Overcoming Design Constraints in 3U VPX Form Factors: Data Movement and Connectivity

Engineers working with 3U VPX architectures face a familiar challenge: modern applications continue to scale in demand for processing capability, storage, and bandwidth, but the form factor stays the same. As size and weight constraints remain fixed, meeting higher performance demands requires smarter strategies. Modularity and scalability — often achieved through mezzanine cards — can expand what 3U VPX systems can do, but only with the right framework in place.

Optical Transceivers

The commercial industry is driving many innovations in optical transceivers, and some of these capabilities are offered in packages that are suitable for industrial and military applications. Module developers can leverage the latest advancements in optical transceivers to improve channel density and signal rates, thereby achieving increased bandwidth within the 3U VPX form factor.

Optical modules are relatively large compared to other components and consume appreciable amounts of power, so increased density in this technology has a significant impact on the overall design. New developments in silicon photonics and wave division multiplexing should bring even more bandwidth potential in the coming years. Optical transceiver technology is an area engineers interested in the 3U VPX form factor should monitor, as it may yield significant gains in data throughput.

Transition From NRZ to PAM4

NRZ encoding transmits 1 bit per unit interval (baud), while PAM4 transmits 2 bits per unit interval, so transitioning from NRZ to PAM4 doubles data rates on a single differential pair.
Many modern devices contain high-speed serial transceivers that support PAM4 signaling. Although some external connectors only support NRZ, manufacturers of 3U VPX FPGA modules are implementing PAM 4 internal to the module.

Several products manufactured by New Wave Design support PAM4 internally, such as the V6067 3U VPX Versal® Premium ASoC FPGA + Ethernet Offload Optical I/O Module, which allows for increased data bandwidth between components without requiring space to route more high-speed serial lanes.

Pigtails vs. Soldering

Instead of soldering, use pigtails that can go on the front panel or standard backplane connection and can be terminated in different ways for greater flexibility. Pigtails enable a variety of optical modules or even a custom module to be fitted into the 3U VPX module after PCB assembly.

Cable Bend Radius

Using cables with a tight bend radius helps route them through the limited space in 3U VPX modules. This flexibility allows for cable paths that exit the module to terminations elsewhere in the chassis or wrap around the module itself, supporting a range of formats and configurations.

For example, New Wave Design once developed a fiber raceway as part of the mechanical assembly in its 3U VPX FPGA modules. This raceway was engineered to preserve the required fiber bend radius during manufacturing, provide secure cable retention, and support both front panel and backplane termination. The result was a more flexible and reliable design optimized for manufacturability.

Multiple Wavelengths

Getting data into and out of the module for processing functionality is a critical element of any 3U VPX module design and overall product architecture. Engineers are constantly challenged with supporting more and more optical channels within the same 3U VPX volume. On the horizon, vendors will provide rugged optical modules that transmit and receive multiple wavelengths over a single fiber.

This technology doesn’t simply pack more fibers into the same diameter, but instead sends more optical channels down a single fiber by utilizing multiple wavelengths concurrently in the same fiber. Instead of 16 fibers for 16 channels, engineers will be able to have one fiber with 16 wavelengths to achieve the same throughput, saving volume, weight, and complexity of fiber optics cables. Much like transceiver technology, multi-wavelength fiber optics is a technology area for design engineers to monitor over the coming years to evaluate this technology and product offering for incorporation into 3U VPX design modules and open architecture embedded computing architectures.

Integrate Ethernet NICs to Protect FPGA Resources

Engineers can consider integrating specialized network interface devices to 3U VPX processing modules to offload high-performance ethernet protocols – such as RoCE v2 – and optimize data movement while reducing processor load in the FPGA. This strategy enhances VPX connectivity and eliminates the need to dedicate separate FPGA resources in valuable chassis slots for data processing, which is time-consuming, expensive, and doesn’t improve SWaP.

An example of such a dedicated network interface device is the NVIDIA® Mellanox® ConnectX®-7 (MC-X7) product, specifically optimized to offload data via Ethernet protocols. By incorporating an MC-X7 with an AMD Versal Prime VM1502 FPGA into a single 3U VPX processing module, for example, enables the FPGA engineer to utilize the maximum resources on the Versal ASoC for processing intensive algorithms, while placing Ethernet protocol offload code onto the MC-X7. This shared resource architecture allows vastly more processing capabilities of a 3U VPX module with the same volumetric constraints.

An important element to keep in mind is higher data rates and processing capability often comes at the expense of increased heat generation and power consumption, a factor that must be considered during design and integration.

Backplane Connectors

VITA 100 introduces a new connector design that delivers increased I/O capacity, faster data transfer rates, and enhanced power delivery to the VPX module. The goal is to maximize FPGA performance within stringent 3U VPX volume and power constraints. Consider using the latest backplane connectors in your design. While the VITA 100 standard is not ratified at the time of this blog post, it is advisable to monitor the progress this standard makes within the open architecture community to understand the benefits it may offer for VPX module design and the constraints it may address.

Signal Integrity Analysis

Signal integrity analysis — particularly of serial channels — is another critical factor to consider when developing 3U VPX processing modules. It’s essential to ensure low-loss electrical paths on the PCB for transferring high-speed data within the module. This not only ensures that VPX data reaches the optical interfaces, but also maintains connectivity to the backplane connector.

Small Form Factor, Big Impact

Maximizing performance in 3U VPX systems demands careful attention to how data moves and how connectivity is maintained within tight physical constraints. By applying the strategies above, engineers can overcome design challenges without compromising SWaP. As open architecture standards evolve, staying flexible and informed will be key to pushing the limits of what 3U VPX modules can do.