Design and UVM Verification of an RTC Subsystem with Temperature Compensation

The real-time clock (RTC) integrated circuit is a special-purpose accurate clock generating circuit that is used in many microcontroller units (MCUs). In this paper, we design an ultra-low power and high-precision RTC subsystem used in general purpose MCUs. A temperature compensation scheme is designed to improve the accuracy of the RTC. The RTC uses a 1Hz clock for generating the accurate time and a 32768-Hz clock for the temperature compensation, which can reduce power consumption while maintaining high accuracy. To get the temperature from the analog-to-digital (ADC), we design an ADC controller. A power management unit (PMU) is designed to control the MCU to enter or exit the ultra-low power mode. We also build a subsystem-level verification environment for the RTC using the universal verification methodology (UVM) platform. The results show that the functions of the RTC under various conditions are correct and coverage reaches 98% in the regression test, the frequency error within the industrial temperature range is ± 1 ppm after calibration, and the accuracy meets the requirement of most MCUs.