Digital Receiver Image Rejection Using Complex Sampling Mixers
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Solution Overview
Problem
Conventional analog super-heterodyne receivers are large, costly, and consume high power due to their analog nature, making them unsuitable for integration into microchips and requiring significant pre-conversion filters and high-frequency narrow band IF filters, which limits their compatibility with digital designs and increases power consumption.
Innovation Solution
A digital receiver architecture utilizing complex multiplication and sampling mixers to separate wanted and image frequencies, allowing for image rejection in the digital domain with reduced power consumption and smaller size, achieved through a four-mixer or two-mixer configuration with proper LO and IF frequency relationships, followed by complex band-pass filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional analog super-heterodyne receivers are used, then RF reception functionality is achieved, but device size, cost, and power consumption increase
Solution Approach 1:
The patent replaces analog super-heterodyne receiver architecture with a digital receiver architecture that performs mixing and filtering in the digital domain. This substitution eliminates the need for complex analog components such as high-frequency narrow band IF filters and significant pre-conversion filters, thereby reducing device size, cost, and power consumption while maintaining RF reception functionality
Solution Approach 2:
The patent changes the operating parameters by moving the mixing and filtering operations from the analog domain to the digital domain. This parameter change allows the use of digital signal processing techniques that are more efficient in terms of power consumption and device complexity, while achieving the same signal processing objectives
2Reliability
If significant pre-conversion filters and high-frequency narrow band IF filters are used, then image frequency rejection is improved, but device size and cost increase
Solution Approach 1:
The patent substitutes physical analog filters with digital filtering operations. The digital receiver performs mixing to produce an intermediate frequency signal, then uses digital filtering to reject image frequencies and noise. This substitution eliminates the need for large physical filter components while maintaining effective image frequency rejection
Solution Approach 2:
The patent moves the filtering operation from the frequency domain (analog filters) to the time domain (digital signal processing). By performing mixing and filtering in the digital domain, the system achieves image frequency rejection without requiring physical filter components, effectively adding a temporal dimension to the filtering process
3Ease of manufacture
If analog components are used for mixing and filtering, then signal processing is achieved, but integration onto microchips is difficult
Solution Approach 1:
The patent replaces analog mixing and filtering components with digital equivalents that can be implemented as integrated circuits. The digital receiver uses digital signal processing techniques for mixing and filtering, which are much easier to integrate onto microchips compared to analog components. This substitution enables full integration while reducing the complexity of individual components
Solution Approach 2:
The patent merges multiple discrete analog components (mixers, filters, amplifiers) into a single integrated digital receiver circuit. By combining these functions into digital signal processing operations that can be implemented on a single chip, the system achieves ease of manufacture and integration while maintaining the necessary signal processing capabilities
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
The digital receiver achieves high selectivity, sensitivity, and fidelity with low power consumption and reduced size, enabling efficient image separation and filtering, suitable for applications like VHF, UHF, GSM, GPS, and Bluetooth communication systems.
Implementation Method 1
A mixer mixes the amplified RF signal with a local oscillator (LO) frequency signal to convert the band-limited RF signals to an IF band along with undesired mixing products
Implementation Method 2
A digital receiver architecture utilizing complex multiplication and sampling mixers to separate wanted and image frequencies, allowing for image rejection in the digital domain
Implementation Method 3
A digital receiver architecture utilizing complex multiplication and sampling mixers to separate wanted and image frequencies, allowing for image rejection in the digital domain
Implementation Method 4
The IF signals from the mixer are generally coupled to an IF filter, which passes mainly the sub-band containing the desired signals
Data Source
AI summary
A digital communication circuit can be implemented can be implemented in a CMOS, or other IC structure. The digital circuit can utilize negative frequency removers or image frequency removers in the digital domain. The circuit can include mixers, switches, a complex filter, a low noise amplifier and summers. The image frequency can be removed digitally.