DIGITALLY CONTROLLED TEMPERATURE COMPENSATION CRYSTAL OSCILLATOR

摘要

PURPOSE:To stabilize an oscillation output by giving a histeresis so as to eliminate chattering in applying digital encoding to temperature information. CONSTITUTION:An output voltage VA of a temperature detecting circuit 11 is inputted to a voltage shift circuit 13 in a temperature encoding circuit 12 and fed to a terminal A of a changeover switch 14. The voltage shift circuit 13 has a function shifting the inputted voltage VA by a prescribed minute quantity and its output voltage VB is fed to the other terminal B of the changeover switch 14. The switch 14 changes over the VA and VB alternately and gives them to an A/D coverting circuit 15 and a discriminating circuit 16. The discriminating circuit 16 compares a digital code corresponding to the VA with a digital code corresponding to the VB and when the both are coincident, the digital code is regarded as the temperature information at that point of time. The temperature information is inputted to a processing circuit 21 and used for the control of the oscillating frequency of the crystal oscillation circuit.