PURPOSE: To shorten an oscillation period of a ring oscillator as operational temperature is raised, in a DRAM in which refresh operation is necessary.
CONSTITUTION: A clock period is varied in accordance with operational temperature. For example, constant voltage is applied to a resistor RA having a positive temperature coefficient, a reference current io flowing in it is converted to voltage by a resistor RB. The voltage is converted to a reference current in by a P channel MOS transistor QP12, and a current in having the same value as the reference current in is made to flow in each inverters I1-I7 by a current mirror circuit. The reference current i0 is decreased as operation temperature is raised, and the reference current in is increased. Thereby, an oscilla-tion period of a ring oscillator is shorten as operation temperature is raised.
KAJIMOTO TAKESHI
HAYASHIGOE MASANORI
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