how to test phase deviation between I and Q signal?

[trashbox]

mixer phase deviation

I want to test the phase deviation from the outputs (I and Q) of a quadrature LC-VCO, and mainly I have the spectrum analyzer, which I use to test the other parameters of LC-VCOs such as center frequency, phase noise. Now how can I test the phase deviation? Should I use a mixer or the other ways?

Thank you very much!

 

[springf2000]

use the VNA,as the following step:
!)calibrate the VNA in your frequency band;
2)test the I phase
3)store it into memory
4)display the data/memory
5)test the Q phase
the display is the deviation between the I and the Q

 

[flyhigh]

Hi,

I am not sure about using VNA to test oscillator phase. One can test phase difference of I/Q branching network using this method, might not be a soultion for active outputs.

You can use 2 channel oscilloscope, put I on one channel, Q on the other and check that one signal is in maximum when the other is passing trough 0. This can work only if the oscilloscope can handle signals on the frequency of your VCO. If not, I think you have to use mixer with known I/Q characteristics. Again, you have to connect them somewhere for comparison (probably oscilloscope again)

flyhigh

 

[flatulent]

The mixer method will also work. Any type of circuit that is used as a phase detector in a PLL will work.

 

[trashbox]

springf2000,thank you for your advice,It is a pity that I have no VNA.

flyhigh,thank you for your advice about using oscilloscope.I will try.

flyhigh,flatulent,would you explain how to use mixer method to detect the phase error? The output from a mixer,whose inputs are I and Q signal,is also a sine wave,how can I detect its phase?

 

[flatulent]

The output of the mixer will contain a DC term plus a double frequency term. Low pass filter the output to get the DC term. The DC term will be proportional to the error from 90 degrees. If the phase difference is exactly 90 degrees the DC will be 0 V.

You can calibrate your measurement by using a single signal generator and transmission lines of different lengths to make different phase differences.