Improving the performance of cable television (CATV) systems is a key issue for service providers as they strive to keep pace with customer demand for new services and technology. New high-performance distribution amplifiers are needed to minimize distortion in order to handle the bandwidth that today's CATV service requires. As a result, ANADIGICS has developed the ACA0861 series of GaAs line amplifier ICs, which features the lowest distortion available for CATV applications.

Because they are monolithic solutions, the ACA0861 amplifiers offer high performance and affordability. "We believe that GaAs MESFET technology is the best fit for this application and that providing the amplifier in a small surface-mount package provides the best performance and lowest total cost," observes Ron Michels, Director of CATV Products. In fact, since they are housed in a surface-mount package, the devices reduce overall system manufacturing costs by enabling fully automated assembly. Additionally, the ACA0861 amplifiers can deliver higher output power than hybrid solutions, allowing CATV service providers to use fewer amplifiers in the overall distribution stream.

"The ACA0861 family of CATV amplifiers offers improved linearity, higher overall gain, flatter frequency response, lower noise figure, and lower power consumption than the hybrid solution. And, they do it at a competitive price," notes Doug Johnson, Design Manager for Line Amplifier products. For example, the ACA0861D input stage amplifier delivers 12.1 dB gain with 18-dB minimum return loss and a 6-dB maximum noise figure, with a typical supply current of 480 mA@12VDC. For a 128-channel system specified at 44dBmV flat output, the device delivers the following typical distortion characteristics: composite triple beat (CTB) of -67 dBc; composite second order (CSO) of -70 dBc, and cross modulation (XMOD) of -66 dBc. By minimizing distortion, the ACA0861 amplifiers allow improved signal quality and more channels through the CATV system.

The renewal of the U.S. cable TV infrastructure is the first major change in the majority of the systems in nearly 30 years. Not only are the basically rusted-out super-VHF systems being torn out, they are being replaced with wideband systems to accomodate more channels and most are also being made totally bi-directional to allow for Internet traffic. Whether such systems will really work well -- with noise focussing up towards the headend -- is still a matter of concern and debate, but the needs of the line amplifiers are well-known and understood. The needs compared to the first solid-state TRW amplifiers of the 60s are dramatically different and it seems that GaAs has a real process advantage for this market.

The noise levels, gains and distortions of these amplifiers -- used in pairs with input plus output amplifiers -- are a superb fit for this new market. The triple-beat specification of -67 dBc for a 44 dBmV flat output was not attainable by previous devices even for 100-channel systems. The power consumption is extremely good for this use, where supply power is at a premium, and the additional output power level will allow much longer cable runs between amplifiers. Although price is not the first characteristic of purchase in these types of parts -- although the overall, encased, amplifier is price-sensitive -- these parts are extremely competitive.