| 摘要 |
PURPOSE: A sniffer circuit is provided to prevent a clock selection signal from being inverted by leakage current by discharging the leakage current generated from a turned-off transistor. CONSTITUTION: A sniffer circuit having an external clock signal applied from the exterior and an oscillating signal of a ring oscillator as inputs in which a clock signal is generated to have the oscillation signal supplied to the inside the system as a system clock when the external clock signal is lower than a predetermined frequency, comprises: a clock signal detector for detecting whether the external clock signal is a normal signal having a frequency higher than a predetermined frequency, and outputting the result of the detection as a clock OK signal and an inverted clock OK signal; a sense amplifier for generating a first and a second amplified output signals corresponding to the clock OK signal, the inverted clock OK signal and the oscillating signal divided by the predetermined frequency, and discharging a leakage current; a reset signal generator for outputting a reset signal corresponding to inverted first and second amplified output signal to the clock signal detector; and a latch for receiving the first and second output signals from a first and a second input terminals, and outputting the clock selection signal corresponding to the inputted first and second amplified output signals.
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