Cartesian RF Modulation Using Three-Level PWM and Pre-Distortion
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Solution Overview
Problem
Conventional Cartesian modulation systems require double balanced mixers and highly linear power amplifiers to avoid spectral re-growth and interference, which complicates the design and increases the complexity of wireless radio-communication transceivers.
Innovation Solution
A Cartesian modulation system using binary pulse width modulated signals with pre-distortion elements and comparators to generate a three-level pulse width modulated RF signal, eliminating the need for double balanced mixers and allowing for relaxed linearity requirements, and incorporating a band-pass filter to suppress unwanted frequency components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If double balanced mixers and highly linear power amplifiers are used in conventional Cartesian modulation systems, then spectral re-growth and interference are avoided, but device complexity and design requirements increase significantly
Solution Approach 1:
The patent changes the operating parameters of the power amplifier by using pulse width modulated signals with switching frequency equal to the RF carrier frequency. This parameter change allows the use of less linear power amplifiers while maintaining spectral compliance through the specific PWM modulation scheme and pre-distortion techniques
Solution Approach 2:
The patent introduces pre-distortion elements as intermediary components that modify the base-band signals before they reach the power amplifier. These pre-distortion elements compensate for the non-linearities of the power amplifier, allowing the use of simpler amplifiers while still achieving the required spectral performance
2Reliability
If double balanced mixers are used to up-mix in-phase and quadrature components, then linearity is maintained, but the design requirements and complexity increase
Solution Approach 1:
The patent replaces the mechanical/double-balanced mixer architecture with a pulse width modulation-based up-conversion scheme. Instead of using double balanced mixers to perform the frequency translation, the system uses PWM modulation where the switching frequency equals the RF carrier frequency, fundamentally changing the mechanism of frequency conversion
Solution Approach 2:
The patent changes the operating mode from continuous analog mixing to pulse width modulation with switching frequency equal to the RF carrier frequency. This parameter change eliminates the need for double balanced mixers while maintaining the necessary signal integrity through pre-distortion compensation
3Object-generated harmful factors
If highly linear power amplifiers are used to avoid spectral re-growth, then transmission compliance is achieved, but power dissipation increases and efficiency decreases
Solution Approach 1:
The patent changes the power amplifier's operating parameters by using PWM signals with switching frequency equal to the RF carrier frequency. This allows the use of less linear, more efficient power amplifiers while maintaining spectral compliance through the specific modulation scheme and pre-distortion techniques
Solution Approach 2:
The patent introduces pre-distortion elements as intermediary components that prepare the signals before amplification. These pre-distortion elements compensate for the reduced linearity of the power amplifier, enabling the use of more efficient amplifiers with lower power dissipation while still achieving spectral compliance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach simplifies the design by reducing the need for double balanced mixers and highly linear amplifiers, avoiding spectral re-growth and enabling efficient transmission with lower power dissipation and increased efficiency, particularly suitable for portable applications.
Implementation Method 1
generation of a multi-level pulse width modulated signal
Implementation Method 2
at least one base-band pre-distortion element
Implementation Method 3
filtered in a band-pass filter 180 in order to reduce the spectral content and avoid spectral interference
Data Source
AI summary
A system and method for Cartesian modulation achieved via generation of a three-level pulse width modulated signal. The system in overview comprises two binary pulse width modulated signal generators receiving signals related to the in-phase and quadrature components of a base-band signal and a combination and amplification stage that combines the signals provided by the two binary pulse width modulated signal generators. The binary pulse width modulated signal generators contain at least one signal comparator and at least one base-band pre-distortion element. The signals related to the in-phase and quadrature components of the base-band signal may be; the positive or negative parts of the in-phase component, the positive or negative parts of the quadrature component, the absolute value or sign of the in-phase component, or the absolute value or sign of the quadrature component. These signals may be distorted by a base-band pre-distortion element before being coupled to the comparators.