Oversampling SAR ADC Noise Shaping With Passive Residue Feedback
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Solution Overview
Problem
Successive approximation register (SAR) analog-to-digital converters (ADCs) face challenges in achieving higher-order noise shaping without increasing power consumption and chip area, as existing noise-shaping methods rely on active operational transconductance amplifiers and are limited to first-order noise shaping.
Innovation Solution
The implementation of a power-efficient oversampling SAR ADC system that filters quantization error on a cycle-by-cycle basis using active or passive filters, with a Sampled Analog Technology (SAT) passive filter technique, allowing for the feedback of filtered errors and decimation to achieve higher-order noise shaping without additional power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If active operational transconductance amplifiers are used for noise shaping, then noise shaping capability is improved, but power consumption increases
Solution Approach 1:
The patent extracts the noise shaping function from active amplifiers and implements it using passive RC circuits. The noise shaping capability is achieved by filtering quantization noise in the feedback path using passive components, eliminating the need for power-consuming active operational transconductance amplifiers while maintaining the essential noise shaping functionality.
Solution Approach 2:
The patent replaces expensive, power-consuming active amplifiers with inexpensive passive RC circuits. The passive filter components (resistors and capacitors) consume negligible power compared to active amplifiers, providing a cost-effective and power-efficient solution for noise shaping in SAR ADCs.
2Measurement precision
If active operational transconductance amplifiers are used for noise shaping, then noise shaping capability is improved, but chip area increases
Solution Approach 1:
The patent removes the bulky active amplifier circuits from the noise shaping implementation and replaces them with compact passive RC filters. This extraction of the active component eliminates the large area requirement while preserving the noise shaping function through passive filtering in the feedback path.
Solution Approach 2:
The patent substitutes area-intensive active amplifiers with minimal-area passive RC components. The resistors and capacitors required for noise shaping occupy significantly less chip area compared to operational transconductance amplifiers, enabling area-efficient high-resolution SAR ADC design.
3Measurement precision
If higher-order noise shaping is implemented using conventional methods, then noise reduction is improved, but device complexity increases
Solution Approach 1:
The patent segments the noise shaping function into separate passive RC filter stages, where each stage contributes to the overall noise transfer function. This segmentation allows higher-order noise shaping to be achieved by cascading multiple simple passive filter sections, avoiding the complexity of high-order active filters while maintaining effective noise reduction.
Solution Approach 2:
The patent employs periodic switching of the DAC during the conversion cycle to generate the quantization noise that is then shaped by the passive filters. This periodic action inherent in the SAR ADC operation works in conjunction with the passive filtering to achieve higher-order noise shaping without requiring complex active circuitry.
Data Source
AI summary
Systems and methods are disclosed for a noise-shaping successive approximation register (SAR) analog-to-digital-converter (ADC) using Sampled Analog Technology (SAT) filter techniques for filter construction. A SAR ADC includes an SAR for receiving an analog input signal and outputting a digital decision, a digital-to-analog converter and logic circuitry for converting the digital decision of the SAR to a present analog residue for a present conversion cycle, a filter for processing a previous analog residue from a previous conversion cycle, and for feeding a processed previous analog residue back to the SAR, a summer for summing the processed previous analog residue from the filter and the present analog residue, and generating a summer output, and a comparator for comparing the summer output and a first reference signal and generating a comparator output. The filter includes a capacitor array for filtering the previous analog residue to generate the processed previous analog residue.