Variable Loop Filter Amplifier for THD+N and Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing amplifier systems face instability issues due to inappropriate loop filter gain settings, leading to compromised THD+N performance and dynamic range, particularly when handling large and small input signals.
Innovation Solution
An amplifier system with a variable filter unit and a controller circuit that adjusts compensation unit parameters based on signal amplitude to optimize gain characteristics, maintaining system stability while enhancing THD+N performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the gain of the loop filter is increased to improve THD+N performance, then the THD+N is improved, but the sigma-delta modulator becomes unstable when large signals are inputted
Solution Approach 1:
The patent implements a variable gain loop filter where the gain is dynamically adjusted based on the amplitude of the input signal. When the input signal amplitude exceeds a threshold, the gain is reduced to prevent sigma-delta modulator instability. When the input signal amplitude is below the threshold, the gain is increased to improve THD+N performance. This dynamic adaptation resolves the contradiction by making the system behavior conditional on the operating state.
Solution Approach 2:
The patent changes the gain parameter of the loop filter based on the input signal amplitude. By detecting the signal amplitude and adjusting the gain parameter accordingly (high gain for small signals, low gain for large signals), the system optimizes THD+N performance while maintaining sigma-delta modulator stability across different operating conditions.
2Stability of the object's composition
If the gain of the loop filter is decreased to maintain sigma-delta modulator stability for large signals, then the stability is maintained, but the THD+N performance is sacrificed when small signals are inputted
Solution Approach 1:
The variable gain loop filter dynamically switches between high gain and low gain modes based on input signal amplitude. For small input signals, the high gain mode provides excellent THD+N performance. For large input signals, the low gain mode ensures sigma-delta modulator stability. This dynamic switching resolves the contradiction by optimizing the gain parameter for the current operating condition.
Solution Approach 2:
The system adjusts the loop filter gain parameter based on the detected input signal amplitude. When small signals are detected, the gain is set to a high value to maximize THD+N performance. When large signals are detected, the gain is reduced to maintain stability. This parameter adaptation eliminates the need to permanently compromise either stability or THD+N performance.
3Manufacturing precision
If a fixed high gain is used in the loop filter to optimize small signal performance, then small signal THD+N is improved, but the system becomes unstable when large signals are inputted
Solution Approach 1:
The patent transforms the fixed gain loop filter into a variable gain loop filter that adapts its gain based on input signal amplitude. The controller circuit detects the signal amplitude and adjusts the gain parameter accordingly, enabling the system to maintain high gain for small signals (optimizing THD+N) while switching to low gain for large signals (maintaining stability).
Solution Approach 2:
The gain parameter of the loop filter is changed from a fixed value to a variable value that depends on the input signal amplitude. This parameter change allows the system to optimize performance for different signal conditions, achieving both small signal THD+N performance and large signal stability through adaptive parameter selection.
4Stability of the object's composition
If a fixed low gain is used in the loop filter to maintain stability for large signals, then system stability is maintained, but small signal THD+N performance is sacrificed
Solution Approach 1:
The variable gain loop filter dynamically adjusts the gain parameter based on the input signal amplitude, switching from low gain (for stability with large signals) to high gain (for THD+N performance with small signals). This dynamic adjustment resolves the contradiction by optimizing the gain for the current operating condition rather than using a fixed conservative value.
Solution Approach 2:
The loop filter gain parameter is transformed from a fixed low value to a variable value that adapts to the input signal amplitude. This allows the system to achieve both stability and optimal THD+N performance by selecting the appropriate gain parameter based on the operating conditions, eliminating the need to permanently compromise small signal performance for the sake of stability.
Data Source
AI summary
An amplifier system includes an output circuit, a processor circuit, a feedback circuit, and a controller circuit. The output circuit outputs an output signal and returns a digital output feedback signal. The processor circuit receives a filtered error audio signal and outputs a pulse width modulation control signal to the output circuit. An addition unit of the feedback circuit adds the negative value of the digital output feedback signal to the digital input signal to obtain the error audio signal. A variable filter unit of the feedback circuit filters the error audio signal and outputs the filtered error audio signal. A compensation unit of the variable filter unit changes the gain characteristics of the variable filter unit. The controller circuit adjusts one or more parameters of the compensation unit according to a pre-compensation signal so as to change the gain characteristics of the variable filter unit.