Threshold control with data receiver

A receiver for receiving ac coupled binary data having a variable duty cycle, comprising:

• controllable offset voltage generating means including an input terminal adapted to be coupled to said source of binary data and also including an output terminal for establishing a direct offset voltage between said input and output terminals under the control of a correction signal, to thereby generate offset binary data;
• positive detection means including input and output terminals for responding to excursions of applied data in a positive polarity relative to a positive average value generated at said output terminal of said controllable offset voltage generating means in response to said applied data;
• negative detection means including input and output terminals for responding to excursions of applied data in a negative polarity relative to a negative average value generated at said output terminal of said controllable offset voltage generating means in response to said applied data;
• alternating current coupling means coupled to one of said input and output terminals of said controllable offset voltage generating means and to said input terminals of said positive detection means and of said negative detection means for applying said binary data thereto for forming said positive average value at said output terminal of said positive detection means and said negative average value at said output terminal of said negative detection means, said positive average value and said negative average value being perturbed in response to duty cycle changes of said binary data;
• summing and coupling means coupled to said output terminals of said positive detection means and of said negative detection means, and to said controllable offset voltage generating means for summing together said positive average value and said negative average value to form said correction signal, and for coupling said correction signal to said controllable offset voltage generating means with a polarity selected for open-circuit correction for controlling said offset voltage in a manner tending to hold a point midway between excursion extremes of said offset binary data at a constant voltage regardless of said duty cycle;
• and
• comparator means coupled to said output terminal of said controllable offset voltage generating means for comparing said offset binary data with a fixed reference voltage for generating decided data therefrom.