A versatile timing microsystem based on wafer-level packaged XTAL/BAW resonators with sub-µW RTC mode and programmable HF clocks

A resistor-based temperature sensor for a real time clock with ±2ppm frequency stability

“…With the same calibration, the RTC achieves a frequency stability of ±2ppm. This represents a significant improvement over previous work [1,3], which required a more costly 5 and 6-point calibration to achieve similar levels of stability.…”

“…This usually involves scaling the oscillator's output frequency in a temperature-dependent manner with the help of a fractional-N division or multiplication scheme [1][2][3][4]. The temperature sensor must then have high accuracy and resolution so as not to compromise the frequency stability and jitter of the compensated output signal [1].…”

“…Recent works [1][2][3], indicate that resistor-based temperature sensors can achieve high resolution in an energy efficient manner, which makes them well suited for RTCs. Their main drawback is that they require multi-point calibration in order to compensate for the non-linear temperature dependence and spread of on-chip resistors.…”

“…Their main drawback is that they require multi-point calibration in order to compensate for the non-linear temperature dependence and spread of on-chip resistors. In the context of RTCs, however, this is allowed, since it is required to accurately compensate for the non-linear temperature dependence of typical quartz-crystal and MEMS oscillators [1][2][3][4].…”

“…In [2,3], a temperature-dependent current generated by an n-well resistor is used to drive a ring oscillator, resulting in a temperature-dependent output frequency. The result is a compact circuit (0.044mm 2 ), which achieves a resolution of 40mK (rms) in a 7.5ms conversion time, and consumes 30µW.…”