Adaptive Audio Voltage Limiting for Non-Boosted Amplifier Clipping
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Solution Overview
Problem
Conventional methods fail to accurately regulate load voltage and battery current in non-boosted audio systems, leading to clipping, reduced loudness, and compromised battery life due to inadequate consideration of ripple and ambient conditions.
Innovation Solution
A voltage regulating circuit comprising a voltage limiter, filter, and selector dynamically adjusts the audio voltage threshold based on anti-clipping, power-based, and current-based limit signals, using real-time measurements of battery voltage, external series resistance, and load resistance to prevent clipping and optimize battery usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high current is drawn from the battery to increase output power, then output loudness is improved, but battery voltage drops due to ESR causing clipping
Solution Approach 1:
The system dynamically adjusts the audio voltage threshold based on real-time measurements of battery voltage, ESR, and load resistance. The voltage limit signal is continuously updated to match changing operating conditions, allowing the system to maximize output power while preventing clipping under varying load and battery states.
Solution Approach 2:
The system implements feedback by measuring the actual battery voltage at the amplifier supply terminal and using this information to adjust the voltage threshold. The measured voltage, combined with ESR and load resistance data, feeds into the voltage limit calculation to prevent clipping while maintaining maximum output power.
2Measurement precision
If conventional filtered voltage sensing is used to limit load voltage, then DC voltage drop is compensated, but AC ripple is not addressed causing inaccurate compensation
Solution Approach 1:
The system extracts and separately analyzes the AC ripple component from the battery voltage by measuring the difference between the raw battery voltage and the filtered DC component. This extracted ripple information is then used to adjust the voltage threshold dynamically, enabling accurate compensation for both DC drop and AC ripple effects.
Solution Approach 2:
The system introduces an intermediary measurement approach by using the known ESR and load resistance values as mediators to calculate the expected voltage drop. This calculated drop serves as a reference to adjust the voltage threshold, providing accurate compensation without being directly affected by the noisy raw voltage measurements.
3Reliability
If decoupling capacitor is added to reduce ripple, then frequency-dependent ripple is reduced, but system complexity and cost increase
Solution Approach 1:
The system replaces the passive mechanical approach of adding decoupling capacitors with an active electronic solution. Instead of using physical components to filter ripple, the system uses digital signal processing and adaptive threshold adjustment to compensate for ripple effects, reducing hardware complexity while maintaining reliability.
4Reliability
If heavily filtered voltage signal is used for voltage limiting, then noise is reduced, but response time to voltage changes is delayed
Solution Approach 1:
The system applies partial filtering by using a light filter instead of heavy filtering, accepting some noise in exchange for faster response. The adaptive threshold adjustment compensates for the reduced filtering by dynamically adapting to voltage changes, achieving both stability and speed through a balance of filtering and active control.
Data Source
AI summary
An audio system includes an amplifier, regulating circuitry, and a filter. The regulating circuitry generates an audio voltage threshold signal based on an estimated value of the supply voltage source of the system, the estimated ESR between the system voltage supply and amplifier voltage supply pin, and the measured output resistance of the system. From these measurements/estimates, an anti-clipping voltage limit signal is generated. Power-budget-based and current-budget-based voltage limit signals are also determined based on first and second functions of the estimated value of the voltage source, respectively. The minimum of these three voltage limit signals is selected as the audio voltage threshold signal. The measurements, estimates and calculations are performed on a periodic basis to continually update the audio voltage threshold signal and thus adaptively regulate the audio system. A de-emphasis filter in the audio signal path compensates for capacitive ripple of the voltage at the amplifier's voltage supply pin.