Inductive Sensor Interface Circuit With Ripple-Reduction Feedback
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Solution Overview
Problem
Existing inductive interface ICs face challenges with high-frequency sinusoidal demodulation due to limitations in generating in-phase signals and high slew-rate requirements, leading to non-linearity errors and excessive filtering delays, which are not acceptable in many applications.
Innovation Solution
The introduction of an amplifier circuit with a ripple reduction feedback loop that extracts and filters out undesired frequency components, allowing for highly linear amplification and operation at higher frequencies without significant delay or SNR degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If square-wave demodulation is used at high carrier frequencies, then demodulation efficiency is improved, but significant high-frequency residual signals are generated causing slew-rate requirements to become excessively high
Solution Approach 1:
The patent extracts the harmful high-frequency residual signal (at 2*fCARRIER) from the demodulated signal using a dedicated filter in the ripple reduction loop, separating it from the useful baseband signal to prevent slew-rate related linearity errors
Solution Approach 2:
The patent implements a ripple reduction feedback loop that continuously monitors the output signal, filters out residual ripple components, and feeds the cleaned signal back to the summing node, thereby maintaining signal linearity while enabling high-frequency operation
2Measurement precision
If heavy filtering is applied before amplification to reduce residue, then signal quality is improved, but excessive delay is introduced which degrades system performance
Solution Approach 1:
The patent performs preliminary filtering of the high-frequency residual signal immediately after demodulation, before the main amplification stage, using a targeted filter that removes only the specific 2*fCARRIER component without requiring heavy broad-spectrum filtering that would introduce excessive delay
Solution Approach 2:
The patent applies filtering with local quality by designing a filter specifically targeted at the known residual frequency (2*fCARRIER) rather than using heavy general-purpose filtering, thereby achieving signal cleaning with minimal delay
3Ease of operation
If sinusoidal demodulation is used with on-chip signal generation, then demodulation is achieved, but generating in-phase high-resolution sinusoidal signals at high frequencies becomes problematic
Solution Approach 1:
The patent replaces complex on-chip sinusoidal signal generation circuits with externally provided square-wave demodulation signals, eliminating the need for complex high-frequency sinusoidal oscillators and phase synchronization circuits while achieving effective demodulation
4Measurement precision
If linear multipliers (Gilbert cells) are used for demodulation, then demodulation accuracy is improved, but input dynamic range becomes limited compared to requirements
Solution Approach 1:
The patent replaces limited-dynamic-range linear multipliers (Gilbert cells) with square-wave demodulation using simple switching elements that can handle large input signal variations, thereby achieving both high input dynamic range and adequate demodulation accuracy
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
Enables operation at frequencies up to 10 times higher than existing ICs, reducing area and cost of LC tanks, and introducing negligible delay while maintaining system linearity and SNR, thus addressing the limitations of prior art.
Implementation Method 1
The pick-up coil typically converts the magnetic field-which may be carrying information, e.g., associated with a position of the target-into an electrical signal
Implementation Method 2
the production of eddy currents in the target. As is known, the production of eddy currents, and resultant magnetic-field reflection, becomes more pronounced at higher frequencies
Data Source
AI summary
An amplifier circuits inductive/magnetic sensor interface can include a main signal path including one or more amplifiers configured to receive an input signal and to produce an output signal based on the input signal. The input signal may include a square-wave demodulated signal having an associated modulation frequency and an undesired frequency component at twice the modulation frequency of the square-wave demodulated signal. The amplifier circuit may include a gain feedback loop configured to set a gain of the amplifier circuit. The amplifier circuit may include a ripple reduction feedback loop configured to receive an intermediate signal on the main signal path and extract the undesired frequency component of the intermediate signal to produce a filtered version of the intermediate signal and provide the filtered version of the intermediate signal to the main signal path.