Current Sensing Circuit With Off-State Voltage Matching
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Solution Overview
Problem
Current detection circuits for solenoid drivers face challenges in accurately detecting currents due to differences in source-drain voltages between drive and sense transistors during off-states, leading to inaccurate current ratios and detection errors.
Innovation Solution
The proposed current detection circuit includes a first sense transistor, a first amplifier, a first voltage control transistor, and a switch, which ensures that the source-drain voltage of the sense transistor matches that of the drive transistor during off-states by short-circuiting the sources or drains, maintaining a constant current ratio and improving detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shunt resistor is used for current detection, then current detection accuracy is improved, but circuit size increases significantly
Solution Approach 1:
The patent uses a sense transistor as a copy of the drive transistor, replicating its structure and characteristics. The sense transistor mirrors the drive transistor's on-resistance and current-voltage relationships, allowing current detection without requiring a physical shunt resistor. This copying approach enables accurate current measurement while maintaining a compact circuit footprint suitable for integration on a single chip.
2Reliability
If the sense transistor is kept off during drive transistor off-state, then power consumption is reduced, but source-drain voltage mismatch causes detection errors
Solution Approach 1:
The patent applies equipotentiality by ensuring both the drive transistor and sense transistor experience identical source-drain voltages during their off-states. By turning off both transistors simultaneously and maintaining equal voltage conditions, the patent eliminates voltage mismatch between the transistors. This approach prevents detection errors caused by differential voltage effects while keeping both transistors in a low-power off state.
3Adaptability or versatility
If multiple solenoid drivers are mounted on one chip, then system integration is improved, but chip size becomes very large
Solution Approach 1:
The patent merges the current detection function with the drive transistor circuit by using the sense transistor as an integrated component rather than a separate shunt resistor. This merging allows multiple solenoid drivers to share common detection circuitry and power supply lines, significantly reducing the overall chip area required while maintaining the capability to monitor multiple drivers simultaneously.
Data Source
AI summary
The present invention provides a current detection circuit, semiconductor device, and a semiconductor system suitable for improving a current sensing accuracy. According to one embodiment, the current detection circuit 12 comprises a sense transistor Tr11 through which a first sense current proportional to the current flowing through the drive transistor MN1 flows, an operational amplifier AMP1 for amplifying the potential difference of the voltage of the external output terminal OUT and the source voltage of the sense transistor Tr11 for outputting the first sense current, a transistor Tr12 provided in series with the sense transistor Tr11 and to which the output voltage of the operational amplifier AMP1 is applied to the gate, and a switch SW3 provided between the external output terminal OUT and the source of the sense transistor Tr11 and turned on when the drive transistor MN1 is turned off.