Filter Frequency Tuning by Phase-Shifted Binary Search
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Solution Overview
Problem
Conventional filter characteristic adjusting methods, such as the master/slave system and direct filter tuning, face challenges including increased circuit complexity, phase error deviations, and lengthy adjustment times due to variations in filter and VCO orders, and require high sampling frequencies and additional correction circuits.
Innovation Solution
A filter characteristic adjusting apparatus that includes a test signal generation unit, a phase shift unit to create a predetermined phase difference, and a control signal generation unit using comparators and logic units for binary search, allowing for rapid and accurate adjustment of filter frequencies without the need for additional PLL circuits or VCOs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a master/slave system with PLL circuit is used to adjust filter characteristic, then frequency accuracy is improved, but device complexity increases due to additional VCO and PLL circuits
Solution Approach 1:
The patent extracts only the essential frequency measurement function from the complex PLL system. Instead of using a full VCO-PLL master/slave system, the invention directly measures the filter's output signal frequency and compares it with the reference frequency, eliminating the need for VCO and PLL circuits while maintaining frequency accuracy.
Solution Approach 2:
The frequency measurement unit is designed to universally measure any filter output signal without requiring a dedicated VCO. The same measurement mechanism works for different filter types and configurations, reducing overall system complexity while maintaining measurement precision.
2Ease of operation
If response waveform period measurement is used for filter tuning, then adjustment capability is achieved, but adjustment time increases due to lengthy measurement processes
Solution Approach 1:
The patent replaces the mechanical/time-consuming response waveform period measurement method with a direct frequency comparison approach. By measuring the frequency of the filter's steady-state output signal and comparing it directly with the reference frequency, the tuning process is significantly accelerated without sacrificing measurement accuracy.
Solution Approach 2:
The system performs preliminary frequency measurement during the filter's normal operation rather than waiting for response waveforms to settle. This allows frequency comparison to be done in parallel with normal filter processing, eliminating the need for separate tuning measurement cycles and reducing overall adjustment time.
3Measurement precision
If high sampling frequency is used for accurate frequency measurement, then measurement precision is improved, but device complexity and resource requirements increase
Solution Approach 1:
The patent changes the measurement parameter from time-domain response waveform period to frequency-domain direct frequency comparison. This parameter transformation allows accurate frequency measurement without requiring high sampling frequencies, as the measurement is performed on the steady-state output signal's frequency content rather than transient response timing.
Data Source
AI summary
There is provided a filter characteristic adjusting apparatus and a filter characteristic adjusting method which can avoid an increase in circuit scale of the filter characteristic adjusting apparatus, and can speedily adjust a characteristic frequency of the filter to a desired frequency. When performing characteristic adjustment for the filter, the test signal generation unit (31) generates a test signal (s14) which is a pulse signal having the same frequency as the characteristic frequency of the filter (10) on the basis of a reference signal (s17), and a phase-shifted test signal (s14′) that is obtained by shifting the phase of the test signal (s14) by a predetermined amount with a phase shift unit (32) in a control signal generation unit (33) is compared with a filter output signal (s16) that is obtained by inputting the test signal (s14) into the filter (10) to obtain a phase difference between the signals, and then the phase difference is subjected to a binary search to generate a control signal (s11).