Decoding circuit for telephone transaction system

Claim 1

A decoding circuit for receiving selected pairs of alternating currents having distinctive frequencies and for delivering a current pulse to a load circuit timed in accordance with its decoded valves comprising: a. a plurality of electrical band-pass filtering circuits, each for sensing a designated current frequency and for passing an output pulse whenever the designated frequency current is applied; b. a plurality of AND-circuits each having two inputs and a single output circuit, each of the input circuits connected respectively to a filtering output circuit, and each ANDcircuit having an output terminal connected to a load, each of said AND-circuits delivering an output pulse to its load circuit only when both input circuits receive current pulses; c. a plurality of bistable multivibrator storage circuits, each having their input circuit connected to an AND-output terminal, each of said storage circuits adapted to a activated by the AND-circuit to apply a voltage to an output terminal to indicate a decoded symbol; d. a diode matrix including a plurality of input conductors each connected to an output terminal of a storage multivibrator, a plurality of bias conductors for sequentially applying bias voltages to the matrix, a single output conductor connected to all the input conductors in series with a plurality of barrier diodes, and a plurality of cross-connected diodes connected between the input conductors and the bias conductors for selectively energizing a predetermined input conductor during a cycle of operations; e. and a plurality of energizing circuits connected to the bias conductors for sequentially applying bias voltages thereto, said energizing circuits controlled by a means for producing synchronizing pulses in timed relation to a utilization circuit.