Self-monitoring line interface circuit
First Claim
1. A line interface circuit having self-contained, self-testing circuit elements for providing battery feed, over-voltage protection, ring insertion, supervision, coding/decoding and hybrid (BORSCHT) functions for a subscriber'"'"'s loop, said line interface circuit comprising:
- a. a feed resistor network connectable to said loop;
b. a dual voltage regulated current source connected to said network;
c. line driving and receive amplifier means connected to said feed resistor network, andd. a microprocessor/DSP for controlling the application of power to said current source and to said line driving and receive amplifier means while said line interface circuit is connected to said loop to enable said circuit elements to provide said BORSCHT functions and for selectively denying power to said line driving and receive amplifier means to place said means in a high impedance state so as to isolate or include said amplifier means in circuit for testing purposes while said circuit is connected to said loop.
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0 Petitions
Accused Products
Abstract
A line circuit whose circuit components are selectively controllable by a microprocessor/DSP to provide normal BORSCHT functions or to be selectively tested without need for an electromechanical relay to isolate the line circuit from the loop conductors. The conventional line transformer is advantageously replaced by a loop current feed resistor network and either a high voltage or a lower voltage battery may be connected to provide loop current to the resistor network through a current regulator circuit and battery switch circuit. In normal operation, an ac feedback path, which includes the line receive amplifier, increases the terminating impedance above the dc value of the feed resistors so the loop termination resistor network may match the characteristic impedance of the loop at the audio frequencies employed. In the testing mode, the microprocessor/DSP selectively applies or denies power to the line driving and receive amplifiers as well as to a level shifting circuit interposed between the codec analog output and the input to isolate or include these components or to provide a codec loop-back path. The condition of the dc feed resistors and protective fuses, the condition of the loop closure detector and of the ringing generator are reported to the microprocessor/DSP over the same terminal normally used for reporting the on-hook and off-hook status of the loop.
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Citations
34 Claims
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1. A line interface circuit having self-contained, self-testing circuit elements for providing battery feed, over-voltage protection, ring insertion, supervision, coding/decoding and hybrid (BORSCHT) functions for a subscriber'"'"'s loop, said line interface circuit comprising:
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a. a feed resistor network connectable to said loop; b. a dual voltage regulated current source connected to said network; c. line driving and receive amplifier means connected to said feed resistor network, and d. a microprocessor/DSP for controlling the application of power to said current source and to said line driving and receive amplifier means while said line interface circuit is connected to said loop to enable said circuit elements to provide said BORSCHT functions and for selectively denying power to said line driving and receive amplifier means to place said means in a high impedance state so as to isolate or include said amplifier means in circuit for testing purposes while said circuit is connected to said loop. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 28, 29)
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18. A method of testing a loop interface circuit having a plurality of circuit elements for providing (battery feed, over-voltage protection, ring insertion, supervision, coding/decoding and hybrid BORSCHT) functions to said loop, including a codec for transmitting analog signals over said loop in response to digital signals from a processor and for sending digital signals to said processor in response to analog signals received over said loop, and loop driving and receive amplifiers intermediate said loop and said codec, said method comprising:
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a. selectively placing said loop driving and receive amplifiers in a high impedance state to isolate the codec'"'"'s input and output from said loop; b. connecting the analog output of said codec to its analog input; and c. causing said processor to apply a digital tone code to, and to analyze the corresponding digital signal returned from, said codec.
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19. A method of testing a loop interface circuit having a plurality of circuit elements for providing (battery feed, over-voltage protection, ring insertion, supervision, coding/decoding and hybrid BORSCHT) functions to said loop, including a codec for transmitting to and receiving from said loop analog signals and for receiving from and transmitting to a processor corresponding digital signals, a driving amplifier respective to each lead of said loop for applying differential analog signals to said loop, and a receive amplifier connected between said leads of said loop, said method comprising:
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a. selectively placing said loop driving amplifier respective to one of said leads in a high impedance state to isolate the codec'"'"'s analog output from said one lead of said loop; b. maintaining the other said driving amplifier and said receive amplifier enabled to transmit analog signals to and receive analog signals from the other of said leads; and c. causing said processor to apply a digital tone code to, and to analyze the corresponding digital signal returned from, said codec. - View Dependent Claims (20, 21, 22, 23, 24)
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25. A method of testing the DC feed resistor network of a loop interface circuit having a plurality of processor controlled circuits for providing (battery feed, over-voltage protection, ring insertion, supervision, coding/decoding and hybrid BORSCHT) functions to said loop including current-limited high or low battery voltage, an amplifier for normally receiving analog signals from said loop and for producing an output determined by the potential between the conductors of said loop, a comparator for monitoring said amplifier output against a threshold set by said battery voltage and for applying a logic level signal to said processor indicative of loop status, said processor verifying the condition of said resistor network, comprising the steps of:
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a. placing said receiving amplifier in a high impedance state to isolate the input and output of said amplifier from said loop; b. applying ground potential to the tip lead and selectively applying said high and said low battery potentials to the ring lead of said loop; c. setting a respective threshold for detecting tip lead and ring lead current through said network in accordance with said selectively applied battery voltage; and d. applying a logic level signal to said processor when each said respective threshold is crossed.
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26. A method of testing the loop closure detector of a loop interface circuit having a plurality of processor controlled circuits for providing (battery feed, over-voltage protection, ring insertion, supervision, coding/decoding and hybrid BORSCHT) functions to said loop including current-limited high or low battery voltage, an amplifier for normally receiving analog signals from said loop and for producing an output determined by the potential between the conductors of said loop, a comparator for monitoring said amplifier output against a threshold determined by said battery voltage and for applying a logic level signal to said processor indicative of loop status, said processor verifying the condition of said loop closure detector, comprising the steps of:
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a. placing said receive amplifier in the high impedance state to isolate its input from said loop and its output from one input of said comparator; b. selectively forcing said one input of said comparator to ground or to a fraction of said battery voltage; and c. applying a fraction of normal battery voltage to the other input of said comparator.
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27. A method of testing the ringing generator of a loop interface circuit having a plurality of processor controlled circuits for providing (battery feed, over-voltage protection, ring insertion, supervision, coding/decoding and hybrid BORSCHT) functions to said loop including current-limited high or low battery voltage, an amplifier for normally receiving analog signals from said loop and for producing an output determined by the potential between the conductors of said loop, a comparator for monitoring said amplifier output against a threshold set by said battery voltage and for applying a logic level signal to said processor indicative of loop status, said processor verifying the condition of said ringing generator, comprising, prior to applying ringing voltage to said loop, the steps of:
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a. placing said receiving amplifier in a high impedance state to isolate the input and output of said amplifier from said loop; b. causing said ringing generator to ramp its output from said battery voltage towards ground potential; c. monitoring the potential at the ring conductor; and d. reporting a logic level signal to said processor when said monitoring of said potential crosses a predetermined threshold.
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30. A method of self-testing of a loop interface circuit having a plurality of circuit elements including an on-board processor for providing BORSCHT functions to said loop, including a codec for transmitting analog signals over said loop in response to digital signals from said processor and for sending digital signals to said processor in response to analog signals received over said loop, and loop driving and receive amplifiers intermediate said loop and said codec, said method comprising:
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a. activating said circuit elements from said on-board processor for placing said loop driving and receive amplifiers in a high impedance state to isolate the codec'"'"'s analog input and output from said loop; and b. monitoring from said on-board processor the idle channel noise that appears at the digital output of said codec.
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31. A line circuit having line driving and receive amplifiers, a codec, and an interface between said codec and said amplifiers to establish the dc level of the analog signals at the codec output, said line circuit providing BORSCHT functions including battery feed, over-voltage protection, ring insertion, supervision, coding/decoding and hybrid under the control of a microprocessor/DSP, the improvement wherein said microprocessor/DSP controls the execution of a plurality of the following steps:
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(a) a loop back test in which the tip and ring driving and receive amplifiers and their interface to the codec are turned off to place them in a high impedance state so as to isolate the codec'"'"'s input and output from the tip and ring conductors of the loop, said microprocessor/DSP applying a digital tone code to the codec'"'"'s digital input, the codec'"'"'s analog output being connected to its analog input and the codec'"'"'s digital output being connected to the microprocessor/DSP for analysis; (b) a tip side transmission test in which the tip side driving amplifier and the receiving amplifier are enabled but the ring side driving amplifier is turned off and placed in a high impedance state;
the microprocessor/DSP issuing a digital tone code to the codec'"'"'s digital input, the codec'"'"'s analog output supplying a test tone to the tip driving amplifier and in which the reflection of the test tone from the resistor network is sensed by the receive amplifier and applied to the codec'"'"'s analog input and the codec'"'"'s digital output is analyzed by the microprocessor/DSP to determine if the enabled amplifiers, loop terminating resistors and coupling capacitors are functional; and(c) a ring side transmission test which performs counterpart functions for the ring side transmission path. - View Dependent Claims (32, 33, 34)
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Specification