Using Pre-Emphasis and Equalization with Stratix GX

New high speed serial interfaces provide a major benefit to designers looking to provide greater data bandwidth across the backplanes or when interfacing chip to chip. However high speed signaling techniques suffer from a number of issues not seen at normal digital signaling levels. One key problem, which applies to all transmission mediums, but particularly related to PCB layout, are frequency dependant transmission losses, caused primarily by skin effect and dielectric loss. This transmission loss can cause greater attenuation of the high frequency component of the signals than that of the lower frequency component, making it difficult for the receiver to interpret the signal, thereby greatly reducing drive length and increasing bit error rate. Two main techniques used to help overcome transmission losses are Pre-emphasis and Receiver Equalization. These methods require extra circuitry in the transmitter and receiver buffers to compensate for high frequency losses.