A 2.8-MHz Aging-Resilient RC Frequency Reference With Periodic Digital Calibration

This paper presents a 2.8-MHz RC oscillator with digitally assisted aging compensation by employing a periodically awakened reference oscillator. The reference oscillator remains in sleep mode for more than 99.9\% of the operating time and is awakened only to periodically calibrate the main oscillator. To validate the proposed architecture without relying on aging-insensitive resistor types, only one type of aging-sensitive P-poly resistor is used throughout the design. The reference oscillator employs temperature compensation using complementary temperature-coefficient (TC) currents generated from $V_{\text{BE}}$ and $\Delta V_{\text{BE}}$, followed by one-point frequency trimming using a digital-to-analog resistor converter (RDAC). Fabricated in a 180\,nm BCD process, this design achieves $\pm$0.4\% frequency inaccuracy over the temperature range from $-$40\,$^\circ$C to 150\,$^\circ$C after batch TC and one-point frequency trimming, with an average per-chip TC of 31.2\,ppm/$^\circ$C. After one week of accelerated aging at 150\,$^\circ$C, the uncompensated frequency drift is approximately 7300\,ppm, while the proposed aging compensation scheme reduces it to 1700\,ppm, corresponding to a 4.3$\times$ reduction in aging-induced frequency drift.