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BPSK with pulse shaping filter

Hallo community,

I'm looking for a bpsk modulator solution for a university/company project.

A fixed 1kHz bitstream should be modulated to a tunable carrier (several 100 kHz to maybe 1 MHz, stepping 10 or 20kHz). A root raised cosine filter for shaping spectrum and for optimizing BER at receiving side is strongly needed.

Do you habe an idea for a DDS Chip or upconverter  which fulfills these requirements? Or is a combination of DDS, FIR and DAC or something the better way to realize it? My biggest issue is the high upsampling, I think. Or do you see other difficulties?

Thank you in advance,

Jo

  • The AD9853 may be useful for your application. You will find the data sheet on analog.com. However, you will note this device is now obsolete, so availability might be a problem.

    What makes this device attractive for your application is that you drive it with your raw bit stream and the output is the modulated RF signal (so called, "bits to RF"). Although the AD9853 does not offer a BPSK format, you can work around this by using its QPSK mode. Then modify your BPSK bit stream to repeat each bit (at twice the BPSK data rate, of course). For example, consider the 1kHz BPSK bit stream below as an example:

    0-0-1-1-0-1-0

    Modify it to the following 2kHz QPSK bit stream by repeating each BPSK bit:

    0-0-0-0-1-1-1-1-0-0-1-1-0-0

    This will appear as QPSK symbols, 00-00-11-11-00-11-00, which mimics a 180-degree BPSK modulation format. You could even do 90-degree BPSK by making one of the QPSK bits static 0 or 1 and using the BPSK bit as the other QPSK bit. For example, fix the MSB of the QPSK symbol as a 1, which yields 10-10-11-11-10-11-10 and mimics 90-degree BPSK.

    The AD9853 also has a built-in pulse shaping filter. It is a 41-tap, programmable, 4x oversampling FIR. This could satisfy your RRC filter requirement.

    The AD9853 also provides a fairly high interpolation range (a maximum of 3906 for QPSK). Although this may not be sufficient for your application, I think it would be relatively trivial to upsample your 1kHz bitstream to accommodate the input rate of the AD9853.

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    EZ Admin