Abstract: A signal detection system with dynamically adjustable detection threshold includes a signal detection comparator having a dynamically adjustable threshold which adjusts the detection sensitivity of the comparator from a quiescent value to a value which is dependent upon the value of an event trigger signal, thus anticipating the amplitude of a second, confirming event trigger signal. Additionally, an alarm window timer activated by an event signal which exceeds the quiescent signal detection comparator threshold, assures that an alarm activator will be enabled only after a second, confirming event trigger signal exceeds the adjusted detector threshold, and which occurs during the active period of the alarm window timer.

Abstract: A passive analog equalizer is connected to the output of an infrared detector to provide increasing pyroelectric detector sensitivity with increasing target frequency in order to provide a detection sensitivity which is substantially flat over the target velocity range of interest. An interruptable modulator is connected to the equalized pyroelectric detector signal to shift its frequency upwardly in order to provide negligible drift, fast recovery from transients, and the ability to quickly shut down the modulator when a transient occurs. A transient detector is operative in response to transients in the pyroelectric detector output signal to provide a window during which the modulator is interrupted in order to prevent transient induced false alarms.