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.

The wheel polygonisation is the harmonic wave along the wheel circumference, which has been widely reported in high-speed railway vehicles in China in recent years. The polygonization mechanism has not been fully understood yet, and this work discusses one possible mechanism through several experiments. Firstly, a field test for the CRH3 high-speed train with polygonal wheels is carried out. It is found that the vibration in vertical takes major responsibility, and there are several resonance bands for the train-track system. Another field test shows that the rail is sensitive to the polygonisation characteristic frequency, but the wheel axle is not. Then the rail local vibration modes are analyzed by the operational deflection shape (ODS) test in the laboratory. A loaded bogie is fixed on the tested track to simulate the real working conditions. The result shows that the frequency of one local mode is 591 Hz, which is a typical wheel polygonisation frequency. Besides, the wheel-rail contact point is not on the vibration node of this local mode. Thus, the resonance of this local rail mode can be one possible mechanism for the high-order wheel polygonisation.