A negative voltage generator includes a current mirror unit, a control
unit, a resistor, and a switching unit. The current mirror unit receives
a first positive voltage from a first positive voltage source and a
second positive voltage from a second positive voltage source and
determines how to generate a first output current and a second output
current according to the difference of a received positive reference
voltage and the second positive voltage. The control unit generates a
control signal whose value depends on the voltage variation of a negative
voltage generated by a negative voltage source, and the on/off state of
the switching unit is determined according to the control signal to keep
the current passing through the switching unit constant and to generate a
first output negative voltage having a constant level.