11.1 Dual-MEMS-resonator temperature-to-digital converter with 40 K resolution and FOM of 0.12pJK2

Precision MEMS oscillators require a temperature-to-digital converter (TDC) that adjusts the multiplication factor of a fractional-N PLL in order to compensate for the MEMS resonator's frequency variation over temperature [1]. This compensation, however, provides a path for the TDC's noise to propagate to the oscillator's output as phase noise (PN). Previous work has sought to minimize this noise, by using high-resolution TDCs, e.g., the MEMS-thermistor based TDC described in [1]. This paper presents a TDC based on dual-MEMS resonators [2–3] that has no significant impact on oscillator PN. In a 130Hz bandwidth (BW), the sensor achieves a thermal-noise-limited resolution of 40µK, leading to a resolution FOM (Energy/Conversion × Resolution2) of 0.12pJK2, 5× better than the state of the art [4].