Patent ID: 7808333

Claim:
An IC for control of a temperature-compensated crystal oscillator, comprising: a power terminal, through which a power voltage and a dock signal are supplied; an input terminal, through which a predetermined control signal is supplied; a PROM circuit in which adjustment data to cancel a temperature characteristic of the crystal oscillator are written, the crystal oscillator having a read mode for reading data written in the PROM circuit and controlling a frequency of the crystal oscillator, an emulation mode for determining data to be written in the PROM circuit, and a write mode for writing the data determined in the emulation mode in the PROM circuit, a first mode selector circuit for switching the crystal oscillator to the emulation mode or the write mode when a first signal in which the power voltage and the clock signal supplied through the power terminal are superimposed, is inputted from the power terminal and a second signal having a predetermined pattern is inputted from the input terminal, wherein the first mode selector circuit includes: a comparator that outputs, as a pulse signal, a result of comparison between the first signal and a predetermined reference voltage; a first flip-flop circuit of predetermined stages, that shifts the second signal based on the pulse signal outputted from the comparator; and a transistor that controls the power voltage based on an output signal of the first flip-flop circuit.