VOIP drop amplifier

The VOIP drop amplifier connects end user equipment to a broadband system, such as that provided by a cable provider. The amplifier includes a splitter for connecting the cable signal to multiple output connectors, and RF amplifiers compensating for losses in the splitter and other passive components in the amplifier. The drop amplifier includes an input connection for accepting a broadband cable signal from a cable system and returning broadband signals to the cable system. The drop amplifier includes an amplification path connecting the input connection to the plurality of output connections through RF amplifiers and a splitter, and a bypass path that bypass the splitter and forward and reverse amplifiers in the amplification path to connect the input connection directly to the output connection for the essential circuits. A sensing circuit monitors the amplifiers and the supply voltages, and selects the bypass path when a failure is detected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to cable television systems, and particularly to splitter/amplifier systems for delivering diverse communication services, including voice over IP (VoIP) telephone services.

2. Description of the Related Art

Cable television operators provide a variety of diverse services to consumers. These services include high speed Internet access, video on demand, pay-per-view services, and VoIP services. Cable operators provide these services multiplexed over a single cable using such techniques as frequency division multiplexing (FDM). These services are characterized by the need to provide forward and reverse communication path. The forward path is used to transmit data to the user, while the reverse path is used to return data to the cable operator. The return data might include orders for video on demand or pay-per-view content or data transmitted by the user for destinations on the Internet.

Key components of CATV systems are drop amplifiers. These amplifiers are inserted into the cable transmission path to make up for losses in the transmission system. Signals are weakened as they pass through cables and components, such as splitters. Splitters are used to separate the services provided by the cable operator for distribution to the appropriate customer equipment for receiving the service.

Typically the return signal operates at a comparatively lower frequency than the forward path. For example, in a typical system the return signal is in a bandwidth of 5 MHz to about 40 MHz, while the forward path operates at 50-1000 MHz. Diplex filters are used to separate the combined forward and return signal into separate components for amplification using separate amplifiers. In some cases the signal level in the reverse path may be sufficiently high so that no reverse path amplifier is required. For example, set top boxes and cable modems typical provide high output levels, making the reverse path amplifier unnecessary.

Among the services provided by the cable provider, it is particularly important that the voice over IP (VoIP) service be reliable. While such services as video on demand or pay-per-view are viewed as luxury or non-essential services, VoIP is used to provide telephone communications. Telephone communication are viewed as vital services, particularly during situations involving medical emergencies or natural disasters where communications may be necessary to make essential reports, such as injuries, life threatening medical conditions, or downed power lines. The VoIP circuits may be viewed as essential services because of the need to maintain the circuits in emergency situations.

Because the amplifiers used in the systems are active components employing complex circuitry and requiring electrical power to operate, the drop amplifiers are potential failure points for VoIP services. In some situations, an emergency or disaster that requires the use of the VoIP services also results in a loss of electrical power, disabling the drop amplifiers and interrupting vital VoIP communications.

Several devices have been developed for VoIP systems. A representative device is shown in Japanese Patent No. 2004-80,483, published Mar. 11, 2004, which shows in FIG. 1 a VoIP adapter for telephone communications that switches from a telephone line network, such as a packet switched telephone network, to a VoIP network to maintain communications when a failure in the telephone line network is detected. Another representative device is shown in Japanese Patent No. 2005-5,875, published Jan. 6, 2005, which also shows in FIG. 1 a device for switching from a telephone line network, such as a packet switched telephone network, to a VoIP network to maintain communications when a failure in the power supply for the telephone line network is detected.

While the above-mentioned patent references describe circuit monitoring and switching to maintain telephone communications, neither describes maintaining VoIP communications despite failure of components in an IP network providing the VoIP infrastructure.

None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus, a VOIP drop amplifier solving the aforementioned problems is desired.

SUMMARY OF THE INVENTION

The VoIP drop amplifier connects end user equipment to a broadband system, such as that provided by a cable provider. The amplifier includes a splitter for connecting the equipment to multiple output connectors, and RF amplifiers compensating for losses in the splitter and other passive components in the drop amplifier. The drop amplifier includes an input connection for accepting a broadband cable signal from a cable system and returning broadband signals to the cable system. The drop amplifier includes an amplification path connecting the input connection to a plurality of output connections through amplifiers and a splitter, and a bypass path that bypasses the splitter and the forward and reverse amplifiers in the amplification path to connect the input connection directly to the output connection for VoIP. A sensing circuit monitors the amplifiers and the supply voltages and selects the bypass path when a failure is detected.

The amplification path includes a forward amplifier for amplifying the forward signals, which are signals originating at the cable operators system, and a reverse amplifier for amplifying the reverse signals, which are those signals originating at the end user's equipment.

The VoIP amplifier further includes a switch circuit for selecting between the amplification path and the bypass path. The switching circuit is controlled by a dc current and voltage sensing circuit.

The dc current and voltage sensing circuit monitors dc voltage supplied to the amplifier circuitry. The sensing circuitry also monitors the current supplied to the forward and reverse amplifiers, or to the forward amplifier alone when the reverse amplifier is not provided in the amplification path. The dc voltage supplied to the VoIP circuitry is compared to a reference value to determine whether the dc voltage is sufficient to operate the VoIP active components. When the dc voltage is insufficient the dc current and voltage sensing circuit operates the switching circuit to select the bypass path.

The amplifier current is compared to two reference values to determine whether the current is within a range including a lower and an upper current limit. When the amplifier current is outside this range, which corresponds to the normal range of expected amplifier currents, the dc current and voltage circuit operates the switching circuit to select the bypass path.

Under normal voltage and current conditions, the dc current and voltage sensing circuit controls the switching circuitry to select the amplification path. The bypass path supplies only the VoIP output or other output connections designated as essential, while the amplification path supplies all of the output connections including the essential and non-essential connections. In a typical case, only the VoIP output is designated as essential.

The forward and reverse amplifiers may provide sufficient gain to compensate for losses in VoIP drop amplifier. Alternatively, these amplifiers may provide additional gain to compensate for losses elsewhere in the cable system, such as losses in the cable connecting the VoIP to the cable operator's system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a drop amplifier designed to reliably maintain the VoIP signal path during a loss of power or a failure of active amplifying components.

FIG. 1illustrates a system employing a VoIP drop amplifier according to the invention. The cable operator provides communication services to a multi-tap point46. The VoIP drop amplifier is connected to the multi-tap connection via a cable that is connected to the RF signal input connector44. The VoIP drop amplifier provides amplification for the forward and return signals and splits the signals, delivering them to the output connectors38and40a-40g.

Connected by cables to the output connectors are various devices for utilizing broadband cable service. Connected to output connector40ais a cable modem24supplying an Internet connection for a personal computer48. Two integrated digital televisions26are connected to output connectors40band40c. IDTV sets are television sets with the ability to interface with a broadband network to receive such services as video on demand (VOD) or electronic program guide (EPG), as well as broadcast TV. Output connector40dis connected to a set top box30, which in turn is connected to a conventional television set28. Output connector40dis connected to a set top box30that in turn is connected to a conventional (non iDTV capable) television set28. A set top box is common for televisions without iDTV capability. The set top box interfaces with broadband networks to deliver such services as VOD and EPG to conventional television sets.

The VoIP connector38is connected via a cable to a second cable modem32, which is connected to a multimedia terminal adapter (MTA)34. The MTA is connected to one or more VoIP telephones36. The remaining output connectors40e-40gare shown as unused, but may be connected to additional devices. For example, an additional cable modem and MTA may be connected to one of the unused connectors to provide additional VoIP telephone service, or a third cable modem for Internet access may be connected to one of the unused output connectors.

The VoIP drop amplifier20is shown powered by an uninterruptible power supply (UPS)22, which provides power to the VoIP drop amplifier20via the input connector42. Alternatively, power may be provided to the VoIP drop amplifier20from a simple wall transformer.

FIGS. 2 and 3are block diagrams by which the basic operating principles of the VoIP drop amplifier20may be understood.FIG. 2shows the amplifier in the normal condition, whileFIG. 3shows the amplifier in a bypass condition.

As shown inFIG. 2, the RF signal to and from the cable system is routed through the input connector44to a first bypass switch52. A switch circuit comprises this first bypass switch52, as well as a second bypass switch54described below. The switch circuit is controlled by dc current and voltage sensing circuitry66. When the dc current and voltage sensing circuitry66detects that the amplifier and voltage supply is normal, the switch circuit routes the RF signal through the amplification path. To set up the amplification path, the first bypass switch52is set to pass the incoming signal to the first diplex filter60. The diplex filter separates the signal into the downstream (50-1000 MHz) signal component coming from the cable system and the upstream (5-40 MHz) signal component coming from the customer's equipment, which is directed back to the cable system. A separate upstream amplifier56and a downstream amplifier58are provided to make up for losses in passive drop amplifier components and provide unity gain. The downstream signal component originates at the cable supplier, passes through the normally open contact of the first bypass switch52, the first diplex filter60, the high frequency amplifier56, the second diplex filter62, and into the splitter64. After subdividing at the splitter64, the signal is routed to the various consumer equipment, as shown inFIG. 1, with the exception of the VoIP telephone equipment. The path to the VoIP connector, after passing through the splitter64, also passes through the second bypass switch54. With the second bypass switch54in the energized condition, the downstream signal passes through the normally open contacts of the second bypass switch54and then to the VoIP output connector38.

The path for the reverse signal, originating at the consumer equipment is into the connectors40a-40gthrough the splitter64, into the second diplex filter62, through the low frequency amplifier58, then through the first diplex filter60and through the normal open contacts of the first bypass switch52. The VoIP reverse signal first passes though the normally open contacts of the second bypass switch54before entering the splitter64.

Preferably, the drop amplifier will provide unity gain (0 db), with losses in the passive components, such as connectors, diplex filters and splitters, being compensated for by the amplifier circuitry comprising the forward amplifier56and return amplifier58. Alternatively, additional gain may be provided by the forward and return amplifiers56and58to make up for losses external to the VoIP drop amplifier20.

When an abnormal condition, such as a loss of power to the VoIP drop amplifier or an abnormal operating condition of the RF amplifiers56and58, is encountered, the dc current and voltage sensing circuit66switches the bypass switches52and54to the normally closed condition, as shown inFIG. 3. In this condition, the path through the diplex filters60and62, the amplifiers56and58, and the splitter64is opened completely, isolating these components from the signal path. In this condition, the bypass path68is activated, connecting only the VoIP output connection to the cable system. If the overall gain in the normal condition was unity (0 dB), isolating the components and connecting the input connector44directly to the VoIP output connector38will restore an essentially lossless communication path through the VoIP drop amplifier20for the VoIP consumer telephone equipment while removing service from the other consumer equipment.

By referring to the simplified schematic diagram ofFIG. 4, the operation of dc current and voltage sensing circuitry can be understood.

The dc current and voltage sensing circuit66monitors the current provided to the low and high frequency amplifiers56and58(seeFIGS. 2 and 3), as well as the dc power supplied to the VoIP drop amplifier. The amplifier voltage is sampled at the VoIP power supply connector42via a voltage sensing circuit. The voltage sensing circuit110filters the dc voltage and scales the voltage using a voltage divider or other technique known in the art. The voltage at point118is then a scaled value representative of the voltage provided to the unit. This voltage is compared to a reference voltage V REF3at a first voltage comparator circuit108. If the scaled voltage falls below the reference voltage, indicating that the supply power is failing or has failed, the voltage comparator108generates a high output signal as its output.

The power supplied to the RF amplifiers (56and58inFIGS. 2 and 3) passes through a sampling resistor R1, also designated100inFIG. 4. The ohmic value of the sampling resistor100is small, so that the voltage drop across the resistor100does not interfere with proper operation of the RF amplifiers56and58by lowering the voltage supplied to the amplifiers at path116. The resistor100is large enough that the voltage drop across the resistor100is easily measurable in the current sensing circuitry. The voltage drop across the sampling resistor R1is amplified at an amplifying stage102, which generates at output114a voltage proportional to the combined current drawn by the RF amplifiers, and the amplifier output114is provided to a high current limit comparator106and a low current limit comparator104. In each circuit the RF amplifier supply current, represented by voltage output114, is compared to a reference value (V REF1or V REF2). If the current exceeds a high current limit value, the high limit comparator106generates a high voltage output value, and if the current drops below the low current limit reference value, the low limit comparator104generates a high voltage output signal. When the current is between the high and low levels, the high and low limit comparators generate a low voltage output. The high and low current limits are selected so that when the current draw anticipated for the RF amplifiers56and58is outside normal limits, the respective current comparator104or106generates a high output signal.

The outputs from the high limit comparator106, low limit comparator104, and the voltage comparator108are summed at common connection point120. If any of the three comparators generates a high-level voltage output, a Schmidt trigger circuit112trips to removes the voltage supplied at point122. Otherwise the Schmidt trigger circuit112generates a dc output signal, V RELAY, at path122. The voltage at path122is used to control the bypass switches52and54of the VoIP drop amplifier20. The hysteresis of the Schmidt trigger112results in the reset point of the Schmidt trigger112being appreciably lower than the trigger voltage, which prevents the bypass switches52and54from cycling between the normal and the bypass condition when the sensed voltage and current values undergo small fluctuations.

FIG. 5is a simplified diagram showing an implementation of the bypass circuitry using relays as the bypass switch52and54components. Each relay is a single pole double throw (SPDT) type with a common pole that is connected to the normally closed contact when the relay coil is de-energized. When the relay coil is energized, the common pole is disconnected from the normally closed contact and connected to the normally opened contact. Alternatively, a single double pole double throw (DPDT) relay can provide the functionality of the pair of SPDT relays.

As shown inFIG. 5the voltage V RELAY, which is the output of the voltage sensing circuit66as shown inFIG. 4, is applied to the relay coils of two SPDT relays202and204. The common pole of the first relay202is connected to the cable system input connector44of the VoIP drop amplifier20. When the voltage sensing circuit66provides a high level output voltage for V RELAY, the relay coil of the first relay202is energized, connecting the input through the first diplex filter60, the high and low frequency amplifiers56and58, the splitter64, and to each of the output connectors40a-40g. The coil of the second relay204is also energized, closing its normally open contact. The second relay204completes the path through the splitter64and to the VoIP output connector38.

When the sensing circuit66detects a loss of power supply voltage or improper amplifier operation, the V RELAY voltage will be deactivated as described above, resulting in the coils of the bypass relays202and204becoming de-energized. When the relay coils are de-energized, the signal path through the amplifiers56and58and splitter64, or the amplification path, is isolated by opening of the normally open relay contacts. The normally closed contacts of the bypass relays202and204are then closed to complete a bypass path68, connecting the cable system to the VoIP output38. Because the splitter64is bypassed in this condition, the bypass path68is nearly lossless. If the VoIP drop amplifier20is designed for unity gain, the VoIP output connector38will be supplied with essentially the same signal level in the bypass condition as in the normal condition. Non-essential consumer equipment, such as the PC Internet connection, will be disconnected from the cable signal when the VoIP drop amplifier20is in the bypass condition.

A complete loss of all power supplied to the VoIP drop amplifier20will result in disabling the voltage and current sense circuitry66. Because the bypass path through the amplifier20is selected using the normally closed contacts of the bypass switches52and54, the loss of power to the VoIP drop amplifier20will result in bypassing the de-energized active circuitry and the splitter64of the drop amplifier20, thus maintaining a loss-free connection to the consumer's VoIP telephone equipment.

In an example implementation, the reverse amplifier58comprises an RF Micro Devices RF2317 integrated circuit based RF amplifier, while the forward amplifier56comprises an ANADigics Inc. ADA10000 integrated circuit based broadband RF amplifier. The comparator circuits104,106, and108are implemented using conventional operational amplifier circuits, such as the LM2900. The current supplied to the two RF amplifier circuits passes through a 1-ohm resistor100, developing a voltage across the resistor100proportional to total amplifier current. This voltage is compared to reference voltage supplied to the current comparators104and106to implement the high and low current limits described above. The low current limit is approximately 180 milliamps (mA), while the high current limit is at approximately 300 mA. The nominal expected current draw for the amplifier circuitry is 250 mA. The current limit values are chosen to be consistent with the range of expected currents for the particular amplifier circuits used in the VoIP drop amplifier20. When amplifier current is outside of the expected range of values, the dc current and voltage sensing circuit66removes the voltage to the coils of the bypass relays52and54, switching the circuit into the bypass condition described above. After a trip due to an out-of-range current, the VoIP resets when the current increases to 200 mA or decreases below 280 mA due to the hysteresis of the Schmidt trigger112circuitry. The voltage sensing circuitry conditions the incoming voltage using filters and surge suppressors, and then employs a voltage divider network to provide a voltage proportional to the supply voltage. This voltage is compared to a reference voltage developed from an integrated circuit voltage regulator to establish the low voltage trip point. The low voltage limit is approximately 13 volts, with the normal supply voltage for the VoIP being 15-volts dc. When the supply voltage drops below the low voltage limit, the voltage and current sensing circuit66removes the voltage to the coils of the bypass relays52and54, switching the circuit into the bypass condition described above. After a trip due to a low supply voltage, the VoIP resets to use the amplification path when the voltage increases to at least 14 volts due to the hysteresis of the Schmidt trigger112circuitry. The circuit components, voltages and currents described above are by way of example and do not limit the invention to the particular components and circuit values detailed.

The dc current and voltage sensing circuit may use other means of detecting faults in the drop amplifier circuitry. For example, the integrated circuit amplifiers used to implement the forward and reverse amplifiers may include an output signal indicating normal operation of the amplifier. The dc current and voltage sensing circuitry could detect the loss of the normal operation signal and trigger the selection of the bypass path. In addition to sensing the dc voltage supplied to the unit, the dc voltage and sensing circuit may sample an ac supply voltage by rectifying and filtering the ac voltage to obtain a dc voltage representative of the ac supply voltage. The representative dc voltage may be compared to a reference and the results of the comparison may be used to control the bypass circuit.

Separate sensing resistors may be provided in the respective current paths supplying the forward and reverse amplifiers. By providing separate sensing resistors, and separate pairs of low and high current comparator circuits, the currents provided to the forward and reverse amplifiers can be monitored separately rather than as a combined value. The current set points of set of low and high current comparators are chosen based on the expected operating currents for the respective amplifier.

In another variation of the VoIP drop amplifier, the amplifier circuitry may include a forward amplifier but no reverse amplifier. This configuration is useful when user components such as a set top box or a cable modem generate reverse signals at sufficiently high levels so that amplification of the return signal from these user components.