Sigma-Delta Integrator Overload Recovery Without Noise Transfer Shift
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Solution Overview
Problem
Sigma-delta modulator based analog-to-digital converters (ADCs) suffer from overload instability, where input signals saturate the ADC, leading to oscillations and instability due to the failure of the feedback loop to remove extra charge from integrators, causing the output to oscillate forever.
Innovation Solution
A non-invasive overload detection and recovery mechanism is implemented, which includes overload detectors to identify consecutive cycles of overload conditions and bias generators to increase current from higher order DACs, allowing the system to recover from overload without altering the noise transfer function, thereby maintaining the signal transfer function and preventing high-frequency component leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the feedback loop is used to remove extra charge from integrators, then the quantization noise is shaped and filtered, but the system becomes unstable when input signals saturate the ADC
Solution Approach 1:
The patent applies preliminary action by detecting overload conditions before they cause sustained oscillations. The detection circuit monitors the ADC output and identifies when the input signal exceeds the ADC's dynamic range, triggering a recovery mechanism that resets the integrator states before the feedback loop can drive the system into unstable oscillation.
Solution Approach 2:
The patent enhances the existing feedback loop by adding an overload detection and recovery mechanism. The detection circuit provides feedback about the ADC input level, and when overload is detected, the recovery circuit adjusts the feedback current to remove extra charge from integrators, stabilizing the system while maintaining the noise-shaping function.
2Measurement precision
If the ADC operates at full dynamic range, then conversion precision is maximized, but overload conditions cause oscillations and instability
Solution Approach 1:
The patent implements beforehand cushioning by preparing a recovery mechanism that activates before overload damage occurs. The detection circuit continuously monitors ADC input levels and triggers the recovery circuit when overload is detected, cushioning against the harmful effects of saturation by rapidly resetting integrator states before sustained oscillations can develop.
Solution Approach 2:
The system performs self-service through automatic overload detection and recovery. The detection circuit autonomously identifies overload conditions, and the recovery circuit automatically adjusts feedback currents to remove extra charge from integrators without external intervention, allowing the ADC to self-correct and return to stable operation.
3Measurement precision
If higher order sigma-delta modulators are used, then noise shaping performance is improved, but overload instability increases
Solution Approach 1:
The patent applies local quality by targeting the specific integrators that become overloaded rather than uniformly affecting all integrators. The recovery circuit selectively adjusts feedback currents to the affected integrators based on overload detection, allowing higher order modulators to maintain their noise shaping performance while stabilizing only the problematic stages.
Solution Approach 2:
The patent uses parameter changes by dynamically adjusting feedback current levels in response to overload conditions. When overload is detected, the recovery circuit modifies the feedback current parameter to remove extra charge from integrators, allowing the system to transition from an unstable overloaded state back to stable operation while preserving the higher order noise shaping characteristics.
Data Source
AI summary
Described is an apparatus which comprises: a first integrator to receive an input signal and to generate a first output; a second integrator to receive the first output or a version of the first output and to generate a second output; and an analog-to-digital converter (ADC) to quantize the second output into a digital representation, the ADC including a detection circuit to detect an overload condition in the second output.