Multi-IF Spectrum Analyzer Spurious Signal Reduction
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Solution Overview
Problem
Current spectrum analyzers are costly, power-intensive, and bulky, making them inaccessible to many users, and they struggle with reducing residual, spurious, and image signals due to inadequate shielding and less accurate components, while also being limited by the need for long RF cables that introduce measurement inaccuracies.
Innovation Solution
A compact, low-power spectrum analyzer using multiple Local Oscillator signals to generate multiple Intermediate Frequencies for signal reduction, with a microcontroller and master clock synthesizer to mask out unwanted signals, and a USB bus-powered design for portability, allowing direct connection to RF sources without cables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple intermediate frequencies and multiple clock configurations are used, then residual, spurious and image signals are reduced, but device complexity increases
Solution Approach 1:
The patent divides the frequency analysis into multiple intermediate frequency (IF) segments, each processed with dedicated clock configurations. By segmenting the signal processing into distinct IF paths (first IF and second IF), the system reduces spurious signals through selective filtering while maintaining manageable complexity in each segment.
Solution Approach 2:
The patent implements dynamic clock configuration switching based on the selected frequency span. The microcontroller automatically selects appropriate clock configurations from multiple available settings, allowing the system to adapt its internal timing parameters to minimize spurious signals for different operating ranges without requiring manual intervention or fixed architecture.
2Measurement precision
If YIG LO is used to provide clean signal, then phase noise is minimized, but power consumption increases
Solution Approach 1:
The patent uses a phase-locked loop (PLL) to generate the local oscillator signal, which provides sufficiently clean phase characteristics for spectrum analysis without requiring the excessive power consumption of a YIG LO. The PLL delivers adequate signal purity at lower power levels, representing a partial action approach that meets performance requirements without over-engineering the solution.
3Measurement precision
If shielding is added to isolate sections, then residual signals are reduced, but weight and cost increase
Solution Approach 1:
The patent replaces mechanical/physical shielding approaches with electronic signal processing methods. By using multiple clock configurations, selective IF filtering, and digital signal processing to identify and eliminate spurious signals, the system achieves residual signal rejection without adding physical shielding materials that would increase weight and cost.
4Weight of moving object
If USB bus-powered design is used, then portability is improved, but power available for processing is limited
Solution Approach 1:
The patent optimizes power consumption by dynamically adjusting operating parameters including clock frequencies and processing rates based on the selected frequency span and measurement requirements. The microcontroller manages power distribution to balance USB bus power constraints with adequate processing capability, allowing the portable device to deliver sufficient performance within limited power availability.
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 solution provides an ultra-low-cost, lightweight, and portable spectrum analyzer capable of accurate RF signal measurement with reduced noise and spurious signals, enabling direct connection to RF sources without cables, thus improving accessibility and measurement precision.
Implementation Method 1
a voltage controlled oscillator to generate a local oscillator signal at a frequency equal to a center frequency of a selected span plus an intermediate frequency
Implementation Method 2
a master phase locked loop to convert a frequency reference signal to a master voltage controlled oscillator signal
Implementation Method 3
a master clock synthesizer to divide the master voltage controlled oscillator signal to generate a clock signal at one-eighth of a frequency of the master voltage controlled oscillator signal
Implementation Method 4
one or more stages of mixers to convert the RF input signal to an intermediate frequency (IF) signal using local oscillator signals
Data Source
AI summary
A method for spurious signal reduction when measuring a spectrum of a radio frequency signal over a frequency span. The radio frequency signal is converted to a sequence of intermediate frequency signals using a sequence of local oscillator signals each having a different frequency. The sequence of intermediate frequency signals are converted to a sequence of digitized intermediate frequency signal sample sets, each set having a frequency value and a signal energy value. The frequency span is divided into frequency sample bins. For each frequency sample bin, all frequency domain samples from the sequence of frequency domain sample sets having a frequency value within the frequency sample bin are associated with that sample bin. For each frequency sample bin, of the frequency domain samples associated with that frequency bin, the frequency domain sample having the signal energy value that is lowest is selected for a combined frequency domain sample set.