Capacitor cancellation method and apparatus
AssigneeLegerity, Inc.
InventorsRobert Kuo-Wei Chen, John C. Gammel, Dewayne Alan Spires
Life of this patent
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Abstract
A capacitor cancellation method and apparatus for use in an interface circuit having a transformer blocking capacitor. The method includes sensing a voltage across the transformer blocking capacitor and generating a cancellation signal to compensate for the effect of the transformer blocking capacitor. The apparatus includes a sensor to sense a differential voltage across the transformer blocking capacitor to develop a capacitor signal and an amplifier to amplify the capacitor signal to obtain a cancellation signal.
Claims29
A method for canceling the effect of a transformer blocking capacitor in an interface circuit on the impedance between tip/ring lines, said method comprising the steps of:
- sensing a differential voltage across the transformer blocking capacitor;
- generating a cancellation signal based on said differential voltage;
- and
- adding said cancellation signal to the tip/ring lines.
A method for controlling the impedance between tip/ring lines in an interface circuit having a transformer blocking capacitor, said method comprising the steps of:
- determining a differential tip/ring current;
- synthesizing an impedance based on said differential tip/ring current;
- adding said synthesized impedance to the tip/ring lines;
- sensing a differential voltage across the transformer blocking capacitor;
- generating a cancellation signal from said sensed differential voltage;
- and
- adding said cancellation signal to the tip/ring lines.
An apparatus for canceling the effect of a transformer blocking capacitor in an interface circuit on the impedance between tip/ring lines, the interface circuit including a CODEC and SLIC for synthesizing an impedance between the tip/ring lines based on a differential current on the tip/ring lines, said apparatus comprising;
- a sensor to sense a differential voltage across the transformer blocking capacitor and develop a capacitor signal from said sensed differential voltage;
- and
- an amplifier to amplify said capacitor signal to obtain a cancellation signal, said cancellation signal cancelling the impedance effect of the transformer blocking capacitor when added to the tip/ring lines.
An apparatus for controlling the impedance between tip/ring lines in an interface circuit, said apparatus comprising:
- a transformer having a transformer blocking capacitor, said transformer coupled between the tip/ring lines for passing frequencies above a first predetermined level;
- a low pass filter coupled between the tip/ring lines for passing frequencies below a second predetermined level;
- a CODEC for generating an impedance voltage based on a portion of current on the tip/ring lines;
- a circuit coupled to said transformer blocking capacitor to sense a differential voltage across said transformer blocking capacitor and develop a cancellation signal based on said sensed differential voltage to place on the tip/ring lines;
- and
- a SLIC coupled between said CODEC and said low pass filter, said SLIC configured to interface said CODEC with the tip/ring lines through said low pass filter, said SLIC synthesizing an impedance between the tip/ring lines based on the impedance voltage generated by the CODEC.
An apparatus for generating a cancellation signal to cancel the effect of a transformer blocking capacitor on impedance between tip/ring lines, said apparatus comprising:
- a circuit having a first input configured for coupling to a first side of the transformer blocking capacitor, a second input configured for coupling to a second side of the transformer blocking capacitor, and an output;
- and
- a SLIC having an input coupled to the output of said circuit and an output configured for coupling to the tip/ring lines.
An apparatus for generating a cancellation signal to cancel the effect of a transformer blocking capacitor on impedance between tip/ring lines, said apparatus comprising:
- an inverter having an input and an output configured for coupling to a first end of the transformer blocking capacitor;
- and
- a first amplifier having a first input configured for coupling to the first end of the transformer blocking capacitor, a second input configured for coupling to a second end of the transformer blocking capacitor, and an output coupled to the input of said inverter and configured for coupling to the second end of the transformer blocking capacitor.
Dependencies are inferred from the claim text.