Half-Bridge Differential Sensor Circuit With Feedback Current Control
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Solution Overview
Problem
Half-bridge circuits used in sensors for monitoring stimuli like pressure and acceleration face challenges in achieving optimal driving and signal read-out, particularly in obtaining a differential output signal that meets noise, power supply rejection ratio (PSRR), and electromagnetic compatibility (EMC) performance requirements, while also being sensitive to temperature changes and lifetime stability of the supply voltage.
Innovation Solution
A half-bridge signal processing circuit with two branches, each comprising a stimulus-responsive sense element and a current source, generating differential output signals, and incorporating a feedback control unit to adjust current sources based on common mode voltage, allowing for robust noise reduction and temperature compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a half-bridge circuit is used instead of a full-bridge circuit, then cost and physical dimensions are reduced, but the ability to achieve optimal differential output signal performance is compromised
Solution Approach 1:
The circuit is divided into two independent branches, each with its own current source and sense element. This segmentation allows each branch to be optimized independently while maintaining overall differential output performance, resolving the contradiction between using a simpler half-bridge structure and achieving full-bridge level signal performance.
Solution Approach 2:
The patent changes the driving parameter from voltage-based to current-based excitation. By using current sources instead of voltage sources and resistor dividers, the circuit achieves better noise performance, PSRR, and EMC while maintaining the half-bridge structure's cost and size advantages.
2Device complexity
If voltage source driving with resistor division is used to form differential output, then circuit complexity is reduced, but noise performance, PSRR, and EMC are degraded
Solution Approach 1:
The patent implements feedback control through adaptive current sources that monitor and adjust the excitation current based on sensor output. This feedback mechanism optimizes the signal-to-noise ratio and improves PSRR and EMC performance while maintaining manageable circuit complexity through intelligent control.
Solution Approach 2:
The patent replaces the mechanical/voltage-based resistor division network with an electronic current source system. This substitution eliminates the harmful effects of resistor thermal noise and improves PSRR by using active current regulation instead of passive voltage division.
3Reliability
If buffering is used to obtain K*Vsupply through resistor division, then offset and life time stability are improved, but the buffer's offset and life time stability limit the overall sensor signal processing performance
Solution Approach 1:
The patent extracts and eliminates the buffering stage entirely by using direct current source excitation. This removes the buffer's offset and stability limitations from the signal path while maintaining the ability to provide stable excitation through the current sources, reducing overall circuit complexity.
4Reliability
If supply voltage changes occur over lifetime, then the output differential voltage magnitude is affected, but using adaptive current sources adds circuit complexity
Solution Approach 1:
The patent uses feedback control in the adaptive current sources to compensate for supply voltage drift over lifetime. The current sources are regulated to maintain constant excitation current despite voltage changes, ensuring stable differential output voltage magnitude without requiring complex external compensation circuits.
Solution Approach 2:
The adaptive current sources are designed to self-regulate and compensate for supply voltage changes automatically. This self-service capability maintains output stability without requiring complex external control systems, balancing reliability improvement with acceptable circuit complexity.
Data Source
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AI summary
The present invention relates to a half-bridge signal processing circuit comprising a first and a second branch. The first branch comprises a first stimulus responsive sense element (Rpos) and a first current source (Isupply1) arranged to provide a current to the first sense element. The second branch comprises a second stimulus responsive sense element (Rneg) and a second current source (Isupply2) arranged to provide a current to said second sense element. The first and the second branch have a terminal (10) in common. The first branch comprises a first node between said the current source and the first stimulus responsive sense element configured to generate a first signal (Vp) related to a voltage over the first sense element. The second branch comprises a second node between the second current source and the second stimulus responsive sense element configured to generate a second signal (Vm) related to a voltage over the second sense element. A differential output voltage signal (Vdiff) is obtained from the difference between the first and said second signal. The differential output voltage signal (Vdiff) can next be used to determine the ratio of Vdiff to a sensor common mode output voltage Vcm.