A digital controlled oscillation circuit of a portable telephone, a method of calculating an oscillation frequency of a crystal oscillator, and an output frequency correction method

摘要

In a portable telephone using a CPU, a storage device, a temperature sensor, a D / A converter, and an A / D converter as control elements and having an oscillation circuit including a crystal oscillator and a variable capacitance diode, Lt; / RTI The storage device previously stores control information for correcting the output frequency drift of the portable telephone set caused by the temperature change. The temperature of the oscillation circuit is sensed by the temperature sensor and converted into a digital value in the A / D converter. The CPU reads the control information corresponding to the sensed temperature from the storage device and applies it to the variable capacitance diode of the oscillation circuit through the D / A converter to maintain the output frequency at a certain level. Also disclosed is a method for efficiently calculating an oscillation frequency of a quartz crystal with a reduced number of measurement points relative to a temperature characteristic of the quartz crystal. A method for accurately performing the temperature compensation described above is also disclosed.