Sigma-Delta ADC Gain Tracking for Dynamic Range Without Glitches
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Solution Overview
Problem
Sigma-Delta analog to digital converters face challenges in maintaining dynamic range due to the need for high gain for small input voltages and reduced gain for larger voltages to avoid saturation, leading to suboptimal gain adjustments and glitches in digital output signals.
Innovation Solution
A Sigma-Delta ADC design incorporating a gain tracker, a digital to analog converter (DAC), and a controller that adjusts gain based on the difference between the analog input and quantizer output, using a series arrangement of discrete-time integrator stages and a sinc filter to determine optimal gain values and reduce glitches by synchronizing gain updates with signal sampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high gain is applied for small input voltages, then sensitivity is improved, but saturation occurs for larger voltages
Solution Approach 1:
The patent implements a programmable gain amplifier with dynamically adjustable gain values. The gain can be switched between different levels (e.g., first gain value and second gain value) based on the input signal amplitude, allowing the system to adapt to varying signal conditions and avoid both saturation and insufficient sensitivity
Solution Approach 2:
The gain parameter of the amplifier is made variable through digital control. The controller adjusts the gain parameter based on detected signal levels, enabling the system to optimize measurement precision for small signals while preventing saturation for large signals by changing the gain parameter appropriately
2Adaptability or versatility
If programmable gain amplifier is used to vary gain, then dynamic range is improved, but glitches occur in digital output signals
Solution Approach 1:
The patent applies dithering noise to the input signal before amplification. This preliminary action randomizes the signal transitions, preventing abrupt gain switching that causes glitches. The dithering is applied continuously to ensure smooth gain transitions and eliminate spurious signals in the digital output
Solution Approach 2:
The patent introduces dithering noise as an intermediary element between the input signal and the gain adjustment mechanism. This intermediary signal smooths out the transitions during gain changes, acting as a buffer that prevents direct coupling of gain switching transients to the output, thereby eliminating glitches
3Reliability
If multiple ADC paths are used to avoid glitches, then signal quality is improved, but device complexity increases
Solution Approach 1:
The patent extracts and addresses the root cause of glitches (abrupt gain transitions) by applying dithering noise, rather than using multiple ADC paths. This approach maintains a single ADC path while eliminating the glitch problem through signal processing, thereby reducing device complexity compared to multi-path solutions
Data Source
AI summary
A Sigma-Delta analog to digital converter (ADC) is described. The Sigma-Delta ADC includes a series arrangement of a gain tracker, a first discrete-time integrator stage and a quantizer between an ADC input and an ADC output. The Sigma-Delta ADC includes a digital to analog converter (DAC) having a DAC input and a DAC output connected to the gain tracker. The Sigma-Delta analog to digital converter includes a controller having a control input connected to the quantizer output. The controller provides a digital input to the DAC input and provides a gain control signal to the gain tracker.