In Europe, DSL technologies dominate broadband access to the Internet. The picture is quite different elsewhere, particularly in the United States and South Korea, where TV cable plays the main part in fast data transmission. This technology is based on the international Data Over Cable Service Interface Specification (DOCSIS) standard. Its latest 3.0 version, which is currently under development, makes considerably higher technical demands on the receivers. EPCOS has already come up with a suitable SAW filter.

The crucial advantage of the new DOCSIS version is that several TV channels can be combined (channel bonding), thus permitting transmission rates of over 100 Mbit/s. This upgrade should make DOCSIS comparable to competitor technologies such as FTTH (fiber to the home) and clear the way for new applications such as high-resolution IPTV (Internet protocol television).

As a rule, the channels to be bonded are not directly adjacent to one another, but can be distributed over a range of up to 100 MHz. This places considerable demands on the receiver and SAW filters. Up to now, narrowband filters have been sufficient, as only one channel (for example 6 MHz in the United States, 8 MHz in Europe) was used for data transfer. EPCOS has developed a series of filters for these applications in recent years that typically operate at a center frequency of 44 MHz or 1.25 GHz. They have proved a great success; over 100 million of these cable-modem filters have been supplied in recent years.

However, the design technology limits the usable relative bandwidth of a SAW filter to about 4 percent, corresponding to 50 MHz. A completely new design has been developed to reach the 100 MHz bandwidth required by the DOCSIS 3.0 standard. It combines the advantages of the previously used filters – such as steep edges and a low temperature drift – with a doubling of the usable bandwidth.

The figure shows the transfer function of the new B1642 filter, which was developed in close collaboration with a leading supplier of tuner ICs.

	ABBILDUNG 1: ATTENNUATION OF B1642 MULTIMEDIA FILTER
With its small amplitude ripple in the pass band, the filter is predestined for cable modems.

The B1642 offers crucial benefits thanks to a very low amplitude ripple over the entire usable band and simultaneously strong suppression of the image frequency. These filters are supplied in a rugged and cost-effective ceramic package with dimensions of 3 x 3 mm².