Negative voltage generator, decoders, non-volatile memory device and memory system that uses a negative voltage

A negative voltage generator (123) contains a DC voltage generator (181) which is adapted to produce a DC voltage (VDC_NEG), a reference voltage generator (182) which is adapted to generate a reference voltage (Vref_NEG), an oscillator (183), is adapted to generate an oscillating clock (CLK_NEG), a charge pump (185) is configured to (NWELL) in response to a pump clock (CLK_NEGP) to generate a negative voltage, and a voltage detector (184). The voltage detector (184) is adapted to detect the negative voltage (NWELL) by comparing a by voltage division of the DC voltage obtained (VDC_NEG) dividing voltage with the reference voltage (Vref_NEG), and the pump clock corresponding to the detected negative voltage based (on the oscillation clock CLK_NEG) to generate.