A linearity-enhanced time-domain CMOS thermostat with process-variation calibration

Area of Science:

• Integrated Circuits
• Semiconductor Devices
• Thermal Management

Background:

• Traditional time-domain CMOS thermostats face accuracy limitations due to large characteristic curves, especially over extended temperature ranges.
• Enhancing on-chip linearity is crucial for improving the precision of temperature sensing in integrated circuits.
• Process variations in semiconductor manufacturing can significantly impact thermostat accuracy and require effective calibration strategies.

Purpose of the Study:

• To propose a linearity-enhanced time-domain CMOS thermostat with process-variation calibration.
• To improve accuracy, expand the operating temperature range, and reduce testing costs of CMOS thermostats.
• To develop a novel temperature-sensing cell for linearised delay generation.

Main Methods:

• A novel temperature-sensing cell combining a simple buffer and a thermal-compensation circuit was designed to achieve linearised delay.
• A linearity-enhanced oscillator was constructed using these cells to generate a highly linear oscillation period.
• One-point calibration was implemented using an adjustable-gain time stretcher and calibration circuit to compensate for process variations.

Main Results:

• A thermostat with a compact area of 0.067 mm² was fabricated using a 0.35-μm CMOS process.
• The thermostat achieved a resolution of 0.05 °C and low power dissipation of 25 μW at 10 samples/s.
• After one-point calibration, the thermostat exhibited an inaccuracy of -0.35 °C to 1.35 °C across a wide temperature range (-40 °C to 120 °C).

Conclusions:

• The proposed linearity-enhanced time-domain CMOS thermostat significantly improves circuit area, accuracy, and operating temperature range compared to existing solutions.
• The integrated process-variation calibration effectively addresses manufacturing inconsistencies, enhancing reliability.
• This design offers a cost-effective and high-performance solution for temperature monitoring in various applications.