Class-D Amplifier Current Sensing via Sample and Hold
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Solution Overview
Problem
Conventional current sensing methods for switching amplifiers, such as class-D amplifiers, face challenges in accurately measuring current due to common mode limitations and voltage swings, leading to potential speaker damage in devices like smartphones and laptops.
Innovation Solution
The implementation of a current sensing system that includes a current mirror circuit and a sample and hold circuit, which effectively senses the average current through a load during all phases of amplifier switching, providing accurate and stable current measurements to protect the speaker from damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current sensing methods are used in switching amplifiers, then the circuit structure is simple, but the current measurement precision is poor due to common mode limitations and voltage swings
Solution Approach 1:
The patent introduces an intermediary current sensing circuit that includes a current mirror circuit and a sample and hold circuit. This intermediary circuit buffers and conditions the current signal before measurement, isolating the measurement process from the high-voltage switching environment. The current mirror circuit creates a scaled replica of the load current, while the sample and hold circuit captures and holds the current value during switching transitions, enabling precise measurement without direct exposure to voltage swings and common mode noise.
2Reliability
If conventional current sensing is used, then the device complexity is low, but the reliability of speaker protection is poor
Solution Approach 1:
The patent implements preliminary action by continuously monitoring the current through the current mirror circuit before any damage can occur to the speaker. The sample and hold circuit captures current values at critical moments in the switching cycle, preparing the data for analysis. This preliminary detection and recording of current conditions enables the protection system to respond rapidly to overcurrent conditions, preventing speaker damage before it occurs rather than reacting after damage has happened.
3Reliability
If accurate current sensing is implemented, then speaker protection is improved, but the circuit complexity increases
Solution Approach 1:
The patent segments the current sensing function into distinct modular components: a current mirror circuit for current replication, a sample and hold circuit for signal capture, and a protection logic unit for decision-making. Each segment performs a specific function independently, allowing for optimized design of each component. The current mirror circuit handles the high-voltage switching environment, the sample and hold circuit processes the timing-critical signal capture, and the protection logic analyzes the data. This segmentation reduces overall complexity by making each component simpler and more specialized rather than requiring a single complex sensing element to perform all functions.
Data Source
AI summary
Systems and methods according to one or more embodiments are provided for sensing a current at an output of a switching amplifier. In one example, a system includes a first transistor switch coupled to a load configured to conduct a current in the load responsive to a first pulse width modulated control signal and a second transistor switch coupled to the load configured to conduct the current in the load responsive to a second pulse width modulated control signal. The system further includes a sample and hold circuit coupled between the load and a current sensing circuit configured to sample a voltage at the second transistor switch for a pre-determined sample time period in response to a midpoint of a second pulse width modulated control signal time period, and configured to provide the sampled voltage to the current sensing circuit.