Virtual Weaver Sampling Mixer for High Image Rejection
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Solution Overview
Problem
Conventional radio receivers using the super-heterodyne architecture face challenges in image rejection, particularly when two distinct received frequencies generate the same intermediate frequency, leading to unwanted interference, and existing solutions like the Weaver architecture require precise filter matching between mixers to achieve high image rejection, which is difficult to implement effectively.
Innovation Solution
The use of a sampling mixer with a parallel array of processing elements and filter means, where each element successively processes input signal samples in a round-robin fashion, eliminates the need for filters between mixers and enables time-division multiplexing, allowing for the implementation of a quadrature-matched pair of mixers that enhance image rejection without phase errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the Weaver architecture is used to achieve high image rejection, then image rejection performance is improved, but the requirement for precise filter matching between mixers increases device complexity and manufacturing difficulty
Solution Approach 1:
The patent extracts the filtering function from the traditional Weaver architecture by removing the analog filters between mixers. Instead, filtering is performed digitally after ADC conversion, eliminating the need for precise analog filter matching while maintaining image rejection performance. This extraction of the filtering function to the digital domain resolves the contradiction between image rejection and device complexity.
Solution Approach 2:
The patent replaces the mechanical/analog filtering system with a digital filtering system. The analog filters that required precise matching are substituted with digital signal processing operations performed on the sampled signals, thereby eliminating manufacturing tolerances and matching requirements while preserving the image rejection capability.
2Measurement precision
If analog filters are used between mixers in the Weaver architecture, then image rejection is improved, but the need for precise filter matching increases manufacturing cost and difficulty
Solution Approach 1:
The filtering operation is extracted from the analog domain and moved to the digital domain. By removing the analog filters between mixers and performing filtering digitally after ADC conversion, the patent eliminates the manufacturing complexity associated with precise analog filter matching while maintaining effective image rejection.
Solution Approach 2:
The patent changes the domain in which filtering is performed from analog to digital. This parameter change allows the system to achieve the same filtering effect without the manufacturing constraints of analog components, as digital filtering can be implemented with standard ADCs and digital signal processing algorithms.
3Device complexity
If conventional analog mixer implementations are used, then the system is simpler, but image rejection performance is insufficient due to phase errors and filter matching issues
Solution Approach 1:
The patent replaces the conventional analog mixer implementation with a sampling mixer followed by digital signal processing. This substitution eliminates phase errors inherent in analog implementations and achieves superior image rejection through digital filtering, while the overall system remains relatively simple in structure.
Solution Approach 2:
The patent performs sampling and ADC conversion at an early stage in the signal path, before the mixing operation. This preliminary action allows subsequent digital signal processing to correct phase errors and achieve precise image rejection, whereas conventional analog implementations would require precise component matching from the start.
Data Source
AI summary
A virtual Weaver architecture filter is implemented using a sampling mixer that successively processes samples of the input signal in round-robin fashion and provides a sum of the samples as multiplied by coefficients emulating quadrature sinusoidal waveforms. A virtual rather than actual local oscillator is reliably implemented without mismatch. Filtering between the Weaver mixers is eliminated in favor of filtering at the sampling input and effective time division multiplexing is achieved by selecting between resistor combinations that implement different scaling coefficients, resulting in an efficient analog implementation of a virtual Weaver architecture.