Trying to understand quadrature signals

Thread Starter


Joined Oct 6, 2011
Hi experts,

I'm Trying to understand this paper on Quadrature Signals.'m

refer to the block diagram in Figure 14 of that paper (QuadSignals.pdf), I am having a hard time following how the 'phase' info is deciphered, when the phase difference is 'always' going to be 90 degrees, since that's the difference between the I(t) and Q(t) branch. Or, in another words, how is it having x(t) broken down to two signals that are 90 degrees out of phase, is going to help decipher the phase info on x(t)?

I wonder if what I am having trouble is my basic concept on phase. To me phase is the 'theta' when x(t)=A sine (2pi*f*t+theta), but it looks like in this paper the 'phase' is defined as 2p*f*t (as shown in their figure 5, where the theta as the phase vary over time.

Looking up Wikipedia, it looks like there are 3 ways to define phase, and the phase in DSP domain is known as the instantaneous phase. And that's confusing me.

If you can explain the concept better than this paper, or Wikipeida, let me know....
Last edited:


Joined Nov 25, 2009
Your first link is broken. You might want to post a valid link or download and attach the .pdf, on condition that it is not subject to copyrights.