A Large Measurable Range Capacitance-to-Digital Converter for Smart Humidity Sensors

Area of Science:

• Electrical Engineering
• Sensor Technology
• Integrated Circuit Design

Background:

• Capacitive sensors are crucial for humidity detection.
• Accurate capacitance-to-digital conversion is essential for sensor performance.
• Existing converters face challenges in range and resolution.

Purpose of the Study:

• To develop a high-resolution capacitance-to-digital converter (CDC).
• To enhance the measurable range of the CDC using disguised zoom-in technology.
• To integrate the CDC with a humidity sensor for a smart system.

Main Methods:

• A third-order cascade of integrators with feed-forward (CIFF) incremental sigma-delta modulator was designed.
• Disguised zoom-in technology was employed to expand the CDC's input range (0-388 pF).
• The CDC was implemented using 0.18 μm complementary metal-oxide-semiconductor (CMOS) technology.

Main Results:

• Achieved 13-bit capacitance-to-digital conversion in 0.8 ms.
• Demonstrated a figure of merit (FOM) of 3.0 nJ/step with low power consumption (169.7 μA at 1.8 V).
• Integrated with a HS1101 humidity sensor, achieving 0.7% relative humidity (RH) resolution from 30%-90% RH.

Conclusions:

• The proposed CDC offers high resolution and an expanded range for humidity sensing applications.
• The design demonstrates efficient power consumption and a competitive FOM.
• Successful integration showcases the CDC's viability in smart sensor systems.