Approximate third-order function generator, temperature compensation quartz oscillation circuit made by using the same, and temperature compensation method

A temperature compensated crystal oscillation circuit, comprising:

• a temperature detection circuit, an approximate third-order function generator for receiving a detection signal from said temperature detection circuit, and a voltage-controlled crystal oscillation circuit for receiving an approximate third-order function generated by said approximate third-order function generator;
• wherein said approximate third-order function generator comprises a first amplifier, a second amplifier and a third amplifier, each for receiving a common input signal and a different fixed level signal, the three different fixed level signals received respectively by the first, second and third amplifiers sequentially increasing in level in such order, each amplifier having input-output characteristics in which a non-inverted or inverted output signal is provided and based on the common input signal and the respective fixed level signal such amplifier also having a function to limit the output signal to within a range defined by a maximum predetermined value and a minimum predetermined value;
• a fourth amplifier for receiving the common input signal and the same fixed level signal as said second amplifier receives, said fourth amplifier having input-output characteristics in which a non-inverted or inverted output signal is provided based on the common input signal and the respective fixed level signal, and having a function to limit the output signal to within a range defined by a maximum predetermined value and a minimum predetermined value;
• and
• a fixed level signal generation circuit for supplying the fixed level signals having the different fixed levels to said first, second, third, and fourth amplifiers, respectively, the output characteristics of said first, third, and fourth amplifiers being set so as to have a same polarity, the output characteristics of the second amplifier being set so as to be inverted to those of said first, third and fourth amplifiers, wherein the output signals from said first, second, third, and fourth amplifiers being added to generate a third-order function component free from a first-order component.

A temperature compensation adjusting method for a temperature compensated crystal oscillation circuit, comprising the steps of:

• measuring an output voltage VCount from a temperature compensation circuit in a predetermined temperature atmosphere;
• measuring an input voltage VCin to said a voltage-controlled crystal oscillation circuit where an oscillation frequency output from said voltage-controlled crystal oscillation circuit coincides with a preset selected frequency at a respective one of a plurality of temperatures T in a desired temperature compensation range;
• approximately representing the measured input voltage VCin and output voltage VCout at a respective temperature by:
• VCin(T)=α3(T−T0)3+α1(T−T0)+α0
• VCout(T)=β3(T−T0′)3+β1(T−T0′)+β0;
• adjusting coefficients β0, β1, β3 and T0′ of the temperature compensation circuit so as to coincide with the coefficients α0, α1, α3, and T0, respectively, inherent to a crystal resonator of the voltage-controlled crystal oscillation circuit.