A 12-b Subranging SAR ADC Using Detect-and-Skip Switching and Mismatch Calibration for Biopotential Sensing...

Area of Science:

• Electrical Engineering
• Biomedical Engineering
• Integrated Circuit Design

Background:

• High-resolution analog-to-digital converters (ADCs) are crucial for biopotential sensing.
• Conventional ADCs suffer from high power consumption, particularly due to digital-to-analog converter (DAC) switching energy.
• On-chip calibration is often required to compensate for component mismatches and ensure linearity.

Purpose of the Study:

• To develop a low-power 12-bit successive approximation register (SAR) ADC for biopotential sensing applications.
• To significantly reduce the DAC switching energy in high-resolution SAR ADCs.
• To implement an effective on-chip mismatch calibration technique without additional hardware overhead.

Main Methods:

• Combined merged-capacitor-switching (MCS) and detect-and-skip (DAS) techniques within a subranging architecture.
• Reused the on-chip DAC for mismatch calibration, processing mismatch data in the digital domain.
• Fabricated the ADC using a 0.18 μm CMOS process.

Main Results:

• Achieved a 96.7% reduction in switching energy compared to conventional methods.
• At 9 kS/s, the ADC demonstrated a Signal-to-Noise and Distortion Ratio (SINAD) of 67.4 dB and an improved Spurious-Free Dynamic Range (SFDR) of 73.5 dB (a 7.2 dB improvement).
• At 200 kS/s, the ADC achieved a SINAD of 65.9 dB and an SFDR of 68.8 dB, with a Figure-of-Merit (FoM) of 13.2 fJ/conversion-step.

Conclusions:

• The proposed MCS and DAS combined technique effectively minimizes DAC switching energy in SAR ADCs.
• On-chip mismatch calibration using the existing DAC is feasible and improves linearity without extra cost.
• The developed 12-b SAR ADC is suitable for low-power biopotential sensing applications requiring high resolution and accuracy.