Method and apparatus for calculating DC offset in a digital gyrator

An apparatus for regulating the DC line current on a telephone line comprising:

• a data access arrangement having an AC output, a DC output and an input coupled with said telephone line, wherein said data access arrangement generates a signal at the AC output which represents the AC voltage across said telephone line and said data access arrangement generates a signal at the DC output which represent the DC voltage across said telephone line;
• a converter, having an output, an inherent output level representing a DC voltage, an AC input, and a DC input, for converting a signal produced by said data access arrangement to a digital signal;
• a first switch for alternatively coupling the AC input of said converter to a system common mode voltage or the AC output of said data access arrangement;
• a second switch for alternatively coupling the DC input of said converter to ground or the DC output of said data access arrangement;
• a processor for filtering said digital signal to derive a first control signal, wherein said processor removes the inherent output level of said converter from said digital signal;
• and
• a first controllable current source controlled by said control signal for setting the DC current on said telephone line.

An apparatus for regulating the DC line current on a telephone line connection between a telephone company central office and a data producing device comprising:

• a data access arrangement (DAA) coupled to said telephone company central office, wherein said DAA comprises an AC/DC signal splitter and a controlled current source;
• a coder/decoder (CODEC) coupled to said DAA for converting signals from said DAA to digital and converting signals to said DAA to analog, wherein said CODEC has a constant inherent output level which skews the output of the analog-to-digital portion of said CODEC;
• a processor coupled to said CODEC, wherein said processor accommodates for said constant inherent output level of the analog-to-digital portion of said CODEC;
• and
• a data source coupled to said processor;
• such that said processor controls said controlled current source.

An apparatus for regulating the DC line current on a telephone line connected through a tip and ring connection coupled to a telephone company central office comprising:

• a data access arrangement (DAA) coupled to said telephone company central office through said tip and ring connection, wherein said DAA comprises;
• an AC/DC signal splitter having an analog AC output, an analog DC output,
• and an input coupled to said tip connection;
• and
• a controlled current source, having a controlled input, coupled between said tip and ring connection;
• an analog-to-digital (A/D) converter having an analog AC input, an analog DC input, and a digital output;
• a first switch for alternatively coupling the analog AC input of said A/D converter to a common mode voltage source or the analog AC output of said AC/DC signal splitter;
• a divider circuit for reducing the voltage out of the analog DC output to an analog divided DC output;
• a second switch for alternatively coupling the analog DC input of said A/D converter to a first ground terminal or the analog divided DC output;
• a processor coupled to the output of said A/D converter for filtering and scaling the output of said A/D converter, and combining the filtered and scaled output of said A/D converter with a data signal to derive a digital control signal;
• a digital-to-analog (D/A) converter having a digital input and an analog output coupled to said controlled current source for regulating the DC line current on said telephone line;
• and
• a third switch for alternatively coupling the digital input of said D/A converter to said digital control signal or a second ground terminal.