0.5 V and 0.43 pJ/bit Capacitive Sensor Interface for Passive Wireless Sensor Systems

Area of Science:

• Integrated Circuits
• Sensor Technology
• Low-Power Electronics

Background:

• Capacitive sensors are crucial for various applications, but often face limitations in power consumption and operating voltage.
• Developing efficient sensor interfaces is key for enabling portable and embedded systems.
• Existing interfaces may struggle with precision and stability under varying environmental conditions.

Purpose of the Study:

• To present an ultra low-power and low-voltage pulse-width modulation (PWM) based ratiometric capacitive sensor interface.
• To evaluate the performance of the interface in terms of resolution, power consumption, and stability.
• To demonstrate the suitability of the interface for integration into complete sensor systems, such as pressure sensors.

Main Methods:

• Design and fabrication of the sensor interface in a standard 90 nm CMOS 1P9M technology.
• Utilizing a pulse-width modulation (PWM) based ratiometric architecture for signal conversion.
• Characterization of the interface's performance, including resolution, power consumption (Figure of Merit - FOM), and sensitivity to Process, Voltage, and Temperature (PVT) variations.
• Integration with a commercial pressure transducer for system-level performance evaluation.

Main Results:

• Achieved an effective resolution of 10 bits with a low supply voltage of 0.5 V.
• Demonstrated an ultra-low active area of 0.0045 mm².
• Obtained a Figure of Merit (FOM) of 0.43 pJ/bit for the sensor interface.
• Exhibited low sensitivity to PVT variations due to the ratiometric design.
• The complete pressure sensor system achieved a FOM of 0.226 pJ/bit with an effective linear resolution of 7.64 bits.

Conclusions:

• The proposed ratiometric capacitive sensor interface offers excellent low-power and low-voltage performance.
• The design's inherent stability against PVT variations is a significant advantage.
• The interface is well-suited for integration into pressure sensors and other applications requiring high efficiency.
• Its characteristics make it a strong candidate for enabling next-generation wireless sensor networks and low-power consumer electronics.