Resistive Sensor Frontend With Switched Offset Voltage for Linear Gain
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Solution Overview
Problem
Current sigma-delta converters for resistive sensors face challenges in achieving a linear transfer function, especially with current input systems, which are sensitive to mismatched reference voltages and require significant resources for accurate matching, and often result in non-linear output due to pulsating currents, particularly problematic for magnetic sensors like AMR.
Innovation Solution
A resistive sensor frontend system with a current input sigma-delta converter that uses a switched offset voltage to tune the gain and improve robustness against non-linearity, featuring a resistive sensor and offset voltage source coupled to provide an input current at a first node connected to an integrator, with a quantizer and decimator to control the offset voltage source for scalable gain and linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a current input sigma-delta converter is used for resistive sensors, then the input voltage range requirement is reduced, but the system transfer function becomes non-linear due to the inverse proportionality between current and resistance
Solution Approach 1:
The patent introduces an offset voltage source as an intermediary element coupled in parallel with the resistive sensor. This offset voltage creates an additional current path that compensates for the non-linearity introduced by the inverse proportionality between sensor current and resistance. The offset current acts as a mediator that linearizes the overall transfer function while maintaining the benefits of current input operation.
2Manufacturing precision
If a direct digital converter (RDC) structure is used to achieve linear transfer function, then linearity is improved, but the output amplitude becomes very small when resistance change is limited to a few percent
Solution Approach 1:
The patent employs a feedback mechanism where the quantizer output is fed back to control the offset voltage source. This self-service approach allows the system to automatically adjust the offset voltage to optimize both linearity and output amplitude. The feedback loop enables the system to maintain linear transfer function while maximizing the useful output signal amplitude based on the actual sensor resistance changes.
3Manufacturing precision
If accurate matching of reference voltages is implemented to improve system linearity, then transfer function linearity is improved, but significant resources are required
Solution Approach 1:
The patent replaces the mechanical/approach of accurately matching multiple reference voltages with an electronic feedback control system. Instead of relying on precise voltage reference matching, the system uses a feedback loop that dynamically adjusts the offset voltage source based on the quantizer output. This substitution reduces the resource requirements for voltage reference matching while maintaining or improving linearity.
4Stability of the object's composition
If a large integrator capacitor is used to limit the output swing of the integrator for pulsating current, then the integrator output stability is improved, but the capacitor occupies significant space in integrated circuit
Solution Approach 1:
The patent changes the parameters of the current input system by introducing an offset voltage source that modifies the current waveform characteristics. By adjusting the offset voltage, the system can reduce the amplitude of pulsating current components while maintaining the average current level. This parameter change allows for a smaller integrator capacitor to achieve the same output stability, thereby reducing the capacitor area in the integrated circuit.
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 system achieves scalable gain and good linearity, reducing the impact of mismatched reference voltages and minimizing the need for large integrator capacitors, thus optimizing resource usage and reducing space requirements in integrated circuits.
Implementation Method 1
One type of resistive sensor uses anisotropic magnetoresistance (AMR) to measure magnetic field strength and/or direction. Anisotropic magnetoresistance sensors are sensitive to both the direction and the strength of the magnetic field.
Data Source
AI summary
A resistive sensor includes a current input sigma-delta converter that uses a switched offset voltage source to provide scalable gain and more linear operation. The sigma-delta converter includes an integrator, a quantizer, and a decimator. In one embodiment, the resistive sensor and offset voltage source are coupled to provide an input current at a first node. The integrator has a first input terminal coupled to the first node, and an output terminal. The quantizer has a first input terminal coupled to the output terminal of the integrator, a second input terminal for receiving a clock signal, and an output terminal coupled to provide a feedback signal to control the offset voltage source. The decimator has an input terminal coupled to the output terminal of the quantizer, and an output terminal for providing an output signal. The switched offset voltage source provides scalable gain and good linearity.