MCXO development included two phases: 1) initial development, and 2) performance enhancement. A typical 1" x 1" implementation is shown at the left in top and bottom views.

Initial development is described in publication 1.

Performance enhancements phase is described in publication 2.

A Microcontroller Compensated Crystal Oscillator (MCXO) is described that incorporates varactor compensation techniques and high precision analog-to-digital and digital-to-analog convertors. Design enhancements are reported which improve stability and spurious noise characteristics and add a "run-time" continuous calibration feature. Temperature stability is improved through firmware enhancements that better utilize the capabilities of the MCXO, resulting in measured performance of ± 0.1 ppm from minus 40 to plus 85° C.  Thermal packaging and calibration temperature protocol improvements are described which reduce differences in thermal gradients between calibration and open-loop run-time operating modes. Aging and frequency drift compensation is implemented by re-calibration performed automatically whenever a reference standard input signal is applied to the MCXO.