Sampling Receiver FIR Mixing for Flexible Channel Downconversion
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Solution Overview
Problem
Current sampling receivers face limitations in bandwidth and channel flexibility due to the requirement for the sample frequency to match the carrier frequency, particularly in systems like GPS/Glonass, and often result in harmonic issues with frequency modulation radio architectures.
Innovation Solution
Incorporating time-variant FIR filters with integrated mixing functionality in direct-sampling receivers to enable complex filter functions and second down-conversion in the discrete time domain, allowing for LO/4 mixing and decimation, which relaxes bandwidth requirements and mitigates harmonic issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sample frequency is matched to the carrier frequency in sampling receivers, then the receiver can process signals at the carrier frequency, but the bandwidth is limited and channel flexibility is reduced
Solution Approach 1:
The patent applies dynamic sampling frequency adjustment by using a numerically controlled oscillator (NCO) to vary the sampling frequency around the carrier frequency. This dynamic approach allows the receiver to process multiple channels and frequency offsets without requiring fixed sampling rate hardware, thereby resolving the contradiction between precise carrier frequency processing and bandwidth flexibility.
Solution Approach 2:
The invention changes the sampling frequency parameter dynamically to achieve different downconversion outcomes. By adjusting the NCO frequency offset, the system can process signals at different frequency offsets from the carrier while maintaining accurate processing, thus enabling both precise carrier frequency handling and adaptable bandwidth/channel selection.
2Reliability
If separate mixer and FIR filter components are used, then each component can be optimized independently, but the overall system complexity increases
Solution Approach 1:
The patent combines the mixer and FIR filter into a single integrated structure where the FIR filter performs both filtering and mixing functions simultaneously. The time-variant FIR filter coefficients enable the filter to execute downconversion (mixing) while filtering, eliminating the need for separate mixer hardware and reducing overall system complexity while maintaining component-level optimization through software-configurable coefficients.
Solution Approach 2:
The FIR filter is designed to perform multiple functions: traditional signal filtering, mixing/downconversion, and frequency translation. This multi-functional approach allows a single component to replace what would traditionally require separate mixer and filter units, reducing system complexity while maintaining the ability to optimize each function through configurable filter coefficients.
3Speed
If traditional mixer architecture is used in FM radio receivers, then frequency conversion is achieved, but harmonic issues arise
Solution Approach 1:
The patent replaces the traditional analog mixer with a digital signal processing approach using a time-variant FIR filter. This substitution of digital processing for analog mixing eliminates the harmonic distortion problems inherent in analog mixers while maintaining fast frequency conversion capabilities through software-controlled filter coefficient adjustment.
Solution Approach 2:
The invention converts the potential harm of fixed sampling rate limitations into a benefit by using dynamic sampling frequency adjustment. The NCO-based approach allows intentional frequency offset sampling that actually improves the ability to reject harmonics and intermodulation products while maintaining accurate signal processing, turning what could be a source of interference into a means of harmonic rejection.
Data Source
AI summary
One embodiment of the present invention relates to a combined mixer filter circuit. The circuit includes a sampler, a plurality of filter branches, and a coefficient generator. The sampler is configured to provide a sampled signal by sampling a received signal at a specified rate. The plurality of filter branches has selectable filter coefficients. The plurality of filter branches are configured to receive the sampled signal and generate a mixed and filtered output signal without a separate mixer component. The coefficient generator is coupled to the plurality of filter branches. The coefficient generator is configured to assign filter coefficient values to the selectable filter coefficients to yield a selected mixing function for the mixed filtered output signal.