Sensor Device Offset Adjustment via Voltage Divider Circuit
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Solution Overview
Problem
Existing sensor devices with bridge circuits face challenges in maintaining a stable offset adjustment range due to manufacturing variations and temperature fluctuations, leading to inconsistent output sensitivity and temperature characteristics between sensor elements and resistors.
Innovation Solution
A sensor device is designed with a constant voltage circuit that includes a variable resistance element, differential amplifier, and error amplifier to maintain a constant voltage between nodes in the voltage dividing circuit, ensuring a stable offset adjustment range and uniform temperature coefficients across impedance elements, thereby minimizing the impact of manufacturing variations and temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resistor for offset adjustment is formed in an IC, then the offset voltage can be adjusted, but the adjustment range varies for each manufacturing lot due to resistance value variation
Solution Approach 1:
The patent changes the parameter being adjusted from resistance value to voltage value. Instead of using a variable resistor whose resistance varies with manufacturing, the invention uses a voltage divider circuit where the output voltage can be precisely controlled by the ratio of two resistors. This voltage ratio can be accurately set during manufacturing and remains consistent across different manufacturing lots, resolving the reliability issue while maintaining adjustability.
2Measurement precision
If a variable resistor is used for offset adjustment, then the offset voltage can be tuned, but the output sensitivity of the bridge circuit varies due to resistor variation
Solution Approach 1:
The invention changes the adjustment parameter from resistance to voltage. The voltage divider circuit allows independent control of the offset adjustment voltage without affecting the bridge circuit's output sensitivity. The sensitivity is determined by the bridge circuit's resistor ratios, while the offset is controlled by the voltage divider's output voltage, separating these two functions and eliminating the coupling problem.
3Measurement precision
If a resistor for adjustment is used, then offset voltage can be corrected at a certain temperature, but fluctuation of offset voltage occurs according to temperature change due to different temperature characteristics
Solution Approach 1:
The patent changes from resistance-based adjustment to voltage-based adjustment. The voltage divider circuit outputs a voltage that can be designed with temperature characteristics matching the sensor element. By controlling the voltage ratio rather than resistance, the system can compensate for temperature effects more effectively, as the voltage can be stabilized or temperature-compensated independently of the sensor's temperature drift.
4Adaptability or versatility
If manufacturing variation is present in resistor values, then the adjustment range of offset voltage varies greatly, but a constant adjustment range is desired for consistent performance
Solution Approach 1:
The invention transitions from adjusting offset via resistance value changes to adjusting offset via voltage value changes. The voltage divider circuit's output voltage depends on the ratio of two resistors, which can be precisely controlled during manufacturing. This voltage ratio approach provides a consistent adjustment range across different manufacturing lots, as the absolute resistance values less critically affect the performance compared to their ratio, thereby improving reliability while maintaining adaptability.
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
This configuration maintains a consistent adjustment range for the offset voltage, reduces temperature-induced fluctuations, and ensures high accuracy in detecting physical quantities across a wide temperature range without affecting sensitivity.
Implementation Method 1
a voltage dividing circuit 21 for dividing voltage between nodes N3 and N4 at both ends in the intermediate pathway
Implementation Method 2
a constant voltage circuit 22 for keeping voltage Vn between the nodes N3 and N4 constant
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
Provided is a sensor device in which it is possible to suppress variation in an offset adjustment range of a bridge circuit due to the influence of manufacturing variation or the like. Voltage (Vn) between nodes (N3, N4) at both ends in a voltage dividing circuit (21) is kept constant. Therefore, even if manufacturing variation is present in the impedance of four impedance elements (Z1 to Z4), the range of change of voltage (Von) of an output node (N5) due to adjustment of the voltage dividing ratio of the voltage dividing circuit (21) becomes substantially constant. In this way, also with respect to output voltage (Vo) (the voltage between an intermediate node (N6) and the output node (N5)) of the bridge circuit (10), the range of change due to the adjustment of the voltage dividing ratio becomes substantially constant. Accordingly, it becomes possible to keep the adjustment range of the offset of the output voltage (Vo) constant without being affected by manufacturing variation in the impedance of the impedance elements (Z1 to Z4).