PWM Clipping Detector Circuit for Stable High-Frequency Sensing
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Solution Overview
Problem
Existing PWM clipping detection circuits are unstable and prone to spurious commutations, especially at high frequencies, and are affected by noise, leading to inaccurate detection of clipping in PWM signals.
Innovation Solution
A clipping detector circuit that includes a timer circuit to monitor edge periods and assert a signal upon elapsed time, and a counter circuit to determine pulse counts, generating a clipping detection signal based on these inputs, improving stability and robustness against noise and high-frequency fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple pulse-counting clipping detection circuit is used, then the device complexity is low, but the stability and reliability of clipping detection deteriorates at high frequencies
Solution Approach 1:
The detection circuit is divided into two independent functional segments: a timer circuit that monitors edge periods and a counter circuit that counts pulses between timer assertions. This segmentation allows each component to perform its function optimally without interfering with the other, improving overall stability while maintaining reasonable complexity.
Solution Approach 2:
A timer circuit is introduced as an intermediary component between the PWM signal and the pulse counter. The timer asserts a signal only when a specific time period elapses since the last edge, effectively filtering out high-frequency noise and spurious commutations while allowing genuine clipping events to be detected.
2Measurement precision
If the detection circuit monitors every pulse edge, then the measurement precision of clipping detection is high, but the circuit becomes susceptible to noise and spurious commutations
Solution Approach 1:
The timer circuit operates periodically, monitoring the time period since the last edge and asserting its signal only when a predetermined time threshold is exceeded. This periodic monitoring approach filters out random noise and spurious commutations that occur more frequently than the expected PWM period, while still detecting genuine clipping events.
Solution Approach 2:
The timer circuit performs preliminary verification by checking whether the time period since the last edge exceeds a threshold before allowing the counter to register a pulse. This preliminary action prevents noise-induced false detections while maintaining accurate clipping detection for genuine events.
3Productivity
If the clipping detection circuit operates at high PWM frequencies, then the productivity of the audio system is improved, but the stability of the detection signal deteriorates
Solution Approach 1:
The circuit replaces direct mechanical pulse-counting with a timer-based time period measurement system. The timer circuit measures the time elapsed since the last edge and compares it against a threshold, substituting the mechanical act of counting every pulse with a more stable time-based measurement that is less susceptible to high-frequency variations.
Data Source
AI summary
A clipping detector circuit includes a timer circuit and a counter circuit. The timer circuit is configured to monitor a time period elapsing since a last occurrence of an edge in a PWM signal, assert a first signal when the time period elapses, and de-assert the first signal and reset the time period as a result of an edge occurring in the PWM signal. The counter circuit is configured to determine a number of pulses in the PWM signal since the last de-assertion of the first signal, and assert a second signal when the number of pulses in the PWM signal since the last de-assertion of the first signal reaches m pulses. The clipping detector circuit is configured to generate a clipping detection signal indicative of whether the pulse-width modulated signal is clipped or not as a function of the first signal and the second signal.