| 摘要 |
a first pull-down transistor driven by data from a semiconductor memory device, for transmitting a power supply voltage of a power supply voltage source to an output line side connected to an external pin; a second pull-down transistor driven by an output signal of an inverter for inverting the data from the memory device, for passing a voltage signal on the output line to a ground voltage; a resister connected between the power supply voltage source and an arbitrary connection point; a comparing switch connected between the connection point and the output line and a reference voltage source, for selectively muting the voltage on the connection point to the output line according to the sizes of a reference voltage of the reference voltage source and the voltage of the output line; and a gate control circuit driven according to the voltage on the connection point and if the voltage on the output line falls under the ground level, for muting the output of the inverter supplied to the second pull-down transistor to temporarily stop the operation of the second pull-down transistor.
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