Automatic Gain Control Using Peak Amplitude for Fast ADC Convergence
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Solution Overview
Problem
Automatic gain control loops that use a reference value representing the square mean energy of a signal are inappropriate for signals with uneven energy distribution, leading to suboptimal utilization of the analog-to-digital converter's dynamic range and prolonged convergence time, especially in cases where the energy distribution is not evenly distributed, such as in video signals like NTSC or PAL.
Innovation Solution
A system and method for automatic gain control that compares digital output signals from an analog-to-digital converter to a predetermined maximum amplitude reference level, adjusting the gain setting by incrementing or decrementing based on the comparison, with a ratio of down step size to up step size greater than the number of possible output samples not at saturation to those at saturation, to ensure stable and rapid convergence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reference value representing the square mean energy of a signal is used in automatic gain control, then the dynamic range of the analog-to-digital converter is maximized under the assumption of evenly distributed energy, but the control becomes inappropriate for signals with uneven energy distribution (such as video signals with synchronization portions and data portions), leading to suboptimal performance
Solution Approach 1:
The patent changes the reference parameter from square mean energy to peak amplitude detection. By detecting the peak amplitude of the input signal and comparing it to a reference peak amplitude, the system adapts to different signal types regardless of their energy distribution characteristics. This parameter change enables the AGC to work correctly with video signals having synchronization portions and data portions, as well as other signals with non-uniform energy distribution.
2Reliability
If a reference value representing the square mean energy of a signal is used, then the calculation incorporates substantial headroom for worst case scenarios, but this prevents full utilization of the analog-to-digital converter's dynamic range in typical cases
Solution Approach 1:
The patent applies partial action by detecting only the peak amplitude rather than calculating the complete square mean energy. This partial measurement is sufficient for gain control purposes and allows the system to utilize the full dynamic range of the ADC in typical cases while still providing adequate headroom for worst case scenarios through the peak detection mechanism.
3Reliability
If the convergence time of the loop is determined on a worst case scenario, then the system is designed to handle the most difficult cases, but the actual convergence time is much longer than necessary for typical signals
Solution Approach 1:
The patent introduces dynamic step size adjustment in the gain control loop. The step size is varied based on the current error magnitude and signal characteristics, allowing the system to converge rapidly for typical signals while still guaranteeing convergence for worst case scenarios. This dynamic adaptation optimizes the convergence time across different signal types without sacrificing reliability.
Data Source
AI summary
Systems and methods for automatic gain control are disclosed. In one aspect of the invention, a system is provided that comprises a programmable gain amplifier that amplifies an input signal based on a gain signal. The system further comprises an analog-to-digital converter that generates at least one digital output signal from the amplified input signal, and an automatic gain control component that determines an adjustment of the gain signal based on a comparison of the at least one digital output signal to a predetermined maximum amplitude reference level.