Inphi unveils first 800-gigabit PAM-4 signal processing chip

Inphi has detailed what it claims is the industry’s first digital signal processor (DSP) chip family for 800-gigabit client-side pluggable modules. 

Dubbed Spica, the 4-level pulse-amplitude modulation (PAM-4) DSP family is sampling and is in the hands of customers.

Source: Inphi

The physical-layer company has also announced its third-generation Porrima family of PAM-4 DSPs for 400-gigabit pluggables. 

The Porrima DSP with integrated laser driver has being made using a 7nm CMOS process; until now a 16nm CMOS has been used. Fabricating the chip using the more advanced process will reduce the power consumption of 400-gigabit module designs. 

Applications

Eight-hundred-gigabit multi-source agreements (MSAs) will enable a new generation of high-speed optical transceivers to come to market.

The 800G Pluggable MSA developing optical specifications for 800-gigabit pluggable modules, is one that Inphi is promoting, while the QSFP-DD800 MSA is extending the double density form factor for 800 gigabits.

Eric HayesThe main two markets driving a need for 800-gigabit modules are artificial intelligence (AI) and data centre switching, says Eric Hayes, senior vice president, networking interconnect at Inphi. 

“AI, while still in its infancy, has all these applications and workloads that it can drive,” he says. “But one thing they have in common when we look at the data centres building large AI clusters is that they have very large data sets and lots of data flow.”

The speed of the input-output (I/O) of the AI processors used in the clusters is rising to cope with the data flows. 

The first-generation AI processors used 25-gigabit non-return-to-zero (NRZ) signalling for the I/O while many of the devices shipping today use 50-gigabit PAM-4. “The latest designs that are coming to market have 100-gigabit I/O and we have the first DSP offering 100-gigabit on the host side,” says Hayes.   

The second application that requires 800-gigabit modules is the advent of 25.6-terabit Ethernet switches used to network equipment within the data centre. 

Inphi says there are two types of 25.6-terabit switch chips emerging: one uses 50-gigabit PAM-4 while the second uses 100-gigabit PAM-4 electrical interfaces. 

“The 25.6-terabyte switch with 100-gigabit I/O is wanted for one-rack-unit (1RU) platforms,” says Hayes. “To do that, you need an 800-gigabit module.” Such switches have yet to reach the marketplace.

Spica and Porrima ICs

The Spica DSP takes 100-gigabits PAM-4 electrical signals from the host and performs retiming and pre-emphasis to generate the 100-gigabit PAM-4 signals used for modulation the optics before transmission. The laser driver is integrated on-chip. 

The transmit path is a simpler design than the Porrima in that the signalling rate is the same at the input and the output. Accordingly, no gearbox circuitry is needed.

The main signal processing is performed at the receiver to recover the sent PAM-4 signals. A hybrid design is used combining analogue and digital signal processing, similar to the design used for the Porrima.

The Spica device supports 2x400-gigabit or 8x100-gigabit module designs and enables 800-gigabit or 8x100-gigabit optical interconnects. The 800-gigabit form factors used are the QSFP-DD800 and the OSFP. Inphi says both designs consume under 14W.

“The first module being built [using the Spica] is the OSFP because the end-user is demanding that, but we also have customers building QSFP-DDs,” says Hayes. 

Meanwhile, Inphi’s Porrima family of devices is targeted at the 400G DR4 and 400G FR4 specifications as well as 100-gigabit module designs that use 100-gigabit PAM-4. 

The two module types can even be combined when a 400-gigabit pluggable such as a QSFP-DD or an OSFP is used in breakout mode to feed four 100-gigabit modules implement using such form factors as the QSFP, uQSFP or SFP-DD.

Transitioning the Porrima to a 7nm process saves 1.5W of power, says Hayes, resulting in an 8W 400-gigabit module. The latest Porrima is sampling and is with customers.

Roadmap

Inphi says optical modules using the Spica DSP will be deployed in volume from the second half of 2021.

Before then, the DSP will be tested as part of customers’ module designs, then be integrated with the software before the complete 800-gigabit module is tested.

“There will then be interoperability testing between the modules once they become available and then small pilot networks using 800-gigabit modules will be built and tested before the go-ahead to mass deployment,” says Hayes. 

All these stages will require at least a year’s work.