Noise canceler for keying pulse in CATV converter

Claim 1

A noise canceler for removing noise pulses from a keying signal defined by a plurality of keying pulses and noise pules, comprising: a canceling pulse generating means for receiving the keying signal and for generating a canceling pulse signal having a canceling pulse upon each leading edge of each keying pulse and noise pulse of the keying signal, each canceling pulse having a pulse width of a first predetermined time period; a delaying means for receiving the keying signal and for delaying each keying pulse and noise pulse of the keying signal by a second predetermined time period to generate a delayed keying signal; and, a canceling means for receiving said delayed keying signal from said delaying means and said canceling pulse signal from said canceling pulse generating means, and for generating a noise canceled keying signal having a pulse corresponding to each received pulse of said delayed keying signal except during a time period in which a canceling pulse of said canceling pulse signal is also received; said canceling pulse generating means including (a) a leading edge detector for detecting a leading edge of each keying pulse and noise pulse of said keying signal, (b) a timer, coupled to said leading edge detector, for generating a clear signal after the lapse of said first predetermined time period from the detection of a leading edge by said leading edge detector, and (c) a latch circuit, coupled to said timer, for latching said keying signal to generate a first level signal at each keying pulse and noise pulse of said keying signal and for clearing in response to said clear signal from said timer to generate a second level signal, said first level signal corresponding to a canceling pulse.