Communication system power loss notification via detection of reverse bias state of a diode based on a threshold voltage

In one aspect of the invention, a method for power loss notification includes receiving at least a threshold voltage from a power supply. The method also includes charging at least one capacitor when the power supply is supplying at least the threshold voltage. The method further includes failing to receive at least the threshold voltage from the power supply, and reverse biasing at least one diode coupled between the power supply and the at least one capacitor. In addition, the method includes detecting the reverse bias state of the diode.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to power delivery systems, and more particularly to a system and method for power loss notification.

BACKGROUND OF THE INVENTION

Computers often communicate over a network using a modem at a subscriber's location. This modem facilitates the communication of data from the subscriber to a remote location, such as to a central office of a service provider. The modem typically receives power from an external power supply. When the modem loses power, the modem generally informs the central office or other remote location of the power loss. This allows the central office to stop transmitting data to the modem when the modem is unable to receive that data.

Modems often use one or more capacitors to store a voltage charge from the power supply. To determine when a power loss occurs, modems typically use power loss circuitry coupled to the capacitors. The power loss circuitry operates to monitor the voltage between the capacitors and the power supply. When the modem loses power, the power loss circuitry generally detects only the voltage stored in the capacitors. As the capacitors discharge, the charge stored in the capacitors falls below a threshold value, often called a “trip point.” The power loss circuitry then generates an output signal indicating that a power loss has occurred. Because the power loss circuitry monitors the level of the voltage charge stored in the capacitors, the circuitry is often referred to as a “level detector.”

A problem with this approach is that a relatively long period of time may elapse between the time the modem loses power and the time the power loss circuitry detects the power loss. The power loss circuitry typically must wait for the capacitors to discharge enough voltage before sensing the power loss. This increases the time between the power loss and the detection of the power loss, and this period of time is often important. For example, the power loss circuitry needs to detect the power loss while enough internal power remains in the modem to transmit a power loss signal to the central office. If too much time elapses before the circuitry detects the power loss, the modem will not have enough power to generate and transmit the power loss signal.

Another problem with this approach is that it typically increases the amount of circuitry used in the modem. For example, this approach often requires the addition of several components, such as additional capacitors coupled to the power supply. These additional components increase the overall cost of the modem and take up space that could be used for other elements in the modem.

SUMMARY OF THE INVENTION

The present invention recognizes a need for an improved system and method for power loss notification, which reduce or eliminate some or all of the problems and disadvantages associated with prior systems and methods.

In one embodiment of the invention, a modem includes communication circuitry operable to facilitate communication over a communication link. The modem also includes at least one capacitor operable to store a voltage when a power supply is supplying at least a threshold voltage to the modem. The modem further includes at least one diode coupled between the power supply and the at least one capacitor. The diode is operable to operate in a forward bias state while the power supply is supplying at least the threshold voltage. In addition, the modem includes a power loss sensor coupled in parallel with the diode and in series with the communication circuitry. The power loss sensor is operable to detect a reverse bias state of the diode and to signal the communication circuitry to communicate a power loss signal over the communication link.

In a particular embodiment of the invention, the power loss sensor comprises a digital detector. The digital detector is operable to detect the presence or absence of a voltage between the diode and the power supply.

In another embodiment of the invention, a method for power loss notification includes receiving at least a threshold voltage from a power supply. The method also includes charging at least one capacitor when the power supply is supplying at least the threshold voltage. The method further includes failing to receive at least the threshold voltage from the power supply, and reverse biasing at least one diode coupled between the power supply and the at least one capacitor. In addition, the method includes detecting the reverse bias state of the diode.

Numerous technical advantages can be gained through various embodiments of the invention. Various embodiments of the invention may exhibit none, some, or all of the following advantages. For example, in one embodiment of the invention, a modem is provided that quickly identifies when a power loss occurs. The modem may then generate a power loss signal informing a central office or other network element of the power loss. By quickly identifying when the power loss occurs, a shorter period of time may elapse between the time the modem loses power and the time the modem detects the power loss. This helps to reduce or eliminate the likelihood that the modem will be unable to generate and transmit the power loss signal to the central office or other network element.

Some embodiments of the invention also simplify the circuitry used in the modem. For example, in one embodiment, fewer capacitors may be coupled to the power supply and used in the modem. This helps to reduce the size and cost of the modem. Also, the modem is not limited to the use of a “level detector.” The modem may, for example, use any digital detector operable to detect the presence or absence of a voltage signal. Although a level detector may still be used to detect a power loss, other less expensive circuits can also be used.

Other technical advantages will be readily apparent to one of skill in the art from the attached figures, description, and claims.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a block diagram illustrating an exemplary communication system10constructed according to the teachings of the present invention. In the illustrated embodiment, system10includes one or more host computers12and a modem14coupled to a power supply16. A communication link18facilitates communication between the modem14and other network elements, such as a central office20coupled to a network22. Other embodiments of system10may be used without departing from the scope of the present invention.

In general, modem14facilitates communication between host12and network22. Modem14may, for example, communicate information to and receive information from network22through central office20. Modem14also receives power from power supply16, and modem14includes a power loss sensor24. Power loss sensor24detects when modem14loses power, or stops receiving at least a threshold voltage, from power supply16. When power loss sensor24detects a power loss, modem14communicates a power loss signal to central office20. In one embodiment, power loss sensor24may include a digital detector operable to detect the presence or absence of power from power supply16.

This invention is described as it relates to the detection of a power loss in modem14. The invention may also be used to detect a power loss in any other apparatus that receives power from a power supply and attempts to perform an action in response to a power loss. For example, the invention may be used in a laptop computer or a personal digital assistant to signal when a battery power supply is losing power. The invention could also be used in a server computer to signal when the server loses power. In response, the software in the laptop computer, server computer, or personal digital assistant may store information in a nonvolatile memory and shut down other programs in an orderly fashion. The invention could further be used in a wireless device, such as a mobile telephone or a BLUETOOTH device, to detect a power loss and communicate a “sign-off” signal over a wireless interface.

Host12is coupled to modem14. In this document, the term “couple” refers to any direct or indirect communication between two or more elements, whether or not those elements are in physical contact with one another. Host12may execute with any of the well-known MS-DOS, PC-DOS, OS-2, MAC-OS, WINDOWS, UNIX, or other appropriate operating systems. Host12may comprise, for example, a desktop computer, a laptop computer, a personal digital assistant, or any other computing or communicating device. In the illustrated embodiment, host12includes an input device26, an output device28, random access memory (RAM)30, read-only memory (ROM)32, CD-ROM, hard drive, or other magnetic or optical storage media34or other appropriate volatile or nonvolatile storage and retrieval devices, and a processor36having a system clock or other suitable timing device or software. Input device26may comprise, for example, a keyboard, mouse, graphics tablet, touch screen, pressure-sensitive pad, joystick, light pen, microphone, or other suitable input device. Output device28may comprise, for example, a video display, a printer, a disk drive, a plotter, a speaker, or other suitable output device.

Modem14is coupled to host12and to communication link18. Modem14provides an interface between host12and communication link18. Throughout this document, the term “modem” refers to any combination of hardware, software, and/or firmware operable to facilitate an interface between a communication link and a host device. For example, modem14may transport information between host12and central office20. The features and elements of modem14may reside externally to host12, or may be partially or completely integrated into host12. For example, modem14could reside integrally within host12, may comprise a device card coupled to a bus within host12, or may comprise a device external to host12communicating with host12over a communication link15. In that case, communication link15could comprise, for example, a local area network (LAN) such as an Ethernet connection. In addition to providing basic interfacing functions, modem14could, in some embodiments, provide routing, bridging, and/or switching functions.

In one embodiment, modem14comprises a digital subscriber line (DSL) modem. In this embodiment, modem14may implement any of the DSL protocols, including full-rate Asymmetric DSL (ADSL), ADSL Lite, and Very-high-rate DSL (VDSL). Modem14may also comprise a cable modem or other suitable communication device. In addition, the invention contemplates other later revisions, modifications, enhancements, or new types of communications techniques. One embodiment of a modem is shown inFIG. 2, which is described below.

Power supply16is coupled to modem14and supplies power to modem14. Power supply16may comprise any suitable source of power for modem14. In one embodiment, power supply16comprises a direct current power supply. Power supply16may reside externally to modem14and/or host12, or may be partially or completely integrated into modem14and/or host12. For example, power supply16could reside within host12, central office20, modem14, or any other suitable location.

Communication link18couples modem14to central office20. Communication link18facilitates communication between modem14and central office20. Communication link18may comprise any communications medium operable to facilitate communication of analog and/or digital signals using ground-based and/or space-based components. Communication link18may, for example, comprise a twisted-pair copper telephone line, a fiber optic line, or a wireless link between modem14and central office20.

In the illustrated embodiment, central office20is coupled to communication link18and to network22. Central office20facilitates communication between modem14and network22. Network22may include any suitable wireline or wireless system that supports communication between network elements using ground-based and/or space-based components. For example, network22may be a public switched telephone network (PSTN), an integrated services digital network (ISDN), a local area network (LAN), a wide area network (WAN), a global computer network such as the Internet, or any other communication system or systems at one or more locations.

In the illustrated embodiment, modem14includes a power loss sensor24. Power loss sensor24is operable to detect when modem14stops receiving at least a threshold voltage from power supply16. When power loss sensor24detects a power loss, power loss sensor24causes modem14to communicate a power loss signal to central office20. This informs central office20that modem14cannot receive information from network22because of the power loss. In one embodiment, power loss sensor24comprises a digital detector. In this document, the phrase “digital detector” refers to any hardware, software, firmware, or combination thereof operable to detect the presence or absence of a voltage signal from power supply16. Power loss sensor24may, for example, comprise a comparator, a digital gate such as an AND gate, or a buffer gate. One embodiment of a power loss sensor is shown inFIG. 3, which is described below.

FIG. 2is a block diagram illustrating an exemplary modem114constructed according to the teachings of the present invention. Modem114may be useful, for example, in system10of FIG.1. In the illustrated embodiment, modem114includes communication circuitry200, a power supply circuit202, a power monitor204, and a power loss sensor124.

Communication circuitry200facilitates communication between one or more hosts112and a central office120over a communication link118. Communication circuitry200may, for example, receive digital information from host112and convert it into analog signals for communication toward a network. Communication circuitry200may also receive analog information over communication link118and convert it into digital signals for communication to host112. Communication circuitry200may comprise any hardware, software, firmware, or combination thereof operable to facilitate communication over communication link118. Communication circuitry118may, for example, include an analog-to-digital converter, a digital-to-analog converter, and a digital signal processor.

Power supply circuit202is coupled to communication circuitry200and to a power supply116. Power supply circuit202receives power from power supply116, generates a voltage signal using the power from power supply116, and communicates the voltage signal to communication circuitry200. Power supply circuit202may comprise any hardware, software, firmware, or combination thereof operable to receive power and provide a voltage signal to communication circuitry200. In one embodiment, power supply circuit202includes a three amp flyback regulator, such as a LM2585T-ADJ switcher, and a transformer.

Power monitor204is coupled to power supply circuit202and communication circuitry200. Power monitor204monitors the voltage signal supplied to communication circuitry200by power supply circuit202. When the voltage of the signal supplied to communication circuitry200falls outside a threshold range, power monitor204generates a reset signal. The reset signal prevents communication circuitry200from operating. When the signal supplied to communication circuitry200is within the threshold voltage range, power monitor204allows communication circuitry200to operate. In this manner, power monitor204prevents damage to communication circuitry200by, for example, an excessive amount of voltage supplied to communication circuitry200. Power monitor204may comprise any hardware, software, firmware, or combination thereof operable to regulate the power supplied to communication circuitry200. In one embodiment, power monitor204comprises a LP2989IM-2.5 Micropower/Low Noise 500 milliamp Ultra-Low Dropout Regulator.

Power loss sensor124is coupled to power supply116, power supply circuit202, and communication circuitry200. Power loss sensor124monitors the voltage level of the power supplied to modem114at a terminal206. When power supply116is supplying power to modem114, power loss sensor124detects a voltage at terminal206and allows communication circuitry200to continue operating. When modem114stops receiving at least a threshold voltage from power supply116, power loss sensor124detects the lack of the threshold voltage at terminal206and causes communication circuitry200to communicate a power loss signal to central office120over communication link118. Power loss sensor124may comprise any hardware, software, firmware or combination thereof operable to detect a power loss at terminal206. One embodiment of a power loss sensor is shown inFIG. 3, which is described below.

To help increase the speed at which power loss sensor124detects a loss of power at terminal206, modem114also includes one or more diodes208and one or more capacitors210. Diode208is coupled in series between power supply116and power supply circuit202. Diode208allows current to flow from terminal206to a terminal212, and diode208limits the current flowing from terminal212to terminal206. For example, when the voltage at terminal206is above a threshold voltage, such as 0.7 volts, diode208operates in a forward bias state, and current may flow through diode208. When the voltage at terminal206drops below the threshold voltage, diode208operates in a reverse bias state, and current may not flow through diode208. In one embodiment, diode208is selected to have a current rating high enough to withstand the ordinary current flowing through diode208when power supply116is supplying power to modem114. Also, diode208may be selected to withstand surge currents experienced in modem114, such as when modem114is coupled to power supply116. In a particular embodiment, modem114also includes a resistor214coupled in series with diode208. Resistor214helps to limit the surge current experienced by diode208in modem114. In addition, diode208may be selected to withstand the back bias voltage when modem114loses power from power supply116. When modem114loses a sufficient amount of power, a higher voltage may exist at terminal212than at terminal206, and a back bias voltage exists across diode208. Selecting a diode208having suitable current and back bias voltage ratings may help to ensure proper operation of modem114. Diode208may comprise any suitable diode or diodes, such as a silicon diode or a Schottky diode. In one embodiment, multiple diodes208may be used in modem114. Any combination of diodes208may be selected to vary the threshold voltage at which diodes208reverse bias and power loss sensor124detects the power loss.

One or more capacitors210are coupled between diode208and, for example, a ground216. Capacitors210receive and store a voltage charge when power supply116supplies sufficient power to modem114to forward bias diode208. Capacitors210may comprise any suitable capacitor or capacitors operable to store sufficient voltage to allow communication circuitry200to continue operating until a power loss notification signal can be communicated to central office120. For example, capacitors210may comprise two 1,000 microfarad capacitors and one forty-seven microfarad capacitor coupled in parallel.

In one aspect of operation, when power supply116supplies power to modem114, at least a threshold voltage appears at terminal206, and power loss sensor124does not detect a power loss in modem114. Also, when power supply116provides power to modem114, diode208is forward biased, and capacitors210store a voltage charge. When power supply116stops supplying at least a threshold voltage to modem114, the voltage stored in capacitors210appears as a voltage at terminal212. The lack of a voltage at terminal206, coupled with the voltage at terminal212, reverse biases diode208. This produces a zero or near-zero voltage at terminal206. Power loss sensor124detects the reverse bias state of diode208and signals communication circuitry200to communicate a power loss signal to central office120.

The use of diode208and capacitor210in modem114helps to increase the speed at which a zero or near-zero voltage signal appears at terminal206. This also increases the speed at which power loss sensor124detects a power loss in modem114. By detecting the loss of power in modem114in less time, communication circuitry200has more time to communicate the power loss signal to central office120. This helps to decrease the likelihood that communication circuitry200will lose power before generating and communicating the power loss signal to central office120.

FIG. 3is a block diagram illustrating an exemplary power loss sensor224constructed according to the teachings of the present invention. Power loss sensor224may be useful, for example, in modem114of FIG.2. In the illustrated embodiment, power loss sensor224includes two comparators300aand300b, resistors302-324, capacitors326-330, a zener diode332, and a transistor334. Other embodiments of power loss sensor224may be used without departing from the scope of the present invention.

Each comparator300is operable to receive a first input336and a second input338. Each comparator300is also operable to receive power through a terminal340, and each comparator300is coupled to a ground through a terminal342. Comparator300is operable to compare the input signals336and338and generate an output signal344based on the comparison. Comparator300may comprise any hardware, software, firmware or combination thereof operable to receive and compare input signals. In one embodiment, comparators300comprise a LM2903 Low Power, Low Offset Voltage, Dual Comparator.

In the illustrated embodiment, resistor320is coupled to a voltage source354. In one embodiment, voltage source354comprises a 3.3 volt direct current voltage signal. Component values for resistors302-324and capacitors326-330may be selected to provide any desired functionality of power loss sensor224. In a particular embodiment, resistors302and304each comprise a 4.99 kilo-ohm resistor; resistors306and308each comprise a one kilo-ohm resistor; resistor310comprises a ten ohm resistor; resistor312comprises a two kilo-ohm resistor; resistors314,316, and318each comprise a 25.5 kilo-ohm resistor; resistors320and322each comprise a 7.5 kilo-ohm resistor; resistor324comprises a ten kilo-ohm resistor; capacitor326comprises a one microfarad capacitor; and capacitors328and330each comprise a 2.2 microfarad capacitor. Other component values may be selected without departing from the scope of the present invention.

Zener diode332may comprise any suitable diode. In one embodiment, zener diode332comprises a TL431CPK adjustable precision shunt regulator. Transistor334may comprise any suitable transistor. In one embodiment, transistor334comprises a NPN transistor. In a particular embodiment, transistor334comprises a MMBT2222 NPN transistor. In the illustrated embodiment, transistor334includes a collector350coupled to a voltage source346and a base352coupled to comparator300a. In one embodiment, voltage source346comprises a 3.3 volt direct current voltage signal.

In one aspect of operation, when modem114is receiving at least a threshold voltage from power supply116, the voltage at terminal206exceeds the voltage at terminal212. This may, for example, be due to the voltage drop across diode208. Comparator300areceives at least a portion of the voltage at terminal212as input signal336aand at least a portion of the voltage at terminal206as input signal338a. Comparator300acompares the signals336aand338aand, because the voltage at terminal206exceeds the voltage at terminal212, outputs a low voltage signal344a. The low voltage signal is communicated to base352of transistor334, which signals communication circuitry200to operate normally.

When modem114stops receiving at least a threshold voltage from power supply116, diode208begins operating in a reverse bias state. The voltage at terminal212exceeds the voltage at terminal206because, for example, capacitors210may contain a voltage charge. Comparator300areceives at least a portion of the voltage at terminal212as input signal336aand at least a portion of the voltage at terminal206as input signal338a. Comparator300acompares the signals336aand338aand, because the voltage at terminal212exceeds the voltage at terminal206, outputs a high voltage signal344a. The high voltage signal344ais communicated to base352of transistor334, which signals communication circuitry200to communicate a power loss signal.

In the illustrated embodiment, the output signal344bof comparator300bis communicated to power supply circuit202. Power supply circuit202may use output signal344bin providing power to communication circuitry200. For example, in one embodiment, power supply circuit202includes a three amp flyback regulator, such as a LM2585T-ADJ switcher, and output signal344bis used as a compensation pin voltage in the flyback regulator.

AlthoughFIG. 3illustrates one embodiment of power loss sensor224, numerous changes may be made without departing from the scope of the present invention. For example, the arrangement and values of components in power loss sensor224is for illustration only. Other arrangements and/or component values may be used without departing from the scope of the present invention.

FIG. 4is a flow diagram illustrating an exemplary method400for power loss notification according to the teachings of the present invention. Although method400is described below as it relates to modem114, the same or similar method may be used by modem14of system10.

Modem114receives power at step402. This may include, for example, modem114receiving power from power supply116. Modem114charges one or more capacitors210at step404. This may include, for example, capacitors210charging when modem114is receiving power from power supply116.

Modem114loses power at step406. This may include, for example, modem114failing to receive at least a threshold voltage from power supply116. Modem114reverse biases diode208at step408. The lack of at least a threshold voltage at terminal206caused by the loss of power, coupled with the voltage at terminal212from the stored voltage in capacitors210, reverse biases diode208. Modem114detects the reverse bias state of diode208at step410. This may include, for example, power loss sensor124detecting the absence of a voltage between power supply116and diode208. After detecting the absence of a voltage, power loss sensor124may take any suitable corrective action, such as instructing communication circuitry200to communicate a power loss signal to central office120.

Although the present invention has been described in several embodiments, a myriad of changes, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present invention encompass such changes, variations, alterations, transformations, and modifications as fall within the spirit and scope of the appended claims.