Tracking analog-to-digital converter for AC signals

An analog-to-digital converter system for converting input AC signals derived from at least a single source thereof to delta-format digital output pulses comprising:

• capacitive means having a pair of terminals, one terminal of which is connected to a source of AC signals for storing a charge representative of the amplitude thereof,
• comparison means coupled to the other terminal of said capacitive means, a reference potential and means for incrementally varying the latter potential by superimposing a component of voltage thereon, said comparison means comparing the potential corresponding to the charge on said capacitive means with said reference potential and providing periodic voltage transitions in response to the incremental variation of the reference potential when the potentials being compared are substantially equal and further providing voltage levels in the absence of said voltage transitions when said last mentioned potentials are unequal,
• digital logic means coupled to said comparison means and being responsive to said voltage levels for generating said delta-format digital output pulses as indicative of a predetermined increment of change in the amplitude of said AC signals,
• a feedback loop coupling said digital logic means to said other terminal of said capacitive means, said feedback loop being actuated by said digital logic means, concurrently with the generation of said delta-format digital output pulses, by causing selective bipolar currents to flow therein for a predetermined time, said bipolar currents restoring a balanced condition by charging said capacitive means to the difference in potential between a given amplitude AC signal and said reference potential, the direction of said bipolar currents being determined by said voltage levels provided by said comparison means.