Delta-Sigma Modulator Limiter for Higher-Order Stability
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Solution Overview
Problem
Higher-order delta-sigma modulators are generally unstable, and existing solutions like feedback steering do not effectively reduce instability, posing challenges for higher-order conversions.
Innovation Solution
Incorporating a limiter within the delta-sigma modulator to decouple instability between different loops, ensuring the stability of the modulator is proportional to the order of a secondary loop, typically second-order, by limiting input values to valid ranges for the quantizer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If higher-order delta-sigma modulators are used to increase conversion capability, then the order and capability of the modulator are improved, but instability increases significantly
Solution Approach 1:
The modulator is divided into multiple independent loops (first loop with higher order, second loop with lower order). Each loop can be analyzed and designed independently, allowing the higher-order loop to provide conversion capability while the lower-order loop ensures stability. The segmentation isolates instability sources to specific loops rather than the entire system.
Solution Approach 2:
A limiter is introduced as an intermediary component between the first and second loops. The limiter acts as a mediator that prevents instability propagation from the higher-order first loop to the lower-order second loop, while still allowing signal transmission. This intermediary component decouples the stability requirements of different loops.
2Reliability
If conventional feedback steering is used to address instability, then an alternative lower-order modulator is constructed, but the instability of the higher-order modulator is not reduced
Solution Approach 1:
Instead of constructing separate alternative modulators, the patent merges the higher-order and lower-order loops into a single integrated modulator structure. The limiter combines the functions of both loops, allowing them to operate simultaneously with the higher-order loop providing capability and the lower-order loop providing stability, eliminating the need for separate alternative structures.
3Productivity
If the order of the delta-sigma modulator is increased beyond second order, then higher conversion capability is achieved, but instability problems increase significantly
Solution Approach 1:
The conversion capability is segmented into the higher-order first loop while stability is assigned to the lower-order second loop. This segmentation allows the system to achieve high conversion performance without proportionally increasing overall instability, as each loop can be optimized independently for its specific function.
Solution Approach 2:
The system changes the order parameter of different loops differently - the first loop uses higher order for performance while the second loop maintains lower order for stability. The limiter enables this parameter differentiation, allowing each loop to operate at its optimal order without compromising the other loop's performance or stability characteristics.
Data Source
AI summary
The stability of a delta-sigma modulator may be improved by limiting a value within the delta-sigma modulator. For example, the value provided to a quantizer may be limited, by a limiter circuit in the delta-sigma modulator, to a value within a single step range of the quantizer. The limiter circuit may be placed in an inner loop of the delta-sigma modulator to decouple the stability of the inner loop from an outer loop. For example, a delta-sigma modulator may be constructed with an inner loop having a sixth order and an outer loop having a second order, in which the stability of the delta-sigma modulator is proportional to that of a second order.