Filter Circuit Frequency Locking for Accurate Center Frequency Selection
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Solution Overview
Problem
Conventional direct up-conversion transmitters face challenges in quickly and accurately selecting the center frequency of a filter, which affects the accuracy of amplitude detection due to the influence of unwanted harmonics in the mixing signal.
Innovation Solution
A filtering circuit comprising a filter, a frequency divider, and a control circuit that dynamically adjusts the control signal to determine the center frequency of the filter's passband, allowing for rapid selection and reducing harmonic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the center frequency of the filter is selected by adjusting the current of the buffer amplifier followed by amplitude detection, then the filter can process signals with larger bandwidth, but the process is time-consuming and harmonics reduce detection accuracy
Solution Approach 1:
The patent applies preliminary action by pre-calibrating the relationship between buffer amplifier current and center frequency before actual signal processing. The system stores calibration data mapping current values to center frequencies, allowing rapid lookup and selection during operation without time-consuming real-time adjustments, thus resolving the time consumption issue while maintaining bandwidth adaptability
Solution Approach 2:
The patent replaces the mechanical/physical adjustment process (manual current adjustment and amplitude detection) with an electronic digital system. The control circuit uses digital signal processing and stored calibration data to automatically determine optimal current settings, eliminating the time-consuming iterative adjustment process and improving both speed and accuracy
2Adaptability or versatility
If the center frequency is selected using conventional amplitude detection methods, then the filter can adapt to different frequencies, but unwanted harmonics affect the detection accuracy
Solution Approach 1:
The patent extracts and removes the harmful harmonic components from the detection process. By using a frequency divider to generate a divided frequency signal and comparing it with the target frequency, the system directly identifies the center frequency without being influenced by harmonics, thus eliminating the source of detection errors while maintaining frequency adaptability
Solution Approach 2:
The patent introduces an intermediary frequency division mechanism as a mediator between the buffer amplifier and the amplitude detection system. The frequency divider converts the output frequency to a divided frequency that can be accurately compared with the target frequency, providing a clean intermediate signal that eliminates harmonic interference and enables precise frequency identification
Data Source
AI summary
A filtering circuit includes a filter, a frequency divider, and a control circuit. The filter is configured to generate a first oscillating signal according to a control signal in a first mode, and perform a filtering process according to the control signal in a second mode. A frequency of the first oscillating signal is determined according to the control signal. The frequency divider is coupled to the filter and configured to divide the frequency of the first oscillating signal to generate a frequency-divided signal. The control circuit is coupled to the filter and the frequency divider, and configured to compare a frequency of the frequency-divided signal and a frequency of a second oscillating signal so as to adjust the control signal in the first mode. A center frequency of a passband of the filter in the second mode is determined according to the adjusted control signal.