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    i/q mixer

    new question:
    than in the transimiter, quadrature structure is still used,why is it used , is the i/q mixer be modulated with the same signal or different two signals ???

    and I have this question
    for qam or qpsk etc........
    when a I/Q(different) modulated signal s1*sin(w*f1)+s2*cos(w*f1) generated by upconverter,when it travel trought I/q downconverter,the original two different signal will be converted to two different complex signal s1*sin(w*f2)+s1*cos(w*f2) and s2*sin(w*f2)+s2*cos(w*f2),f2 can be equal to f1 if it is a direct convertion receiver, these two if signal have carrier overlap not orthogonal~~~~~,how can it be rendered or demodulated?


    the original question:
    why the quadrature mixer structure is used especially in some low if receiver, just for the convience of adding a polyphase filter to reject image?

    got it! thanks to 2,3,4

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    ads iq mixer

    i/q modulation means double the information on the same BW, hence more spectrum effficiency



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    iq mixer upconverter

    IQ mean that ur dealing with complex signals , so u can make complex filters , and so on , it is essential for direct conversion , and low IF

    khouly



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    q upconverter

    You kind of get twice the information with an I/Q output than with a single output. For many demodulation or other applications, that allows you to run your A/D converters and 1/2 the clock rate. So there is a clear tradeoff between microwave complexity and DSP complexity.



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    baseband i and q downconverter

    Quote Originally Posted by safwatonline
    i/q modulation means double the information on the same BW, hence more spectrum effficiency
    The signal content transmitted by I and Q from Baseband DAC are identical
    or not identical? Or, the I path and Q path have a 90° phase difference?

    Added after 1 minutes:

    Quote Originally Posted by khouly
    IQ mean that ur dealing with complex signals , so u can make complex filters , and so on , it is essential for direct conversion , and low IF

    khouly
    Why I need I and Q in Direct Conversion? The I Q path required by low IF
    is due the image rejection, but how come Zero IF need I and Q also?



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    Re: why i/q downconverter or upconverter mixer is used

    think of i and q as x and y cartesian plane.

    with x and y, you get two dimensions space. if your data is represented by x and y plane, you get more data points. i.e., (3,4), (3,-5).

    with just i or q, you get x or y only, a one dimenion space.

    i and q can be different data. they are modulated by two orthogonal signals (cos and sin) which are 90 degree phase apart. it doesn't mean the data is 90 degree apart.

    i and q channel can also be used as synchronization detection.



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    why i/q downconverter or upconverter mixer is used

    to szekit
    I know that is qpsk/qam etc
    the problem is that when a I/Q(different) modulated signal s1*sin(w*f1)+s2*cos(w*f1) ,when it travel trought I/q downconverter,the original two different signal will be converted to two different complex signal s1*sin(w*f2)+s1*cos(w*f2) and s2*sin(w*f2)+s2*cos(w*f2),f2 can be equal to f1 if it is a direct convertion receiver, these two if signal have carrier overlap not orthogonal~~~~~,how can it be render?



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    why i/q downconverter or upconverter mixer is used

    hello,
    i don't get ur question clearly but if i understand correctly , the signal u r talking about I and Q signals are s1 and s2 , then to separate them in superheterodyne Rx u first get ur modulated signal to the IF frequ. i.e. signal=S1*sin(IF*t)+S2*cos(IF*t)
    then u separate them at the second stage by using two IF signals (sin(IF*t) and cos(IF*t)) which will separated the two signals i.e. sI=s1 and sQ=s2

    notes: 1-sin(w1*t) is the right expression not w*f1
    2- if u use real signals for downconversion then u get ashifted version of the o/p
    3- if u use complex signals for downconversion u still get shifted versions (i.e. in both cases u will never get a case like the one u stated as the I and Q signals are 90 out of phase and are treated by the same manner so they will stay out of phase



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    Re: why i/q downconverter or upconverter mixer is used

    If you use an I/Q upconverter, and feed the same signal into both I and Q ports, you would have BPSK modulation. If the I and Q signals were different, you would have a more complex type of modulation, such as QPSK, NPSK where N is 3,4,5..., QAM, etc



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    Re: why i/q downconverter or upconverter mixer is used

    Quote Originally Posted by biff44
    If you use an I/Q upconverter, and feed the same signal into both I and Q ports, you would have BPSK modulation. If the I and Q signals were different, you would have a more complex type of modulation, such as QPSK, NPSK where N is 3,4,5..., QAM, etc
    Does baseband processor use adding and substracting to get real and imag
    part signal?



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    Re: why i/q downconverter or upconverter mixer is used

    Quote Originally Posted by biff44
    If you use an I/Q upconverter, and feed the same signal into both I and Q ports, you would have BPSK modulation. If the I and Q signals were different, you would have a more complex type of modulation, such as QPSK, NPSK where N is 3,4,5..., QAM, etc
    Does the different signals of I and Q have any relation, such as phase delay but
    identical content? Or, I and Q signal from baseband are totally different in QPSK
    mode.



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    why i/q downconverter or upconverter mixer is used

    I/Q is used to perform complex modulation/demodulation. In low -IF, I/Q down mixer
    is used to do spectrum shifter and reject image at negnative frequency with polyphase filter.



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