Circuit arrangement for the temperature compensation of AT-cut crystal oscillators, and method for the adjustment of the compensation

摘要

A circuit arrangement for the temperature compensation of oscillators exhibiting crystals cut in the AT direction and located within a given range of cutting angles, which exhibits a voltage- controlled tuning element slightly influencing the frequency of the crystal, and two such temperature compensation circuits (16, 18) which are thermally coupled to the crystal and generate a compensation voltage which is suitable for compensating for the temperature dependence of the crystals allocated to the two limit cutting angles of the said cutting angle range, the circuit arrangement also exhibits a linear interpolation element (14) with adjustable proportionality factor, the two inputs of which are in each case connected to the outputs of the temperature compensation circuits (16, 18) whereas the output of the interpolation element (14) is connected to the tuning element (12) influencing the frequency of the oscillator, this output supplying the weighted sum of the two compensation voltages tuned to the cutting angle of the given crystal. The temperature compensation circuits can also be used for several oscillators. In the method used for adjusting temperature compensation of the circuit arrangement, the arrangement is brought to a temperature of approximately 25 DEG C in a first step, and the frequency of the oscillator is set to the nominal frequency of the crystal with the aid of a tuning element separated from the interpolation element, at a centre position of the interpolation element. After that, the temperature is significantly changed and the frequency is set to the same value by means of the linear interpolation element.