Abstract:
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.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/589,337, filed Jul. 19, 2004. 

   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&#39;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&#39;s system. 
   These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a typical CATV system incorporating a VOIP drop amplifier according to the present invention. 
       FIG. 2  is a functional block diagram of the VoIP drop amplifier according to the present invention operating under normal operating conditions. 
       FIG. 3  is a functional block diagram of the VoIP drop amplifier according to the present invention switched to the bypass operating condition after detecting a fault in the system. 
       FIG. 4  is a simplified schematic diagram of an embodiment of current and voltage sensing circuitry that may be used in the VoIP drop amplifier according to the present invention. 
       FIG. 5  is a simplified schematic diagram of an embodiment of a VoIP drop amplifier according to the present invention using relays as the bypass switches. 
   

   Similar reference characters denote corresponding features consistently throughout the attached drawings. 
   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. 1  illustrates a system employing a VoIP drop amplifier according to the invention. The cable operator provides communication services to a multi-tap point  46 . The VoIP drop amplifier is connected to the multi-tap connection via a cable that is connected to the RF signal input connector  44 . The VoIP drop amplifier provides amplification for the forward and return signals and splits the signals, delivering them to the output connectors  38  and  40   a - 40   g.    
   Connected by cables to the output connectors are various devices for utilizing broadband cable service. Connected to output connector  40   a  is a cable modem  24  supplying an Internet connection for a personal computer  48 . Two integrated digital televisions  26  are connected to output connectors  40   b  and  40   c . 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 connector  40   d  is connected to a set top box  30 , which in turn is connected to a conventional television set  28 . Output connector  40   d  is connected to a set top box  30  that in turn is connected to a conventional (non iDTV capable) television set  28 . 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 connector  38  is connected via a cable to a second cable modem  32 , which is connected to a multimedia terminal adapter (MTA)  34 . The MTA is connected to one or more VoIP telephones  36 . The remaining output connectors  40   e - 40   g  are 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 amplifier  20  is shown powered by an uninterruptible power supply (UPS)  22 , which provides power to the VoIP drop amplifier  20  via the input connector  42 . Alternatively, power may be provided to the VoIP drop amplifier  20  from a simple wall transformer. 
     FIGS. 2 and 3  are block diagrams by which the basic operating principles of the VoIP drop amplifier  20  may be understood.  FIG. 2  shows the amplifier in the normal condition, while  FIG. 3  shows the amplifier in a bypass condition. 
   As shown in  FIG. 2 , the RF signal to and from the cable system is routed through the input connector  44  to a first bypass switch  52 . A switch circuit comprises this first bypass switch  52 , as well as a second bypass switch  54  described below. The switch circuit is controlled by dc current and voltage sensing circuitry  66 . When the dc current and voltage sensing circuitry  66  detects 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 switch  52  is set to pass the incoming signal to the first diplex filter  60 . 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&#39;s equipment, which is directed back to the cable system. A separate upstream amplifier  56  and a downstream amplifier  58  are 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 switch  52 , the first diplex filter  60 , the high frequency amplifier  56 , the second diplex filter  62 , and into the splitter  64 . After subdividing at the splitter  64 , the signal is routed to the various consumer equipment, as shown in  FIG. 1 , with the exception of the VoIP telephone equipment. The path to the VoIP connector, after passing through the splitter  64 , also passes through the second bypass switch  54 . With the second bypass switch  54  in the energized condition, the downstream signal passes through the normally open contacts of the second bypass switch  54  and then to the VoIP output connector  38 . 
   The path for the reverse signal, originating at the consumer equipment is into the connectors  40   a - 40   g  through the splitter  64 , into the second diplex filter  62 , through the low frequency amplifier  58 , then through the first diplex filter  60  and through the normal open contacts of the first bypass switch  52 . The VoIP reverse signal first passes though the normally open contacts of the second bypass switch  54  before entering the splitter  64 . 
   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 amplifier  56  and return amplifier  58 . Alternatively, additional gain may be provided by the forward and return amplifiers  56  and  58  to make up for losses external to the VoIP drop amplifier  20 . 
   When an abnormal condition, such as a loss of power to the VoIP drop amplifier or an abnormal operating condition of the RF amplifiers  56  and  58 , is encountered, the dc current and voltage sensing circuit  66  switches the bypass switches  52  and  54  to the normally closed condition, as shown in  FIG. 3 . In this condition, the path through the diplex filters  60  and  62 , the amplifiers  56  and  58 , and the splitter  64  is opened completely, isolating these components from the signal path. In this condition, the bypass path  68  is 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 connector  44  directly to the VoIP output connector  38  will restore an essentially lossless communication path through the VoIP drop amplifier  20  for the VoIP consumer telephone equipment while removing service from the other consumer equipment. 
   By referring to the simplified schematic diagram of  FIG. 4 , the operation of dc current and voltage sensing circuitry can be understood. 
   The dc current and voltage sensing circuit  66  monitors the current provided to the low and high frequency amplifiers  56  and  58  (see  FIGS. 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 connector  42  via a voltage sensing circuit. The voltage sensing circuit  110  filters the dc voltage and scales the voltage using a voltage divider or other technique known in the art. The voltage at point  118  is then a scaled value representative of the voltage provided to the unit. This voltage is compared to a reference voltage V REF 3  at a first voltage comparator circuit  108 . If the scaled voltage falls below the reference voltage, indicating that the supply power is failing or has failed, the voltage comparator  108  generates a high output signal as its output. 
   The power supplied to the RF amplifiers ( 56  and  58  in  FIGS. 2 and 3 ) passes through a sampling resistor R 1 , also designated  100  in  FIG. 4 . The ohmic value of the sampling resistor  100  is small, so that the voltage drop across the resistor  100  does not interfere with proper operation of the RF amplifiers  56  and  58  by lowering the voltage supplied to the amplifiers at path  116 . The resistor  100  is large enough that the voltage drop across the resistor  100  is easily measurable in the current sensing circuitry. The voltage drop across the sampling resistor R 1  is amplified at an amplifying stage  102 , which generates at output  114  a voltage proportional to the combined current drawn by the RF amplifiers, and the amplifier output  114  is provided to a high current limit comparator  106  and a low current limit comparator  104 . In each circuit the RF amplifier supply current, represented by voltage output  114 , is compared to a reference value (V REF 1  or V REF 2 ). If the current exceeds a high current limit value, the high limit comparator  106  generates a high voltage output value, and if the current drops below the low current limit reference value, the low limit comparator  104  generates 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 amplifiers  56  and  58  is outside normal limits, the respective current comparator  104  or  106  generates a high output signal. 
   The outputs from the high limit comparator  106 , low limit comparator  104 , and the voltage comparator  108  are summed at common connection point  120 . If any of the three comparators generates a high-level voltage output, a Schmidt trigger circuit  112  trips to removes the voltage supplied at point  122 . Otherwise the Schmidt trigger circuit  112  generates a dc output signal, V RELAY, at path  122 . The voltage at path  122  is used to control the bypass switches  52  and  54  of the VoIP drop amplifier  20 . The hysteresis of the Schmidt trigger  112  results in the reset point of the Schmidt trigger  112  being appreciably lower than the trigger voltage, which prevents the bypass switches  52  and  54  from cycling between the normal and the bypass condition when the sensed voltage and current values undergo small fluctuations. 
     FIG. 5  is a simplified diagram showing an implementation of the bypass circuitry using relays as the bypass switch  52  and  54  components. 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 in  FIG. 5  the voltage V RELAY, which is the output of the voltage sensing circuit  66  as shown in  FIG. 4 , is applied to the relay coils of two SPDT relays  202  and  204 . The common pole of the first relay  202  is connected to the cable system input connector  44  of the VoIP drop amplifier  20 . When the voltage sensing circuit  66  provides a high level output voltage for V RELAY, the relay coil of the first relay  202  is energized, connecting the input through the first diplex filter  60 , the high and low frequency amplifiers  56  and  58 , the splitter  64 , and to each of the output connectors  40   a - 40   g . The coil of the second relay  204  is also energized, closing its normally open contact. The second relay  204  completes the path through the splitter  64  and to the VoIP output connector  38 . 
   When the sensing circuit  66  detects 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 relays  202  and  204  becoming de-energized. When the relay coils are de-energized, the signal path through the amplifiers  56  and  58  and splitter  64 , or the amplification path, is isolated by opening of the normally open relay contacts. The normally closed contacts of the bypass relays  202  and  204  are then closed to complete a bypass path  68 , connecting the cable system to the VoIP output  38 . Because the splitter  64  is bypassed in this condition, the bypass path  68  is nearly lossless. If the VoIP drop amplifier  20  is designed for unity gain, the VoIP output connector  38  will 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 amplifier  20  is in the bypass condition. 
   A complete loss of all power supplied to the VoIP drop amplifier  20  will result in disabling the voltage and current sense circuitry  66 . Because the bypass path through the amplifier  20  is selected using the normally closed contacts of the bypass switches  52  and  54 , the loss of power to the VoIP drop amplifier  20  will result in bypassing the de-energized active circuitry and the splitter  64  of the drop amplifier  20 , thus maintaining a loss-free connection to the consumer&#39;s VoIP telephone equipment. 
   In an example implementation, the reverse amplifier  58  comprises an RF Micro Devices RF2317 integrated circuit based RF amplifier, while the forward amplifier  56  comprises an ANADigics Inc. ADA10000 integrated circuit based broadband RF amplifier. The comparator circuits  104 ,  106 , and  108  are implemented using conventional operational amplifier circuits, such as the LM2900. The current supplied to the two RF amplifier circuits passes through a 1-ohm resistor  100 , developing a voltage across the resistor  100  proportional to total amplifier current. This voltage is compared to reference voltage supplied to the current comparators  104  and  106  to 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 amplifier  20 . When amplifier current is outside of the expected range of values, the dc current and voltage sensing circuit  66  removes the voltage to the coils of the bypass relays  52  and  54 , 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 trigger  112  circuitry. 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 circuit  66  removes the voltage to the coils of the bypass relays  52  and  54 , 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 trigger  112  circuitry. 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. 
   It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.