Analog ALC crystal oscillators for high-temperature applications

A fundamental mode and a third-harmonic mode integrated high-performance au tomatic level controlled (ALC) crystal oscillators for high-temperature app lications (up to 250 degrees C), are described in this paper, These oscilla tors were specially designed for a pressure measurement system in high-temp erature environments, which output signal is the difference between both ge nerated frequencies. Frequency variations smaller than 0.0001 ppm/s for each oscillator and a fr equency drift of about 2.5 ppm/year of the frequency difference are the mea sured performance concerning, respectively, the short-term (1 s) and long-t erm frequency stability of these integrated high-performance crystal oscill ators over the 30 degrees C-225 degrees C temperature range. Other importan t characteristics are the very stable and constant oscillation levels (simi lar to 1.1 Vpp), the small second-harmonic distortion (-60 dB), and the pha se noise (-95 dB at 50 kHz shift). The characteristics of these oscillators make them also suitable for many o ther measurement systems (time, temperature, and other physical and chemica l quantities), especially if they are constrained to operate under severe t emperature conditions.