| 摘要 |
PROBLEM TO BE SOLVED: To suppress variation of duty of an output clock signal when an external clock signal is input. SOLUTION: An oscillation circuit has an oscillator 30 oscillating at an amplitude corresponding to an internal power supply voltage and generating an internal clock signal; switches 28, 29; an NMOS 13 for a tolerance input circuit; a first stage driver 15; and a coupling capacitor 27. The switches 28, 29 are brought into an off state when the external clock signal is input into clock terminals 1, 2, and in an on state when the oscillator 30 oscillates. The NMOS 13 changes the amplitude of the input clock signal with an on resistance value, and outputs it from a drain electrode. The first stage driver 15 drives an output of the drain electrode of the NMOS 13, and outputs a clock signal. When the input clock signal rises, the coupling capacitor 27 changes a gate voltage of the NMOS 13 to keep the on resistance value constant. COPYRIGHT: (C)2008,JPO&INPIT
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