Sigma-Delta Converter Input Level Control Using Digital AGC Feedback
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Solution Overview
Problem
Sigma-Delta converters face challenges in handling large dynamic ranges of input signals due to limited operating ranges, leading to instability and saturation, particularly with signals like OFDM, which result in the need for complex and power-consuming automatic gain control (AGC) systems both before and after the converter.
Innovation Solution
A method that generates a control signal from the digital domain output of the Sigma-Delta converter to monitor consecutive equal samples, allowing for precise adjustment of the input signal level by comparing this signal to a reference value and adjusting the gain of a variable gain amplifier upstream, ensuring the converter operates within its stable range without additional processing power or circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If complex automatic gain control systems are used before and after the converter, then the operating range is extended, but the power consumption and device complexity increase
Solution Approach 1:
The patent extracts the AGC function from external complex circuits and implements it within the Sigma-Delta converter itself. The control signal generation is integrated into the converter's digital domain, eliminating the need for separate AGC systems before and after the converter, thus reducing overall device complexity while maintaining extended operating range capability
Solution Approach 2:
The Sigma-Delta converter is designed to perform multiple functions: analog-to-digital conversion and automatic gain control. The same digital domain circuitry that processes the converted signal also generates the control signal for gain adjustment, making the converter a multi-functional device that reduces overall system complexity
2Adaptability or versatility
If complex automatic gain control systems are used before and after the converter, then the operating range is extended, but the power consumption increases
Solution Approach 1:
The patent eliminates power-hungry external AGC circuits by integrating the control signal generation directly into the Sigma-Delta converter's digital domain. This extraction of the AGC function from separate power-consuming circuits significantly reduces overall power consumption while maintaining the ability to handle large dynamic ranges
Solution Approach 2:
The Sigma-Delta converter performs its own automatic gain control by generating the control signal from its own digital domain output. This self-service capability eliminates the need for external AGC systems, thereby reducing power consumption while extending the operating range
3Measurement precision
If conventional Nyquist-rate converters with fine resolution quantizers are used, then the conversion accuracy is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent changes the quantizer resolution parameter from fine (8-16 bits) to coarse (1-5 bits) and compensates by using Sigma-Delta modulation with feedback. This parameter change reduces device complexity while maintaining conversion accuracy through the noise shaping and oversampling characteristics of the Sigma-Delta architecture
Solution Approach 2:
The patent introduces dynamic feedback control into the quantization process. The feedback loop dynamically adjusts the quantization error distribution, allowing a simple coarse quantizer to achieve the performance of complex fine-resolution converters. The system adapts continuously rather than relying on static high-resolution components
Data Source
AI summary
The invention relates to adjusting an input signal level of a Sigma-Delta converter. A control signal indicative of an input signal level to said Sigma-Delta converter is generated, and the input signal level to said Sigma-Delta converter is adjusted in dependence of said control signal. The control signal is generated as a signal indicating an operating condition of said Sigma-Delta converter. In this way, internal signals from the Sigma-Delta converter can be used to determine the state of the Sigma-Delta converter, i.e. whether it is operating within its operational input range or not, and whether it is close to the limits of the operational input range. This provides a simple, but accurate guidance of an automatic gain control upstream of the Sigma-Delta converter.