By Larry F. Roeshot, Pennsylvania State University
Cable television systems began with single channel amplifiers operating in a low VHF band. As the demand for cable television grew, along with technology, amplifiers were designed to cover more than two octaves and performed several additional functions, including automatic slope and gain controls.
The use of integrated circuits to satisfy some of these requirements has been limited in modern cable television amplifiers. This paper examines some of the present-day and future uses of IC's in cable television equipment in view of cost, performance, and reliability.
The development of cable television system techniques--such as the method of ALC control, tilt mode, operating level, gain, etc., together with the time consuming proof-of-feasibility for each approach--has been too dynamic to warrant any costly IC designs.
This limitation has been particularly true at VHF frequencies with physically large components which are not compatible with thin film IC's. In addition, the operating levels normally encountered in cable television amplifier output stages are beyond the present state of the art for IC's.
To determine the feasibility of thick films at VHF, a thick film broadband amplifier is shown. Using this technique, components can be trimmed to precise tolerances on low cost replaceable modules.
With the flexibility of thick film hybrid integrated circuits, utilization of these devices in cable television equipment can be expected within the next few years.