Sensor Signal Conditioning Circuit for Phase Shift Compensation
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Solution Overview
Problem
Analog front-end circuits for piezoresistive sensors coupled to resonant micro-mirrors face challenges in minimizing phase shifts due to temperature variations, leading to inaccurate sensing of resonance frequency changes, which existing solutions attempt to address with wide-bandwidth operational amplifiers or switched-capacitor architectures, resulting in increased power consumption, complexity, and residual phase shifts.
Innovation Solution
A circuit with a feedback loop that detects periodic signals at a higher frequency than the input signal, using a band-pass filter to adjust the cut-off frequency of the conditioning circuit block and a low-pass filter to filter out noise, allowing for phase shift compensation without additional components like NTC resistors, and a signal generator to superimpose a periodic signal for compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If wide-bandwidth operational amplifiers are used to minimize phase shifts, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent changes the operating parameters of the operational amplifier by dynamically adjusting its bandwidth according to the signal frequency being measured. The amplifier operates at minimum bandwidth necessary for the current signal, reducing power consumption while maintaining measurement precision. This is achieved through a control system that monitors signal frequency and adjusts the amplifier's bandwidth parameter accordingly.
Solution Approach 2:
The patent implements dynamic adjustment of the operational amplifier's bandwidth parameter based on real-time signal conditions. Instead of operating continuously at wide bandwidth, the system adapts the amplifier's characteristics to match the instantaneous signal frequency, enabling power savings during low-frequency operations while maintaining precision when high-frequency signals are present.
2Measurement precision
If switched-capacitor architectures are used to compensate phase shifts, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent employs a feedback mechanism where the output signal is monitored and used to adjust the operational amplifier's bandwidth parameter. This closed-loop control system automatically compensates for phase shifts by adjusting amplifier parameters based on the actual signal being measured, achieving precision without requiring complex switched-capacitor circuitry.
Solution Approach 2:
The patent replaces complex mechanical or circuit-based phase compensation mechanisms (such as switched-capacitor networks) with a control-theoretic approach using feedback and dynamic parameter adjustment. This substitution simplifies the overall device architecture while maintaining or improving phase shift compensation performance.
3Reliability
If additional components like NTC resistors are added for temperature compensation, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent implements self-service temperature compensation where the system uses its own operational parameters (signal frequency, amplifier bandwidth) to automatically adjust and compensate for temperature-induced phase shifts. The control system monitors temperature effects and adjusts amplifier parameters accordingly, eliminating the need for external NTC resistors or separate temperature compensation circuits.
Solution Approach 2:
The patent makes the operational amplifier serve multiple functions: signal amplification, phase shift compensation, and temperature compensation. By dynamically adjusting the amplifier's bandwidth parameter based on both signal frequency and temperature conditions, the single component performs what would traditionally require multiple specialized components, reducing overall device complexity.
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 approach reduces phase shifts and noise, enabling accurate sensing of resonance frequency changes with reduced silicon area and power consumption, and does not require temperature calibration, effectively addressing the limitations of existing solutions.
Implementation Method 1
a piezoresistive sensor associated to a MEMS micro-mirror... the piezoresistive sensor 10 comprises four piezoresistors R1, R2, R3, R4 in a full-bridge arrangement
Implementation Method 2
a band-pass filter configured to selectively detect a periodic signal at a second frequency, the second frequency higher than the first frequency
Implementation Method 3
a low-pass filter coupled at the converter output node of the analog-to-digital converter and having a low-pass cut-off frequency lower than the second frequency, the low-pass filter configured to filter out the periodic signal from the converted digital signal
Data Source
Figure 1~2B
Figure 3~4
Figure 5~6
AI summary
A circuit (12) for sensing an input analog signal generated by a sensor (10) at a first frequency and generating an output digital signal (ADC_out') indicative of the input analog signal sensed is described. The circuit (12) comprises: - a conditioning circuit block (121) configured for receiving at an input port (PZR_P, PZR N) the input analog signal and generating at an output port a conditioned analog signal, and - an analog-to-digital converter (122) configured for providing at a converter output node a converted digital signal (ADC_out) resulting from conversion to digital of the conditioned analog signal. The circuit further comprises: - a feedback circuit block (125) between the converter output node and a control input of the conditioning circuit block (121), the feedback circuit block (125) comprising a band-pass filter configured to selectively detect a periodic signal at a second frequency higher than the first frequency and being configured to act on the conditioning circuit block (121) to counter variations of the periodic signal at the second frequency, and - a low-pass filter (126) coupled at the converter output node having a low-pass cut-off frequency lower than the second frequency, the low-pass filter (126) configured to filter out the periodic signal from the converted digital signal (ADC_out) to generate the output digital signal (ADC_out').