Modem chip for subscriber carrier system

This paper is focused on the design and realization of a custom IC applied as the backbone of a subscriber carrier system. The chip contains both a modulator and demodulator, and is realized on a small die size in a standard low voltage bipolar technology. The carrier system architecture is such that, for both the exchange and the subscriber modem, the same IC can be used with a minimum of external components. Specifically interesting on the IC itself is the overall DC coupling in order to reduce the number of output pins and external components, the biasing and powering scheme which results in a very low power dissipation (mandatory for line-charged battery operation), the wide range of automatic gain control, and the precautions taken to prevent carrier intermodulation.