We use Ad9361 RF transceiver,and we tested the ADC SINAD perfermance.The result is not optimistic. It seems something influence the quality of the signal.So the effective bits is just 4.5bits when rx digital sampling rate is 100MHz.We tested in different configurations:
1、same VCO frequency，different rx sampling rate：
LO：2.4G VCO:1280MHz 20MSPS ;
LO：2.4G VCO: 1280M 40MSPS ;
LO：2.4G VCO: 1280M 80MSPS ;
2、same rx sampling rate，different VCO frequency
LO：2.4G VCO: 1280M 40MSPS；
LO：2.4G VCO: 1281M 40MSPS；
LO：2.4G VCO: 1282M 40MSPS；
LO: 2.4G VCO:800M 100MSPS;
Receive a 1M tone.We got the IQ seperate data, and made FFT,then got the power spectrum.The power spectrum descripts there are two noise beside the main freq.And the two nosie is diffrent along to the VCO frequency.
To view the analyzed data please reference the attached document.
The nosie on the left side of the main signal is marked up.
My question is how to optimize the SINAD to increase the effective bits.If the niose is from the loop filter of the vco?What should I do to make it better?
Looking forward to hearing from you,Thank you!