Receiving Circuit Phase-Shifted IF Signal Filtering
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Solution Overview
Problem
Conventional receiving circuits for standard time electromagnetic waves face challenges in signal quality due to the need for low cut-off frequency filters or high-order filters, which complicate the circuit and degrade signal accuracy when processing intermediate frequency signals around 30 Hz.
Innovation Solution
The proposed receiving circuit employs a frequency converter/detector circuit with multiple mixer circuits generating phase-shifted intermediate frequency signals, which are then combined using an adder circuit, allowing for improved signal processing with a simple filter configuration and enhanced accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low pass filter with low cut-off frequency is used to remove intermediate frequency components, then the intermediate frequency component is sufficiently attenuated, but the signal quality is degraded
Solution Approach 1:
The patent divides the signal processing into multiple stages: first generating intermediate frequency signals at a higher frequency (e.g., 120 Hz) through frequency conversion, then attenuating these higher frequency components using a low pass filter with a relatively high cut-off frequency (e.g., 30 Hz). This segmentation allows effective attenuation while preserving the desired low frequency signal components, resolving the contradiction between achieving sufficient attenuation and maintaining signal quality.
2Measurement precision
If a high order low pass filter is used to remove intermediate frequency components, then the intermediate frequency component is sufficiently attenuated, but the circuit becomes more complicated and larger in scale
Solution Approach 1:
The patent changes the operating frequency parameter of the intermediate frequency signal generation stage, converting the signal to a higher frequency (e.g., 120 Hz) before attenuation. This parameter change allows the use of a simple first-order low pass filter with a high cut-off frequency (30 Hz) to achieve the same attenuation effect that would otherwise require a complex high-order filter, thus reducing circuit complexity while maintaining filtering performance.
3Productivity
If the intermediate frequency is set to around 30 Hz, then the frequency conversion is efficient, but a filter with large time constant is required which complicates the circuit
Solution Approach 1:
The patent performs preliminary frequency conversion to generate intermediate frequency signals at a higher frequency (e.g., 120 Hz) before the filtering stage. This preliminary action at a higher frequency allows the subsequent low pass filter to use a larger cut-off frequency (30 Hz), which corresponds to a smaller time constant, thereby simplifying the filter circuit while maintaining efficient frequency conversion.
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 achieves a filtering effect equivalent to a four-fold increase in signal frequency, enabling effective removal of intermediate frequency components with a single-stage low pass filter, thereby improving signal quality and reducing circuit complexity.
Implementation Method 1
plural mixer circuits each for mixing the electric signal amplified by the amplifier circuit with the oscillation signal generated by the local oscillation circuit to generate an intermediate frequency signal
Implementation Method 2
an adder circuit for combining the plural demodulated signals output respectively from the plural detecting circuits
Implementation Method 3
a filter circuit for removing an intermediate frequency component from the demodulated signal acquired by the frequency converter/detector circuit
Data Source
AI summary
A receiving circuit is provided with an amplifier circuit for amplifying the electric signal received by an antenna circuit, a frequency converter/detector circuit for converting a frequency of the electric signal amplified by the amplifier circuit to acquire an intermediate frequency signal, and for detecting the intermediate frequency signal to acquire a demodulated signal, and a filter circuit for removing an intermediate frequency component from the demodulated signal acquired by the frequency converter/detector circuit. Further, the frequency converter/detector circuit is provided with a local oscillation circuit for generating an oscillation signal, plural mixer circuits each for mixing the electric signal amplified by the amplifier circuit with the oscillation signal generated by the local oscillation circuit, whereby plural intermediate frequency signals are generated, which are shifted in phase from each other, plural detecting circuits for detecting the plural intermediate frequency signals generated by the plural mixer circuits, respectively to output plural demodulated signals, and an adder circuit for combining the plural demodulated signals output respectively from the plural detecting circuits.