IF Filter Center Frequency Tuning Using Pseudo Sine Phase Comparison
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Solution Overview
Problem
The existing methods for adjusting the center frequency of an IF filter in radio tuners are prone to errors due to indirect simulation and require external adjustments, increasing man-hours and environmental setup needs.
Innovation Solution
A tuner with an IF filter, a pseudo sine wave generation circuit, a switch circuit, and an F0 adjustment circuit that adjusts the center frequency by comparing phases of a pseudo sine wave with the filtered signal, and an S meter adjustment circuit to adjust signal levels internally.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a replica oscillation circuit is used to adjust the IF filter center frequency, then adjustment can be performed without external equipment, but adjustment accuracy deteriorates due to simulation errors
Solution Approach 1:
The patent uses a replica oscillation circuit that copies the characteristics of the actual IF filter circuit. By oscillating the replica circuit and counting its frequency, the system can determine the center frequency F0 of the IF filter without needing external adjustment equipment. The replica circuit is designed to simulate the electrical characteristics of the actual filter, allowing indirect measurement of the center frequency.
Solution Approach 2:
The replica oscillation circuit acts as an intermediary between the IF filter and the frequency counter. Instead of directly measuring the IF filter's center frequency (which would require external equipment), the system uses the replica circuit as a mediator that can be oscillated and measured, thereby indirectly obtaining the center frequency information.
2Measurement precision
If external signals are used for S meter adjustment, then accurate calibration can be achieved, but adjustment complexity and man-hours increase
Solution Approach 1:
The system uses an internally generated test signal to calibrate the S meter, eliminating the need for external signal sources. The test signal generation circuit produces a known signal level that passes through the IF filter and IF amplifier to the S meter, allowing the system to self-calibrate its detection threshold without external equipment or complex adjustment procedures.
Data Source
AI summary
A center frequency F0 of an IF filter is effectively adjusted. The IF filter filters a down-converted signal centering around the center frequency F0. A pseudo sine wave generation circuit generates a pseudo sine wave having a level change of at least two steps respectively on both positive and negative sides. The pseudo sine wave is made to pass through the IF filter by a switch circuit, and in the state, an F0 adjustment circuit adjusts the center frequency F0 in the IF filter 14 by comparing a phase of the pseudo sine wave with a phase of a signal after passing through the IF filter.