Sigma-Delta RMS Converter With Difference-of-Squares Feedback
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Solution Overview
Problem
Existing RMS-to-DC converters are insensitive to the precise shape of the input signal and have limited dynamic range due to high sensitivity to DC offsets and quantization noise, which affects their accuracy and applicability in high-resolution applications.
Innovation Solution
A sigma-delta difference-of-squares RMS-to-DC converter system that combines analog signal multiplication and filtering with digital feedback to produce a digital output, employing oversampling techniques and chopper stabilization to reduce noise and offset errors, thereby extending the dynamic range and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional RMS-to-DC converters are used, then the conversion is insensitive to input signal shape, but the dynamic range is limited due to high sensitivity to DC offsets and quantization noise
Solution Approach 1:
The converter is divided into separate functional blocks: a squaring circuit that processes the input signal, a subtraction circuit that removes DC offsets, and a sigma-delta modulator that performs high-resolution conversion. This segmentation allows each block to optimize for its specific function, improving overall dynamic range while maintaining signal shape insensitivity.
Solution Approach 2:
A feedback path is introduced where the digital output is converted back to analog and subtracted from the squared input signal. This feedback mechanism continuously compensates for DC offsets and quantization errors, extending the dynamic range while preserving the insensitivity to input signal shape characteristics.
2Measurement precision
If high-resolution conversion is achieved through oversampling, then quantization noise is reduced, but the device complexity increases due to additional filtering and processing stages
Solution Approach 1:
A squaring circuit is introduced as an intermediary that transforms the input signal before processing. This squaring operation shifts the signal spectrum, allowing the subsequent sigma-delta modulator to achieve high-resolution conversion with reduced quantization noise without requiring excessive oversampling ratios or complex filtering stages.
Solution Approach 2:
The sigma-delta modulator changes the sampling parameter by operating at a higher oversampling ratio, which spreads quantization noise over a wider bandwidth. Combined with the squaring circuit's spectral transformation, this achieves high conversion resolution with manageable filtering requirements, balancing precision and complexity.
3Measurement precision
If DC offset sensitivity is reduced through calibration, then measurement accuracy improves, but the ease of operation decreases due to additional calibration steps
Solution Approach 1:
The feedback path enables the converter to automatically compensate for DC offsets during normal operation without requiring external calibration. The system self-corrects by continuously comparing the squared input signal with the feedback signal and adjusting accordingly, maintaining measurement accuracy while simplifying operation.
Solution Approach 2:
Automatic feedback-based DC offset compensation is implemented, where the digital output is converted to analog and subtracted from the input signal. This continuous self-adjustment mechanism eliminates the need for manual calibration steps, improving both measurement accuracy and ease of operation simultaneously.
Data Source
AI summary
A sigma-delta difference-of-squares RMS-to-DC converter and method for performing such a conversion in which a square of an analog feedback signal is combined differentially with a square of an analog input signal, thereby producing an analog product signal that includes at least one signal component corresponding to a difference between such signal squares. This analog product signal is filtered and digitized to produce a digital output signal to be available for use downstream in or with the host system, with such digital output signal also being converted to the analog feedback signal.