Lossless test point

Abstract

Devices, systems and methods for selectively and alternately connecting and disconnecting the primary signal path through an amplifier in a communications network that propagates content from a head end to a plurality of subscribers to a test point connection of the amplifier, based on whether a test probe is engaged with the test point connection.

Description

LOSSLESS TEST POINTCROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of priority under 35 U.S.C. § 119(e) to U.S. Provisional Application. No. 63 / 662,138 filed June 20, 2024, the contents of which is incorporated herein by reference in its entirety.BACKGROUND

[0002] The subject matter of this application relates to improved systems and methods that deliver CATV, digital, and Internet services to customers and more specifically to an improved test point connection for an amplifier in a CATV network.

[0003] Cable Television (CATV) services historically provided content to large groups of subscribers from a central delivery unit, called a "head end," which distributes content to subscribers from this central unit through a branch network comprising a multitude of intermediate nodes. Modem Cable Television (CATV) service networks, however, not only provide media content such as television channels and music channels to a customer, but also provide a host of digital communication services such as Internet Service, Video-on- Demand, telephone service such as VoIP, and so forth. These digital communication services, in turn, require not only communication in a downstream direction from the head end, through the intermediate nodes and to a subscriber, but also require communication in an upstream direction from a subscriber and to the content provider through the branch network.

[0004] To this end, such CATV head ends included a separate Cable ModemTermination System (CMTS), used to provide high speed data services, such as video, cable Internet, Voice over Internet Protocol, etc. to cable subscribers. Typically, a CMTS will include both Ethernet interfaces (or other more traditional high-speed data interfaces) as well as RF interfaces so that traffic coming from the Internet can be routed (or bridged) through the Ethernet interface, through the CMTS, and then onto the optical RF interfaces that are connected to the cable company's hybrid fiber coax (HFC) system. Downstream traffic is delivered from the CMTS to a cable modem in a subscriber's home, while upstream traffic is delivered from a cable modem in a subscriber’s home back to the CMTS. Many modernCATV systems have combined the functionality of the CMTS with the video delivery system (EdgeQAM) in a single platform called the Converged Cable Access Platform (CCAP). Still other modern CATV architectures (referred to as Distributed Access Architectures or DAA) relocate the physical layer (e.g.., a Remote PHY or R-PHY architecture) and sometimes the MAC layer as well (e.g., a Remote MACPHY or R-MACPHY architecture) of a traditional CCAP by pushing it / them to the network’s fiber nodes. Thus, while the core in the CCAP performs the higher layer processing, the remote device in the node converts the downstream data sent by the core from digital-to-analog to be transmitted on radio frequency, and converts the upstream RF data sent by cable modems from analog-to-digital format to be transmitted optically to the core.

[0005] Regardless of which architectures were employed, historical implementations of CATV systems bifurcated available bandwidth into upstream and downstream transmissions i.e., data was only transmitted in one direction across any part of the spectrum. For example, early iterations of the Data Over Cable Service Interface Specification (DOCSIS) specified assigned upstream transmissions to a frequency spectrum between 5 MHz and 42 MHz and assigned downstream transmissions to a frequency spectrum between 50 MHz and 750 MHz. Later iterations of the DOCSIS standard expanded the width of the spectrum reserved for each of the upstream and downstream transmission paths, the spectrum assigned to each respective direction did not overlap.

[0006] Still later iterations of the DOCSIS standard utilized OrthogonalFrequency Division Multiplexing (OFDM) as a cable data transmission format. The purpose of OFDM / OFDMA technology is to maximize the efficiency of data transmissions across a cable data network by optimizing the QAM modulation level used for each subcarrier of RF frequency bandwidth. Although originally defined for use directly in the downstream direction, OFDM technology was adapted for multiple access (Orthogonal Frequency Division with Multiple Access - OFDMA) for use in the upstream direction. In each direction, a relatively wide channel is subdivided into many small subcarriers. In the downstream direction, each of these subcarriers may use its own Quadrature Amplitude Modulation (QAM) level, which equates to a different bit capacity per subcarrier QAM symbol. In the upstream direction, groups of subcarriers are combined and, when timemultiplexed, create the atomic unit of upstream bandwidth assignment known as a “minislot.” Tn the upstream direction, all subcarriers of a minislot are assigned the same QAM level and thus all subcarriers of a minislot have the same bit capacity per QAM symbol.

[0007] Recently, cable operators have searched for additional alternative architectures to satisfy ever-increasing demand for both upstream and downstream services. One such proposed architecture, for example, is foil duplex (FDX) DOCSIS technology. With FDX DOCSIS, upstream and downstream spectrum is no longer separated, allowing up to 5 Gbps upstream service and 10 Gbps downstream service over the cable access network. In a full duplex system, because the CCAP / R-PHY core knows the characteristics of its own downstream transmission, it can distinguish upstream communications transmitted in the same frequencies that it provides those downstream services. Full duplex technology, however, is unsuitable in the longer HFC plants that exist in most operators’ networks. Furthermore, in FDX systems, subscribers must be organized into “interference groups” to mitigate interference in downstream transmissions to some subscribers caused by upstream transmissions by other subscribers, but the presence of amplifiers located between a customers’ premises and the closest node inhibits the separation of those customers into groups because the amplifiers cause all subscribers to interfere with each other. Theoretically, this problem could be addressed by eliminating the amplifiers running fiber to each subscriber’s premises, or including cancellation in the amplifiers, but both are costly.

[0008] Other proposed architectures would increase the spectrum of both services to customers in both upstream and downstream directions, moving the split between these services upwards. For example, the proposed DOCSIS 4.0 standard would extend the upper frequency of the downstream spectrum from 1218 MHz to 1794 MHz while moving the maximum split between the upstream and downstream services from 204 / 258 MHz to as high as 684 / 834 MHz. These architectures are often referred to as Extended Spectrum DOCSIS (ESD). Again, however, upgrading the equipment from the head end to the subscribers premises to accommodate the increase in bandwidth is expensive.

[0009] A common theme of all these evolutions of the CATV architecture is the need to provide ever increasing amounts of bandwidth. One deleterious influence on bandwidth is noise; as noise increases relative to signal strength, less of the availablebandwidth becomes usable. In a typical CATV or other communications network, a signal is propagated over a transmission medium, such as an optical fiber or a coaxial cable, for often a great distance before reaching a customer. Signal degradation occurs over this length and is typically recovered using one or more amplifiers.

[0010] Many electronic components, such as amplifiers in a communications network, include test points for diagnostics, but which are not active when in ordinary use. Thus, during a diagnostic procedure, when a mating connector is present a signal may propagate through the test point to test circuitry, but otherwise the test point will not be used. Unfortunately, inclusion of the test points causes significant loss / noise during operation, even when no diagnostic circuitry is connected to the test point. This insertion loss relative to the gain available, and to the gain target of the system, therefore interferes with these goals.[00111 What is desired, therefore, are improved devices, systems and methods for reducing noise (loss) in circuitry having test points.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

[0013] FIG. 1A shows a portion of an exemplary communications system in which a node supplies a signal to a large number of customers via a network of cables and amplifiers.

[0014] FIG. IB shows an exemplary amplifier circuit in the system of FIG. 1A, with a test point connection.

[0015] FIG. 2 shows a test point connection of FIG. IB comprising a novel split grounding sleeve, with a selectively attachable mating connector.

[0016] FIGS. 3A and 3B show respective circuits that use the split grounding sleeve and mating connector of FIG. 2 to isolate a test point from the remaining circuitry of the amplifier of FIG. IB.

[0017] FIGS. 4-7 each show alternate devices for isolating a test point from the remaining circuitry of the amplifier of FIG. IB.DETAILED DESCRIPTION

[0018] FIG. 1A shows an exemplary communications network 10 that extends from a node 12 to a plurality of cable modems 18 in the homes of subscribers.Communications signals are propagated over the network via trunk cable 19, and each cable modem 18 is fed by a respective tap 16 and feeder cable 17. The system 10 shown in FIG. 1A may be an HFC system as previously described, where the node 12 is served by a head end having a CCAP (not shown), or alternately the node 12 may be one in a DAA architecture, e.g., an RPD, RMD, etc. The cable 17, 19 may comprise coaxial cable, although those of ordinary skill in the art will appreciate that other transmission media may be used, such as fiber optic cable, and that although the system 10 does not show the cabling between the node 12 and any devices upstream from the node e.g., a head end, another node, etc. may also benefit from the systems and methods disclosed in the present application.

[0019] The system of FIG. 1A also utilizes one or more amplifiers 14, which are necessary because the signal that propagates along cable 19 degrades over the cable length and is also degraded by the passive elements along the cable 19, such as taps 16. This necessitates the periodic spacing of amplifiers along the length of the cable to recover the signal.

[0020] As previously noted, amplifiers in a communications network, include test points for diagnostics, but which are not active when in ordinary use. Thus, during a diagnostic procedure, when a mating connector is present a signal may propagate through the test point to test circuitry, but otherwise the test point will not be used. Referring, for example, to FIG. IB, an exemplary amplifier 100 may receive a downstream signal at a northbound input 102 and an upstream signal at a southbound input 104. The amplifier 100 amplifies both the downstream and upstream signals, and therefore includes diplexers 106a, 106b proximate the northbound and southbound inputs 102, 104, respectively so that the downstream signal may be separated from the upstream signal and routed through path 108 while the upstream signal is routed through path 110. In this manner, each of the downstreamand upstream signals may be individually amplified by amplifiers 112a, 112b, respectively. The exemplary amplifier 100 ideally has a maximum amount of available gain to maximize its versatility and minimize the frequency or necessity of other plant upgrade techniques. Moreover, the amplifier 100 is preferably manufactured to be very low cost and very low power, which means only using a single gain stage.

[0021] The amplifier 100 also includes one or more test point connections 114.Test point connections on amplifiers 100 are typically provided at the common port of diplexers 106a, 106b so that diagnostics can be taken at either side of the amplifier 100. Each of these test point connections 114 is bidirectional and passive, consisting of a simple resistor-divider. Unfortunately, inclusion of the test point connections causes significant loss / noise during operation, even when no diagnostic circuitry is connected to the test point. This is because test point connections are grounded and therefore will draw some amount of current from the upstream and downstream signal paths, even when no test probe is connected.

[0022] The present application therefore discloses an improved test point connection, and methods for using a test point connection, of an amplifier which mitigates this insertion loss. The disclosed test point connection is not active until it is in use and therefore improves isolation from nearby circuitry so as to reduce loss from the active test point when not in use. Specifically, the embodiments disclosed in the present specification reduce insertion loss by separating the test points from the surrounding circuitry except when the test points are being probed i.e., the presence of the probe is what connects the test points to the surrounding circuitry. In some embodiments, the disclosed test point connection may be integrally formed into the circuit board of an amplifier, while in other embodiments, the disclosed test point connection may be a plug-in module. The amplifier 100, for example, typically comprises a printed circuit board with receptacles for replaceable plug-in modules, such as downstream plug-in 116, upstream plugin 1 18, attenuation plug-in 120, etc. by which customized signal processing may be provided to the amplifier 100. The disclosed test point connection may in some embodiments be such a plug-in module.

[0023] FIG. 2 shows an exemplary plug-in test point connector 130 comprising a split grounding sleeve 132 having an inner conductor 134 (shown in FIG. 3 A) and an outerconductor 136 isolated from the inner conductor 134. The inner conductor 134 and outer conductor 136 are respectively connected to either side of a terminating resistor 138 in a resistor-divider 140 that, in turn, is connected to the common port of a respective diplexer 106a, 106b. The outer conductor 136 is split into two or more segments i.e., the split grounding sleeve itself does not connect the test point 114 to the primary signal path of the amplifier 100, hence does not itself ground the test point connection 114. Instead, the plug-in test point connector 130 also comprises a mating sleeve 134 that may be mounted around, or otherwise connectable to, the split grounding sleeve 132 while a test probe is connected to the inner conductor 134. In some embodiments, the mating sleeve 134 may be connected to, or connectable to, a test probe. The mating sleeve 134 includes conductive members 142 positioned such that, when the mating sleeve 134 is engaged with the split grounding sleeve 132, the conductive members 142 electrically connect the segments of the outer conductor 136, meaning that the mating sleeve 134 connects the test point comiection 114, and the signal path of the amplifier 100 to ground when the mating sleeve 134 engages with the split grounding sleeve 132. In this manner, when no probe is connected to the test point 114, the divider 140 floats without a ground reference and would therefore not draw current from the primary signal path without a probe being inserted. A probe may be inserted along with a mating sleeve 134 that connects or shorts the segments of the outer conductor 136, thus connecting the terminating resistor 138 (and divider 140) to ground so that diagnostics may be performed.

[0024] While the embodiment of FIG. 3 A is simple, it leaves a resistive stub(dead end) hanging off of the primary signal path, which can be undesirable in an RF circuit. FIG. 3B shows an alternative approach, which uses an RF switch 150. The switch 150 has a default state that holds the switch open, e.g., the default state of the switch is “high” and fully disconnects the stub from the primary signal path of amplifier 100 until a probe is connected, at which point the switch 150 closes and connects the stub of the resistor-divider 140 to the primary signal path of amplifier 100.

[0025] Although the embodiment of FIG. 3A, together with that of FIG. 3B, shows a switch 150 in conjunction with a plug-in test connector 130 separated into a split grounding sleeve 132 and a mating sleeve 134 that, together, both isolate the outer conductor136 from a ground connection and isolate the resistor divider from the primary signal path of the amplifier until a test probe is connected to the test point connection 1 14, the present specification discloses alternate embodiments of test point connections 114 that separate the test points, including resistive stubs, from the signal path of the amplifier except when the test points are being probed. FIG. 4, for example shows an alternate embodiment of a test point connection 1 14 comprising an inner conductor 134 electrically isolated from an outer conductor 136. Like the embodiments of FIGS. 3A and 3B, the inner conductor 134 and outer conductor 136 are respectively connected to either side of a terminating resistor 138 in a resistor-divider 140 that, in turn, is connected to the common port of a respective diplexer 106a, 106b. Unlike the embodiments of FIGS. 3A and 3B, however, the outer conductor 136 is not split, and therefore is always connected to ground. Isolation of the test point connector 114 is provided by the switch 150, which again is in a default “high” that fully disconnects the test point connection 114 from the primary signal path of amplifier 100 until a probe is connected. In this embodiment, a sensor 162 detects whether a test probe is connected to the center conductor 134 and when that occurs, closes the switch 150 to connect the test point connection 114 to the primaiy signal path of the amplifier 100.

[0026] In the embodiment of FIG. 4, the sensor 162 may comprise a Hall effect sensor. A Hall effect sensor produces a voltage proportional to an axial component of the magnetic field vector B. Thus, when a test probe is connected to the center conductor 134, the resulting magnetic field produces the voltage needed to close the switch 150.

[0027] Although the embodiment of FIG. 4 uses a Hall effect sensor to close the switch 150, any appropriate sensor may be utilized. For example, FIG. 5 shows an optical detection circuit that can sense the presence of a near field object, in this case the test probe. Similar to the Hall Effect sensor approach, an optical sensor 164 may be positioned proximate the location that the probe will be when it is installed in the test point. This could be the bottom of the test point (facing up), or through the side of the connector using either the split sleeve ground or a window / hole in the side of the sleeve ground. FIGS. 6 and 7 show still other embodiments where a physical switch 168 can be used such that the switch sits at the bottom of the connector and is pressed by the probe when the probe is fully inserted into the test point connector. This can be implemented either as a switch that is in line with thesignal path (FIG. 6), or as a switch that controls the logic control of a second RF switch 168 that is in line with the signal path (FIG. 7). The logic of the switch 168 preferably can be implemented either using a weak pull-up that is pulled to ground when the mechanical switch is pressed, or a weak pull-down that is shorted to Vcc when the switch is pressed.

[0028] It will be appreciated that the invention is not restricted to the particular embodiment that has been described, and that variations may be made therein without departing from the scope of the invention as defined in the appended claims, as interpreted in accordance with principles of prevailing law, including the doctrine of equivalents or any other principle that enlarges the enforceable scope of a claim beyond its literal scope. Unless the context indicates otherwise, a reference in a claim to the number of instances of an element, be it a reference to one instance or more than one instance, requires at least the stated number of instances of the element but is not intended to exclude from the scope of the claim a structure or method having more instances of that element than stated. The word "comprise" or a derivative thereof, when used in a claim, is used in a nonexclusive sense that is not intended to exclude the presence of other elements or steps in a claimed structure or method.

Claims

CLAIMS1. A test point connector for an amplifier in a communications network that delivers content to a plurality of subscribers from a head end, the amplifier having a primary signal path through the amplifier that propagates the content, the test point connector comprising: an inner conductive member electrically isolated from an outer conductive member; and a switch member configured to selectively and alternately connect and disconnect at least a portion of the outer conductive member from the primary signal path.

2. The test point connector of claim 1 where the switch member is configured to alternately connect and disconnect at least a portion of the outer conductive member from the primary signal path when a test probe is connected to the test point connector.

3. The test point connector of claim 1 configured as a plug-in module for the amplifier.

4. The test point connector of claim 1 integrated into the amplifier.

5. The test point connector of claim 1 where the switch member comprises a first component that selectively and alternately connects and disconnects at least a portion of the outer conductive member from the primary signal path, and a second component, operatively connected to the first component, that causes the first component to selectively and alternately connect and disconnect at least a portion of the outer conductive member from the primary signal path when a test probe is engaged with the test point connector.

6. The test point connector of claim 6 where the first component is an electrical switch.

7. The test point connector of claim 6 where the second component is a sensor that activates the electrical switch when the test probe is engaged with the test point connector.

8. A method of selectively connecting a test point of an amplifier in a communications network that delivers content to a plurality of subscribers from a head end,the amplifier having a primary signal path through the amplifier that propagates the content, the method comprising: selectively connecting at least a portion of an outer conductor of the test point connector to the primary signal path of the amplifier when a test probe is engaged with the test point, the outer conductor ; and selectively disconnecting the at least a portion of an outer conductor of the test point connector from the primary signal path of the amplifier when a test probe is not engaged with the test point.

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