A Constant Energy-Per-Cycle Ring Oscillator Over a Wide Frequency Range for Wireless Sensor Nodes

Area of Science:

• Electrical Engineering
• Integrated Circuit Design
• Low-Power Electronics

Background:

• Wireless Sensor Nodes (WSNs) require highly energy-efficient components.
• Conventional current-starved ring oscillators (CSROs) face limitations in energy efficiency, especially at lower frequencies.
• Minimizing short-circuit current is critical for improving oscillator power consumption.

Purpose of the Study:

• To present a novel energy-efficient oscillator design for WSNs.
• To enhance the operational efficiency of switched-capacitor DC-DC converters.
• To reduce the energy-per-cycle (EpC) of oscillators in low-power electronic systems.

Main Methods:

• Developed an oscillator design that minimizes time spent in critical voltage ranges to avoid short-circuit current.
• Implemented a current-feeding scheme with gate voltage control for wide frequency range operation.
• Fabricated a test chip using a 0.18 μm CMOS process and conducted performance measurements.

Main Results:

• The proposed oscillator achieved a constant energy-per-cycle (EpC) of 0.8 pJ/cycle across a 21-60 MHz frequency range.
• Demonstrated superior efficiency compared to conventional CSROs below 300 kHz at 1.8 V.
• Integrated into a switched-capacitor DC-DC converter, resulting in 11%-56% improved efficiency for specific load power values.

Conclusions:

• The proposed oscillator design offers significant energy savings for WSNs.
• The design provides a more efficient alternative to conventional CSROs, particularly in low-frequency applications.
• The application in DC-DC converters highlights its potential for enhancing the performance of energy-harvesting and low-power systems.