This application generally relates to network equipment for the distribution of RF modulated data and audio/video content over a Hybrid Fiber Coaxial (HFC) cable network. In particular, this application describes a low insertion loss network equipment having an extended RF bandwidth.
Network devices that receive and transmit RF content and AC power over the same transmission line may utilize an AC/RF power passing choke filter to separate and combine the AC power component (below 60 Hz) from the RF signal component (greater than 5 MHz). Separation of the components facilitates processing of content within, for example, an HFC node or RF amplifier by presenting a low impedance to the 60 Hz AC power signal while simultaneously presenting a high impedance to the >5 MHz RF signal component, thereby directing and passing the AC power signal through the RF choke to the network device power supply while allowing the RF signal to pass to and from the network device RF processing circuitry.
Existing filters provide an RF passband from 5 MHz up to 1218 MHz with approximately 20 amperes of AC current capacity. However to support the continued demand for increased speed and capacity of transmitting and receiving data from network subscribers, the upper RF passband limit will need to increase from 1218 MHz to up to 3 GHz or greater.
The choke utilized in the filter to separate and combine the AC and RF signal is an inductor capable of handling the relatively high amount of current required to power the network devices.
The operating bandwidth of a typical inductor may be increased by reducing its outer diameter of its core, the number of wire turns wrapped around the core and/or by reducing the inter winding capacitance between loops of the wire in proportion to the wire size and the outer diameter.
However, increasing the bandwidth of a choke is difficult given the relatively high current carrying requirements of the choke. A reduction in the outer diameter of the core and/or the wire, or of the wire size may not be feasible because such changes may increase the flux density of the core and result in core saturation at high current. This in turn may influence the RF signal with an impedance that varies with the frequency of changes in the AC power signal resulting in a distortion of the RF signal referred to as Hum Modulation.
These and other problems with existing chokes will become apparent upon reading the specification.
A network device includes a) an interface configured to be coupled to a coaxial transmission line that simultaneously carries AC power and RF modulated content; b) content processing circuitry configured to route content and power communicated via the transmission line to one or more secondary network devices; and c) a choke coupled to the interface to route power communicated over the conductor to the internal power supply circuitry to facilitate powering the content processing circuitry within the network device. The choke includes a core. The core includes a first portion having a conical geometry and a second portion having a cylindrical geometry. A wire makes a plurality of turns around the core starting from the first portion and ending in the second portion.
A passive electrical component includes a core. The core includes a first portion having a conical geometry and a second portion having a cylindrical geometry. A wire makes a plurality of turns around the core starting from the first portion and ending in the second portion.
The problems described above are overcome by providing a network device that includes a choke optimized to support the evolution of HFC networks from 1.2 GHz to 1.8 GHz and beyond to 3 GHz.
The challenges/tradeoffs in designing an AC power choke for low insertion loss, a 5 MHz to 3 GHz extended RF spectrum with a relatively flat frequency response, a current capacity of 20 amperes, and low hum modulation include several conflicting considerations. For example, a choke that has too much inductance may cause resonances at high RF frequencies because of the stray capacitance combined with the inductance of the choke. The LC resonances may fall within the desired frequency range causing an increased insertion loss at those resonance points degrading the RF signal. However, too little inductance results in excessive insertion loss at low RF frequencies.
In addition to the RF content, AC power may be provided over the provider cable 115 from a network power supply 130 to power the network device 100 and other network devices 120. In this regard, voltage present on the provider cable 115 may be generally unregulated and may, for example, be anywhere between 30 and 95 volts AC. The network device 100 may include power regulation circuitry 125 that converts the AC unregulated voltage to one or more DC regulated voltages that are in turn utilized to power other circuitry 110 of the network device 100. For example, the power regulation circuitry 125 may include various switching and linear power regulators for converting the AC unregulated voltage to a regulated DC voltage.
In an embodiment, the network device 100 includes an AC/RF filter 105 that includes a choke that exhibits an inductance in the order of 5 uH to couple and decouple the AC power with the RF content signal to and from the provider cables 115 and direct AC power to the power regulation circuitry 125 associated with the network device 100. In this regard, the AC/RF filter 105 facilitates an increase in RF spectrum capability to 3 GHz while maintaining adequate RF performance characteristics of insertion loss, frequency response, and low frequency noise generation. Moreover, the AC/RF filter 105 is rated to handle, for example, in the range of 20 amperes to facilitate routing AC power from the AC power source 130 to the network device 100 power supply 125 and to a plurality of network devices 120 connected by provider cable 115.
As shown more clearly in
Referring back to
In an embodiment, the wire 207 turns around the core 205 in a first direction in regions R1 and R2, and turns around the core 205 in an opposite direction in regions R3 and R4 to form an inductor having a series opposing connection in which the mutually induced electromotive force (emf) opposes the self-induced emf.
As shown in
In operation, the conic structure of the winding on the initial portion of the ferrite core builds enough impedance without self-resonance and effectively reduces the insertion loss of the network device, thereby expanding the bandwidth without significantly impacting the overall inductance of the component 105. For example, as shown in
Referring to
While network device and component used therein have been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the claims. Therefore, it is intended that the present methods and systems not be limited to the particular embodiment disclosed, but that the disclosed methods and systems include all embodiments falling within the scope of the appended claims.
This application claims the benefit of U.S. Provisional Application No. 62/892,245 filed Aug. 27, 2019, which is incorporated herein in its entirety.
Number | Date | Country | |
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62892245 | Aug 2019 | US |