FAILSAFE DIFFERENTIAL AMPLIFIER CIRCUIT

摘要

Differential input fail safe circuitry is disclosed that detects missing or too low differential signals combined with a frequency lower than a frequency limit where a final safe condition is detected and signaled. The output signal form the fail safe circuitry is held in a given state that is an invalid representation of the differential input signal. A frequency detector, complementary offsetting auxiliary amplifiers with limit frequency roll offs are used to detect the fail safe condition. In addition a delay circuit is used that requires tha fail safe condition to exist for some time before the fail safe circuit is active. Initialization circuitry ensures a proper power up conditions where the circuitry is enabled to detect the fail safe conditions and guarantees a reliable failsafing irrespective of the previous state of the signal.