Loop current detector with threshold setting impedance
AssigneeAT&T Bell Laboratories
InventorDaniel M. Joffe
Life of this patent
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Abstract
In a loop circuit closure detector, a circuit which connects a voltage comparator to the loop circuit is biased so that the comparator indicates loop circuit closure at a predetermined minimum non-zero value of loop current. Comparator inputs are both coupled to supply voltage connections by approximately equal-attenuation paths and are both coupled to said loop circuit by approximately equal-attenuation paths.
Claims12
A loop circuit current detector including a coupling network for applying detector input signals to a comparator, said coupling network including a bridge circuit, and said detector being characterized in that there are provided
- means for balanced said bridge circuit,
- means for imposing a predetermined offset bias on an input terminal of said comparator, and
- means, responsive to detector input signals, for biasing said comparator input terminal in opposition to said offset bias.
A current level detector comprising
- means for receiving a predetermined supply voltage,
- a pair of terminals at which detector input voltages are produced to indicate current-level-responsive information regarding input signals to said detector,
- means for biasing said pair of terminals to approximately the same voltage, the voltage difference between said terminals being independent of said supply voltage,
- means, in said biasing means, and responsive to current level of said input signals to said detector, for modifying the voltage difference between said terminals in a first predetermined direction by an amount corresponding to said current level, and
- means, responsive to said supply voltage, for applying an offset bias to at least one of said terminals to modify the voltage difference between said terminals in a second predetermined direction by a predetermined amount which is independent of both said input current level responsive signals and said supply voltage.
Dependencies are inferred from the claim text.