A Direct Current-Sensing VCO-Based 2nd-Order Continuous-Time Sigma-Delta Modulator for Biosensor Readout Applications

Area of Science:

• Electrical Engineering
• Integrated Circuit Design
• Sensor Technology

Background:

• Current-sensing readout circuits often require complex trans-impedance amplifiers.
• Traditional sigma-delta modulators can suffer from high in-band quantization noise.
• Scaling and power efficiency are critical for Internet of Things (IoT) applications.

Purpose of the Study:

• To propose a novel second-order voltage-controlled oscillator (VCO)-based continuous-time sigma-delta modulator (CTSDM).
• To enable direct quantization of current signals, eliminating the need for extra trans-impedance amplifiers.
• To achieve high performance and low power consumption for current-sensing readout applications.

Main Methods:

• Implementation of a second-order noise shaping capability using a proportional-integral (PI) structure and VCO phase integrator.
• Utilization of a current-steering digital-to-analog converter in the feedback path for current signal subtraction.
• Design of a scaling-friendly architecture suitable for miniaturization.

Main Results:

• Achieved a measured signal-to-noise and distortion ratio (SNDR) of 74.6 dB at a 10 kHz bandwidth.
• Demonstrated ultra-low power consumption of 44.8 μW at a 1.2 V supply voltage.
• Obtained a Figure-of-Merit (FoM) of 160.76 dB, indicating high efficiency.

Conclusions:

• The proposed VCO-based CTSDM offers a simplified and efficient solution for current-sensing readout.
• The design is highly suitable for power-sensitive IoT applications due to its low power consumption and high performance.
• The architecture's scalability and stability ensure its applicability in advanced integrated systems.