Bidirectional Current Sense Circuit Using Segmented Transistors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current sensing in bidirectional battery currents requires external resistors, leading to small voltage drops and stringent ADC requirements, posing challenges in noise, offset, and dynamic range, and adding additional voltage drops, especially at high currents.
Innovation Solution
A method and circuit that sense bidirectional currents without external resistors by using power and sense transistors, control circuits, and an ADC to mirror and regulate current fractions, allowing voltage drop regulation and feedback measurement, eliminating the need for external resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an external resistor is used to sense bidirectional battery current, then the current can be transformed into a measurable voltage, but the voltage drop across the resistor becomes very small requiring high precision ADC with stringent noise and offset requirements
Solution Approach 1:
The patent segments the current sensing function by using separate sense transistors (first and second sense transistors) for bidirectional current sensing, with each transistor dedicated to one direction. This segmentation allows each transistor to be optimized for its specific function, improving measurement precision while reducing the complexity requirements for the ADC by providing larger, more manageable voltage signals for each sensing direction.
Solution Approach 2:
The patent introduces sense transistors as intermediary elements between the battery and the ADC. These sense transistors act as mediators that amplify the small voltage signals that would otherwise require high-precision ADCs. By using the sense transistors as intermediaries, the system achieves accurate current sensing with standard ADC specifications.
2Measurement precision
If an external resistor is used for current sensing, then current measurement is enabled, but additional voltage drop occurs especially at high currents
Solution Approach 1:
The patent changes the parameter of resistance by using transistors with dynamically controllable resistance instead of fixed external resistors. The sense transistors operate in their linear region with controlled gate voltages, allowing their effective resistance to be optimized for minimal voltage drop while maintaining sufficient voltage signal for accurate measurement. This parameter change enables the system to achieve current measurement capability with significantly reduced energy loss.
3Measurement precision
If sense transistors are used with identical active areas to power transistors, then the sensing capability is improved, but the voltage drop becomes too large
Solution Approach 1:
The patent applies local quality by making the active area of the sense transistors significantly smaller than the active area of the power transistors. This local differentiation allows the sense transistors to have higher resistance for better sensing capability in their specific location, while the power transistors maintain large active areas for low resistance and minimal voltage drop in their location. Each component has optimized local properties suited to its function.
Data Source
AI summary
Method and circuits for sensing a bidirectional current without requiring an external sense resistor are disclosed. In a preferred embodiment the invention is applied for fuel gauging of one or more batteries and comprises a charger/active diode, which can source current into the battery and sink current from the battery to supply a mobile electronic device. The invention can be applied to any other application requiring sensing of bidirectional currents. A regulated cascode forces a voltage drop over a power transistor and a sense transistor to be the same. A feedback current is measured by an ADC. The integration of these current measurements over time is equal to the actual charge of the battery.