A temperature-to-digital converter for a MEMS-based programmable oscillator with better than ±0.5ppm frequency stability

MEMS-based programmable oscillators have emerged as a promising alternative to crystal-based frequency references, with previously reported work demonstrating sub-ps integrated jitter [1]. Here we show frequency stability better than ±0.5ppm from -40 to 85°C, along with Allan Deviation (i.e., long term jitter) better than 0.005 ppm for 0.1, 1, and 10 second strides. Since the MEMS resonator has a well-defined temperature dependence, the key to this performance is a stable and low-noise temperature-to-digital converter (TDC) that utilizes a thermistor on the same die as the MEMS resonator.