IF Filter Band Switching With Frequency Correction in Radio Receivers
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Solution Overview
Problem
In radio receivers, the center frequency of the passband changes when switching from a wide band to a narrow band, leading to deteriorated reception performance due to interference and signal attenuation.
Innovation Solution
A radio receiver design that includes a quadrature demodulator, a band pass filter, a filter information storage unit, and a frequency correction unit, which controls the passing characteristic of the band pass filter from a wide band to a narrow band, and corrects the oscillation frequency based on the difference in center frequencies to maintain consistent reception performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the passband width is switched from wide band to narrow band, then the reception sensitivity is improved by preventing adjacent channel interference, but the center frequency shifts causing deterioration of reception performance
Solution Approach 1:
The patent implements a feedback mechanism where the center frequency detection unit continuously monitors the center frequency of the band-pass filter, and the frequency correction unit automatically adjusts the local oscillator frequency based on detected deviations. This closed-loop control ensures that when the passband width is switched between wide and narrow bands, any center frequency shifts are automatically compensated, maintaining consistent reception performance across different operating modes.
Solution Approach 2:
The patent dynamically changes the operating parameters of the band-pass filter and local oscillator based on the selected passband width. When switching from wide band to narrow band mode, the system adjusts not only the filter bandwidth but also compensates for the resulting center frequency shift by modifying the local oscillator frequency, thereby maintaining proper signal alignment throughout the reception process.
2Adaptability or versatility
If the center frequency is changed when switching passband width, then the passband can be optimized for different signal conditions, but the intermediate frequency signal frequency no longer aligns with the passband center causing signal attenuation
Solution Approach 1:
The patent employs dynamic adjustment mechanisms that allow the band-pass filter and local oscillator to adapt their characteristics in real-time. When the passband width is changed to optimize for different signal conditions (wide band for AFC, narrow band for reception), the system dynamically recalibrates the center frequency alignment through the frequency correction unit, ensuring that the intermediate frequency signal remains properly positioned within the passband throughout the operation.
3Productivity
If a band-pass filter is used before AD conversion to band-limit the IF signal, then the signal processing efficiency is improved, but the center frequency shift when switching bands causes interference and signal loss
Solution Approach 1:
The patent implements a feedback mechanism where the center frequency detection unit continuously monitors the center frequency of the band-pass filter, and the frequency correction unit automatically adjusts the local oscillator frequency based on detected deviations. This closed-loop control ensures that when the passband width is switched between wide and narrow bands, any center frequency shifts are automatically compensated, maintaining consistent reception performance across different operating modes.
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
Prevents deterioration of reception performance by ensuring the frequency of the intermediate frequency signal aligns with the center frequency of the passband, even when the passband width is changed, thereby minimizing interference and maintaining signal integrity.
Implementation Method 1
a quadrature demodulator mixing an oscillation signal outputted from an oscillator and a radio frequency signal to generate an intermediate frequency signal
Data Source
AI summary
An IF filter band-limits an intermediate frequency signal outputted from a mixer. An AFC unit controls the oscillation frequency of a PLL so that the frequency of the intermediate frequency signal is a predetermined frequency. When the AFC unit controls the oscillation frequency of the PLL, a band control unit controls the passing characteristic of the IF filter to the passing characteristic of a wide band, and after the completion of the control, controls the passing characteristic of the IF filter to the passing characteristic of a narrow band. A frequency correction unit refers to a filter information storage unit, and corrects the oscillation frequency controlled by the AFC unit according to the difference between the center frequency of the passband of the passing characteristic of the wide band and the center frequency of the passband of the passing characteristic of the narrow band.