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Converter measurement and de-embedding

Question asked by alhum on May 20, 2014
Latest reply on May 22, 2014 by Dr_joel
Hi all,

I am doing some measure on a converter and have some little problems with de-embedding. I use an N5241A (A.09.90.11).

1) I do a swept IMD converters measurement with swept fc and fixed LO. I use an external EXG generator controlled by the PNA-X as the LO source. I would like to use power compensation on the LO path because I have a switch matrix between the DUT and the calibration plane. When I load the s2p file containing the s-parameters to be used for power compensation (this s2p file has a single line at the LO frequency), I got a warning message saying that interpolation should be turned on since this port frequency can go up to 3 GHz (this is not true, I do a measurement with fixed LO). I think the 3 GHz comes from the EXG frequency range. Then when I enable fixturing, I got a fatal error and the network application is terminated.

2) If I compensate manually the LO level for the measurement describe in 1) and enable de-embedding and power compensation only for the input and output port, I got a small error when comparing the IMD3 measurement done at the calibration plane and the IMD3 measurement with de-embedding. This error looks to be systematic and approximately -0.2 dB. However I believe my s2p files used for input and output de-embedding are correct because I use them for many other measurements with success (SMC, NF, ...).

3) I am also doing some group delay measurements (SMC+phase). I get the same mean group delay at the calibration plane and with de-embedding. However, with de-embedding, the trace is very noisy. I have attached 2 captures with and without enabling fixturing. I believe this noise may come from my s2p files but I don't understand why, as already said, all the other measurements done with these s2p files are correct.

Many thanks!