Class-D PWM Modulator Transition Control for Pop Noise Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Class-D amplifiers in personal audio devices experience transient noise issues, such as pops and clicks, during transitions like muting or powering down, due to quantization noise caused by the disparity between output and feedback resolutions in digital closed-loop PWM modulators.
Innovation Solution
The implementation of a class-D amplifier system with digital closed-loop PWM modulators that include a digital integrator and control logic to decrease or increase the residue of the output value toward an integer multiple of the feedback resolution over multiple clock cycles, forcing the output to an approximate 50% duty cycle, thereby reducing transient noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If digital closed-loop PWM modulators are used in class-D amplifiers, then power efficiency and audio signal accuracy are improved, but quantization noise causes transient pops and clicks during transitions
Solution Approach 1:
The control logic detects a transition condition and begins adjusting the residue of the digital integrator before the actual transition occurs. By preemptively modifying the residue over multiple clock cycles and forcing the output to 50% duty cycle, the system prepares the modulator state in advance to eliminate quantization noise pops and clicks during the transition.
Solution Approach 2:
The residue adjustment mechanism acts as an intermediary between the digital integrator output and the PWM encoder. By introducing the residue modification step and duty cycle forcing as intermediate processing stages, the system mediates the transition process to prevent direct quantization noise from reaching the output, thereby reducing transient pops and clicks.
2Measurement precision
If the output resolution of the digital integrator is finer than the feedback resolution, then audio signal precision is improved, but the residue between output and feedback values causes transient noise during transitions
Solution Approach 1:
The control logic extracts the residue component from the digital integrator output by separating it from the integer multiple of feedback resolution. This extracted residue is then deliberately adjusted over multiple clock cycles to eliminate the discontinuity that would otherwise cause transient noise during transitions.
Solution Approach 2:
The system changes the residue parameter of the digital integrator over time during transition conditions. By dynamically adjusting the residue from its initial value to zero (or nearest integer multiple of feedback resolution) across multiple clock cycles, the system transforms the abrupt parameter change into a gradual transition, thereby eliminating transient noise while preserving the fine output resolution.
3Speed
If the system transitions quickly between states, then response time is improved, but transient pops and clicks increase in magnitude
Solution Approach 1:
Instead of making a single abrupt transition change, the system applies periodic adjustments to the residue over multiple clock cycles. This periodic action distributes the transition across discrete time steps, maintaining fast overall response while reducing the magnitude of transient noise by avoiding a single large discontinuous change.
Data Source
AI summary
A class-D amplifier system includes one or more pulse width modulation (PWM) output paths at least one of which includes one or more digital closed-loop PWM modulators (DCL-PWMM) in which at least one of the DCL_PWMM includes a digital integrator that provides an output value and receives a feedback value. The output value has an output resolution and the feedback value has a feedback resolution that is coarser than the output resolution. The output value is the sum of an integer multiple of the feedback resolution and a residue. Control logic decreases/increases the residue of the digital integrator toward an integer multiple of the feedback resolution over a plurality of clock cycles in response to a request to transition the class-D amplifier and forces an output of the DCL_PWMM to have an approximate 50% duty cycle after decreasing/increasing the residue over the plurality of clock cycles.