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Zetex revamps LNB design with new IF switch

Posted: 16 Feb 2007 ?? ?Print Version ?Bookmark and Share

Keywords:Zetex Semiconductors? low noise block? LNB design? IF switch? IF signal?

Robinson: All elements of design, layout, technology and packaging were important.

The development of the ZXHF5000 from Zetex Semiconductors marks a breakthrough in low noise block (LNB) design. The 4:2 IF switch features integrated gain and control functions that, according to Zetex, dramatically improve IF signal reliability, eliminate false switching and reduce circuit complexity.

Like other technological feats, product development was not without immense challenges, the biggest of which, said Richard Robinson, DBS marketing manager, was achieving the 30dB channel isolation up to frequencies of 2GHz while adding a flat wide band gain (19dB from 200-2150MHz) and the high levels of integration. To address this, development was not centered on silicon design only. Work on the package was just as important, as well as producing accurate models that would allow reliable simulation of the silicon, package and PCB combined. "All elements of design, layout, technology and packaging were important," noted Robinson.

A new approach
The ZXHF5000 is a big leap in direct broadcast by satellite (DBS) signal distribution and control innovation. "For several years or more, there have just been slight modifications on the existing building blocks," explained Robinson. "The ZXHF5000 changes the architecture of the system, makes things different. It has given us a platform capability and can be adapted to other new products."

The ZXHF5000 can also work in new low-power applications. With built-in power-management features, the ZXHF5000 shuts down all the unused sections of the device while keeping a match to the inputs. It also operates from 3.3V, thus it can be used in a low-voltage system and used with a switching converter for a low-power system.

Moreover, the ZXHF5000 satisfies developers' requirements for reliable performance and design flexibility at low cost. The reduction in components cuts down on manufacturing expenses. For a typical two-output LNB, there are over 18 components saved including three active ICs.

Compared to alternative solutions, the ZXHF5000 is operationally robust. For example, when channel hopping, the LNB goes through all kinds of switching states and sees various control signals. The ZXHF5000 ignores all unwanted signals and transients so it does not falsely switch.

The device also delivers good performance over temperature, and has undergone full reliability testing. These features are imperative as the LNB has to withstand all weather conditions and is rarely switched off as long as there is an STB connected.

The 4:2 switch is the world's first to feature integrated gain and control functions.

Meeting standards
To increase design flexibility and help minimize PCB area, the RF inputs can also be reprogrammed to be in reverse order. This can be done by applying a logic control signal. As a result of this innovative mirroring function, two devices can be mounted back-to-back on a double-sided PCB such that the two sets of RF inputs are aligned.

Impedance matching was another key requirement. Integrated pre-amplifiers ensure that the RF signal inputs are 50-ohm matched, enabling direct driving by the gain stage or mixers in standard LNB architectures. The two IF outputs are independent from each other and are matched to drive a 75-ohm cable load to the STB. The two outputs are highly linear and achieve an output third-order intercept point of 16dBm across the band while keeping current consumption to a minimum, ensuring low signal distortion.

With LNB and satellite distribution product development ongoing worldwide, the ZXHF5000, according to Robinson, has been developed to meet specifications for the global market. Thus, it conforms to the U.K. specifications as well as those of India's.

- Celeste dela Torre
Electronic Engineering Times-Asia

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