Current Sense Amplifier Offset Trimming for Low-Drift Detection
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Solution Overview
Problem
Current sense amplifiers face challenges in achieving high-speed, high-precision current detection with low power consumption, particularly due to nonlinear temperature dependence of ON resistance and the difficulty in accurately performing offset trimming, leading to temperature drift.
Innovation Solution
A current sense amplifier configuration that includes a preamplifier and a switch to detect voltage drops across a drive transistor, with an offset trimming mechanism to adjust the preamplifier's offset voltage, using transistors with similar temperature characteristics and adjustable resistors to minimize temperature dependence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current detection resistor is connected in series to the drive transistor, then current detection precision is improved, but power consumption increases
Solution Approach 1:
The patent extracts the current detection function from a separate series resistor and integrates it into the existing drive transistor by utilizing the transistor's ON resistance (Rdson). This eliminates the need for an additional current detection resistor, thereby avoiding the extra power consumption that would result from adding another series component while maintaining current detection capability.
Solution Approach 2:
The drive transistor is made to serve dual functions: both driving the load and detecting the current. By using the inherent ON resistance of the drive transistor for voltage drop measurement, the same component performs both power delivery and sensing functions, eliminating the need for dedicated detection hardware and reducing overall power consumption.
2Use of energy by moving object
If the ON resistance Rdson is used for current detection, then power consumption is reduced, but measurement precision deteriorates due to nonlinear temperature dependence
Solution Approach 1:
The patent implements offset trimming functionality that measures and compensates for temperature-dependent variations in the ON resistance. By continuously monitoring the offset voltage and adjusting the detection circuit accordingly, the system maintains accurate current measurements despite temperature-induced nonlinearities in the Rdson characteristic.
Solution Approach 2:
The patent changes the operating parameters of the detection circuit by introducing offset trimming that dynamically adjusts the measurement baseline. This allows the circuit to compensate for temperature-dependent parameter changes in the ON resistance, maintaining measurement precision across varying thermal conditions while continuing to use the Rdson for detection.
3Device complexity
If offset trimming is not performed accurately, then device complexity is reduced, but temperature drift increases
Solution Approach 1:
The patent performs offset trimming as a preliminary calibration step before normal operation. By pre-adjusting the offset voltage to account for temperature dependencies, the system establishes an accurate baseline that compensates for thermal drift during subsequent operation, maintaining stability without requiring complex real-time adjustment mechanisms.
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 enables precise current detection with reduced temperature drift by effectively trimming the offset voltage, ensuring accurate operation across varying temperatures.
Implementation Method 1
measures a voltage drop in a drive transistor to measure the current flowing through the drive transistor
Implementation Method 2
a switch, which connects the input end of a common mode voltage and the negative output
Data Source
AI summary
A current sense amplifier measures a voltage drop in a drive transistor LS to measure the current flowing through the drive transistor LS. The current sense amplifier includes a preamplifier pre-amp, to which a voltage across the drive transistor LS is inputted, and which obtains a positive output and a negative output corresponding to a voltage difference of the inputted voltage across the drive transistor; and a switch sw, which connects the input end of a common mode voltage vcm and the negative output, the common mode voltage vcm serving as the operation reference of the preamplifier pre-amp. A change of the positive output caused by turning on/off the switch sw can be detected.