GB2345216A - Signal handling apparatus - Google Patents

Abstract

A video signal matrix comprises an input module, an output module, a switching module, the input module comprising a plurality of coaxial video inputs and at least one output connector, and including a converter adapted to convert coaxial video signals supplied to the inputs into differential signals and supply those differential signals to its output connector, the output module comprising at least one input connector and a plurality of video outputs and being adapted to transfer signals input in differential form to its output, and the switching module comprising at least one input connector and at least one output connector and being adapted to cross-connect signals between channels, the matrix further comprising flexible cables terminated with connectors compatible with the input and output connectors of the modules, each cable being adapted to carry a plurality of differential signals. The output module preferably includes a convertor to supply signals at the outputs thereof in single ended (coaxial) form. Thus, connections within the matrix are purely by way of flexible connectors carrying either all the switched channels, or a plurality of them in conjunction with other similar cables. Connections between the units can be straight forward and reconfigured with little difficulty. In addition, the use of flexible cables terminated with suitable connectors for interconnections between the units means that they can be provided in the form of discrete units which can be employed in a variety of configurations. Thus, the system can be updated at will to cope with larger number of channels or to provide additional redundancy.

Description

SIGNAL HANDLING APPARATUS The present invention relates to signal handling apparatus. It is particularly, but not exclusively, concerned with apparatus for switching a number of digital image signals, such as for use in digital broadcasting, as between a plurality of channels.

In general, there are two signal formats for video image. Single ended signals (signal plus ground) can be carried on a coaxial cable which is satisfactory for point to point transmission over a controlled impedance path of up to 300 metres. It is not possible to include T or Y junctions in the signal path, and any discontinuities in the characteristic impedance will reduce the signal quality and hence the possible distance that it can be carried.

The alternative is to employ differential signalling, in which the transmitted signal is the difference between the levels on a pair of signal lines. External sources of interference usually operate equally on both lines of the twisted pair, and therefore the effect on the transmitted signal is minimised. Differential transmission is more tolerant of T and Y junctions, but as the speed of transmission rises the length of the spur thus formed must be kept short. Over long distances, the twisted pair cable used for differential signalling is less effective than coaxial cable.

In the field of video broadcasting, it is routinely necessary to switch signals between channels. Thus, a number of channels arrive carrying video signals, which must be selectively switched between the channels so that each signal can exit on a desired channel. The industry standard for achieving this is to take the incoming signals on coaxial cable and feed these into a rack unit. Here they are converted to differential signals and passed along a back plane or mother board at the rear of the rack unit. The mother board is provided with an array of sockets for piug-in cards, which thus define a number of T junctions in the signal path. Above a certain transmission speed, this will degrade the signal quality. Cards are added as necessary to cope with the number of channels present. For very large systems, one back plane is insufficient and the signal will have to be routed to several back planes, which can be done in either signal format but adds considerably to the cost in terms of additional electronics and connectors.

These systems can operate well at slower transmission speeds, but can meet difficulties when called upon to cope with the 360 Mbits-' (for example) called for by modern digital television broadcasting.

In addition, the structural arrangement of the cards is unsatisfactory in that static sensitive circuit cards must be stored and handled when the system is re-configured, and there is a perceived difficulty in opening up the equipment to add additional cards. Furthermore, the maximum size of the equipment is set when it is originally ordered, by virtue of the physical size of the rack unit and the number of plug-in cards that it can therefore accommodate.

The present invention seeks to provide a flexible system with good signal quality that can be expanded to larger sizes in a simple fashion with a minimum of technical knowledge. In addition, it seeks to provide a system which can cope reliably with the transmission speeds called for by digital video broadcasting.

It therefore provides a video signal matrix, comprising an input module an output module a switching module the input module comprising a plurality of coaxial video inputs and at least one output connector, and including a converter adapted to convert coaxial video signals supplied to the inputs into differential signals and supply those differential signals to its output connector; the output module comprising at least one input connector and a plurality of video outputs and being adapted to transfer signals input in differential form to its output; the switching module comprising at least one input connector and at least one output connector and being adapted to cross-connect signals between channels the matrix further comprising flexible cables terminated with connectors compatible with the input and output connectors of the modules, each cable being adapted to carry a plurality of differential signals.

It is naturally preferred that the output module includes a convertor to supply signals at the outputs thereof in single ended (coaxial) form.

However, the form of output is not crucial to the invention. Thus, connections within the matrix are purely by way of flexible connectors carrying either all the switched channels, or a plurality of them in conjunction with other similar cables. Connections between the units can be straight forward and re-configured with little difficulty. In addition, the use of flexible cables terminated with suitable connectors for interconnections between the units means that they can be provided in the form of discrete units which can be employed in a variety of configurations. Thus, the system can be updated at will to cope with larger number of channels or to provide additional redundancy.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying Figures, in which: Figure 1 is a schematic view of an input module ; Figure 2 is a schematic view of a switching module; Figure 3 is a schematic view of an output module ; Figure 4 illustrates a 32 channel switching matrix built with the modules of Figures 1-3; Figure 5 shows a preferred form of input module ; Figure 6 shows input modules according to Figure 5 in a redundant configuration; and Figure 7 shows a 64 channel fully redundant system assemble from the modules of Figures 1-3,5 and 6.

Referring to Figure 1, the input module 10 comprises a plurality of BNC connectors 12 for receiving coaxial signals. The signals are passed via coaxial cable to a convertor 14 which converts the signals into differential format. The differential signals are then fed to a single multi-way output connector 16 which can be of standard type, for example SCSI-3.

Figure 2 shows a switching module 20 with an input multi-way connector 22 and an output multi-way connector 24. Between these connectors is a switching means 26 which operates on the plurality of differential signals derived from the multi-way connector 22 in a known fashion to switch them between the channels and output them to appropriate channels on the multi-way output connector 24.

Figure 3 shows an output module, in which signals arrive via a multiway connector 32 and are passed to a convertor 34 which converts them into coaxial format. The separate signals are then fed to a plurality of BNC connectors 36.

In Figures 1-3, a relatively small number of channels are shown for simplicity. However, in practice it is more useful for the connectors to employ a larger number such as 16,32 or 64 and so on.

Figure 4 shows how the modules can be assemble to provide a simple 32-way switching matrix. A total of 32 input coaxial signals arrive at the input module 10, illustrated as cable bundle 40. A single flexible cable 42 is connected to the output 16 of the input module 10 at one end, and at its other end to the input 22 of the switching module 20. A further flexible cable 44 is connected to the output connector 24 of the switching module 20 at one end, and to the input 32 of the output module 30 at its other end. The output module 30 then provides an array of coaxial output connectors, to which are attached a bundle 46 of 32 output coaxial cables.

A control and power unit 48 is provided which provides electrical power to all three modules and provides the necessary control for the switching module 20.

Thus, in this arrangement the input coaxial signals are first transformed in their entirety to differential signals, which are then switched between channels as appropriate, the output channels then being reconverted to coaxial format and output as necessary. The only work necessary to install the system is physical fixing of the four boxes in place, followed by connection of two interconnecting signal cables between units, any necessary power and control lines, and the input and output coaxial signal cables. This is in stark contrast to an existing system in which the cabinet must be opened and static sensitive cards handled into place as necessary.

Figures 5 and 6 show preferred forms of the input module. In this case, it is divided into a core input module 10a, substantially as per the module 10 of Figure 1 but somewhat shorter in depth, together with a connector module 10b which simply provides a rack of input BNC connectors which are carried forward to the interface between the two modules 10a and 10b. The coaxial signals are thus transferred to one unit to the other.

This then allows the connector module 10b to be removed and replace with a redundant connector module 10c. This provides the same number of input coaxial connectors, but duplicates these at two sites so as to allow connection to a pair of core modules 10a. This therefore provides full redundancy. In the event of one unit 1 Oa having to be replace, it can be detached from the connector module 10c without affecting signal performance as signals can be routed via the remaining core module.

Figures 5 and 6 illustrate input units, but this modification is also preferably applied to the output modules 30.

Figure 7 shows a fully redundant 64 channel system. An incoming bundle 50 of 64 coaxial cables is split into two groups of 32 cables 50a and 50b. Bundle 50a is fed to a redundant connector module 52, and from there into a pair of core input modules 54,56. Likewise, bundle 50b is fed into a connector module 58 and thence into core input modules 60 and 62.

A first 64 channel switching unit 64 is then fed with signals on appropriate flexible cables from the input units 56 and 62. Thus, it receives all 64 channels. Likewise, a second similar switching unit 66 receives signals from the other input modules 54,60, likewise receiving copies of all 64 channels.

Output units are provided, in the form of two 32 channel connector blocks 68,70, each of which is provided with a pair of 32 channel output units 72,74 and 76,78 respectively. The output of the first 64 channel switching unit 64 is then fed in two groups of 32 channels to each of the output units 74,78. In a similar fashion, the 64 channel output of switching unit 66 is fed along two flexible cables, each carrying 32 channels, each leading to one of the output units 72,76.

Corresponding sets of 32 channels are then combined at the connection module 68,70 to yield a total of 64 coaxial output channels in two groups of 32.

A pair of control and power units 80,82 provide sufficient power to supply all modules and activate and deactivate modules as necessary to make sure that no signals collide and that all signals can follow a path through the matrix. From time to time, the route chosen will be altered so as to check the reliability of all pathways.

It will be apparent that every channel can follow either one of two entirely distinct routes through the matrix and therefore the matrix is fully redundant. Notwithstanding this, all 64 channels have been constructed from distinct modules connected only via internal power and signal connections together with simple multi-way connectors on straightforward flexible cables :

Claims (5)

1. CLAIMS 1. A video signal matrix, comprising an input module an output module a switching module the input module comprising a plurality of coaxial video inputs and at least one output connector, and including a converter adapted to convert coaxial video signals supplie to the inputs into differential signals and supply those differential signals to its output connector; the output module comprising at least one input connector and a plurality of video outputs and being adapted to transfer signals input in differential form to its output; the switching module comprising at least one input connector and at least one output connector and being adapted to cross-connect signals between channels the matrix further comprising flexible cables terminated with connectors compatible with the input and output connectors of the modules, each cable being adapted to carry a plurality of differential signals.
2. 2. A video signal matrix according to claim 1 wherein the output module includes a convertor to supply signals at the outputs thereof in single ended form.
3. 3. A video signal matrix according to claim 1 or claim 2 in which connections within the matrix are by way of flexible connectors carrying all the switched channels.
4. 4. A video signal matrix according to any preceding claim in which the units are discrete.
5. 5. A video signal matrix substantially as herein described with reference to and/or as illustrated in the accompanying drawings.