ANADIGICS introduced the ARA1400 next generation reverse amplifier for use in cable modems and interactive set-top boxes. The ARA1400 offers the high performance characteristics required by interactive set-top boxes and cable modems designed to support interactive CATV, high speed Internet services, and telephony over the Internet. The CATV reverse amplifier with step attenuator delivers up to 33 dB gain at 5 volt operation and provides the lowest distortion and best output noise power in the industry, while conforming to MCNS/DOCSIS standards developed by the cable industry.

In interactive CATV applications, the outgoing signal requires varying levels of amplification to reach the closest system node depending on the proximity to the node. The ARA1400 amplifier uses an integrated digitally controlled precision step attenuator to increase signal output power to the necessary levels. The precision attenuator varies gain in 4 dB steps over a range of 56 dB, providing greater performance than variable gain amplifiers. The use of a precision step attenuator insures that the ARA1400 satisfies the tight DOCSIS specifications for attenuation accuracy.

In addition to providing a greater attenuation range, the ARA1400 also features a higher level of integration by incorporating additional RF switching on board. "The ARA1400 is the next evolution of ANADIGICS reverse amplifiers, providing high performance and higher levels of integration." said Ron Michels, Director, Cable & Broadcast Business Segment. "This part reflects ANADIGICS commitment to providing lower cost solutions by greatly increasing on-chip functionality."

"The unprecedented combination of low distortion and low output noise figure of the ARA1400 not only meets the demanding specifications of the cable industry, but gives cable modem and cable set-top box designers a solution with plenty of margin, increasing ease of manufacture," notes Ray Waugh, Design Engineer. "The use of gallium arsenide (GaAs) allows ANADIGICS to offer a CATV reverse amplifier with this level of performance."

If the upstream -- interactive -- part of the cable systems of the future are going to work at all it will start in a solid design in the cable modem. The additive nature of noise in the reverse feed from subscriber to head-end is a truly frightening set of circumstances for an RF engineer. As the number of users on a cable system increases the noise will increase and one has to feel that at some point the "elastic just has to break." There are a lot of factors involved and many of those are outside the control of the consumer. Many systems will probably install cable repeater amplifiers based on the downstream feed signal levels -- because that is what they have always calculated -- instead of thinking about the most vulnerable signals: the upstream data. Although it is a smaller bandwidth it is still the most vulnerable.

The ARA1400 will give the upstream signal the best start it could get: an excellent noise figure of 1.7 dB with 33 dB of available gain, and the ability to vary the signal level so that an attempt can be made to get the signals arriving in each upstream node at least within some controllable range of one another. The design is also a major challenge to silicon vendors who have been seeing this application as a major business opportunity for themselves; the performance bar has been raised significantly with the ARA1400.