Loop Filter Assist DAC Timing for Class-D Feedback Error Reduction
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Solution Overview
Problem
Class-D amplifiers experience feedback errors due to errors in the loop filter and CM limit amplifier, leading to distortions and noise in audio applications, which are not effectively minimized by increasing power or eliminating current through the loop filter.
Innovation Solution
A system comprising a loop filter, a driver, a digital-to-analog converter (DAC), and a control circuit that determines delays to synchronize current sourcing and sinking with the driver output, ensuring that the DAC provides matching currents at the output of the integrator or loop filter, thereby minimizing feedback errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current is increased through the loop filter to reduce feedback errors, then feedback error reduction is achieved, but power consumption increases and the system becomes less efficient
Solution Approach 1:
The assist DAC circuit performs preliminary action by pre-generating the exact current that will be needed by the loop filter at the precise moment it is required. The control circuit predicts the driver output and activates the assist DAC accordingly, so that when the loop filter needs current, it is already available, eliminating feedback errors without requiring continuous high current flow that would increase power consumption.
Solution Approach 2:
The assist DAC circuit serves itself and the loop filter by autonomously generating the required current based on control signals. The system becomes self-sufficient in providing the necessary current compensation, eliminating the need for external power-intensive solutions while maintaining feedback error reduction.
2Reliability
If the loop filter is designed to eliminate current flow to reduce feedback errors, then feedback errors are minimized, but the system loses the ability to effectively process signals
Solution Approach 1:
The assist DAC circuit acts as an intermediary between the driver output and the loop filter. It provides the necessary current compensation without requiring current to flow through the loop filter in the traditional sense. This mediator approach allows feedback error minimization while preserving signal processing capability, as the assist DAC delivers the compensation current directly to where it is needed.
3Reliability
If delay detection and synchronization circuits are added to synchronize DAC current sourcing with driver output, then feedback errors are reduced, but device complexity increases
Solution Approach 1:
The control circuit implements feedback by continuously monitoring the driver output and using this information to adjust the assist DAC current sourcing in real-time. The delay detection circuit measures the timing relationship between driver output and DAC response, and this feedback is used to synchronize the current sourcing precisely, reducing feedback errors while managing complexity through intelligent control rather than complex hardware.
4Manufacturing precision
If the DAC is controlled to source or sink current based on predicted driver output, then signal quality is improved, but the control complexity increases
Solution Approach 1:
The control circuit performs preliminary action by predicting the driver output before it actually occurs. Based on this prediction, the control circuit pre-activates the assist DAC to source or sink the appropriate current. This timing approach improves signal quality by ensuring the current is ready when needed, while managing control complexity through predictive algorithms rather than reactive complex control mechanisms.
Data Source
AI summary
This disclosure relates generally to a system for mitigating error in an amplifier. The system may include a loop filter; a driver; a digital-to-analog converter (DAC) configured to source and to sink current; an edge selector configured to determine a first delay between the driver receiving a signal to provide a driver output signal and the driver providing the driver output signal; a timing circuit configured to determine a second delay between the DAC receiving a signal to provide a DAC output current and the DAC providing the DAC output current; and at least one controller configured to control the DAC to source or to sink the DAC output current at a time corresponding to a beginning of the driver output signal, and control the DAC to stop sourcing or sinking the DAC output current at a time corresponding to an end of the driver output signal.