Class-D Output Stage Tri-State Control for Low-Signal Power Saving
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Solution Overview
Problem
Existing class-D amplifier output stages consume significant power due to components generating pulse width modulated signals, particularly in low power applications, and do not efficiently manage power based on signal amplitude and activity.
Innovation Solution
A tri-state control scheme is implemented where switches are controlled based on the durations of signal levels, with independent control signals turning switches on or off proportionally to signal activity, allowing for reduced power consumption during low signal volumes and sufficient power during high volumes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional class-D amplifier uses components to generate pulse width modulated signals, then the output stage can drive the load effectively, but the power consumption becomes significant
Solution Approach 1:
The patent implements dynamic control of the output stage by adjusting the duty cycle of the output signal based on the amplitude of the input signal. When the input signal amplitude is low, the output stage remains in a high-impedance state with minimal power consumption. When the input signal amplitude increases, the output stage transitions to an active state to provide sufficient power delivery. This dynamic adaptation resolves the contradiction between power delivery capability and power consumption.
Solution Approach 2:
The patent changes the impedance parameter of the output stage dynamically. The output stage transitions between high-impedance (low power consumption) and low-impedance (high power delivery) states based on the signal amplitude. This parameter change allows the system to achieve effective load driving only when necessary, thereby reducing overall power consumption while maintaining power delivery capability when required.
2Reliability
If the output stage maintains continuous operation to ensure sufficient power delivery, then the load can be driven reliably, but power consumption increases during low signal volumes
Solution Approach 1:
The patent employs dynamic impedance switching to maintain reliability only when necessary. The output stage monitors the input signal amplitude and transitions to a low-impedance active state when the signal exceeds a threshold, ensuring reliable power delivery. When the signal amplitude is below the threshold, the output stage switches to a high-impedance state, dramatically reducing power consumption. This dynamic behavior resolves the contradiction by providing reliability conditionally rather than continuously.
Solution Approach 2:
The patent implements periodic monitoring of the input signal amplitude with hysteresis to prevent oscillation. The output stage switches between active and high-impedance states based on threshold comparisons, creating a periodic on-off pattern that follows the signal envelope. This periodic action ensures reliable power delivery during high-signal periods while minimizing power consumption during low-signal periods, resolving the contradiction between reliability and power consumption.
3Loss of energy
If the output stage uses a switching architecture for high efficiency, then power consumption is reduced, but the components generating the modulated signal consume significant power
Solution Approach 1:
The patent extracts and eliminates the complex pulse width modulation generation components (comparator, sawtooth waveform generator) from the system. Instead, it directly uses the sigma delta modulated digital signal to control the output stage switching. This extraction removes the significant power-consuming components while maintaining the switching architecture's energy efficiency, thereby resolving the contradiction between energy efficiency and control component power consumption.
Solution Approach 2:
The patent uses a simplified control approach where the digital sigma delta modulated signal directly controls the output stage without requiring analog reconstruction. This copying of the digital control signal to directly drive the switching elements eliminates the need for power-hungry analog signal generation components, maintaining switching efficiency while reducing control component power consumption.
Data Source
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AI summary
Power consumption of an output stage such as a class-D output stage may depend on the amplitude and the activity of the signal being output. Here, control signals may be generated to independently control coupled switches of the output stage and to provide a tri-state control scheme for the output stage. These control signals may be generated based on durations of different levels of an input signal over one or more periods of time.