Microchip’s compact, low-power 1.6-terabit PHY

Microchip Technology’s latest physical layer (PHY) chip has been developed for next-generation line cards.

The PM6200 Meta-DX2L (the ‘L’ is for light) 1.6-terabit chip is implemented using TSMC's 6nm CMOS process. It is Microchip’s first PHY to use 112-gigabit PAM-4 (4-level pulse-amplitude modulation) serialiser/ deserialisers (serdes) interfaces.

Stephen Docking

Microchip’s existing 16nm CMOS Meta-DX1 PHY devices are rated at 1.2 terabits and use 56-gigabit PAM-4 serdes.

System vendors developing line cards that double the capacity of their switch, router or transport systems are being challenged by space and power constraints, says Microchip. To this aim, the company has streamlined the Meta-DX2L to create a compact, lower-power chip.

“One of the things we have focussed on is the overall footprint of our [IC] design to ensure that people can realise their cards as they go to the 112-gigabit PAM-4 generation,” says Stephen Docking, manager, product marketing, communications business unit, at Microchip.

The company says the resulting package measures 23x30mm and reduces the power per port by 35 per cent compared to the Meta-DX1.

IC architecture

The Meta-DX1 family of 1.2-terabit physical layer (PHY) Ethernet chips effectively comprise three 400-gigabit cores and support the OIF’s Flexible Ethernet (FlexE) protocol and MACsec encryption.

The Meta-DX2L architecture. Source: Microchip

The Meta-DX1 devices, launched in 2019, support the Precision Time Protocol (PTP) used to synchronise clocks across a network with high accuracy that is a requirement for 5G.

The new Meta-DX2L is a single chip although Microchip hints that other family devices will follow.

The Meta-DX2L can be viewed as comprising two 800-gigabit cores. The chip does away with FlexE and the PTP protocol but includes retiming and gearbox modes. The gearbox is used to translate between 28, 56 and 112-gigabit rates.

“We still see customers working on FlexE designs, so the lack of it [with the Meta-DX2L] is not due to limited market demand but how we chose to optimise the chip,” says Docking.

The same applies to PTP. The Meta-DX1 performs time stamping that meets 5G’s Class C and Class D front-haul clocking requirements. “The difference with the Meta-DX2L is that it is not doing time stamping,” says Docking. But it can work with devices doing the time stamping.

“In a 5G system, if you add a PHY, you need to do it in such a way that it doesn’t add any uncertainty in the overall latency of the system,” says Docking. ”So we have focussed on the device have a constant latency.” This means the Meta-DX2L can be used in systems meeting Class C or Class D clocking requirements.

The chip also features a 16x16 crosspoint switch that allows customers to use different types of optical modules and interface them to a line card’s ASIC or digital signal processor (DSP).

The Meta-DX2L’s two cores are flexible and support rates from 1 to 800 Gigabit Ethernet, says Docking.

As well as Ethernet rates, the device supports proprietary rates common with artificial intelligence (AI) and machine learning.

For AI, an array of graphic processor units (GPUs) talk to each other on the same line card. “But to scale the system, you have to have multiple line cards talk to each other,” says Docking. “Different companies that design GPUs have chosen their own protocols to optimise their communications.”

Such links are not aligned with the Ethernet rates but the Meta-DX2L supports these proprietary rates.

Microchip says the Meta-DX2L will sample this quarter.

1.6 terabits, system resilience and design challenges

The PHY’s 1.6-terabit capacity was chosen based on customers’ requirements.

“If you look at the number of ports people want to support, it is often an even multiple of 800-gigabit ports,” says Docking.

The Meta-DX2L, like its predecessor PHY family, has a hitless 2:1 multiplexer. The multiplexer function is suited for centralised switch platforms where the system intelligence resides on a central card while the connecting line cards are relatively simple, typically comprising PHYs and optical modules.

In such systems, due to the central role of the platform’s switch card, a spare card is included. Should the primary card fail, the backup card kicks in, whereby all the switch’s line cards connect to the backup. The 2:1 multiplexer in the PHY means each line card is interfaced to both switch cards: the primary one and backup.

Kevin So

For line cards that will have 32 or 36 QSFP-DD800 pluggable modules, space is a huge challenge, says Docking: “So having a compact PHY is important.”

“The physical form factor has always been a challenge and then density plays into it and thermal issues,” says Kevin So, associate director, product line management and marketing, communications business unit, at Microchip. “And when you overlay the complexity of the transition from 56 to 112 gigabits, that makes it extremely challenging for board designers.”

Applications

The 1.6-terabit PHY is aimed at switching and routing platforms, compact data centre interconnect systems, optical transport and AI designs.

Which application takes off first depends on several developments. On one side of the PHY chip sits the optics and on the other the ASIC, whether a packet processor, switch chip, processor or DSP. “It’s the timing of those pieces that drive what applications you will see first,” says So.

Modular switch-router platform showing how the Meta-DX2L is used. Source: Microchip

“Switching and packet processor chips are transitioning to 112-gigabit serdes and you are also starting to see QSFP-DD or OSFP optics with 112-gigabit serdes becoming available,” adds Docking. “So the ecosystem is starting for those types of systems.”

The device is also being aimed at routers for 5G backhaul applications. Here data rates are in the 10- to the 100-gigabit range. “But you are already starting to hear about 400-gigabit rates for some of these access backhaul routers,” says So.

And with 400 Gigabit Ethernet being introduced on access pizza-box routers for 5G this year, in two years, when Microchip’s customers release their hardware, there will likely be denser versions, says So.

“And by then we’ll be talking about a DX3, who knows?” quips So.