There's no shortage of interfaces to use between ADCs/DACs and microprocessors, microcontrollers, or FPGAs. Depending on your conversion speed, resolution, channel count, pinout, PB board real estate, and other factors, you can choose basic serial, basic parallel, SPI, I2C, I2S, or LVDS DDR, to name a few.
But when you need a very high-speed interface between a converter and an FPGA, especially with a high channel count, a relatively new kid on the block offers great performance potential: JESD204B, which came out in 2011. It's the latest revision in a cycle that started with JESD204 in 2006 and went on to JESD204A in 2008. This is not just a wishful-thinking standard. Converter ICs for this standard are available from several vendors, including Analog Devices, NXP, and Linear Technology Corp.
JESD204B supports 12.5Gbps bit rates per differential lane, and it is targeted at applications such as digital radio, radar, and high-end ultrasound. JESD204A goes up to 3.125Gbps, as does JESD204, which lacks the multi-channel synchronization capabilities of the A version.
Each enhancement of the standard added features and performance, but the latest version is (to put it politely) complex. JESD204B's channel setup, format, protocol, handshaking, error correction, framing, synchronization, latency aspects, and various clocks are much more involved than those of its predecessors. Testing it, debugging it, and verifying it is not something you can do without a 30 to 40GHz bandwidth scope, good probes, test suites, and more. Further, with the speeds involved in JESD204B, the PCB material and layout are major factors in a successful implementation.
Even if you don't need the performance of JESD204B immediately, it's probably a good idea to become somewhat familiar with it. Hey, that's part of your ongoing education process (also known as job security or employability). Further, with the ever-increasing demands placed on designers -- something we know as mission creep -- you may find the interface you were hoping to employ just won’t do, and you'll need to step up to JESD204B. I suggest you start by checking out this Webinar and these three articles from EDN. Of course, our illustrious leader Max Maxfield has also penned a few words on this topic.
In addition to the test tools and test suites that JESD204B demands, your FPGA will need some drivers and application software. You won't have time or expertise to find them yourself, but FPGA vendors know this and are working with the standards committee and converter vendors. Some have already come out with the software you'll need. But check how complete those offerings are and how the source has verified them. Trust, but verify, as the old saying goes.
Have you had any experience with the JESD204, JESD204A, or JESD204B standards in an FPGA deployment? Please post a comment and share with us.
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