Hi there,
I used the M8190A soft front panel software for generating waveform and BPSK modulation scheme and sent it to the instruments and it is upconverted to 5Ghz carrier Rf in PSG. The output of the M8190A + PSG is shown as the screenshot. But the EVM is so high in this case. I guess we can reduce EVM, I tried in M8190A soft front panel to do it, but it did not change the EVM. Can I follow any other way to improve the output of M8190A + PSG so that we can reduce the EVM. I believe if the EVM is reduced to 2% then the spectrum of the signal will be more flat.
Thanks
!
Hi Mahfuza,
There are four things that you can try to reduce to improve the EVM.
1.) Reduce PSG carrier leakage.
2.) Reduce IQ Skew
3.) Reduce IQ Gain Imbalance.
4.) Pre-distort the waveform
Pre-distorting the BPSK waveform to correct the imperfections of the PSG and M8190A will give you the biggest improvement.
If you want to try that first I suggest you download MATLAB IQTools from Keysight.com. I believe it has a pre-distortion function built into it.
https://www.keysight.com/main/facet.jspx?&cc=US&lc=eng&k=MATLAB+IQTools&pSearch=tnmSearch&hasLuckySearch=true
The other three things are done using adjustments on the PSG and the M8190A.
The RF carrier leakage is adjusted under the IQ Impairments by adding a DC offset to the I and Q channels.
IQ Skew is a time difference between the I and Q channel. This is dependent on the PSG, the M8190A and the cables connecting them. Adjustment can be made using the M8190A start triggers. Adjustment may be in the 50 ps range depending on your cables.
IQ Gain imbalance is caused by different voltages levels for the I and Q channels. You can match these by adjusting the M8190A output voltages on the I and Q channels. Adjustment may be in the range of 0.1 dB or less.
The N7621B Signal Studio for Multitone Distortion application Help file has a section "Optimize the Signal Performance Before Correction" that discusses this things.
https://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=1217877&nid=-11143.0.00&id=1217877
The PSG sweet spot is around 0 dBm. Yes you can get 10-15 dBm or more output power but the EVM will suffer.
Be sure to reduce signal analyzer attenuation to a few dB above where you get an overload indication to optimize the analyzer dynamic range.
Hope this helps
Pete