Load Transistor Current Measurement Using Segmented Sensing
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Solution Overview
Problem
Current circuit arrangements face measurement errors when trying to measure low load currents due to voltage offsets between the load and measuring transistors, leading to inaccurate current sensing.
Innovation Solution
A circuit arrangement with two parallel load transistors and a measuring transistor, where a reverse-control circuit regulates the load transistors to maintain a consistent operating point, ensuring accurate current measurement by adjusting the control voltage and increasing the closing resistance to counteract offset effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single measuring transistor is used to measure load current, then the measurement is simple, but measurement error increases at low currents due to voltage offset
Solution Approach 1:
The patent divides the measuring transistor into two separate transistors (first measuring transistor and second measuring transistor) with different channel cross-sections. This segmentation allows each transistor to operate in an optimal range, preventing voltage offset from causing measurement errors at low currents while maintaining simplicity of the overall measurement approach.
Solution Approach 2:
Different measuring transistors are assigned different channel cross-sections tailored to specific current ranges. The first measuring transistor has a larger channel cross-section for measuring higher currents, while the second measuring transistor has a smaller channel cross-section for measuring lower currents. This local optimization of transistor characteristics resolves the measurement accuracy issue without complicating the circuit architecture.
2Measurement precision
If load current is high, then measurement accuracy is good, but the control voltage must be very much higher than offset which limits applicability
Solution Approach 1:
The measurement function is segmented across two transistors with different channel cross-sections, allowing the system to maintain measurement accuracy across a wide range of load currents rather than requiring high control voltages. Each transistor handles a specific current range optimally.
Solution Approach 2:
The patent changes the parameter of channel cross-section between the two measuring transistors. By selecting transistors with appropriately different channel cross-sections, the system can accurately measure both low and high currents without requiring the control voltage to be very much higher than the offset voltage, thus expanding adaptability across current ranges.
3Reliability
If voltage offset exists between load and measuring transistors, then the measuring current is not exactly proportional to load current, but the error is negligible at high currents
Solution Approach 1:
The patent applies local quality by using measuring transistors with channel cross-sections specifically matched to different current ranges. This ensures that the proportionality between measuring current and load current is maintained with high precision across the entire operating range, eliminating the need to accept negligible error as a compromise.
Solution Approach 2:
By changing the channel cross-section parameter of the measuring transistors to match different load current ranges, the system maintains exact proportionality between measuring and load currents even when voltage offset exists. This resolves the contradiction by making the measurement reliable and precise simultaneously across all current levels.
Data Source
AI summary
The measurement of a current through a load transistor is described.