Broadcom Corp, Los Angeles has announced the 64/256 Quadrature Amplitude Modulation digital-transmission receiver for cable television applications. The QAMLink architecture, initially developed with Scientific-Atlanta Inc, was first announced as a three-chip offering at the NCTA Cable ’94 show in May. The BCM3100 integrates these three chips into a low-cost CMOS chip. In 256-Quadrature Amplitude Modulation mode, the BCM3100 QAMLink Receiver achieves digital transmission speeds of 40Mbps. This increases the coaxial cable channel capacity 10 to 25 times. Using proprietary signal processing algorithms, circuit designs and layout techniques, Broadcom integrated Quadrature Amplitude Modulation demodulation, Nyquist filtering, carrier and timing synchronisation and adaptive equalisation into a single low-cost chip. Operating in 64-Quadrature Amplitude Modulation mode, the BCM3100 enables a standard 6MHz analogue channel to carry 30Mbps of digital data. With 64-Quadrature Amplitude Modulation, cable operators can send around 20 movies using MPEG I compression and 10 movies using MPEG II compression over a single 6MHz NTSC channel. The QAMLink receiver uses adaptive decision-feedback equalisation to combat the effects of channel distortions often found in cable television systems. An adaptive equaliser requires signal processing power of about 1,000m operations per second to blindly adapt to the channel distortions in real time. The single-chip receivers cost $50 each in quantities of 1,000 and up.
