While CPUs rely on busses such as PCI or PCI Express, FPGAs are built to interface directly with IO devices. With this comes a set of particular IO requirements and an ANSI/VITA 57 FMC specification driven by the VITA working group.

An FMC does not require any defined bus, but instead defines the maximum amount of FPGA connectivity to connect directly with IO devices fitted to the mezzanine. Physically, an FMC format mezzanine card is a similar width to a PMC or XMC card, but around half the length and with different host connectors.

Not all hosts will necessarily support the full connectivity needed for some FMCs and there is no fixed number of connections, but FMC permits up to 160 parallel IO connections (or 80 LVDS) and up to 10 full-duplex high-speed serial links. With newer generation FMC hosts often having 1.8V tolerant FPGA IO and older FMC using 2.5V technology, it’s important to ensure the host FMC FPGA is capable of supporting the IO voltage required for the device. For the right combination of IO, FMCs eliminate the need for bus interface devices, reducing cost and gaining maximum IO performance.

The FMC Advantage

FMCs are fertile ground for custom developments as there is no reason why FMCs can’t be used implement mixed technology on one card absorbing system specific IO with the minimum of design.

During power up, the host interrogates the mezzanine to determine its primary power supply requirement and then provides it, if it is able to. Since the FMC relies on the host instead of regulating its primary power supply, more PWB real-estate opens up for IO or other functions.

FMC modules are available in air-cooled and rugged conduction-cooled formats with single and double wide configurations. Singe wide FMCs are by far the most common.

The key to FMCs is IO flexibility on a small open standard mezzanine card. Non-FMC based FPGA IO solutions still provide slightly higher levels of IO density, but only for the highest levels of performance requirements. Typical FMCs allow for around four to eight ADC/DACs <1Gsps per channel, up to two or four ADC/DACs in the multi-GSPS per channel range. Other FMC functions on the market include fiber-optics, DSP, Ethernet and digital IO.

What is FMC+?

A new generation of FMC modules known as FMC+ are emerging through the VITA 57.4. FMC+ modules use a host connector with additional rows to increase the number of high-speed serial connections from 10 full duplex to 24 full duplex channels. Through the use of an additional connector, some FMC+ modules increase the channel count to 32 full duplex. An FMC+ host can also accommodate FMC modules for backwards compatibility.

Curtiss-Wright Defense Solutions offers a range of high performance FMC solutions, allowing system integrators to meet the demanding networking and I/O requirements of RADAR, EW, SIGINT, COMINT, ECM, ESM and C4ISR applications.

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