(12) United States Patent
Hayashi et al.
(io) Patent No.: (45) Date of Patent:
US 7,139,548 B2 Nov. 21, 2006
A semiconductor integrated circuit device has an oscillation circuit using either an oscillator or an oscillation module, as an external part of a reference oscillation circuit. Two external terminals are provided in correspondence with the oscillation circuit. A control terminal (base terminal) of a transistor of the oscillation circuit is connected to one external terminal, and part of an output of the transistor is fed back to the control terminal. The other external terminal is connected to a power source voltage terminal via a resistive element of a high resistance value. Capacitor elements are connected between the two external terminals. When an oscillator is connected to the one of the external terminals, the other external terminal is fixed to a constant potential. When an electronic part for oscillation (oscillation module) is connected, the other external terminal is set into an open state.
11 Claims, 7 Drawing Sheets