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Connectors are Critical for VME to VPX Transitions

In demanding fields like military and transportation, connectors are helping VME and VPX developers push performance to new levels.

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Connectors are Critical for VME to VPX Transitions

The harsh, high performance fields that have used VME technologies for decades are making the transition to its successor, the VPX bus. As this evolution occurs, connectors are a critical element for product designers in military, transportation, and other markets that require ruggedness.

Density, signal integrity, and speed are all focal points for connectors when design engineers create backplanes and modules. Engineers and marketers at the recent Embedded Tech Trends conference also noted that connectors are a key consideration for mainstream designs and as the role of fiber optic cabling expands.

These factors get more scrutiny when companies switch to a next-generation technology like VPX, which was approved in 2007. Fields like military and transportation have long development cycles, so the transition to VPX has only vigorously ramped up in recent years. Aircraft, one of the fields that’s driving this transition, have several space limitations, such as ARINC chassis, which often house racks of circuit boards.

“There’s growing demand for VPX, often in ARINC 404 enclosures,” said Kenneth Brown, program manager at LCR Embedded Systems Inc. “VPX offers infinite capabilities; it has nearly unlimited I/O. No two customers want the same I/O coming out of the system.”

Brown described six different architectures for configuring VPX boards and backplanes. They each provide different levels of cost, flexibility, signal integrity, and other parameters. To make decisions, design teams need to set their goals for cost, risk, flexibility, scheduling, and performance. As they analyze these tradeoffs, engineers also have the option of combining concepts to create hybrid architectures.

This versatility can pose something of a challenge for developers. When engineers pick one of the VPX profiles, they typically want to use commercial off the shelf (COTS) boards. However, its versatility can make it difficult to find compatible VPX modules. Connector issues can arise when different design teams configure connectors using incompatible pin layouts. While many pins have dedicated functions, some can be customized.

“The profiles define pins for backplanes and plug-in modules, so they often don’t use all the pins in the connector,” said Greg Rocco of MIT’s Lincoln Lab. “Users want to reduce the number of user-defined pins to increase interoperability.”

Speakers at the conference also noted that while their companies can usually find multiple providers for connectors, the performance level varies. In demanding environments like military and transportation, minor differences in connectors can have a big impact on overall system performance.

“High-speed connectors are becoming very challenging; engineers need to figure out what companies meet their requirements,” said David Hinkle of Elma. “One vendor may be at one level; another vendor may be at another level.”

VPX backplane

Figure 1 Elma’s VPX backplane.

Once issues like these are resolved, other factors influence connector decisions. In many of the rugged VPX operating environments, signal integrity is a primary factor. It’s also becoming a driving force for many connector development teams.

“Today, our signal integrity people are telling the mechanical engineers what they need,” said Michael Walmsley, global product management director at TE Connectivity’s Aerospace Defense and Marine Business Unit. “The signal integrity guys have a lot of power in the company.”

Walmsley also noted that there’s growing interest in optical and RF communications. This is driven by increasing performance demands and longer cable runs. Some of the VITA 66 optical modules have as many as 24 lanes for communications, he added.

Improved density is one factor that’s evolving to help fiber’s role in military products. Power consumption has been among the factors slowing the adoption of fiber, but transitions from electrical to optical are fast becoming more efficient.

“We can put 48 fibers in an MT connector with low power, 100mW for 10 gigabits per second,” said Michael Tetu, senior business development advisor at Reflex Photonics. “For applications that need ultra-dense I/O, there are full duplex 300Gbps transceivers that have 12 lanes running at 25Gbps.”

Reflex Photonics optical modules

Figure 2 Reflex Photonics optical modules.

While fiber is getting more attention, most speakers said decisions regarding when to use fiber instead of copper are usually pretty straightforward. Copper isn’t anywhere close to obsolete.

“Fiber is looking better and better for going between boxes,” Rocco said. “Copper still has a long way to go inside the chassis.”

The pressure to cram more electronics into a VPX chassis is expected to continue. As density and speeds increase, the negative effect of heat follows. Some companies feel that liquid cooling will see greater emphasis, impacting backplane designs. Specialized knowledge has been required to create systems that use liquid cooling, but that’s changing.

“There are solutions for people who have no plumbing expertise,” said Michael Humphrey, program manager at Parker Aerospace. “There’s some premium to be paid in weight and cost, but it’s not as big as people might expect. There can be a four- to five-times benefit in density when you go from air cooling to liquid cooling.”

The VME-VPX marketplace isn’t huge, but it’s growing steadily. Brian Arbuckle, a market analyst at IHS Markit, expects revenues to grow from $493 million in 2015 to $576 million in 2020 and noted that VPX is rapidly expanding its position in the market.

 

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