Four-Block Sense Amplifier for Accurate H-Bridge Current Sensing
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Solution Overview
Problem
Current sense amplifier circuits for class-D audio amplifiers face challenges in accurately measuring load current with high linearity and common-mode rejection, especially in high-power automotive and consumer applications, where the power FETs are connected with bondwires to ensure uniform current density, making it impractical to route all current through a single sense resistor.
Innovation Solution
A sense amplifier circuit comprising four amplification blocks with specific transistor configurations and bias voltage sources, connected in a Bridge-Tied-Load configuration, allows for the combination of four-quadrant signals into a single differential voltage signal, enabling accurate current sensing by using sense resistors in series with low-side power FETs and high-side power FETs, and employing cascode transistors and diodes to manage high common-mode swings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sense resistors are placed in series with power FETs to measure load current, then current sensing accuracy is improved, but device complexity increases due to multiple sense resistors and amplification blocks
Solution Approach 1:
The current sensing function is segmented into four separate amplification blocks, each handling a specific quadrant of the H-bridge output. Each block contains a sense resistor and amplification circuitry, allowing independent measurement of current in each quadrant. This segmentation enables accurate current sensing across the full operating range while maintaining modular design simplicity.
Solution Approach 2:
The four separate current measurements from the H-bridge quadrants are merged into a single differential voltage signal through the sense amplifier circuit. The amplification blocks combine their outputs to produce a unified current representation that can be processed by subsequent circuitry, reducing the number of signals that need to be handled independently.
2Stability of the object's composition
If bondwires are used to connect power FETs for uniform current density, then current distribution is improved, but current sensing becomes more difficult as current cannot be routed through a single sense resistor
Solution Approach 1:
The current measurement is segmented into four separate measurements, one for each quadrant of the H-bridge. Each amplification block measures the current through its associated power FET independently, accommodating the bondwire connection topology that distributes current across multiple paths. This segmentation makes current sensing feasible despite the inability to use a single series sense resistor.
Solution Approach 2:
Each amplification block is designed with local sense resistors positioned to measure current in its specific quadrant. This local measurement approach allows accurate current sensing in each region while maintaining the overall uniform current distribution provided by the bondwire connections. Each block has optimized local characteristics for its specific measurement task.
Data Source
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AI summary
A sense amplifier circuit comprising a first-, second-, third- and fourth-amplification-blocks, each amplification-block comprising: an amplification-block-transistor comprising and an amplification-block-resistor. The amplification-block-transistor includes: a first-conduction-channel-terminal, a second-conduction-channel-terminal that is connected to an amplification-block-output-node, and a control-terminal that is connected to an amplification-block-control-node. The sense amplifier circuit also comprises: an amplification-block-resistor connected in series between an amplification-block-input-node and the first-conduction-channel-terminal; a first-bias-voltage-source connected to the amplification-block-control-nodes of the first- and third-amplification-blocks, a second-bias-voltage-source connected to the amplification-block-control-nodes of the second- and fourth-amplification-blocks. The sense amplifier circuit also comprises: a first-common-mode-voltage-resistor connected in series between a first-sensed-output-terminal and a common-mode-voltage-node; and a second-common-mode-voltage-resistor connected in series between a second- sensed-output-terminal and the common-mode-voltage-node.