Programmable ELDC Gain in SAR Delta-Sigma ADC Quantizers
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Solution Overview
Problem
Continuous-time delta-sigma analog-to-digital converters (ADCs) using successive approximation register (SAR) quantizers face challenges with slow conversion speed due to their successive nature, necessitating excess loop delay compensation (ELDC) to address the conversion delay, which complicates programming and calibration of the ELD gain.
Innovation Solution
Incorporating a charge pump with digitally programmable capacitance into the ELDC circuit to adjust the gain of either the ELDC DAC or the SAR DAC, allowing for efficient programming and calibration of the ELD gain, enabling flexible and precise compensation for conversion delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a SAR ADC is used as a quantizer in a delta-sigma ADC to reduce power consumption, then power efficiency is improved, but conversion speed deteriorates due to the successive nature of the conversion process
Solution Approach 1:
The patent divides the conversion process into two independent parallel paths: a fast path that handles excess loop delay compensation using a separate DAC, and a successive approximation path that performs precise quantization. This segmentation allows the SAR ADC to operate at low power while the ELDC path compensates for speed limitations, resolving the contradiction between power efficiency and conversion speed.
2Measurement precision
If excess loop delay compensation is implemented to address SAR conversion delay, then conversion accuracy is improved, but device complexity worsens due to additional ELDC DAC and control circuits
Solution Approach 1:
The patent merges the ELDC DAC and SAR DAC into a unified capacitive array structure where both DACs share common capacitors and control logic. The ELDC control signal and SAR control signal work together to activate specific capacitors, eliminating the need for separate ELDC circuitry and reducing overall device complexity while maintaining conversion accuracy.
Solution Approach 2:
The capacitive array serves multiple functions: it acts as the DAC for the SAR quantizer, the ELDC DAC for delay compensation, and the summing node for combining signals. This multi-functionality eliminates redundant components and simplifies the overall circuit architecture while achieving both precision and speed requirements.
3Adaptability or versatility
If traditional ELDC methods are used with fixed gain, then circuit simplicity is maintained, but adaptability worsens due to inability to adjust gain for different operating conditions
Solution Approach 1:
The patent implements dynamic gain adjustment by making the capacitance values programmable through control signals. The ELDC gain can be adjusted by changing the capacitance ratio between ELDC capacitors and SAR capacitors, allowing the system to adapt to different operating conditions such as varying sampling rates or input signal characteristics while maintaining reasonable programming complexity through systematic capacitor sizing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the tuning range and precision of the ELD gain, improving the efficiency and accuracy of the SAR-based delta-sigma ADCs by allowing for cycle-to-cycle gain adjustments and self-calibration, thereby addressing the limitations of traditional ELDC methods.
Implementation Method 1
a charge pump coupled to either the first set of capacitors or the second set of capacitors, the charge pump having a programmable capacitance to adjust a gain
Data Source
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AI summary
An excess loop delay compensation (ELDC) technique for use with a successive approximation register (SAR) based quantizer in a continuous time delta-sigma ADC is described. The techniques can efficiently program and calibrate the ELD gain in ELD compensation SAR quantizers. An ELDC circuit can include a charge pump having a digitally programmable capacitance to adjust a gain, such as the gain of the ELDC digital-to-analog converter (DAC) or the gain of the SAR DAC.