US20020136394A1 - Signal coupler using high voltage and low voltage filtering - Google Patents
Signal coupler using high voltage and low voltage filtering Download PDFInfo
- Publication number
- US20020136394A1 US20020136394A1 US10/077,570 US7757002A US2002136394A1 US 20020136394 A1 US20020136394 A1 US 20020136394A1 US 7757002 A US7757002 A US 7757002A US 2002136394 A1 US2002136394 A1 US 2002136394A1
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- US
- United States
- Prior art keywords
- signal
- pass filter
- low pass
- pots
- filtered
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- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0002—Modulated-carrier systems analog front ends; means for connecting modulators, demodulators or transceivers to a transmission line
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M3/00—Automatic or semi-automatic exchanges
- H04M3/005—Interface circuits for subscriber lines
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M3/00—Automatic or semi-automatic exchanges
- H04M3/005—Interface circuits for subscriber lines
- H04M3/007—Access interface units for simultaneous transmission of speech and data, e.g. digital subscriber line [DSL] access interface units
Abstract
Description
- This patent application is a continuation of pending patent application entitled SIGNAL COUPLER USING LOW VOLTAGE FILTERING, having a filing date of Apr. 9, 1998, and a Ser. No. of 09/057,953.
- The invention relates to a signal coupler for telephone lines containing both plain old telephone service (POTS) and digital signals where low voltage filtering is used in the POTS channel.
- Modem data networks commonly use complex digital signal processing (DSP) devices called modems to transport data over communication channels. Data is typically transported via an analog transmission signal, which is representative of a synchronous, constant rate bit stream. This form of communication channel is suitable for the transmission of real-time information such as voice or video.
- Often it is desirable to transmit both Plain Old Telephone Service (POTS) and digital data, either by Asymmetric Digital Subscriber Line (ADSL) or some other method, over the same line. The POTS frequency spectrum ranges from 300 to 3400 Hz. The ADSL frequency spectrum ranges from 24 kHz to 1100 kHz.
- As shown in FIG. 1, the data and POTS signals are transmitted over standard telephone lines between a central office and a subscriber's home. The subscriber may have several modems and a POTS service. The subscriber is typically connected to a central office by twisted copper wire pair. At the central office, a signal coupler is used to filter, split and digitize signals coming into the central office from a subscriber. The digital signals are processed through switching networks and then sent through another signal coupler to another subscriber. Alternatively, the digital signal may be transmitted to another central office before being sent through another signal coupler to another subscriber. The signal coupler converts the digital signals from the switching circuits into analog signals for transmission to the subscriber as well as converting the analog input from the subscriber into digital signals, which are sent to the switching circuits.
- The transmission lines between the central office and the subscriber may be twisted copper pairs, as shown in FIG. 1. Other possibilities for transmission lines include fiber optics. In any case, the equipment at the central office and at the subscriber must be protected against power cross, lightning strikes, or other high voltage events and current surges on the telephone line. The main voltage protection is accomplished outside of the central office. However, secondary voltage protection is usually included in the signal coupler. In FIG. 2, the signal from the subscriber appears on the TIP and RING lines and the secondary voltage protection is shown as the
circuit protection 101. - After the voltage and current protection is accomplished, the signal is split into data and voice lines. The data is sent at frequencies in the 20-30 kilohertz range and up while POTS voice information is nominally below 3000 Hz. The splitting, then, is normally done by using a high-pass filter for the data lines and a series of low-pass filters for the POTS lines. The series of filters is further required to remove the noise from the incoming telephone cable. FIG. 2 shows the typical filtering circuit for the POTS. In FIG. 2, the voice filtering is accomplished by a multistage filtering circuit. The typical low pass filter used in the multistage filtering circuit has two to four stages of filtering.
- The POTS signal from the subscriber, after passing through the
protection circuit 101, is filtered by the multistagelow pass filter 102. The multiple stages allow for filtering of multiple orders (i.e., a first order filter has only one stage while a second order filter has two stages). The components of each stage include an inductor pair and a capacitor.Stage 1 in FIG. 2, for example, has inductor L1 connected in series with the TIP line afterprotection circuit 101 and inductor L1′ connected in series with the RING line after the protection circuit. Capacitor C1 is connected across the TIP and RING lines after the inductor pair L1 and L1′. The remaining stages have similar components. In addition, thelow pass filter 102 includes resistors R1 and R2 connected in a series with the TIP and RING lines before they are connected toStage 1 and resistors R3 and R4 connected in series with the TUP and RING lines after they exit stage N. In addition, the low pass filtering circuit may include an additional inductor pair acting as a common mode choke which rejects signals common to both input lines. The common mode choke is connected beforestage 1 and is connected similar to inductor pair L1 and L1′. - Each component of the filtering circuit (i.e., the resistors, inductors, and capacitors) must be capable of withstanding the high battery voltage (48 V) and high DC currents (typically 25 mA) used in the subscriber loop. This necessitates that each of the components in the filtering circuit be discrete components, which require a large amount of space on the circuit board. This space requirement restricts the number of lines that can be placed on a given circuit board. It is desirable, then, to reduce the amount of filtering which must be accomplished in the high voltage mode.
- Accordingly, the present invention provides a signal coupler circuit, which provides the circuit protection and the filtering in a way that allows conservation of space on the circuit board at the central office. This is done by filtering the voice lines, at least in part, in a portion of the circuit where the high battery voltage is no longer present.
- An analog signal capable of containing both POTS and data signals is present between the TIP and RING lines. The TIP and RING lines are the components of a standard twisted pair configuration of telephone service. The invention, however, is not restricted to twisted pairs and is useful for any transmission method of telephone service.
- The signal between TIP and RING is first inputted to a voltage surge protection circuit. The surge protection circuit limits voltage spikes and current surges, which could damage other components. The main voltage and current surge protection is connected to the transmission line outside of the central office so that the protection required on the circuit board inside the central office is secondary circuit protection.
- The output signal from the protection circuit is inputted to a low-pass filter. The low-pass filter occupies a minimal amount of space while being capable of accommodating the high voltage telephone lines. In the preferred embodiment, only one stage of filtering is used. More stages of filtering could be used at this point but, because of the high battery voltage, these stages utilize a great deal of circuit board space.
- The output signal from the low-pass filter is then sent to a standard subscriber loop interface circuit (SLIC) device. The SLIC is a standard chip, which splits the two incoming lines into four lines, a pair of receive lines and a pair of transmit lines.
- The transmit lines are finally filtered after the SLIC chip to remove the remainder of the noise. When the filtering is done after the signal is passed through the SLIC component, the high battery voltage is no longer present. The filtering components, then, can exist on a single chip and will take up much less space on the circuit board. Alternatively, some of the filtering may be accomplished digitally after the signal has been digitized by the CODEC.
- The present invention provides a way of dispensing with the multistage high-voltage filtering which typically occurs before the SLIC in favor of low voltage, and therefore smaller and more compact, filtering on the transmit lines after the SLIC. The resulting savings in space will allow more signal couplers to exist on a given circuit board.
- FIG. 1 illustrates a block diagram of a telephone subscriber loop;
- FIG. 2 illustrates a circuit diagram of a prior art POTS filtering arrangement;
- FIG. 3 is a block diagram of a device to accomplish the present invention for POTS filtering;
- FIG. 4 is a circuit diagram of the preferred embodiment of the present invention of POTS filtering; and
- FIG. 5 shows a second embodiment where part of the low voltage filtering is accomplished on the digital side of the circuit.
- In accordance with the present invention, most of the POTS filtering is removed from areas of the circuit which require components capable of handling the high battery voltage and DC current of the telephone subscriber loop to areas of the circuit where only low voltage filtering is required.
- FIG. 3 shows a block diagram of the
signal coupler 100, which will accomplish this result. TheTIP line 10 andRING line 11 represent the two wires of the twisted copper pair.TIP line 10 andRING line 11 are inputted to theprotection circuit 101. Theprotection circuit 101, a standard well-known circuit, provides the voltage and current protection necessary to guard the remainder of the device from high voltage and high current surges typically caused by lightning strikes, power cross, or other unexpected electrical events. The Bellcore administrative standard LATA Switching System Generic Requirements (LSSGR), the standard adopted by all Bell operating companies, has a first level lightening strike test and a second level lightening strike test. (See Lucent Technologies, Overvoltage Protection of solid-State Subscriber Loop Circuits, APPLICATION NOTE, February 1997, at 9-10). In the first level test, the circuit must survive the tests outlined in Table 1. The circuit need not survive the second level test, but no electrical shock or fire hazards can be created.TABLE 1 Bellcore First Level Lightning Strike Test Pulse (us) VP (V) (Rise Time/Decay Time) Ipeak (A) Reps ±600 10/1000 100 50 ±1000 10/360 100 50 ±100 10/1000 100 50 ±2500 2/10 500 50 - In a typical subscriber loop, the battery voltage across
TIP 10 andRING 11 is 48 V and the loop may typically carry a current of from 23-35 mA. Although the current is nominally 25 mA, it could range as high as 120 mA. - The output signal from the
protection circuit 101 onlines low pass filter 109. It is a good practice to use different numbers for components that are different (particularly when one is prior art and one is part of the invention). In addition, the lines DSLT 12 andDSLR 13 are inputted tohigh pass filter 106.Low pass filter 109 passes the POTS signal while not passing the data signal.High pass filter 106 does not pass the POTS signal while passing the data signal. In this way, the data path is separated from the POTS path. - In addition to splitting the POTS signal and the data signal,
low pass filter 109 also provides enough filtering to prevent overloading of the subscriber loop interface circuit (SLIC) 103. This requires that thelow pass filter 109 have at least one stage. In the preferred embodiment,low pass filter 109 has only one stage of filtering. The output oflow pass filter 109 isPTIP 14 andPRING 15. SignalsPTIP 14 andPRING 15 are inputted toSLIC 103. - The subscriber loop interface circuit (SLIC)103 is a standard integrated circuit which includes the function of splitting two lines which carry both transmit and receive signals (i.e., bi-directional transmission) into four lines, two of which carry the transmit signal and two of which carry the receive signal. The
SLIC 103 must also handle the 48 volt battery voltage supplied by the central office and 25 mA of current or more, as opposed to the typically 5 V commonly handled by such circuits. SLIC chips are standard chips and may be purchased, for example, from Lucent Technologies, AMD, Harris, or Mitel. The Lucent Technologies chip L7585 is the preferred component used with this invention. With the use of the standard SLIC chip, the filtering circuit shown in FIG. 3 will appear identical to a standard prior art filtering circuit for compatibility with existing equipment. - The
SLIC 103 outputs the transmitted signals onlines lines signal coupler 100, to the subscriber.Lines TIP 10 andRING 11 will carry both the transmit and the received signals, the transmit signals being those that are received into thecoupling circuit 100 and the receive signals being those that are received out of thecoupling circuit 100. - The transmit signals, on
lines VTX 18 andVRTX 19, are inputted to alow voltage filter 104. Filter 104 finishes filtering the incoming transmit signals. The receive signals,RCVP 16 andRCVN 17, are not filtered in this circuit. These signals would be filtered in another circuit as transmit signals before being switched into the circuit illustrated here as receive signals. The other coupling circuits and the switching circuits are shown in FIG. 1. - The four lines—RCVP16,
RCVN 17,VTX 20 andVRTX 21—are connected to coder/decoder circuit (CODEC) 105.CODEC 105 receives thedigital signal DRX 22 and outputs the analog receive signal betweenlines CODEC 105 receives the filtered analog transmit signal betweenlines DRT 23.CODEC 104 may also receive aclock signal 24 and aframing signal 25 in order to coordinate with a digital processing and switching circuit at the central office. - The
high pass filter 106, in addition to filtering out the POTS signal, also filters the 48 V battery voltage from between lines DSLT 12 andDSLR 13. The output lines ofhigh pass filter 106,lines Hybrid 107.Hybrid 107 performs the same two-wire to four-wire function thatSLIC 103 performs without the necessity of being capable of handling the high battery voltage or the associated high DC current. The Hybrid may need to operate with high current in higher frequency ranges. The four-wire side ofHybrid 107 includes receive signals on receivelines lines wires CODEC 108.Codec 108 converts the analog transmit signals received onlines line 31 and the digital receive signals received online 30 to analog signals output onlines digital lines - FIG. 4 illustrates
signal coupler 100 showing in greater detail the circuitry within thecircuit protection circuit 101, thelow pass filter 109 and thehigh pass filter 106. - The
circuit protection 101 in FIG. 4 has two components, current protection and voltage protection. The current protection onTIP line 10 is accomplished by resistor R1 in series with fuse F1. OnRING line 11, the current protection is accomplished by resistor R2 in series with fuse F2. The combination of resistor and fuse adhere to the Bellcore specifications, fuses F1 and F2 opening only in second level testing. In the embodiment shown in FIG. 4, R1 and R2 are both 5.6 Ohm resistors. - The voltage protection is provided by component Z, which acts as a triggered voltage shunt. Monolithic protection devices consisting of one or more SCR-type thyristers are commonly available under the trade names such as SURGECTAR (Harris, Inc.), SIDACTOR (Teccor, Inc.) and LB1201 SLIC Protector (Lucent Technologies, Inc.). Although any device which prevents the voltage between
lines TIP 10 andRING 11 from exceeding the Bellcore standard could be used, devices such as the SIDACTOR have the advantage of being benign until they are triggered. Preferably, Z is a SIDACTOR. Component Z is connected acrosslines TIP 10 andRING 11 with an output leg attached to a protection ground GNDPN. After Z triggers, it shunts the voltage across it directly to GNDPN. Preferably, Z should be chosen so that it triggers at around 200 volts. - The
low pass filter 109 in FIG. 4 is a single-stage LRC circuit.Line 12 is connected in series with resistor R3, inductor L1, and resistor R5.Line 13 is connected in series with resistor R4, inductor L2 and resistor R6. Capacitor C1 is connected across the two lines, from a point between inductor L1 and resistor R5 to a point between inductor L2 and resistor R6. Inductors L1 and L2 comprise a four terminal inductor with an iron core. In FIG. 4, R3 and R4 are 15 Ohm resistors, R5 and R6 are 20 Ohm resistors, L1 and L2 are 18 mH inductors and C1 is a 0.022 uF capacitor. - Although the low pass filter illustrated in FIG. 4 is the preferred embodiment, other embodiments will be apparent to one skilled in the art. For example, providing an initial coupled inductor as a common mode choke, adding further stages of filtering or using different combinations of resistors, capacitor and inductor in the filtering are options. The components of the low pass filter, however, operate with the 48 volt battery voltage provided at the central office and the inductors have to pass tens of milliamperes of current without saturation. As such, the components require a large amount of circuit board space.
- The
high pass filter 106 in FIG. 4 includes capacitor C2 and transformer T1. Transformer T1 has a first side and a second side. The first side is split and a first coil P1 and a second coil P2 of the first side are coupled through capacitor C2. An input lead of the first coil P1 is connected to line DSLT 12 and the opposite input lead of the first coil P1 is connected to a lead of capacitor C2. The opposite lead of capacitor C2 is connected to an input lead of the second coil P2. The opposite input lead of coil P2 is connected to lineDSLR 13. The two leads of the second coil of transformer T1 are connected toHybrid 107. - The
high pass filter 106 illustrated in FIG. 4 is of a standard type, any circuit which separates the high frequency data input from the DC and POTS signals can be used. After this separation is accomplished, theHybrid 107 need only operate at low voltage. - The
low voltage filter 104 can be any continuous time filter, which provides the desired filtering. Several of these filters are well known in the art. Among the well known integrated circuit continuous time filters are Gm-C filters and MOSFET-C filters. Each of these filter types can be implemented with multiple stages providing for filters of several orders. A standard ladder filter (which employs inductors and capacitors for a multistage filtering circuit similar to the high voltage filter shown in FIG. 2) will accomplish the low voltage filtering, however it is difficult to accurately construct an inductor on an IC chip and implementation with individual components will take a great deal of space on the circuit board and defeat the purpose of the invention. - A second embodiment of the invention is shown in FIG. 5. The embodiment shown in FIG. 5 differs from the preferred embodiment shown in FIG. 4 in that part of the filtering is shifted to the digital side of
CODEC 105. In this embodiment, the filtering is split between a Low Voltage Filter 110 and aDigital Filtering Circuit 111 located online 23. - The examples illustrated here are representative examples and in no way limit the scope of this application. Other obvious embodiments of the invention will be apparent to one skilled in the art and are included within the scope of this application. One obvious embodiment is to not have a data path so that only POTS signals are processed.
Claims (6)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US10/077,570 US20020136394A1 (en) | 1998-04-09 | 2002-02-15 | Signal coupler using high voltage and low voltage filtering |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/057,953 US6418221B1 (en) | 1998-04-09 | 1998-04-09 | Signal coupler using low voltage filtering |
US10/077,570 US20020136394A1 (en) | 1998-04-09 | 2002-02-15 | Signal coupler using high voltage and low voltage filtering |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US09/057,953 Continuation US6418221B1 (en) | 1998-04-09 | 1998-04-09 | Signal coupler using low voltage filtering |
Publications (1)
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US20020136394A1 true US20020136394A1 (en) | 2002-09-26 |
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Family Applications (2)
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US09/057,953 Expired - Fee Related US6418221B1 (en) | 1998-04-09 | 1998-04-09 | Signal coupler using low voltage filtering |
US10/077,570 Abandoned US20020136394A1 (en) | 1998-04-09 | 2002-02-15 | Signal coupler using high voltage and low voltage filtering |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
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US09/057,953 Expired - Fee Related US6418221B1 (en) | 1998-04-09 | 1998-04-09 | Signal coupler using low voltage filtering |
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US (2) | US6418221B1 (en) |
AU (1) | AU3478299A (en) |
WO (1) | WO1999053661A1 (en) |
Cited By (8)
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US20060082219A1 (en) * | 2004-10-12 | 2006-04-20 | At&T Corp. | Broadband coupler technique for electrical connection to power lines |
US20060291493A1 (en) * | 2005-06-23 | 2006-12-28 | Schley-May James T | Network interface device with a remote power source |
US20070242757A1 (en) * | 2006-04-18 | 2007-10-18 | 2Wire, Inc. | Method and Apparatus for Communicating Between Devices Having No Common Electrical Ground |
US20070263852A1 (en) * | 2006-04-18 | 2007-11-15 | 2Wire, Inc. | Method and apparatus for providing power to a network interface device via telephone lines |
US7305006B1 (en) * | 2001-08-24 | 2007-12-04 | Westell Technologies, Inc. | System for allowing a single device to share multiple transmission lines |
US20080175212A1 (en) * | 2006-04-18 | 2008-07-24 | Richard Barry Angell | Remote antenna system |
US20100080381A1 (en) * | 2008-09-30 | 2010-04-01 | Tesu Ion C | Method and Apparatus for Supplying DC Feed to a Subscriber Line |
US20100080380A1 (en) * | 2008-09-30 | 2010-04-01 | Yan Zhou | Method and Apparatus for Supplying DC Feed to a Subscriber Line |
Families Citing this family (17)
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US6188750B1 (en) * | 1998-11-19 | 2001-02-13 | Excelsus Technologies, Inc. | Impedance blocking filter circuit |
US6212259B1 (en) * | 1998-11-19 | 2001-04-03 | Excelsus Technologies, Inc. | Impedance blocking filter circuit |
US6744883B1 (en) * | 1999-01-12 | 2004-06-01 | Paradyne Corporation | Filter system and method to suppress interference imposed upon a frequency-division multiplexed channel |
US6937719B2 (en) * | 1999-02-15 | 2005-08-30 | Nokia Networks Oy | Multiplexing and demultiplexing of narrowband and broadband services in a transmission connection |
US6628782B1 (en) * | 1999-10-26 | 2003-09-30 | Adtran Inc. | Ring voltage termination by means of a spare fuse |
EP1172981A3 (en) * | 2000-07-10 | 2006-11-15 | Broadcom Corporation | Analogue front end for xDSL |
US7039180B1 (en) * | 2000-12-20 | 2006-05-02 | Cisco Technology, Inc. | Method and apparatus for enabling multiple protocol communication over a network |
US6978011B1 (en) * | 2001-03-02 | 2005-12-20 | Alcatel | Enhanced low pass filter |
TW516276B (en) * | 2001-07-09 | 2003-01-01 | Primax Electronics Ltd | Full-duplex low-pass filter adapted for communication network |
US6842518B2 (en) * | 2001-12-13 | 2005-01-11 | Legerity, Inc. | Frequency-dependent impedance synthesis for DSL interface circuits |
US6940969B2 (en) * | 2001-12-13 | 2005-09-06 | Legerity, Inc. | Capacitor cancellation method and apparatus |
US7268993B2 (en) * | 2004-05-25 | 2007-09-11 | Sbc Knowledge Ventures, L.P. | Integrated protector and splitter |
EP1901540A1 (en) * | 2006-09-13 | 2008-03-19 | Ycl Electronics Co., Ltd. | ADSL splitter |
US10348418B1 (en) * | 2014-07-22 | 2019-07-09 | Esker Technologies, LLC | Transient and spurious signal filter |
US10417143B2 (en) | 2015-10-08 | 2019-09-17 | Esker Technologies, LLC | Apparatus and method for sending power over synchronous serial communication wiring |
US10128906B2 (en) | 2016-07-11 | 2018-11-13 | Esker Technologies, LLC | Power line signal coupler |
US10560154B2 (en) | 2016-07-11 | 2020-02-11 | Esker Technologies, LLC | Power line signal coupler |
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2002
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US7305006B1 (en) * | 2001-08-24 | 2007-12-04 | Westell Technologies, Inc. | System for allowing a single device to share multiple transmission lines |
US7145440B2 (en) | 2004-10-12 | 2006-12-05 | At&T Corp. | Broadband coupler technique for electrical connection to power lines |
US20060082219A1 (en) * | 2004-10-12 | 2006-04-20 | At&T Corp. | Broadband coupler technique for electrical connection to power lines |
US20060291493A1 (en) * | 2005-06-23 | 2006-12-28 | Schley-May James T | Network interface device with a remote power source |
US7672448B2 (en) | 2005-06-23 | 2010-03-02 | 2Wire, Inc. | Network interface device with a remote power source |
US20080175212A1 (en) * | 2006-04-18 | 2008-07-24 | Richard Barry Angell | Remote antenna system |
US20070263852A1 (en) * | 2006-04-18 | 2007-11-15 | 2Wire, Inc. | Method and apparatus for providing power to a network interface device via telephone lines |
US7526034B2 (en) * | 2006-04-18 | 2009-04-28 | 2Wire, Inc. | Method and apparatus for communicating between devices having no common electrical ground |
US20070242757A1 (en) * | 2006-04-18 | 2007-10-18 | 2Wire, Inc. | Method and Apparatus for Communicating Between Devices Having No Common Electrical Ground |
US7965977B2 (en) | 2006-04-18 | 2011-06-21 | 2Wire, Inc. | Remote antenna system |
US20110228867A1 (en) * | 2006-04-18 | 2011-09-22 | Richard Barry Angell | Remote antenna system |
US8238821B2 (en) | 2006-04-18 | 2012-08-07 | 2Wire, Inc. | Remote antenna system |
US8520835B2 (en) | 2006-04-18 | 2013-08-27 | 2Wire, Inc. | Method and apparatus for providing power to a network interface device via telephone lines |
US20100080381A1 (en) * | 2008-09-30 | 2010-04-01 | Tesu Ion C | Method and Apparatus for Supplying DC Feed to a Subscriber Line |
US20100080380A1 (en) * | 2008-09-30 | 2010-04-01 | Yan Zhou | Method and Apparatus for Supplying DC Feed to a Subscriber Line |
Also Published As
Publication number | Publication date |
---|---|
US6418221B1 (en) | 2002-07-09 |
WO1999053661A1 (en) | 1999-10-21 |
AU3478299A (en) | 1999-11-01 |
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