| 摘要 |
<p>A crystal oscillator compensation circuit (13) has an oscillator crystal (12) excited by a piezoelectric oscillator circuit (19), whereby the frequency (f) can be shifted in certain limits by means of a variable-capacity diode (14). The crystal temperature is measured by a temperature sensor (17) which retransmits a temperature signal by means of an analog/digital converter (22) to a microprocessor with a bus (24), and input/output port (15), a PROM (16) and a logic circuit (18). This microprocessor calculates, on the basis of the temperature signal allowing for a known regularity and characteristic numbers stored in the PROM memory for the crystal concerned, a temperature compensation signal which is transmitted by means of a D/A converter (21) to the variable-capacity diode. The temperature compensation signal (UK) has a value such that the effect which it creates on the frequency of the piezoelectric oscillator compensates exactly for the effect on the frequency produced by the measured temperature variation. Such a crystal oscillator compensation circuit is much less costly and requires far less room than a corresponding conventional circuit of identical accuracy, which called for thermostats adjusted with a very high degree of precision. Other compensation circuits serve to compensate for the effects of ageing or acceleration.</p> |
