GENERAL DESCRIPTION
A phase-locked transmit clock is transmitted in parallel with the data streams over a fifth LVDS link. Every cycle of the transmit clock 28 bits of input data are sampled and transmitted. At a transmit clock frequency of 66 MHz, 28 bits of TTL data are transmitted at a rate of 462 Mbps per LVDS data channel. Using a 66 MHz clock, the data throughput is 1.848 Gbit/s (231 Mbytes/s). The multiplexing of the data lines provides a substantial cable reduction. Long distance parallel single-ended buses typically require a ground wire per active signal (and have very limited noise rejection capability). Thus, for a 28-bit wide data bus and one clock, up to 58 conductors are required. With the Channel Link chipset as few as 11 conductors (4 data pairs, 1 clock pair and a minimum of one ground) are needed. This provides a 80% reduction in required cable width, which provides a system cost savings, reduces connector physical size and cost, and reduces shielding requirements due to the cables’ smaller form factor.
National Semiconductor
