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Loop current monitor circuitry and method for a communication system
| Details |
Inventors: Scott, Jeffrey W.; Krone, Andrew W.; Sooch, Navdeep S.; Welland, David R.;
Assignee: Silicon Laboratories, Inc. (Austin, TX)
Primary Examiner: Hudspeth; David R.
Assistant Examiner: Lerner; Martin
Attorney, Agent or Firm: O'Keefe, Egan & Peterman, LLP
Monitor circuitry is disclosed that produces a loop current monitor signal indicative of the DC loop current passing through DC holding circuitry, which may be part of phone line side circuitry that may be connected to phone lines. This loop current monitor signal may be digitized and then communicated across an isolation barrier to powered side circuitry as digital information representative of the DC loop current levels in the phone lines. Example embodiments for the monitor circuitry are also disclosed, such as a MOS transistor, for which the monitor signal is the drain current of the MOS transistor, and an external resistor, for which the monitor signal is a voltage associated with the external resistor. |
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DETAILED DESCRIPTION We claim: 1.
A communication system, comprising: phone line side circuitry capable of being coupled to phone lines through an isolation barrier; a DC holding circuit within said phone line side circuitry; and monitor circuitry having as an output a loop current monitor signal that is indicative of a DC loop current passing through said DC holding circuit, the phone line side circuitry configured to transmit information to the isolation barrier that is indicative of said DC loop current.
2.
The communication system of claim 1, further comprising powered side circuitry capable of being coupled to said phone line side circuitry through an isolation barrier.
3.
The communication system of claim 2, further comprising said isolation barrier coupled between said phone line side circuitry and said powered side circuitry.
4.
The communication system of claim 3, wherein said isolation barrier comprises one or more capacitors.
5.
The communication system of claim 4, wherein digital information is communicated across said isolation barrier.
6.
The communication system of claim 1, wherein said DC holding circuitry comprises a MOS transistor, said monitor circuitry comprises an external resistor coupled to said MOS transistor, and said loop current monitor signal is a voltage associated with said external resistor.
7.
The communication system of claim 1, wherein said monitor circuitry comprises a MOS transistor and a drain current of said MOS transistor is said loop current monitor signal.
8.
The communication system of claim 7, wherein said DC holding circuit comprises a first MOS transistor connected such that a DC loop current passes through said first MOS transistor, wherein said monitor circuitry comprises a second MOS transistor having its gate coupled to a gate of said first MOS transistor and having its source coupled to a source of said first MOS transistor.
9.
The communication system of claim 8, wherein a size of said second MOS transistor is selected to be a desired ratio of a size of said first MOS transistor so that a current through said second MOS transistor is a desired ratio of a current through said first MOS transistor
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