Silicon bipolar circuits for wideband FM CATV transmission

In optical transmission of analog multi-channel cable television, an alternative to lower the cost of system components is that of employing wideband frequency modulation. This approach requires wideband FM modulation circuits with GHz operation and demanding linear performance. In this paper we describe wideband FM modulator and demodulator circuits implemented in a 25GHz-ft silicon bipolar technology, that show for the first time 80-channel transmission attainable. Most notably, the use of emitter coupled multivibrator VCOs achieved record modulator linearity over a 1.5-2.5GHz frequency range, and proved to outperform in linearity and noise the best wideband optoelectronic modulators. The demodulator response is linear over the range from 1-3.5GHz. Modulator phase noise is -122.5dBc/Hz @ 50MHz, and was found to be improvable through a novel phase noise reduction technique.