch-mode power amplifier. By pre-compensating the input signal with inverse non-linearity characteristics, the overall system achieves linear input-output relationship. This preliminary action corrects the non-linearity issue before it affects the output signal quality.
3Loss of energy
If digital polar transmitter design is used to achieve high power efficiency and small silicon area, then power efficiency is high and area is small, but the transmitters are only suitable for narrowband modulated signals
Solution Approach 1:
The patent transitions from the polar coordinate system (amplitude-phase) used in digital polar transmitters to a Cartesian coordinate system (in-phase-quadrature). This dimensional change enables the use of IQ modulation schemes that support wideband signals while maintaining the benefits of switch-mode power amplifiers and digital processing, thus expanding bandwidth capability without sacrificing power efficiency.
4Adaptability or versatility
If hybrid polar transmitter designs are used to enable wideband phase modulation, then wideband capability is achieved, but the transmitters suffer from amplitude and phase quantization noise requiring significant noise shaping
Solution Approach 1:
The patent replaces the hybrid polar architecture with a fully digital IQ-based transmitter architecture. This substitution eliminates the quantization noise issues inherent in hybrid designs by performing all signal processing in the digital domain using IQ modulation, thereby achieving wideband capability without requiring complex noise shaping circuits.
5Speed
If digital algorithms operating at very high clock frequencies (four times carrier frequency) are used, then processing speed is sufficient, but such clock frequencies are not implementable in practical CMOS and subscriber communication units
Solution Approach 1:
The patent applies partial pre-distortion processing at a reduced clock frequency that is practical for CMOS implementation. Rather than requiring full processing at four times the carrier frequency, the digital pre-distortion algorithm operates at a lower, manufacturable frequency while still achieving sufficient linearization performance through the switch-mode power amplifier approach.
Data Source
AI summary
A radio frequency (RF) transmitter (200, 400) has at least one digital signal processing module (210, 410) and at least one power amplifier module (230). The digital signal processing module (210, 410) includes at least one digital pre-distortion component (250) arranged to receive at least one complex input signal, perform two-dimensional non-uniform mapping of the complex input signal to a first, in-phase, digital pre-distortion control word and a further, quadrature, digital pre-distortion control word, and output the in-phase and quadrature pre-distortion digital control words. The power amplifier module (230) includes a first, in-phase, array of switch-mode power cells (510) and at least one further, quadrature, array of switch-mode power cells (520). The two-dimensional non-uniform mapping has a pre-distortion profile (350) at least partly based on an input/output relationship for the power amplifier module (230) arranged to generate an analogue RF signal based at least partly on the in-phase and quadrature digital pre-distortion control words.