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  1. #1
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    envelope detectors

    I'd like to extract a QAM signal's amplitude and phase from its IF (@40MHz) signal.
    I figure an envelope and phase detector will do the job, however I'd like some more information on the design issues entailed. Can anyone point me to a paper or book that describes these in some detail?

    Also is there another way to get amplitude&phase?

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    Re: Phase detectors and envelope detectors

    You will need a local phase reference to do the angels. QAM is expensive enough to do that you should not economize on the detector method. Using the I and Q coherent detectors and level slicers should be done.

    If you are making a low cost system, OOK or FSK would be cheaper.



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  3. #3
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    Re: Phase detectors and envelope detectors

    I point you to chapter 8 of Digital Modulation Techniques book.


    Link to the book
    :)
    http://www.elektroda.pl/eboard/searc...tml+techniques



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  4. #4
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    Thanks for your replies. Sorry I wasn't quite specific.
    The QAM modulation (and demodulation) is done digitally and afterwards that I/Q is combined digitally, oversampled and then converted to analog at an IF freq of let's say 30MHz using eg @D9856.
    (Taken from @D: The @D9856 integrates a high-speed direct-digital synthesizer (DDS), a high-performance, high-speed 12-bit Digital-to-Analog converter (DAC), clock multiplier circuitry, digital filters, and other DSP functions onto a single chip, to form a complete quadrature digital upconverter device. The @D9856 is primarily intended to function as a universal upstream and downstream I/Q modulator for interactive HFC cable network applications, where cost, size, power dissipation, and dynamic performance are critical attributes.)

    What I want to do is design a predistortion circuit in the Tx path right after the low pass filtering of the Tx DAC and for this I need amplitude and phase info which is not available from the baseband modem.



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