A High-Accuracy RC Time Constant Auto-Tuning Scheme for Integrated Continuous-Time Filters

Area of Science:

• Electrical Engineering
• Analog Integrated Circuit Design
• Semiconductor Device Physics

Background:

• Resistor-capacitor (RC) time constant variations in CMOS technology, driven by process and temperature fluctuations, pose significant reliability challenges for continuous-time analog circuits.
• Absolute RC time constant values can deviate by over ±50%, impacting circuit performance and necessitating robust compensation strategies.

Purpose of the Study:

• To propose and validate a novel on-chip auto-tuning scheme for accurate resistor-capacitor (RC) time constant control in integrated circuits.
• To enhance the reliability and precision of continuous-time analog filters by mitigating process, voltage, and temperature (PVT) variations.

Main Methods:

• Implementation of a discrete master-slave auto-tuning concept for RC time constant regulation.
• Integration of parasitic capacitance cancelation to eliminate unwanted parasitic effects.
• Application of symmetric comparison to minimize comparator DC offset influence.
• Utilization of a successive approximation procedure to accelerate the tuning process.

Main Results:

• Validation in 55 nm CMOS technology using a fourth-order active-RC low-pass filter demonstrated significant improvements in tuning accuracy.
• The proposed scheme achieved an average tuning error of 2.21% and a maximum error of 3.67% under PVT variations and input offset voltage.
• The achieved tuning error is substantially lower compared to conventional auto-tuning schemes.

Conclusions:

• The developed on-chip auto-tuning scheme effectively addresses the long-standing challenge of RC time constant variability in integrated circuits.
• The proposed techniques, including parasitic capacitance cancelation and symmetric comparison, lead to higher tuning accuracy and improved circuit reliability.
• This work offers a robust solution for precise analog circuit design, particularly for continuous-time filters operating under diverse environmental and process conditions.