Quartz crystal oscillator, which uses quartz crystal as the resonator, has excellent frequency stability and very low phase-noise characteristics. They can be found in many applications that require a highly precise and stable frequency reference. However, due to the intrinsic characteristics of the crystal, the uncompensated crystal oscillators have temperature stability over ±50ppm....[ Read more ]

Quartz crystal oscillator, which uses quartz crystal as the resonator, has excellent frequency stability and very low phase-noise characteristics. They can be found in many applications that require a highly precise and stable frequency reference. However, due to the intrinsic characteristics of the crystal, the uncompensated crystal oscillators have temperature stability over ±50ppm.

Conventional design of Temperature-Compensated Voltage-Controlled Crystal Oscillator (TC-VCXO) uses an external varactor diode as the frequency tuning element and temperature compensation network to compensate the temperature dependence. Due to the lack of the ability for integration and automatic calibration, the production cost of TC-VCXO is very expensive.

In this thesis, an analog compensation technique using op-amps and resistors network with digital calibration ability is proposed such that automatic calibration can be achieved. This technique is capable of enhancing the temperature stability of a VCXO to be less than ±2.5ppm. A fully integrated VCXO, without the crystal resonator, with a very linear and temperature invariant tuning range is also proposed. The maximum deviation of the linearity of the proposed VCXO is less than ±5% with a temperature range from -45°C to 85°C. By combining this VCXO with the analog compensation technique, a low cost and high performance TC-VCXO with tuning range of ±15ppm and temperature stability of ±2.5ppm over a temperature range from -45°C to 85°C is developed.