Multi-Channel RF Receiver IF Planning for Spurious Signal Separation

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Solution Overview

Problem

Current radio communication systems face challenges in maintaining a good signal/noise ratio due to spurious signals generated by non-linearities in analog-digital converters and analog parts, which can interfere with useful signals and reduce the quality of transmission.

Innovation Solution

A receiving device with multiple conversion chains, each with a unique intermediate frequency and sampling frequency pair, is used to minimize interference by selecting frequencies that optimize the signal/noise ratio, and a calibration method to determine the best frequency pairs based on the environment and signal positions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single high-frequency ADC is used to digitize the whole frequency band, then the number of analog and ADC chains is reduced, but spurious signals from ADC non-linearities cannot be eliminated and interfere with useful signals

Engineering Contradiction:

Improvenumber of analog and ADC chainsVSAvoidspurious signals interfering with useful signals

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The frequency band is segmented into multiple intermediate frequency bands, each processed by a separate conversion chain with its own ADC. This segmentation isolates the spurious signals generated by each ADC to specific frequency regions, preventing them from interfering with useful signals in other regions. The patent divides the 5 MHz system band into multiple intermediate frequency ranges (e.g., 70-75 MHz, 80-85 MHz, etc.), each handled by a dedicated conversion chain.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Intermediate frequency conversion stages are introduced as mediators between the radiofrequency input and the final digitization. These conversion chains with different intermediate frequencies act as intermediaries that separate the spectral content, allowing useful signals to be processed without direct interference from ADC spurious products. The intermediate frequency translation creates a frequency domain separation that isolates harmful spurious signals from useful signal bands.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If multiple conversion chains with different intermediate frequencies are used, then spurious signals are separated from useful signals, but the device complexity increases

Engineering Contradiction:

Improveinterference between spurious and useful signalsVSAvoidnumber of conversion chains

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

Multiple conversion chains are designed with identical functional architecture and components, allowing them to perform the same signal processing functions at different intermediate frequencies. Each chain is a universal template that can be replicated and configured for different frequency ranges, reducing design complexity while achieving signal separation. The patent uses the same mixer, filter, and ADC architecture for each conversion chain, merely tuned to different intermediate frequencies.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If the intermediate frequency and sampling frequency are optimized for each conversion chain, then the signal/noise ratio is improved, but the configuration and calibration complexity increases

Engineering Contradiction:

Improvesignal/noise ratioVSAvoidfrequency pair configuration

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The intermediate frequency and sampling frequency parameters are systematically varied across different conversion chains to optimize signal/noise ratio. Each chain uses a specific pair of parameters (intermediate frequency, sampling frequency) that is tailored to its designated frequency range and signal characteristics. The patent specifies different sampling frequencies (e.g., 100 MHz, 120 MHz, 140 MHz) and intermediate frequencies for different chains, creating an optimized parameter set for each conversion path.

Inventive Principle:

Principle #35Parameter changes

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 effectively increases the signal/noise ratio for each channel, reducing spurious interference and improving the quality of transmission by separating useful signals from noise, and can adapt to different environments by adjusting the number of conversion chains used.

Implementation Method 1

In a mixer connected to a local oscillator, the signal of the selected channel is transposed into a signal at the intermediate frequency

Methodology Applied

Scientific EffectFrequency mixing: Heterodyne

Data Source

PatentUS8874054B2Broadband multi-channel radiofrequency receiver

Publication Date: 2014.10.28 EADS SECURE NETWORKS SAS

AI summary

A device for receiving a broadband multi-channel radiofrequency signal includes a radiofrequency analog input stage connected to an intermediate-frequency conversion stage. The conversion stage includes at least one conversion chain having a frequency mixer that transposes the signal to an intermediate frequency connected to the input of an analog-digital converter with a high frequency sampling rate. The intermediate and sampling frequencies in each conversion chain are selected such that, considering the noise generated by the sampling overtones of the corresponding analog-digital converter, each of the radiofrequency signal channels has a signal/noise ratio that is greater at output than a predetermined value of at least one conversion chain.