The microcomputer compensated crystal oscillator - practical application of dual-harmonic mode quartz thermometry

A precision frequency source based on dual harmonic mode quartz thermometry - Q-Tech´s microcomputer compensated crystal oscillator (MCXO) is described. System architecture, thermometry, compensation method, environmental and long-term performance characteristics are presented. Problems arising from the need to employ frequency synthesis and discrete-time compensation are addressed. Test results indicate that an initial frequency-temperature stability of 1E-8 over a temperature range of -50°C to +85°C is readily achievable, but that long-term stability depends upon the unique resonator. Aging characteristics that have not been previously characterized for precision clocks and the dependence of long-term stability on the differential aging rate between resonator harmonic modes are presented.