A 1-μW/MHz RC Oscillator With Three-Point Trimmed 2.1-ppm/°C and Single-Point Trimmed 8.7-ppm/°C Stability From40 °C to 95 °C

Abstract

This article presents techniques to improve the frequency stability of RC oscillators by performing firstand second-order temperature compensation without needing resistors with opposite temperature coefficients (TCs). Using the proposed three-point digital trim, a prototype 100-MHz frequency-locked loop (FLL)-based RC oscillator fabricated in a 65-nm CMOS process achieves an inaccuracy of ±140 ppm over −40 • C to 95 • C, 83-ppm/V voltage sensitivity, 1.3-ppm Allan deviation floor, and 1-µW/MHz power efficiency. When only a single-point trim is performed using a multiple linear regression model leveraging the strong correlation between three switched resistors, the frequency inaccuracy is ±587 ppm.

A Temperature- and Aging-Compensated RC Oscillator With ±1030-ppm Inaccuracy From40 °C to 85 °C After Accelerated Aging for 500 h at 125 °C

“…17 depicts the outcomes of an aging test carried out on seven samples, wherein a p-poly resistor is substituted for R 0 in the main TCOs (it is worth noting that the R 0 of the reference TCOs is represented by an n-poly resistor, while the R 1 of both the main and reference TCOs is a VIA resistor). This test provides a fair comparison the state of the art, since most TCOs reported in the literature use p-poly resistors [16], [19], [20], [22], [36]. Before aging, the inaccuracy of uncompensated main TCOs is ±870 ppm, while after 500 h of aging, it degrades to ±6210 ppm, as shown in Fig.…”

“…I NTEGRATED RC oscillators are becoming increasingly popular as clock sources in various applications, replacing bulky crystal or MEMS oscillators due to their smaller physical footprint, lower power consumption, and lack of expensive offchip components [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24]. These oscillators achieve excellent short-term frequency stability through novel methods that compensate for the frequency inaccuracy caused by the temperature coefficient (TC) of resistors used in the reference RC networks [11], [12], [16], [17], [19], [20], [22]. Over the past decade, numerous papers have been published to improve the temperature stability of RC oscillators, resulting in a significant improvement in their frequency accuracy, which is now comparable to crystal oscillators [22].…”

“…To evaluate the effect of resistor aging on the oscillator's frequency, a temperature-compensated frequency-locked loop (FLL)-based RC oscillator prototype using a p-poly resistor was designed, and its long-term stability was measured by baking it at 125 • C. The results, plotted in Fig. 1, show that resistor aging significantly affects the oscillator's frequency, causing more than 5000-ppm drift after 1000 h [23]. In addition, a 5000-ppm frequency drift of RC oscillators using a p-poly resistor was observed from an aging experiment at 150 • C for one week [24].…”