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VMEbus A/D Boards Coherently Sample Multiple Channels at Rates to 1.5 GHz

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Echotek Corporation Announces the Release of a High-Speed A/D Converter Board Echotek Corporation announced the release of its newest A/D converter board, which provides up to two A/D converter channels of 8-bit, 1.5 GHz A/D conversion and programmable FPGAs in a single 6U VME 64X slot. Model number ECAD-2-081500. The ECAD-2-081500 uses Maxim MAX108, 8-bit, 1.5 GHz A/D converters that support intermediate frequencies (IF) up to 1.4 GHz and A/D sample rates from 100 MHz to 1.5 GHz. The following signals can be received through front-panel connectors: Analog Input, A/D Clock, Sync Signal, Trigger, 128-bit Auxiliary Data Input, and LVDS Input. This two-channel A/D converter board supports data output through the Dual RACE++ interface, the LVDS output port, or the VME64X interface. Each channel is equipped with a FIFO buffer that is 4 Msamples deep and interfaces to the "user-programmable" FPGAs. The board supports up to three large "user-programmable" Xilinx Vertex FPGAs per channel for hardware-based DSP processing. The ECAD-2-081500 supports continuous waveform and counted burst applications, allowing the board to be controlled in either of these operating modes. Board set up, control registers, and "user-programmable" FPGAs are made accessible through the VME interface. Single-piece pricing for this unit starts at $13,000.

Echotek's ultra-fast Model ECAD-2-081500 digitizer boards, and indeed many of the company's related board-level products, serve high-end niche applications. Nonetheless, they're examples of leading-edge digitizers. Note that you can also feed in as many as 128 signals to each channel via Mictor connectors on one of these boards. Also, A/D clocking, sync signals, and triggering signals can also be fed in through front-panel-mounted SMA connectors. Clocks, in particular, can be buffered and then distributed to more than one channel so that multiple channels can be sampled simultaneously. Likewise, sync and trigger signal distribution also permits multiple ECAD-2-081500 digitizer board sets to start acquisitions at the same time. More on this in a moment. If you're working with software-defined radios in the 800 MHz to 1 GHz band, for example, an ECAD-2-081500 could replace lots of discrete IF components, filters, mixers, and the like, instead delivering a digitized signal for downstream DSP processing. The 8-bit A/D converter serves adequately at the signal-to-noise ratios typically needed. Speaking of A/D converters, Maxim's MAX108 chips really bring conversion fire to the front ends on these boards. The MAX108's are 8-bit PECL-compatible chips that sample at up to 1.5 Gsamples/s. Fabbed with bipolar transistors, these ICs include track-and-hold (T/H) amplifiers. The on-chip T/H sports a 2.2 GHz full-power input bandwidth, which results in high performance (typically 7.5 effective bits) at the Nyquist frequency. The MAX108s also include a fully differential comparator and decoding circuitry to reduce out-of-sequence code errors. Unlike some ultra high speed A/D chips that can have errors resulting in false full- or zero-scale outputs, the MAX108 limits the error magnitude to one LSB. Multi-Channel Coherency Back to the ECAD-2-081500 boards. In use, an ECAD-2-081500 could also be used for radar or laser development where channel-to-channel coherent digitization is mandatory. Indeed, according to Echotek president and CEO Ralph Kimball, these boards were initially designed for a customer who needed to instrument a phased-array radar. "The key there was that the customer needed coherence across multiple channels," says Kimball. "Synchronization was really important." Kimball emphasizes that other applications benefit from this kind of performance, too. "Military ELINT and SIGINT systems are examples where radar-beam forming is needed," he says. "In those applications, multiple antennas are used in arrays, and the wavefront of return signals reveals the angle of arrival. Similarly, the boards can be used in laser radars where range resolution is called for." Multiple Options Not mentioned in the company's press release is the fact that Echotek offers its ECAD-2-081500s as a series, with a variety of options. That's in keeping with the reprogrammability of the boards' FPGAs. These systems are typically used in quite dedicated non-jellybean applications. As such, the ability to reconfigure and choose hardware options makes a lot of sense. For starters, ECAD-X-081500 models can be ordered with one or two channels, and with a variety of FPGA type and size options from 1 million to 1.6 million gates. You can, for example, equip a board with one, two, or three Xilinx XCV1000E FPGAs/channel, or one, two, or three Xilinx XCV1600E FPGAs/channel. The FPGA configuration files are stored in flash that's reprogrammable over the system's VMEbus interface. There are also LVDS (low-voltage differential signalling) I/O options. You can opt for no LVDS transmitters or receivers, or choose configurations with one channel with an LVDS receiver, or a two-channel board with an LVDS receiver and transmitter. A system requires at least two FPGAs/channel, so you can opt for two FPGAs for 40 LVDS channels, or three FPGAs for 80 channels. Large Virtex FPGAs are also used. These support very high data rates. Kimball also points to the product's user-reprogrammable FPGAs as a way to support a wide variety of intellectual-property algorithms. "The FPGAs do massive parallel processing," tells Kimball. "The high-bandwidth LVDS I/O required for the original radar application demanded 4.5 Gbytes/s/link speeds to support daisy-chained beam forming." An Altera Stratix FPGA is also housed. It follows the system's A/D acts as a demultiplexer. "This takes advantage of the fact that LVDS is fast," says Kimball. "The Stratix FPGA takes 750 MHz PECL streams and fans out to lower data rates. It handles I/O and ties the buses together." In some versions, the A/D de-mux is handled by an Altera Mercury FPGA. The de-mux configuration is also stored in on-board flash. For more information contact Kimball at Echotek Corp. 555 Sparkman Dr. Suite 400 Huntsville, AL 35816 Phone: (256) 721-1911 FAX: (256) 721-9266

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