Page tree
Skip to end of metadata
Go to start of metadata

You are viewing an old version of this page. View the current version.

Compare with Current View Page History

« Previous Version 2 Current »


Why, when assembling an I/Q modulator or demodulator using MIXER_B/MIXER_F, is a phase shift of +90 degrees applied to the LO signal rather than -90 degrees?


In an ideal I/Q modulator or demodulator, the I channel is mixed with cos(2Ï€ fLO t), while the Q channel is mixed with -sin(2Ï€ fLO t):

Using the identity:

cos(fLO = cos(s)·cos(t) - sin(s)·sin(t)

We can relate -sin(2Ï€fLOt) to cos(2Ï€fLOt) by:

cos(fLO + π/2) = cos(fLO)·cos(π/2) - sin(fLO)·sin(π/2) = -sin(fLO)

Therefore, applying a 90 degree phase shift to cos(2Ï€fLOt) is identical to -sin(2Ï€fLO t).

  • No labels