Class D Amplifier Switching Ramp for Startup Click Elimination
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Solution Overview
Problem
Class D audio amplifiers produce audible click noise during startup and shutdown due to energy transitions in the output filter stage, which requires a bulky and costly speaker cutoff relay to mitigate.
Innovation Solution
A method that determines a timing interval to systematically transition the peak voltage of the capacitor, incrementally increasing or decreasing the switching times of the switches to eliminate audible transient voltage excursions, thereby eliminating the need for a speaker cutoff switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a speaker cutoff relay is inserted to disconnect the speaker during transients, then click noise is reduced, but device complexity and cost increase
Solution Approach 1:
The harmful transient energy is extracted from the system by diverting it through a discharge path (resistor and diode) that bypasses the speaker, eliminating the need for a speaker cutoff relay while still protecting against click noise
Solution Approach 2:
A diode is introduced as an intermediary component to control the direction of current flow during transients, allowing energy to be diverted away from the speaker without requiring a complex relay mechanism
2Object-affected harmful factors
If a speaker cutoff relay is used to eliminate click noise, then audible transient voltage excursions are reduced, but system cost increases
Solution Approach 1:
The solution replaces an expensive, complex relay with inexpensive passive components (resistor and diode) that perform the same protective function with minimal cost and maximum reliability
Solution Approach 2:
The mechanical relay system is replaced with an electronic circuit using passive components, eliminating mechanical wear and complexity while achieving the same noise reduction effect
3Object-affected harmful factors
If speaker is disconnected during transients, then click noise is eliminated, but loss of time occurs during startup and shutdown
Solution Approach 1:
The discharge path is pre-configured in the circuit so that transient energy is automatically diverted as soon as it occurs, eliminating the need to wait for relay activation and reducing transition time
Data Source
AI summary
A method of minimizing an audible click noise from a speaker in a Class D audio power amplifier upon shutdown or startup of a switching stage having two switches series connected at a node, the speaker being connected to the node via an output filter comprising an inductor and a capacitor, the switches being controlled by a controller. The method including the steps of determining a timing interval at the node to transition a peak voltage of the capacitor, the capacitor voltage being a speaker voltage; and eliminating the audible transient voltage excursion across the speaker that causes a click noise during the timing interval, wherein at startup ON and OFF times of the switches are incrementally increased from zero to a normal mode and at shutdown the ON OFF times of the switches are incrementally decreased from the normal mode to zero.