AT525682B1 - Cable Network Device - Google Patents

Abstract

A cable network device (50), in particular a multi-connector, comprising a first series of interconnected directional couplers (56) which are connected to a downstream signal input (52), each directional coupler in the first series having a separate connection port (60 ) and a second series of interconnected directional couplers (62) connected to an upstream signal output (54), the downstream signal input (52) and the upstream signal output (54) being separate, and pairs of directional couplers which formed of a directional coupler from each of the first series and the second series, are interconnected to allow an upstream signal path routed through the terminal port (60) and the directional couplers (56) in the first series to upstream signal output (54) reached.

Description

Description

OBJECT OF THE INVENTION

This invention relates to a cable network device for use in cable television and broadband networks and more particularly to a multi-line device.

BACKGROUND OF THE INVENTION

In a broadband network, amplifiers are used to amplify electrical signals from a central cable headend to an individual user downstream or from the individual user back to the headend upstream. Upstream and downstream frequencies are separated in the frequency domain, with the upstream signals using a lower frequency range and the downstream signals using a higher frequency range. Multiple lines are arranged within the network such that a plurality of ports are provided for connection to user homes, each port typically being connected to a single home.

[0003] In order to provide households with an upstream signal network that is always faster and has a broader bandwidth, the frequency ranges have to be changed. To ensure this, amplifying devices using directional couplers instead of diplex filters are often used, since amplifying devices without diplex filters ensure the changes in frequency ranges and, unlike amplifiers with diplex filters, do not have to be upgraded every time the frequency ranges change. However, such amplifiers can cause degradation of the downstream signal due to signal reflections.

SUMMARY OF THE INVENTION

The invention provides a cable network apparatus comprising a first series of interconnected directional couplers connected to a downstream signal input, each directional coupler in the first series being connected to a separate connection port, and a second series of interconnected directional couplers, which are connected to an upstream signal output, the downstream signal input and the upstream signal output being separate, and pairs of directional couplers, each consisting of a directional coupler of the first series and the second series, are interconnected to form an upstream signal path which is passed through the connector port and the directional coupler in the first series to achieve the upstream signal output.

Preferably each directional coupler is connected to an adjacent coupler of the same series and also to a single directional coupler of the other series.

The directional couplers of the first series are preferably microstrip couplers, preferably with a coupled port of the microstrip directional coupler connected to the connection port.

An isolated port of the microstrip coupler is preferably connected to the other directional coupler in the pair of directional couplers.

Preferably, the directional couplers of the second series are ferrite directional couplers.

The cable network device is preferably configured such that an isolation from downstream signal input to upstream signal output is greater than 40 dB, and more preferably greater than 60 dB.

The cable network device may be a multi-port device.

Such a cable network device can be used in combination with an amplifier that includes a directional coupler to form separate upstream and downstream paths.

The invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a schematic representation of a prior art amplifier and multiport arrangement;

Figure 2 is a schematic representation of a multiple connector according to the invention;

Figure 3 is a schematic representation of an amplifier for use by the manifold of Figure 2; and

FIG. 4 is a graph showing isolation versus frequency for the multiport of FIG.

DESCRIPTION

An illustration of a prior art amplifier 10 used in a broadband, data and/or telecommunications network is shown in Figure 1, where the amplifier 10 uses directional couplers 12, 14 instead of diplex filters to provide upstream and separate downstream signals for amplification. The input port 16 receives the upstream signal 20 and divides it into separate upstream and downstream paths by means of directional couplers 12, 14. The amplifier elements 22,24 amplify the signals transmitted along the unidirectional signal paths between the directional couplers 12,14. At the output 26, the amplified downstream signal 30 goes to the splitter 32, which is connected to two 12-way multiple connectors 34, 34', each connector providing twelve connection ports to connect users to the network.

The splitter 32 has a finite return loss such that a portion of the amplified signal 30 is reflected back to the amplifier 10. The reflected signal 40 travels upstream and is amplified by the upstream amplifier element 24 . At the input 16, this amplified reflection signal 41 is partially reflected again due to the finite return loss at the input 16. The secondarily reflected and amplified signal 42 travels back downstream in the same direction as the original signal 20. Depending on the gain of the amplifier elements 22, 24, the signal levels, return loss, modulation and timing of the signals, these signal reflections can degrade the original signal Signal 20 lead.

In order to overcome these disadvantages, the present invention provides a 12-way multiple connection 50, as shown in FIG. 2, which provides twelve connection ports, as is the case with the prior art multiple connections shown in FIG is. The manifold 50 includes a separate downstream input 52 and an upstream output 54, with an interconnected series or cascade of twelve directional couplers 56 in the downstream path connecting to each connector port 60, 60', 60", 60". and an interconnected series or cascade of twelve directional couplers 62 in an upstream path that returns upstream signals to the separate upstream output 54. Each cascade is terminated by a resistor 55, 55', typically having a value of 75 ohms. For multiple connections with fewer ports, e.g. a 4-way connection, each cascade consists of the same number of directional couplers as there are connection ports.

Directional couplers 56 are microstrip couplers, also known as toggle connectors, with the output 57 of each microstrip coupler 56 being connected to the input 58 of the next microstrip coupler 56 to allow the downstream signal received at input 52 , to reach all connection ports. Each connector port 60 is connected to a coupled port 64 of microstrip coupler 56, with a portion of the downstream signal being extracted from input 52 to feed each connector port, which in turn is connected to a coaxial cable leading to a connected household leads.

The isolated port 66 of each microstrip coupler 56 is connected to a single directional coupler 62 in the interconnected cascade of directional couplers 62 in the upstream return path leading to the upstream output 54 . Each directional coupler in the first cascade associated with the downstream input 52 is paired with a single directional coupler in the second cascade associated with the upstream output 54 . Thus, an interconnected pair of directional couplers is provided for each connection port. The directional couplers 62 are preferably transformer-type ferrite directional couplers.

If desired, an optional high pass filter 70 having a pass frequency above the lowest expected downstream frequency, typically in the 100 or 200 MHz range, is placed between the input 52 and a first directional coupler 56 . An optional low pass filter 72 with a pass frequency below the highest expected upstream frequency, typically in the 400-700 MHz range, is placed between the output 54 and the directional coupler 62 that is closest to the output 54 .

In use, a downstream signal present at the downstream signal input 52 travels along the first cascade formed of microstrip couplers 56, and a small, defined portion of the signal energy is coupled to each connector port 60. Due to the nature of the directional coupler, the downstream signal does not appear on isolated port 66.

An upstream signal, which is generated in a connected household, passes from the connection port 60 to the isolated port 66 of the microstrip coupler 56, and from there to the directional coupler 62, which is connected to the isolated port 66, with low insertion loss. The upstream signal is not present at the output port 57 of the microstrip directional coupler 56 because the nature of the directional coupler provides port-to-port isolation.

The upstream signals of the respective connection ports 60 travel along the upstream path connecting the second cascade of directional couplers 62 and are passed through the optional low-pass filter 72 to the upstream output port 54 .

This configuration results in a multiple connection with separate and HF-isolated downstream input ports and upstream output ports, which can be connected to an amplifier 80 with separate downstream output 82 and upstream input 84, see Figure 3. Each reflected downstream signal achieves this upstream gain element 86 does not because isolation exists between the separate upstream and downstream connectors of manifold 50. Therefore, it is not amplified and cannot reach the input port 88 of the amplifier 80. Therefore, there is no reflection signal traveling in the same direction as the original downstream signal. The reflected signal cannot travel in the opposite direction through the downstream amplifier element 90.

For a 12-way connector with a high-pass filter set at 200 MHz and a low-pass filter set at 400 MHz, the isolation between the downstream input port 52 and the upstream output port 54 is shown in Figure 4 on a scale of 12 to 1900 MHz and 0 to -100 dB and is well above 60 dB.

The high isolation avoids reflection problems and also avoids problems with amplifier oscillations. For a typical amplifier, >40 dB upstream-downstream isolation in the multiport would be sufficient to avoid reflection problems.

Claims (10)

patent claims A cable network device (50) comprising a first series of interconnected directional couplers (56) connected to a downstream signal input (52), each directional coupler (56) in the first series having a separate connection port (60 ) and a second series of interconnected directional couplers (62) connected to an upstream signal output (54), wherein the downstream signal input (52) and the upstream signal output (54) are separate, and pairs of directional couplers that are formed from one directional coupler each of the first series and the second series, are interconnected in such a way that an upstream signal path, which is routed through the connection port (60) and the directional coupler (56) of the first series, the upstream signal output (54) reached. 2. The cable network device of claim 1, wherein each directional coupler is connected to an adjacent coupler of the same series, and is also connected to a single directional coupler of the other series. 3. The cable network apparatus of claim 1 or claim 2, wherein the directional couplers (56) of the first series are microstrip couplers. The cable network device of any preceding claim, wherein a coupled port (64) of the microstrip directional coupler (56) is connected to the termination port (60). The cable network device of any preceding claim, wherein an isolated port (66) of the microstrip coupler (56) is connected to the other directional coupler (62) in the pair of directional couplers. The cable network apparatus of any preceding claim, wherein said second series directional couplers (62) are ferrite directional couplers. 7. The cable network apparatus of any preceding claim configured to have greater than 40 dB isolation from downstream signal input (52) to upstream signal output (54). The cable network apparatus of any preceding claim configured to have greater than 60 dB isolation from downstream signal input (52) to upstream signal output (54). 9. The cable network device of any preceding claim, wherein the cable network device is a multi-port device. 10. Use of a cable network device according to any one of the preceding claims in combination with an amplifier (80) comprising a directional coupler to form a separate upstream input (84) and downstream output (82). 2 sheets of drawings