AM Receiver IIR Filter Control for Step-Induced Click Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing AM modulated receiver systems experience oscillations in the demodulated signal due to step changes in the amplitude of the receiving signal, resulting in unwanted clicks, particularly when dealing with increasing or decreasing slopes, which are not effectively addressed by current automatic gain control and filtering methods.
Innovation Solution
The proposed solution involves increasing the output signals of each delay unit in the lowpass infinite-impulse-response filter when a step occurs in the amplitude of the attenuated baseband signal, using a control signal from the automatic gain control to inform the filter about step changes and accounting for delays through a delay buffer, thereby ensuring negative feedback and preventing oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a lowpass infinite-impulse-response filter with order at least two is used to determine the time average DC value, then the filtering performance is improved, but oscillations are generated in the filter output when steps occur in the input signal
Solution Approach 1:
The control unit increases the output signals of delay units before the oscillations can fully develop, based on advance detection of step changes in the input signal. This preliminary action counteracts the inevitable oscillatory response of the IIR filter to step inputs, eliminating clicks in the demodulated signal while preserving the filtering performance.
2Device complexity
If step attenuators with discrete levels are used for cost and performance reasons, then the device complexity is reduced, but the amplitude slope of the receiving signal becomes stepped rather than continuous
Solution Approach 1:
The invention converts the harmful effect of stepped amplitude changes from discrete attenuators into a beneficial control signal. The control unit detects these step changes and uses them to adjust the IIR filter output, transforming the source of oscillations into the trigger for their elimination. This allows simple discrete attenuators to be used without compromising signal quality.
3Measurement precision
If the IIR filter is activated by a step in the signal, then the time average DC value is determined, but oscillations are generated that are transferred to the demodulated signal output
Solution Approach 1:
The system implements feedback by monitoring the input signal for step changes and using this information to adjust the filter output. The control unit detects when a step occurs in the attenuated baseband signal and responds by increasing the output of delay units, creating a feedback mechanism that actively suppresses oscillations while maintaining accurate time average determination.
Data Source
Figure 1~2
Figure 3~4
Figure 5A~5B
AI summary
A method and an apparatus for leveling an increasing or decreasing slope of an AM modulated receiving signal attenuates said AM modulated receiving signal by means of an attenuation curve with a stepwise slope corresponding to said increasing or decreasing slope of said AM modulated receiving signal, filters said attenuated AM modulated receiving signal within AM-demodulation with a lowpass infinite-impulse-response filter (14) of at least second order and increases the level of each delay-unit's output signal of said infinite-impulse-response filter (14) each time a step in said attenuated AM modulated receiving signal arriving at the input of said infinite-impulse-response filter (14).