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Altera_Forum's avatar
Altera_Forum
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16 years ago

NCO : phase modulation

Hi,

I'm trying to build a qpsk modulator with the nco megacore.

I don't understand how to set the value of φPM.

φPM=P/(2**Pwidth). But is it in radian, in degree ?

My example :

clock : 100MHz,

phase accumulator precision : 32 bits (=4.2950e+007 for a 1MHz output)

angular resolution : 16 bits

magnitude precision : 14 bits

What is the value of φPM for :

phase_angle=2*pi ?

phase_angle=3*pi/2 ?

pahse_angle=pi ?

phase_angle= pi/2 ?

thank you

1 Reply

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    To my opinion, the scaling of P is obvious from the IP manual equations. The range is always a full cycle. If you understand P as signed quantity, the represented range is +/- pi. You have to specify Pwidth, which isn't listed in your example, but I guess it's default 16 Bit. Then you have 0x7fff / 0x8000 respresenting +/- pi.