How to measure the phase error of VCO outputs?

when testing a vco, how can I get the phase information of the I/Q mismatch?Which equipment should I use to test the phase error?

Thanks!

There are some method to measure the I/Q unbalance.

1) You can use a Netwrok analyzer. In this case you have to enter not in the two ports, but after the generator (usually is possible in the main network). So you can measure the unbalance (phase and amplitude).
2)If the frequency is under 2.7 GHz you can use the AD8302 RF/IF gain and phase detector: you put the I and Q in the inputs and you measure a DC that it is proporcional to the unbalance
3) use a generator as up converter: in this case you can send I and Q in the two inputs (only if I and Q are digital) and use the generator as upconverter seeing the output in the spectrum. In the output will be present the LO, an high signal at left or right to the LO and a low signal at the opposite late. The difference in dB between the two signals is the phase + amplitude unbalance

dinone,
Thank u very much for your reply, but I still have some problems about the first method:
1.What is the function of a generator?
2. How to cnnect the Network Analyzer, VCO module and generator?
3.Which mode of the Network Analyzer should I choose: reflection or transmission?

Thanks!

wangliangk

the network analyzer has internally two generator that send the signal in the two network ports. Its know how much is the energy that send in every port and read the energy that return to the same port. The signals that read are sent at the digital instrument part. Usually (in the R&S ZVM for sure) this signal are present in two external connectors and return in the instruments by other two connectors. If you take off this connection and enter directly on the two ports that enter in the Digital part you can measure the difference of the two signal as the s21 or s12 phase. The only attention is in the level of the signal that you can send to the two ports. I did this measurement and it works well.

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