FAIL-SAFE ACTIVE BAND-PASS FILTER

摘要

AN IMPROVED FAIL-SAFE ACTIVE BAND-PASS FILTER This disclosure relates to an improved fail-safe electronic filter circuit including a common-emitter transistor amplifier having a feedback path. The feedback path includes an R-C twin-T network which is imperfectly nulled to only provide regeneration at a preselected frequency. An emitter-fol-lower circuit operates to isolate the series resistance branch of the R-C twin-T network from the collector of the transistor amplifier so that an output signal is only available during the presence of a signal having the preselected frequency and in the absence of a critical component or circuit failure.