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Ultra-fast A/D board packs 2GHz silicon

Posted: 20 May 2005 ?? ?Print Version ?Bookmark and Share

Keywords:data-acq boards? data-acq? sdr? dsp? vxs-architecture?

Pentek continues to churn out DSP, SDR (software defined radio), and ultra-high-speed data acquisition boards and systems at a prodigious rate. Its wares now include boards for VME, VXS, PMC, XMC, and cPCI form-factors. However, the company isn't alone in pursuing SDR designs. Witness the Tek Microsystems board we recently reviewed. It costs about $19,000.

It's also a VXS-architecture board, operating with five channels based on Analog Devices AD6645 chips. Unlike Pentek's converters, these devices are 14bit ICs, but sample at slower rates than the lower-resolution Atmel chips.

The AD6645 converters work at 105MS/s. Board maker Innovative Integration also uses the AD6645 in its high speed data acquisition board. So dies Echotek in its ECDR-4-14105 board that we reviewed last year. I suppose it's only a matter of time before Atmel's new A/D eclipses the Analog Devices part, spawning a new round of leapfrogging.

Like Tek Micro's VXS-compatible board, the competitively priced Pentek board (the single-channel version starts at about $16,000) uses Xilinx Virtex-II Pro FPGAs (field programmable gate arrays). Pentek's board can pack an optional VXS interface, too. That can give you two 4x full-DUX VITA-41 links, each capable of peak rates to 1.25GBps. These links support Gigabit fabrics such as Xilinx Aurora, Serial RapidIO, or PCI Express.

Very New A/D Silicon

As Pentek's exhaustive press release states, this latest Model 6826 data-acq board, with its massive heat sink, derives its blazing performance in part from the pair of Atmel AT84AS008 A/D converter chips it uses. This 10bit IC is so new, however, that there is scant information about it, not even on Atmel's Web site. Yuk!

Nonetheless, the 6826 packs either one or two of these Atmel 10bit RF converters. These are driven either in a single-ended or differential mode, with RF applied through front-panel 50-ohm coax connectors. A transformer-coupled input works to 1GHz, but a higher frequency input is also available as an option.

The Model 6826 also uses a dual-stage de-MUX that packs groups of eight data samples into 80-bit words for delivery to the Virtex-II Pro FPGA. It does this at one eighth the sampling frequency. This circuit also uses an Atmel AT84CS001 de-multiplexer.

The AT84CS001 is a 10bit 1:4 ratio or 1:2 ratio de-MUX in a ball grid array package. It reduces a 10bit data stream by two or four. It operates in an LVDS-compatible (low voltage differential signaling) architecture, where it runs at a 2.2GHz sampling rate.

Advanced Sync

In the Model 6826 VME A/D converter board, the A/D converter sample clock is an external signal that can be anywhere from 150MHz to as high as 2GHz. This clock is applied to an on-board power splitter, where it gets distributed to both AT84AS008 A/D converters in the dual-channel 6826, as well as to the board's sync/gate circuitry. The 6826's sync and triggering circuitry also supports synchronous data-acq across multiple 6826 boards.

Although more detailed information on the Model 6826 will undoubtedly be forthcoming as time goes by, it seems to be shaping up a competitive high-speed front-end for SDRs, as well as realtime recorders, and other high-end DSP systems. When more info is available about the Atmel A/D chips, and how they're used on the Model 6826 board, I'll let you know.

Or, you may be able to get more details directly right away from Mario Schiavone at Pentek, Inc., One Park Way, Upper Saddle River, NJ 07458-2311. Call him at 201-818-5900, Ext. 229. Fax: 201-818-5904.

- Alex Mendelsohn


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