Noise-Shaping SAR ADC Using Digital DSM Residual Feedback
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Solution Overview
Problem
Conventional noise-shaping SAR ADCs face issues with high current consumption and area usage due to active circuits, while passive approaches compromise delta-sigma modulation performance.
Innovation Solution
A noise-shaping SAR ADC design incorporating a digital delta-sigma modulator (DSM) with multiple feedback DACs, where quantization errors are digitized and modulated in the digital domain, allowing for reduced current consumption and compact size without the need for active circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If active circuits like operational amplifiers are used for delta-sigma modulation, then modulation performance is improved, but current consumption and area increase
Solution Approach 1:
The patent replaces active operational amplifier circuits with a passive switched-capacitor circuit implementation of the delta-sigma modulator. This substitution eliminates the need for continuous DC bias current while maintaining the modulation function through periodic switching operations, thereby reducing power consumption while preserving modulation performance.
Solution Approach 2:
The switched-capacitor circuit employs periodic switching at the sampling frequency to achieve delta-sigma modulation. The periodic charging and discharging of capacitors through switches creates the necessary feedback mechanism without requiring active amplification, enabling modulation performance with zero static power consumption.
2Reliability
If active circuits like operational amplifiers are used for delta-sigma modulation, then modulation performance is improved, but device area increases
Solution Approach 1:
The patent replaces area-intensive operational amplifier circuits with compact switched-capacitor implementation. The switched-capacitor approach uses small capacitors and switches that occupy significantly less silicon area while achieving the same delta-sigma modulation function through time-domain switching rather than continuous analog amplification.
Solution Approach 2:
By using periodic switching at high frequency, the patent achieves modulation performance without requiring large analog amplifiers. The time-averaged effect of periodic switching creates the necessary feedback gain, allowing the use of small capacitors and compact switch structures that minimize device area.
3Use of energy by moving object
If passive switched-capacitor circuits are used for delta-sigma modulation, then current consumption and area are reduced, but modulation performance deteriorates
Solution Approach 1:
The patent achieves high modulation performance with passive switched-capacitor circuits by operating at high switching frequencies. The periodic switching creates effective feedback gain through the relationship between switching frequency and capacitor charge transfer, enabling precise modulation without active amplifiers. The high frequency operation ensures adequate signal-to-noise ratio and accurate quantization.
Solution Approach 2:
The switched-capacitor circuit performs multiple functions: it acts as the delta-sigma modulator, the feedback DAC, and the quantizer simultaneously. This multi-functionality eliminates the need for separate active amplifier stages, achieving modulation performance with a unified passive structure that consumes minimal current.
4Measurement precision
If traditional noise-shaping SAR ADC is used, then resolution is achieved, but quantization noise is not effectively suppressed
Solution Approach 1:
The patent implements a delta-sigma feedback loop where the quantization error is fed back through a switched-capacitor modulator and subtracted from the input signal. This feedback mechanism shapes the quantization noise spectrum, pushing noise energy to higher frequencies beyond the signal bandwidth, thereby suppressing in-band quantization noise while maintaining resolution.
Solution Approach 2:
By performing oversampled periodic conversions and applying delta-sigma modulation at the sampling frequency, the patent shapes quantization noise to higher frequency bands. The periodic nature of the switching creates a noise transfer function that attenuates low-frequency quantization noise, effectively suppressing noise in the signal bandwidth while preserving measurement resolution.
Data Source
AI summary
In one aspect, an apparatus includes: a first feedback digital-to-analog converter (DAC) to receive a first feedback signal from a first successive approximation register (SAR) and output a first analog signal; a comparator to compare the first analog signal with a reference voltage; the first SAR to store a digital value based on the comparison and provide the first feedback signal to the first DAC; a second feedback DAC to receive a modulated quantized residual error based on the comparison and output a second analog signal; a second SAR to store a quantized residual error; and a delta-sigma modulator (DSM) to modulate the quantized residual error and provide the modulated quantized residual error to the second feedback DAC.