Supply Voltage Conditioning Circuit for Noise-Immune Boost Switching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Noise in the supply voltage of Class-H boosted amplifiers and audio compressors causes random boost switching and variations in limiter gain, leading to spurious tones and degraded total harmonic distortion (THD) ratings due to incomplete noise removal by existing low pass filters.
Innovation Solution
A supply voltage conditioning circuit comprising a differential amplifier, comparator, sample and hold circuit, and delay circuit that filters the supply voltage by determining a noise margin and sampling the input voltage only when the difference exceeds this margin, ensuring the output supply voltage is substantially noise-free and tracks underlying changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a low pass filter is used to reduce noise amplitude in the supply voltage, then the noise amplitude is reduced, but the noise is not completely removed and random boost switching still occurs
Solution Approach 1:
A sample and hold circuit is introduced as an intermediary component between the low pass filter and the boost control logic. This circuit samples the filtered supply voltage at specific moments and holds the sampled value, effectively blocking the remaining noise from reaching the boost decision circuitry while allowing the control signal to pass through cleanly.
Solution Approach 2:
The system performs preliminary filtering through the low pass filter before the final sampling decision. By reducing the noise amplitude in advance through filtering, the subsequent sample and hold circuit can make clean sampling decisions without being affected by high-frequency noise variations.
2Productivity
If hysteresis is implemented between boost on and boost off thresholds to prevent frequent switching, then switching frequency is reduced, but noise in the supply voltage still causes random boost switching near the threshold
Solution Approach 1:
The sample and hold circuit acts as an intermediary that decouples the noisy supply voltage from the boost decision logic. By sampling the voltage at discrete moments and holding that value, it provides a stable reference for the hysteresis comparator, preventing noise-induced threshold crossings while maintaining the hysteresis switching behavior.
Solution Approach 2:
The sample and hold circuit dynamically selects when to sample the supply voltage, adapting to the operating conditions. The sampling timing and hold duration are optimized to capture stable voltage levels while ignoring noise transients, making the boost control responsive to real voltage changes while immune to noise.
3Reliability
If noise margin is increased to prevent random switching, then switching stability is improved, but the ability to track underlying changes in supply voltage is reduced
Solution Approach 1:
The sample and hold circuit uses dynamic sampling strategies where the sampling rate and hold duration adapt to the rate of change of the supply voltage. When the voltage changes slowly, longer hold periods provide noise immunity; when voltage changes rapidly, more frequent sampling ensures accurate tracking of underlying trends while filtering out high-frequency noise.
Solution Approach 2:
The circuit employs periodic sampling of the supply voltage at optimized intervals. This periodic action allows the system to regularly update the held voltage value, ensuring that underlying changes in supply voltage are captured while the periodic nature itself provides natural filtering of aperiodic noise components.
Data Source
AI summary
A supply voltage conditioning circuit comprises a differential amplifier, a comparator, a sample and hold (S/H) circuit, and a delay circuit. The differential amplifier receives an input supply voltage and a reference voltage, and outputs a difference signal. The comparator receives the difference signal and a value representative of a noise margin, and outputs a control signal indicative of whether the difference signal is greater than the value representative of the noise margin. The S/H circuit samples the input supply voltage in response to the control signal indicating the difference signal is greater than the noise margin, and outputs a substantially noise free supply voltage. This allows the output supply voltage to track underlying changes in the input supply voltage but filter out noise in the input supply voltage. The delay circuit receives and delays the output supply voltage to generate the reference voltage.