Temperature-compensated crystal oscillator and method of temperature compensation

A temperature-compensated crystal oscillator including a voltage-controlled crystal oscillating circuit for setting said voltage-controlled crystal oscillating circuit into oscillation by the use of a crystal resonator, the oscillation frequency of said voltage-controlled crystal oscillating circuit being controlled with a temperature compensation signal for performing the temperature compensation of said crystal resonator, comprising:

• a temperature sensor for detecting an operating temperature of said crystal oscillator;
• analog temperature compensating means for generating a temperature compensation voltage of an approximate quadratic function or an approximate cubic function corresponding to the temperature characteristic of said crystal resonator based on the temperature detected by said temperature sensor, and for supplying said generated voltage to said voltage-controlled crystal oscillating circuit;
• and
• digital temperature compensating means for AD converting the temperature detected by said temperature sensor, for outputting temperature compensation data in digital form which has been stored in advance in a memory in association with said AD converted value, for DA converting said temperature compensation data into a temperature compensation voltage in analog form, and for supplying said temperature compensation voltage to said voltage-controlled crystal oscillating circuit,
• characterized in that the oscillation frequency of said voltage-controlled crystal oscillating circuit is controlled based on both of temperature compensation voltages from both of said temperature compensating means.