Tone elimination circuit
AssigneeMotorola, Inc.
InventorsMichael J. Gay, W. David Pace
Life of this patent
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Abstract
A cancellation circuit which may be utilized in a subscriber loop interface circuit to allow a tone to be supplied in the receive path of the hybrid circuit to be received by the calling subscriber and for cancelling said tone from being transmitted to a called subscriber that is coupled via a carrier channel to the hybrid circuit. The cancellation circuit comprises circuitry responsive to the tone appearing on the transmit path for supplying in-phase and quadrature phase signals at the frequency of this tone to cancel the same to prohibit transmission thereof while simultaneously varying the output impedance of the hybrid circuit at the frequency of the applied tone.
Claims5
In a hybrid circuit providing interface between a pair of unidirectional transmission paths and a balanced two-wire bidirectional subscriber loop including signal generator means responsive to signal inputs for supplying a driving signal into the subscriber loop and being responsive to differential signals on the subscriber loop for supplying driving signals onto the transmit path of the unidirectional transmission paths and having a feedback loop coupled from an output of the signal generator to the input thereof, a cancellation circuit responsive to an impulse signal of predetermined frequency being inserted on the transmit path from the signal generator and a continuous wave signal of said predetermined frequency for generating a first, antiphase, signal of equal magnitude to said impulse signal at a first output thereof, said antiphase signal being summed with said impulse signal to reduce the level of the same.
Dependencies are inferred from the claim text.