Speaker Current Sense Ground Switching for Negative Voltage Accuracy
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Solution Overview
Problem
Negative voltages on speaker nodes complicate the measurement of speaker current, leading to accuracy, linearity, and harmonic distortion issues due to leakage currents in switches connected to sense nodes in systems that measure speaker temperature and excursion.
Innovation Solution
A circuit design incorporating high side and low side transistors, sense resistors, and switch networks that selectively provide either the ground node or sense node potential as a ground potential to switch networks, coupled with an analog-to-digital converter, to accurately measure speaker current despite negative voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If switches are connected to sense nodes to measure speaker current, then current measurement capability is enabled, but leakage current occurs due to negative voltages causing accuracy and linearity problems
Solution Approach 1:
The patent implements dynamic ground switching where the ground reference for the sense amplifier is selectively changed based on the voltage polarity at the sense node. When negative voltage is detected at the sense node, the ground reference is switched to follow this negative potential, preventing leakage current and maintaining measurement accuracy throughout the full voltage range
Solution Approach 2:
The patent introduces an intermediate ground switching mechanism that mediates between the negative voltage conditions and the sense amplifier. By using additional switches and ground references as intermediaries, the system adapts to negative voltage conditions without allowing leakage current to corrupt the measurement
2Adaptability or versatility
If Class-D amplifier operates in recycle mode with negative voltage on output terminal, then amplifier functionality is maintained, but speaker node experiences negative voltage causing switch leakage
Solution Approach 1:
The ground reference for the sense amplifier is made dynamic rather than fixed, automatically adjusting to follow the voltage potential at the sense node. This dynamic adaptation allows the system to maintain proper switching operation whether the sense node is at positive, negative, or zero voltage during recycle mode
Solution Approach 2:
The patent changes the operating parameter of the sense amplifier's ground reference from a fixed potential to a variable potential that tracks with the sense node voltage. This parameter change enables the amplifier to operate correctly through the full voltage range including negative voltages during recycle mode
3Device complexity
If fixed ground reference is used for sense amplifier, then circuit design is simplified, but measurement accuracy deteriorates under negative voltage conditions
Solution Approach 1:
The sense amplifier's ground reference is transformed from a static connection to a dynamically switchable connection that adapts to voltage conditions. This dynamic approach increases circuit complexity but is necessary to maintain measurement precision across all operating conditions including negative voltages
Data Source
AI summary
A circuit includes a pair of high side transistors, a pair of low side transistors, a first sense resistor coupled to one of the low side transistors at a first sense node, and a second sense resistor coupled to another of the low side transistors at a second sense node. The first and second sense resistors couple together at a ground node. The circuit includes a first switch network coupled to the first sense resistor, a second switch network coupled to the second sense resistor, a first pair of switches configured to selectively provide a potential of the ground node or a potential of the first sense node as a ground potential to the first switch network, and a second pair of switches configured to selectively provide the potential of the ground node or a potential of the second sense node as a ground potential to the second switch network.