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how to measure the mismatch between I and Q in receiver

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byron

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we designed a RFIC which includes a direct conversion receiver front-end, anyone knows how to measure the mismatch between I and Q at the output of the mixer. Thanks!
 

Mmm,

Do you have good IQ-Modulator/Transmitter?
Then you could transmit a complex signal and look at I and Q in the base band and compare them?
 

crosscoupling

If you used just a psk signal and looked for the level in the lower of the two I or Q you could find cross coupling caused by not having 90 degrees exactly and also from phase locking not being exact.
 

If you meant the I/Q gain imbalance and phase imbalance, just inject a single carrier at the RF input and observe the I/Q output with a good digital oscilloscope, which can easily give the gain and phase imbalance readings.
 

Could you recommend some models of digital oscilloscope

jon2000 said:
If you meant the I/Q gain imbalance and phase imbalance, just inject a single carrier at the RF input and observe the I/Q output with a good digital oscilloscope, which can easily give the gain and phase imbalance readings.
Click to expand...


Could you recommend some models of digital oscilloscope which can easily give the gain and phase imbalance readings.


Thanks
 

byron said:
we designed a RFIC which includes a direct conversion receiver front-end, anyone knows how to measure the mismatch between I and Q at the output of the mixer. Thanks!
Click to expand...

I assume you have I/Q sources as LO or internal synthesizer, I guess textronix digitalized oscilloscope could be used. Just use the measure function to measure the amplitude and phase different.

By the way, since it is direct conversion, you might not try to downconvert the RF input to DC. Maybe offset a bit the downconverted signal from DC.

If you have external LO (quadrature), try to vary the amplitude and phase to get better measurement of the mismatch. If it is internal, try to vary the reference frequency, and measure the mismatch at different frequency.

Could you input signal at the input of the mixer quadraturely?
 

Actually, the network analyzer is a good tool for this. I to port 1, Q to port 2. Very accurate phase/gain balance measurements versus frequency.
 

I dont think digital oscilloscope can give unbalance information of I/Q signal in detail.I just know if you use the Agilent instrument -89600,you can get the result what's you want.Other instruments can demoulate the input I/Q signal are your choice too.
 

toonafishy said:
Actually, the network analyzer is a good tool for this. I to port 1, Q to port 2. Very accurate phase/gain balance measurements versus frequency.
Click to expand...

what i concern for using network analyzer is the proper termination, since it is two port measurement. meanwhile, the calibration could also be a problem.
 

A simple resistor matching network using 1% resistors takes care of this nicely. Its really the best way I have found to do this. You should try it.
 

application note regarding measuring I/Q using Network

toonafishy said:
A simple resistor matching network using 1% resistors takes care of this nicely. Its really the best way I have found to do this. You should try it.
Click to expand...

Hi!,Toonafishy,
How are you doing!
Do you have any application note regarding measuring I/Q using Network
Analyzer?

Thanks for your help

uummcc
 

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