Analog Sensing Circuit With Feedback Phase Compensation
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Solution Overview
Problem
Analog front-end (AFE) circuits in sensing systems, particularly those used with resonant micro-mirrors, face challenges in maintaining phase stability due to temperature variations, leading to phase drift and shifts in resonance frequency, which can impair accurate sensing and control.
Innovation Solution
A circuit architecture that includes a conditioning circuit, an ADC, a feedback circuit with a band-pass filter to detect and counter variations in periodic signals, and a low-pass filter to generate a digital output, which compensates for phase shifts without additional components like NTC resistors and avoids temperature calibration, using a reference periodic signal superimposed on the input signal to adjust the cut-off frequency and bias current of operational amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional AFE circuits are used without phase compensation, then device complexity and power consumption are lower, but phase drift occurs due to temperature variations affecting operational amplifier cut-off frequencies
Solution Approach 1:
The patent implements a feedback circuit that continuously monitors the phase of the input signal and adjusts the cut-off frequency of the operational amplifier accordingly. The feedback circuit compares the actual phase with the desired phase and generates a correction signal that modifies the bias current of the operational amplifier, thereby compensating for temperature-induced phase drift and maintaining phase stability.
Solution Approach 2:
The patent dynamically changes the cut-off frequency parameter of the operational amplifier based on temperature variations and signal characteristics. By adjusting the bias current and cut-off frequency in real-time, the circuit adapts to changing conditions and maintains optimal phase performance without requiring additional compensation components.
2Reliability
If NTC resistors are added for temperature compensation, then phase stability improves, but device complexity and silicon area increase
Solution Approach 1:
The operational amplifier circuit performs its own phase compensation by using its internal resources (bias current control) to counteract temperature effects. The feedback circuit utilizes the existing signal path and operational amplifier components to generate the necessary compensation, eliminating the need for external NTC resistors and reducing silicon area.
3Measurement precision
If temperature calibration is performed, then measurement precision improves, but ease of operation deteriorates due to calibration requirements
Solution Approach 1:
The patent performs preliminary phase compensation by pre-configuring the feedback circuit to automatically adjust the operational amplifier's cut-off frequency based on expected temperature variations. This preliminary action ensures that the circuit is always ready for accurate measurements without requiring manual calibration procedures before operation.
4Reliability
If the cut-off frequency of operational amplifiers is adjusted for phase compensation, then phase stability improves, but noise rejection performance may be affected
Solution Approach 1:
The patent dynamically adjusts the cut-off frequency of the operational amplifier based on the actual phase error detected by the feedback circuit, rather than using a fixed compensation value. This dynamic adjustment allows the circuit to optimize both phase stability and noise rejection by adapting the cut-off frequency to the specific operating conditions and signal characteristics.
Data Source
AI summary
A circuit configured to sense an input analog signal generated by a sensor at a first frequency and to generate an output digital signal indicative of the sensed input analog signal. The circuit includes a conditioning circuit, an ADC, a feedback circuit, and a low-pass filter. The conditioning circuit is configured to receive the input analog signal and to generate a conditioned analog signal. The ADC is configured to provide a converted digital signal based on the conditioned analog signal. The feedback circuit includes a band-pass filter configured to selectively detect a periodic signal at a second frequency higher than the first frequency and to act on the conditioning circuit to counter variations of the periodic signal at the second frequency. The low-pass filter is configured to filter out the periodic signal from the converted digital signal to generate the output digital signal.