An Aging-Robust 32MHz RC Frequency Reference with 0.4ppm Allan Deviation and ±1550ppm Inaccuracy from -40°C to 125°C after a 1-Point Trim

Abstract

RC-based frequency references [1-6] are widely used for clock generation in SoCs since they are compact, low power, and can achieve medium frequency accuracy. Designs based on low-TC poly resistors can achieve inaccuracies of a few 100 ppm[1-5], but this is dwarfed by their drift, which can be as large as 5000 ppm after accelerated aging [5-6]. Although designs based on via-metal [4] or diffusion [6] resistors exhibit significantly lower drift, in the order of several 100 ppm, their larger TCs mean that a 2-point trim is required to achieve inaccuracies of several 100 ppm. This paper presents an aging-robust 32 MHz RC frequency reference based on diffusion resistors and a BJT-based temperature compensation scheme. After a low-cost 1-point trim, it achieves ± 1550ppm inaccuracy from -40 C to 125 C, which increases to ± 2350ppm after accelerated aging. Due to the extensive use of dynamic error-correction techniques, it also achieves an Allan deviation floor of 0.4 ppm, corresponding to state-of-the-art short-term stability.