An Energy Efficient and Temperature Stable Digital FLL-based Wakeup Timer with Time-Domain Temperature Compensation

Area of Science:

• Integrated Circuits
• Low-Power Electronics
• Embedded Systems

Background:

• Accurate timing is crucial for low-power embedded systems, but temperature variations can significantly impact oscillator and timer frequencies.
• Existing temperature compensation techniques often introduce considerable power and hardware overhead.
• Digital intensive frequency-locked loops (DFLLs) offer a flexible platform for timing applications.

Purpose of the Study:

• To develop an on-chip digital intensive frequency-locked loop (DFLL)-based wakeup timer with effective time-domain temperature compensation.
• To achieve precise frequency stability across a wide temperature range with minimal power and hardware overhead.
• To demonstrate the feasibility of a novel temperature compensation strategy using complementary resistors.

Main Methods:

• Implemented a DFLL-based wakeup timer incorporating an embedded temperature sensor.
• Utilized the deterministic temperature characteristics of complementary resistors for frequency stabilization.
• Modulated the activation time window of complementary resistors to compensate for temperature-induced frequency drift.
• Fabricated the chip in 40 nm CMOS technology.

Main Results:

• Achieved a fine trimming step of ± 1 ppm, resulting in a frequency error below ± 20 ppm after trimming.
• Demonstrated temperature stability of 8 ppm/ºC over a temperature range of -40ºC to 80ºC.
• Attained high energy efficiency of 0.9 pJ/cycle.
• Showcased negligible power (2%) and hardware overhead (<1%) by reusing the DFLL structure for temperature sensing.

Conclusions:

• The proposed DFLL-based wakeup timer with time-domain temperature compensation effectively stabilizes operating frequency across temperature variations.
• This approach offers a low-overhead, energy-efficient solution for precise timing in embedded systems.
• The technique of exploiting complementary resistor characteristics presents a viable method for background temperature sensing and compensation.