Multi-Feedback ΣΔ RMS-to-DC Converter for Stable Wide Dynamic Range
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Solution Overview
Problem
Sigma-delta modulators used for converting root-mean-square (RMS) signal values to direct current (DC) signals face instability issues due to quantization error, especially when dealing with high input power levels, which limits their dynamic range and accuracy in applications like mobile communication equipment.
Innovation Solution
The implementation of multiple feedback paths, including lowpass filtered and constant gain feedback paths, lowpass and highpass filtered paths, or multiple lowpass filtered paths, combined with additional feedforward or feedback paths, stabilizes the sigma-delta closed-loop behavior and minimizes the RMS level of the quantization error, thereby extending the input-referred dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single feedback path is used in the sigma-delta RMS-to-DC converter, then the circuit structure is simple, but the system becomes unstable due to quantization error, especially at high input power levels
Solution Approach 1:
The feedback path is segmented into multiple parallel paths with different transfer functions. The first feedback path has transfer function H1(s) and the second feedback path has transfer function H2(s), where each path processes the quantization error differently. This segmentation allows the system to maintain stability by distributing the feedback control across multiple paths rather than relying on a single path that would require complex compensation.
Solution Approach 2:
The patent introduces an intermediary feedback mechanism where the quantization error is fed back through multiple paths with different characteristics. These feedback paths act as intermediaries that shape the quantization noise spectrum and provide stable closed-loop operation. The multiple feedback paths mediate between the quantization error and the integrator, preventing instability without requiring complex pole-zero compensation.
2Measurement precision
If filtering is applied in the feedback path to reduce quantization error, then the dynamic range is extended, but the circuit complexity increases
Solution Approach 1:
The patent changes the parameters of the feedback paths by assigning different transfer functions H1(s) and H2(s) to the two feedback paths. This parameter differentiation allows each path to contribute differently to the overall feedback control, achieving quantization error reduction and dynamic range extension without requiring complex high-order filtering in a single path. The parameter variation across parallel paths simplifies the overall filter structure.
3Reliability
If multiple feedback paths with different transfer functions are implemented, then system stability is improved and dynamic range is extended, but the device complexity increases
Solution Approach 1:
The multiple feedback paths serve multiple functions simultaneously: they provide stable closed-loop operation, shape the quantization noise spectrum, extend the dynamic range, and reduce systematic errors. By making the feedback system multi-functional through parallel paths with different transfer functions H1(s) and H2(s), the patent achieves comprehensive performance improvement without requiring separate complex compensation circuits for each function.
Data Source
AI summary
Architectures of ΣΔ difference-of-squares RMS-to-digital converters employing multiple feedback paths. Additional feedback paths enable a stable ΣΔ closed-loop behavior in different topologies where the RMS level of the quantization error processed by the squaring non-linearity is minimized. Such feedback paths include lowpass filtered and constant gain feedback paths, lowpass and highpass filtered paths or multiple lowpass filtered paths. These can be combined with multiple integrators in the forward path, with frequency compensation provided by additional feedforward or feedback paths. Electronic configurability can further extend the total input referred dynamic range (DR) of such architectures.