AM Receiver Demodulation Leveling for Stepwise AGC Slopes
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Solution Overview
Problem
Existing AM receivers experience oscillations in the demodulated signal due to stepwise attenuation of AM modulated receiving signals, resulting in unwanted clicks, particularly when dealing with increasing or decreasing slopes, which are not effectively managed by conventional automatic gain control and lowpass infinite-impulse-response filters.
Innovation Solution
The method involves attenuating the AM modulated receiving signal with a stepwise slope-matched attenuation curve and using a lowpass filter with delay units, where each delay unit's output is increased by the amount of the step in the attenuation curve, and a delay buffer is used to synchronize the control signal with the lowpass filter, preventing oscillations by providing negative feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If stepwise attenuation is used in the AGC system, then the signal level is controlled within a predetermined range, but oscillations occur in the demodulated signal causing unwanted clicks
Solution Approach 1:
The invention applies preliminary action by compensating for the stepwise attenuation effect before the signal undergoes demodulation. The compensation signal is generated in advance based on the detected attenuation steps and is added to the lowpass-filtered signal to preemptively counteract the oscillations that would otherwise occur during AM demodulation.
Solution Approach 2:
The invention implements feedback by using the lowpass-filtered signal to detect attenuation steps and generating a compensation signal that is fed back to cancel the oscillations. The system continuously monitors the filtered signal for step changes caused by AGC attenuation and automatically generates compensating signals to eliminate the harmful oscillations.
2Measurement precision
If a lowpass infinite-impulse-response filter is used for demodulation, then the time average DC component is determined, but oscillations are generated when steps occur in the attenuated signal
Solution Approach 1:
The invention introduces an intermediary compensation signal that mediates between the lowpass-filtered signal and the final demodulated output. This compensation signal acts as a bridge, transferring the step information from the filtered signal to cancel the oscillations in the demodulated signal, thereby protecting the measurement precision while eliminating harmful oscillations.
3Ease of manufacture
If discrete step attenuators are used for cost and performance reasons, then the attenuation is implemented with discrete levels, but the increasing or decreasing slope of the receiving signal is not smoothly managed
Solution Approach 1:
The invention uses feedback to detect the discrete attenuation steps introduced by the step attenuator and generates compensation signals that restore the smooth slope characteristics. By monitoring the lowpass-filtered signal for step changes and automatically generating compensating signals, the system masks the discrete nature of the attenuator while maintaining signal slope continuity.
Data Source
AI summary
A method and an apparatus for leveling an increasing or decreasing slope of an AM modulated receiving signal attenuate the AM modulated receiving signal with an attenuation curve with a stepwise slope corresponding to the increasing or decreasing slope of said AM modulated receiving signal, filters the attenuated AM modulated receiving signal within AM-demodulation with a lowpass infinite-impulse-response filter of at least second order and increases the level of each delay-unit's output signal of the infinite-impulse-response filter each time a step in the attenuated AM modulated receiving signal arrives at the input of said infinite-impulse-response filter.