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This project covered the development of a 16 output Optical to IF Switch which acts as the optical receiver in a DVB-S optical distribution network converting the signal in the fibre to RF and then to a form suitable for STBs. The product was based on the Romeo and Juliet ASIC chip set initially developed under a previous ESA funded Artes project. A unique feature of the product is that it is designed so that expansion units may be connected to the basic unit. These expansion units are connected to fibres carrying signals from other orbital locations, and in this way any connected STB may, using the Diseqc signalling protocol, select signals from any of the orbital locations connected. It is the Juliet “band shifting” ASIC which enables the Switch’s functionality to be realised in a cost effective manner, and a key aspect of the project is the design and fabrication of a revised version of this ASIC. This is necessary to mitigate some of the deficiencies in the performance of the first iteration ASIC and to provide a chip suitable for use in this and other products.
In the switch design care had to be taken to enable the signal to be split and processed to provide the 16 outputs whilst maintaining the signal fidelity. In addition the multiple Juliet ASICs consume considerable power meaning that careful consideration of the heat dissipation was required. The requirement for a simple low cost RF connection between the base and expansion units means that a low insertion force connector with good RF properties is required. The work on the Juliet ASIC required understanding the version 1 device’s phase noise and frequency response, and modifying the design to improve the performance.
The existing receivers (GTUs) for optical DVB-S distribution systems can service up to four STBs. Scaling the GTU design to provide more ports requires the realisation of large matrix switches, the design of which is complex, expensive, and results in a physically large product. The new optical to IF switch can service 16 STBs, and by making use of the band tuning capabilities of the Juliet ASIC, avoids the need for a matrix switch, resulting in a compact cost effective product. In addition to this, the ability to attach expansion units enables the reception of content from up to four different satellites, with the STB signalling which channels are received using the DISEQC control protocol. This functionality is not provided by any existing product.
The product acts as the optical receiver in an optical DVB-S distribution system. Current receivers in these systems can only support up to four STBs, however this new product will enable up to sixteen STBs to be driven from a single fibre feed. In addition to this the design allows for expansion units, with separate fibre feeds carrying signals from other orbital locations, to be connected to the base unit, thus enabling any connected STB to receive signals from up to four orbital locations.
The input optical signal is converted to RF by a photodetector, and then amplified and split using the Romeo LNA ASIC prior to being fed to eight Juliet ASICs which provide the 16 outputs from the product. The Juliet ASICs undertake the necessary band translations to move the four satellite bands from the bespoke frequencies used to transport them in the fibre, to those frequencies expected by a conventional STB. If present, terrestrial signals in the frequency range 88 to 860 MHz are filtered from the incoming signal, and then recombined with the satellite signals at the unit’s output. Provision is made for combining the product with an add-on unit, carrying signals from another satellite, by incorporating a SPDT RF switch which can route the signals from the add-on unit to the STB instead of those from the base unit. This selection is made based on DISEQC signalling from the STB. Control of the unit, including the satellite band selection by the Juliet ASICs, the DISEQC communications with the STB, the communications with the add-on unit, the output level control, as well as the initialisation and other setup of the Juliet ASICs is undertaken by a microprocessor.
WP 1.1 Generate Specifications (GIL)
WP 1.2 IF Switch Electrical Design
WP 1.3 Test System Design
WP 1.4 Mechanical Design
WP 1.5 Firmware
WP 1.6 GIL Project Administration
WP 1.7 Foundry Mask Set and Wafer Fabrication
WP 2.1 Generate Specifications (Riverbeck)
WP 2.2 ASIC Development
WP 2.3 EDA Tools
WP 2.4 ASIC Evaluation Testing and Quality Checks
WP 2.5 Riverbeck Administration and Control.
The project has been successfully completed. The version 2 Juliets with a revised design have exhibited the desired performance and are now in manufacture. Similarly the Optical to IF Switch has been designed and shown to perform to the required specification. Production of the unit is now underway, and is being marketed by Global Invacom under the brand name SwitchBlade