Special mode activation circuit for selectively activating a special mode circuit of a semiconductor integrated circuit device

摘要

A special mode activation circuit is disclosed for activating a special mode circuit within a semiconductor integrated circuit when the voltage of an input signal at an input terminal of the integrated circuit reaches a special high voltage level that is substantially above a low voltage level range of signals normally associated with binary logic levels. The special mode activation circuit comprises a voltage reduction subcircuit, a voltage detection subcircuit, and an active pullup subcircuit. The voltage reduction subcircuit reduces the voltage of the input signal to generate a reduced voltage input signal. The voltage detection subcircuit is responsive to the reduced voltage signal to prevent activation of the special mode circuit when the reduced voltage input signal is less than a preset threshold value and to activate the special mode circuit when reduced voltage input signal exceeds the preset threshold value. The active pullup subcircuit maintains the voltage of the reduced voltage input signal above a minimum voltage to (1) prevent leakage current through the voltage reduction subcircuit, (2) reduce the voltage change required in the reduced voltage input signal to activate the special mode circuit, and (3) reduce the possibility of induced latchup.