Patent ID: 6512414
Filing Date: 2003-01-28
Classification: H03H

Abstract:
An automatic filter tuning control system for tuning a characteristic frequency of a filter to a target frequency, the system comprising:circuit configuration replacing means for replacing an original circuit configuration of the filter with an alternative tuning-dedicated circuit configuration while the filter is being tuned, wherein the filter with the alternative configuration has the same characteristic frequency as that of the filter with the original configuration and shows a signal-to-noise ratio higher than that of the filter with the original configuration; a characteristic tuner, which measures one or some periods of an oscillating waveform appearing at an output of the filter with the alternative configuration when an impulse signal, pulse signal or step signal is input as a test signal to the filter; detects the characteristic frequency of the filter in accordance with the period measured; and then supplies a tuning signal to the filter, thereby adjusting a difference between the characteristic and target frequencies; wherein the characteristic tuner comprises: a frequency divider for dividing the frequency of a clock signal that has been delivered as a reference signal; a test signal generator for generating a test signal from the clock signal with the divided frequency; a counter for measuring one or some periods of the oscillating waveform, which appears at the output of the filter responsive to the test signal, synchronously with the clock signal; a frequency detector for detecting the characteristic frequency of the filter based on the period measured by the counter; and an up/down counter for changing the tuning signal in accordance with the difference between the detected characteristic frequency and the target frequency; and a controller, which issues a tuning instruction to start the characteristic tuner and then stores a level of the tuning signal when the difference between the characteristic and target frequencies of the filter enters a tolerance range, wherein in operating the filter, the controller restores the filter to the original configuration, stops operating the characteristic tuner and controls the characteristics of the filter using the tuning signal stored.