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Quadrature RF outputs — Parallax Forums

Quadrature RF outputs

Michael OBannonMichael OBannon Posts: 19
edited 2008-03-28 19:09 in Propeller 1
Is there a general method for generating two RF signals of the same frequency in quadrature using the Propeller without additional chips? I'm looking for a way to program a variable frequency oscillator (VFO) with quadrature output in the range of 3.5 to 14.5 MHz.

Any help would be appreciated.

Comments

  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2008-03-28 18:57
    Michael OBannon,

    There are two counters in each COG of the Propeller that can be programmed to generate a frequency ranging fro DC to 128MHz.
    You could·"sync" them within·90 Deg of one another by adjusting their Phase registers to produce a quadrature·style output.·

    Note: The output will be a square wave, so a low-pass filter of at least 3 times your target frequency will be necessary to convert it into a sine wave.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • Michael OBannonMichael OBannon Posts: 19
    edited 2008-03-28 19:09
    Beau,

    Would I do this by loading the PHSB register with a value equal to one fourth of the FRQA register? Then both FRQA and FRQB would be loaded with the same values?

    Would I also need to add an increment to PHSB to adjust for an instruction delay between the start commands to the two counters?

    BTW, square waves are fine for my application.

    Thanks very much for your help!
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