SAR-ADC Nonlinear Feedback for Wide-Dynamic-Range RMS Conversion
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Solution Overview
Problem
Existing analog-to-digital conversion techniques for determining the root mean square (RMS) value of an analog alternating current (AC) signal over a wide dynamic range are prone to inaccuracies due to dependencies on process tolerances, temperature, and supply voltage, especially when using logarithmic amplification, which corrupts the output signal and reduces accuracy.
Innovation Solution
A circuit comprising a successive-approximate analog-to-digital converter (SAR-ADC) with a feedback branch that translates a digital signal using a predetermined function, converting it into an analog feedback signal to compare with the input signal, allowing for precise and reliable conversion of signals with a large dynamic range, including those with non-linear characteristics, thereby reducing dependencies on external influences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If logarithmic amplification is used in the analog domain to determine RMS value, then the dynamic range is improved, but the accuracy deteriorates due to dependence on process tolerances, temperature, and supply voltage
Solution Approach 1:
The patent replaces the analog logarithmic amplifier with a digital logarithmic function implementation. The SAR-ADC converter converts the analog input signal to digital values, and then a digital signal processor calculates the logarithm of these values. This substitution eliminates the temperature and process tolerance dependencies inherent in analog logarithmic amplifiers while maintaining the ability to handle wide dynamic ranges, thereby resolving the contradiction between improved adaptability and worsened accuracy.
2Device complexity
If conventional SAR-ADC with linear characteristic is used, then the circuit complexity is reduced, but the sensitivity in lower power regions is insufficient for signals with large dynamic range
Solution Approach 1:
The patent applies parameter changes by implementing a non-linear transfer characteristic in the SAR-ADC converter. Specifically, the converter uses different gain factors for different input signal ranges: a first gain factor for lower power regions and a second, lower gain factor for higher power regions. This allows the converter to maintain high sensitivity in lower power regions while still handling large dynamic ranges, without significantly increasing circuit complexity beyond the basic SAR-ADC structure.
Data Source
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AI summary
A circuit (100) includes a successive-approximate analog-to-digital converter (110), which includes a feedback branch (120) and is operated, for example, according to the weighing method. The feedback branch (120) is set up to translate a digital signal (184) according to a predetermined function (170) and to further convert the translated digital signal (184) into an analog feedback signal (186). For example, the predetermined function (170) can be an exponential function. In this way it may be possible to convert an input signal (182) into an output signal (187) by means of a non-linear characteristic (800).