Oversampled SAR ADC Reference Ripple Cancellation Using Dual DACs
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Solution Overview
Problem
Existing SAR ADCs face challenges in mitigating reference voltage ripple while maintaining low power consumption and small form factor, especially in high-resolution applications, as traditional methods like large capacitors and DAC redundancy are inadequate.
Innovation Solution
Implementing a non-switching DAC in conjunction with a switching DAC, using previous conversion results to cancel reference voltage ripple by applying previous code to the non-switching DAC during successive approximation, leveraging oversampling to equalize reference voltages and reject ripple as common mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If large bypass capacitors are used to mitigate reference voltage ripple, then reference voltage stability is improved, but device area and power consumption increase
Solution Approach 1:
The patent segments the reference voltage generation into two independent sources: a switching DAC that generates the primary reference voltage during conversion, and a non-switching DAC that generates a ripple-free reference voltage. By dividing the reference voltage function into these separate components, the system eliminates the need for large bypass capacitors while maintaining stability.
Solution Approach 2:
The non-switching DAC acts as an intermediary element that provides a clean reference voltage to cancel out the ripple generated by the switching DAC. This intermediary component enables ripple mitigation without requiring large capacitive elements or high power consumption.
2Productivity
If DAC redundancy techniques are used to allow higher ripple, then conversion speed is improved, but measurement precision deteriorates
Solution Approach 1:
The non-switching DAC serves as a mediator that subtracts the ripple component from the switching DAC output. This allows the switching DAC to operate at higher speeds with larger swing while the non-switching DAC cleans up the reference, preserving both speed and precision.
Solution Approach 2:
The system performs preliminary anti-action by generating the opposite of the ripple signal through the non-switching DAC before it corrupts the conversion result. By anticipating and counteracting the ripple effect in advance, the system maintains high precision even during fast conversions.
3Productivity
If switching DAC is used for fast conversion, then conversion speed is improved, but reference voltage ripple increases
Solution Approach 1:
The patent separates the switching function from the reference stability function. The switching DAC handles fast conversion operations while the non-switching DAC handles reference stability, eliminating the harmful ripple effect while preserving conversion speed.
Solution Approach 2:
The patent converts the harmful ripple effect into a beneficial cancellation mechanism. By intentionally generating a known ripple pattern through the switching DAC and then using the non-switching DAC to generate the exact opposite pattern, the system transforms the harmful ripple into a cancelable artifact that can be subtracted out.
Data Source
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AI summary
A method for reference ripple cancellation in an oversampled single-ended Successive Approximation Register (SAR) Analog to Digital Converter (ADC) includes sampling an input voltage onto a plurality of first capacitors of a switching Digital to Analog Converter (DAC) during a sampling phase. A first output of the switching DAC is compared to a second output of a non-switching DAC during a first conversion phase. A first digital code is generated from the comparison of the first output to the second output. The first digital code is applied to the non-switching DAC during a second conversion phase subsequent to the first conversion phase.