Ken Dyer, Director, Engineering Architecture, is the author of a 112G Long Reach (LR) SerDes PHY article in eeweb.com/EE Times network.
The 112G is coming on to the market to comply with growing demands for greater bandwidth for next generation data centers as well as for advanced applications like artificial intelligence (AI) and machine learning, as well as 5G communications.
Dyer calls Rambus’ 112G LR SerDes PHY “the top contender to boost greater performance with acceptable power and area” for those next generation data center and network systems designs. His article details the new advanced SerDes PHY. However, he explains to SoC and network system designers that they may want data in different ways.
He said, “They also may opt to have a forward error correction (FEC) on the output of the receiver to improve bit error rate (BER) of the received data. FEC performs that operation by using redundancy. It transmits slightly faster than the data required, hence extra information is transmitted. By reviewing the extra information in the received signal, FEC determines if mistakes have occurred or not.”
Dyer calls special attention to today’s higher serial data rates and added that four-level pulse amplitude modulation or PAM-4 has made its entrance and explained how it plays into the 112Gbps SerDes PHY.
He said that “We first need to look at Nyquist loss for NRZ data for a generic legacy channel and for 112Gbps data transmission. Nyquist loss is the insertion loss of the input signal at half the symbol rate. For NRZ at 112Gbps, its nominally 56GHz. NRZ is two-level data and it’s at a relatively low 70 decibels (dB) at 56 Gigahertz (GHz).
“In short, crosstalk has more power than the signal, hence signal-to-noise ratio (SNR) is negative. This means error-free communication or signal recovery is not possible. In this case, if a transmitter is operated at 56Gpbs, data would not be received at all. Therefore, PAM-4 becomes a more viable solution than the traditional NRZ (non-return-to-zero).”
Be looking for sequels to this first 112G LR article in eeweb.com/EE Times network. Articles, like this one, are designed to help SoC and data center system designers to prepare their next generation designs.