Comparator with hysteresis for interfacing with a ground-referenced A.C. sensor

A circuit suitable for detecting transitions of an A.C. signal having a voltage which oscillates about a reference potential, the circuit providing hysteresis-type switching action and providing a symmetrical output waveform, the circuit comprising:

• (a) input means including an input terminal for receiving the A.C. signal, a control terminal coupled to a control node for receiving a control voltage, and an output terminal for providing a first output signal, said input means being responsive to the A.C. signal voltage and to the control voltage such that the first output signal is enabled upon the A.C. signal voltage being different from the control voltage by a first predetermined amount;
• (b) feedback means having an input terminal coupled to the output terminal of said input means and having an output terminal coupled to the control node, said feedback means being responsive to the first output signal for switching the output terminal of said feedback means between a first state and a second state, the first state being effective to render the conrol voltage at the control node substantially equal to the reference potential;
• (c) bias means coupled to the control node for establishing the control voltage at the control node at a bias voltage whenever the output terminal of said feedback means is in the second state, the bias voltage being different from the reference potential by substantially twice the first predetermined amount;
• (d) clamping means coupled between the input terminal of said input means and a source of the reference potential for restricting the voltage of the A.C. signal from being different from the reference potential in excess of a second predetermined amount;
• and
• (e) circuit output means electrically coupled to said control node and having a symmetrical output signal thereon having a first level when said output terminal of said feedback means is in said first state and having a second level when said output terminal of said feedback means is in said second state.