AFE7950EVM: SNR at 4.9GHz not matching with datasheet reported values

Hi AK,

Close-in phase noise is not added in SNR specification as SNR is a measure of white noise. Phase noise specs are separately given in section '7.7 PLL/VCO/Clock Electrical Characteristics' of AFE7950 full datasheet. 

FFT bins in 1.5MHz bands on each side fundamental tone are excluded from SNR. To do this in HSDC Pro, first find the number of bins to notch by dividing 1.5MHz by RBW shown at the top right corner of FFT plot. In the case of plot you attached, this is 1.5MHz/7500Hz = 200. Click on 'Test Options' in Top Menu bar and select 'Notch Frequency bins' option. Then enter 'Number of bins to be removed on either side of fundamental' as 200 and click 'OK'.

The matching circuits on AFE7950EVM is for 9.5GHz band for all channels. The input matching circuit RXA and RXC channels has high loss at 4.9GHz. But loss in RXB and RXD channels' input circuit is is not that high. So, I recommend using B and D channels for measurements at 4.9GHz. 

Also note that typical condition for datasheet plots is DSA = 4dB. To set RXB DSA to 4dB you can use command 'AFE.DSA.setRxDsa(1,4)'. With these settings, I can see SNR close to typical specification given in DS. Refer to HSDC Pro FFT plot below. 

Regards,

Vijay