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New to Data Conversion and need some help! ADS6422 interfacing.

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I am looking at using an ADS6422 to take in four 5MHz signals from an array of antennas that receive a basic 2.5GHz signal. The signal from the antennas is taken down to 5MHz and I have been tasked with the analogue to digital conversion and PIC programming. As such I have a PIC18f2620 ready to program, but ADC is an area of expertise that I am sorely lacking- even how to implement into a circuit!

I just wanted to check that it was in fact possible to interface the ADS6244 and the PIC (via SPI?), and if there are any example circuits/SPICE models that I could look into to get started on this.

Any help would be greatly appreciated!

Cheers,

 

Andy Griffiths

 

Note: The reason we are wanting a high sampling rate is so we can have a large number of samples per period. We are attempting to beamform the four signals, and my predecessor indicated that because, for the moment, we are using a pure, unmodulated 2.5GHz signal it would be best to simply delay the signals rather than using complex coefficients. This is simply for demonstration purposes at the moment, so that we can show that the principle application works, and then we'll probably move on to more complex implementation. I have previously only been involved with software and hardware implementation is a particularly grey area for me.

  • Hi,

    I am not clear on what you wish to do yet. 

    The signal you wish to sample is around 5MHz, correct?  What would be the sample rate then?  Or is the sample rate 5MHz?

    For the PIC programming, what are you wishing to do with the PIC?   Are you wanting to use the PIC to drive the SPI signals to the ADS6422 to program the register space of the data converter?  We do not have example code for exactly this function, but we do have on our evaluation modules a couple of ways to control the SPI lines.  For the ADS6422 EVM, we have the TSW1200 Capture Card that uses a Xilinx Virtex 4 to drive the SPI lines of the data converter, and this logic was written in Verilog.

    (Keep in mind that many modes of the operation of the ADS6422 can be had without SPI register programming, but some functions such as fine gain control would require SPI programming.)  I expect the PIC device would be a suitable choice for doing that, but we have either used a USB to general purpose IO device such as from FTDI to do that function or we have used the FPGA to drive the SPI port.

    What would you be using the capture the digital data from the ADS6422?  An FPGA?  Again, we have the TSW1200 capture card that has an FPGA programmed to receive the digital data and fill up a memory buffer.  Also, we now offer an adapter board that lets the digital data from the ADS6422 EVM be brought into an off the shelf FPGA development platform such as the Xilinx Virtex series or the Altera Stratix series, and then you could develop your own FPGA design using the design tools for that FPGA and the develolment platform.

    The ADS6422 EVM can be found here:  http://focus.ti.com/docs/toolsw/folders/print/ads6422evm.html

    The TSW1200 Capture Card can be seen here:  http://focus.ti.com/docs/toolsw/folders/print/tsw1200evm.html

    The bridge cards to either Xilinx or Altera development platforms can be found here:

    http://focus.ti.com/docs/toolsw/folders/print/fmc-adc-adapter.html

    http://focus.ti.com/docs/toolsw/folders/print/hsmc-adc-bridge.html

    Regards,

    Richard P.

  • In reply to Richard Prentice:

    We have slightly changed our plan and will be linking the ADC to a computer... Do you provide some kind of interface for the ADS6422? I require a sample rate >50MSPS as the baseband signal (which is at 5MHz) needs to be oversampled so that we can beamform the four incoming signals.

  • In reply to Andrew Griffiths:

    Hi,

    What do you mean by interface?

    Again, our TSW1200 Capture Card is made to plug into the ADS6422 EVM, and from there the TSW1200 can interface to the data converter, capture a buffer of data and upload to the PC by wau of a USB cable for processing.  On the PC side, we offer a User Interface as well as Matlab code that can be used as a starting point for controlling the hardware and getting the data for processing.  But there would still need to be an FPGA or some such device to connect to the digital data bus to catch the data at the sample rate. 

    If you are still referring to the SPI port for connection to a computer for control, many of our EVMs have the USB to general purpose IO device FT245RL from FTDI, and the computer can control the SPI port through a USB connection by 'bit-banging' three of the general purpose IO pins on a cycle by cycle basis to create the SPI clock, SPI enable and SPI data pattern. 

    In either case, schematics for our ADC EVMs and TSW1200 Capture Card are available from the TI web site in the User Guides for these boards.

    Regards,

    Richard P.

  • In reply to Richard Prentice:

    That is precisely what I need!! Could you send me a link?

  • In reply to Richard Prentice:

    I have just looked at the price and am not sure whether we can budget for that at this time (as well as the rest of the equipment we need to purchase)

    Is there a cheaper option?

  • In reply to Andrew Griffiths:

    Hi,

    I'm not sure what you are looking at - since i mentioned a number of things along the way.  Are you looking at the price of the TSW1200 as listed on the web?  We do not have a cheaper capture card for LVDS data formats at these speeds.  Are you concerned about the cost of acquiring a TSW1200 for lab use, or the cost of the FPGA-based solution for data capture for a production situation?

    Regards,

    Richard P.

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