Speaker Connection Detection in Class D Audio Output Circuits
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Solution Overview
Problem
Conventional methods for determining speaker connection in audio amplifiers, particularly in class D power amplifiers, face challenges in accurately distinguishing between connected and disconnected speakers due to high-frequency signal interference and delays in current level comparisons, leading to erroneous determinations.
Innovation Solution
A sound output device with a configuration that includes first and second filters to remove high-frequency components from input and output signals, peak current detection units to identify peak values, and a comparison unit to determine speaker connection based on the ratio or difference between these peak currents, thereby compensating for signal delays and frequency interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If class D power amplifier with PWM signal is used to achieve high efficiency and fast response, then productivity and speed are improved, but high-frequency components in the output signal cause measurement errors in speaker connection detection
Solution Approach 1:
The patent divides the output signal into two frequency components using separate filter circuits: a first filter extracts high-frequency PWM components while a second filter extracts low-frequency audio components. This segmentation allows independent processing of each frequency range, enabling accurate speaker connection detection by comparing low-frequency current levels without interference from high-frequency PWM signals.
Solution Approach 2:
The patent introduces low-pass filter circuits as intermediary elements between the power amplifier output and the detection circuits. These filters act as mediators that selectively pass only the low-frequency audio signal components while blocking high-frequency PWM components, thereby enabling accurate measurement of speaker connection status without the harmful effects of high-frequency interference.
2Power
If high-frequency PWM signal frequency is increased to improve amplifier performance, then power and efficiency are improved, but output current level increases making it difficult to distinguish speaker connection status
Solution Approach 1:
The patent applies different quality characteristics to different frequency components of the output signal. The first filter circuit is designed with high-pass characteristics to handle high-frequency PWM signals, while the second filter circuit is designed with low-pass characteristics to handle low-frequency audio signals. This local quality differentiation allows the system to maintain high power output while accurately detecting speaker connection through the low-frequency component.
Solution Approach 2:
The patent skips the problematic high-frequency PWM components by using the second filter circuit to extract only the low-frequency audio signal components for speaker connection detection. This allows the system to rush through the harmful high-frequency interference and directly access the useful low-frequency information needed for accurate detection.
3Reliability
If constant speaker connection monitoring is implemented for safety applications, then reliability is improved, but device complexity increases compared to startup-only detection
Solution Approach 1:
The patent designs the filter-based detection system to serve multiple functions: it continuously monitors speaker connection status, provides accurate detection during operation, and works with class D power amplifiers specifically. The same filter circuits and comparison logic are used throughout operation, eliminating the need for separate detection mechanisms and reducing overall system complexity despite continuous monitoring capabilities.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution accurately determines speaker connection or disconnection by eliminating high-frequency interference and signal delays, preventing erroneous determinations and ensuring stable speaker status detection during operation.
Implementation Method 1
a first filter configured to remove a high-frequency component of the sound input signal
Implementation Method 2
a second filter configured to remove a high-frequency component of the sound output signal
Implementation Method 3
a PWM generator that generates a pulse width modulation (PWM) signal for changing a duty ratio of a pulse according to an input signal level
Implementation Method 4
The low-pass filter 70 removes a high-frequency component from the PWM output signal S3 output from the power amplifier 60 to generate an analog sound signal S4 in an audible band
Data Source
AI summary
A sound output device of the present disclosure includes a controller, a power amplifier, a low-pass filter, and a speaker. The controller includes first and second low-pass filters configured to remove high-frequency components of a sound input signal and a sound output signal, a first peak detection unit configured to detect a peak current of the sound input signal from which the high-frequency component has been removed, a second peak detection unit configured to detect a peak current of the sound output signal from which the high-frequency component has been removed, and a comparison unit configured to compare the peak current with the peak current and determine connection or disconnection of the speaker when a level of the peak current is equal to or higher than a certain level.