AGC Feed-Forward Delay for Analog TV Signal Noise
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Solution Overview
Problem
Conventional automatic gain control (AGC) systems for analog television signals introduce a processing delay due to gain adjustments being made after the horizontal sync pulse has passed, leading to undesirable results from high-frequency noise amplification and limited flexibility in adjusting low-frequency and high-frequency responses.
Innovation Solution
Introducing an intentional delay in the signal path to allow for measurement and application of feed-forward amplitude corrections within the same horizontal line, enabling more precise gain adjustments and reducing high-frequency noise amplification while maintaining effective low-frequency noise rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If gain adjustments are made after horizontal sync pulse measurement, then the AGC loop can be implemented with conventional discrete-time processing, but this introduces a one-line delay that causes high-frequency noise amplification and reduces system responsiveness
Solution Approach 1:
The patent applies preliminary action by measuring the horizontal sync pulse level and calculating the required gain adjustment before the current horizontal line is fully processed. The gain correction is then applied to the next horizontal line, eliminating the one-line delay. This is achieved by measuring Hsync level at the start of line processing and preparing the gain correction in advance, so that when the line is displayed, the correction is already in effect.
2Measurement precision
If feed-forward amplitude correction is applied without signal path delay, then high-frequency noise amplification occurs, but introducing delay reduces the ability to apply corrections within the same horizontal line
Solution Approach 1:
The patent measures the horizontal sync pulse amplitude and calculates the feed-forward gain correction in advance, before the current horizontal line completes. The correction is then applied to the subsequent line, achieving precise amplitude control without introducing unnecessary delay. This preliminary calculation of the correction value allows the system to act as quickly as possible within the processing constraints.
3Stability of the object's composition
If the AGC system uses feedback control only, then the system is stable, but the response time is slow due to the inherent delay in the feedback loop
Solution Approach 1:
The patent combines feedback control with feed-forward control. The feed-forward component calculates the required gain adjustment based on the measured Hsync level and applies it in advance to the next line, significantly improving response speed. The feedback component continues to provide stability by continuously monitoring and making minor adjustments. This dual approach allows the system to respond quickly while maintaining stability.
Solution Approach 2:
The patent maintains the feedback control mechanism where the actual Hsync level is measured, compared to a target level, and the error is used to adjust the gain. This feedback loop ensures stability by continuously correcting any deviations from the desired amplitude. The feedback works in conjunction with the feed-forward control to provide both rapid response and long-term stability.
Data Source
AI summary
Systems and methods are disclosed for automatic gain control (AGC) for analog television signals using feed-forward signal path delay. Adjustments to the AGC frequency response are achieved by introducing an intentional delay in the signal path of sufficient length to allow time for measurement of a horizontal sync pulse level and for application of a feed-forward amplitude correction based upon this measurement to the same horizontal line.