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AD9208: Higher Phase Noise observed for the DDC Enabled capture

Question asked by Dwijen.Pandya on Jan 11, 2018
Latest reply on Feb 13, 2018 by UmeshJ

Hi, I am evaluating AD9208 using AD9208-3000EBZ+ADS7-V2EBZ+ACE software.

 

Following is test setup details

RF In: 2.2GHz

RF In Amplitude: -1.7dBFS

 

I am measuring noise density at 5MHz and 10MHz offset. For this I am integrating bin noise in 30KHz range around 5MHz (or10MHz) offset and calculating dBFS/Hz number. Following table shows comparison between noise density measured when Full BW mode was used and when DDC mode was used. RF Input Signal Phase Noise and ADC clock phase noise is given in the separate column. Keysight MXG Sig Gen is used as both RF In and ADC Clock Source

 

The noise density is increased by around 4~5dB when DDC is enabled. 

What could be reason behind this degradation?

 

Offset from CenterNoise Density Measured (dBc/Hz), Data Captured in Full BW ModeNoise Density Measured  (dBc/Hz), Data Captured in DDC Enabled ModeRF In Phase Noise (dBc/Hz)Clock Phase Noise (dBc/Hz)
200K-135.1372125-133.6362125-135-132
250K-133.1862125-132.6542125-135-132
400K-131.5712125-131.9092125-134-133
600K-132.4202125-131.6242125-134-134
800K-132.5452125-131.6392125-134-135
1.8M-139.6032125-137.2362125-143-143
5M-144.5032125-139.4142125-156-155
10M-144.3182125-139.8412125-159-159
-200K-134.2982125-133.3832125-135-132
-250K-133.4982125-133.1292125-135-132
-400K-131.7302125-131.7362125-134-133
-600K-131.6642125-131.2832125-134-134
-800K-133.1852125-131.5762125-134-135
-1.8M-139.7372125-137.0722125-143-143
-5M-143.3272125-139.5342125-156-155
-10M-144.6492125-140.1612125-159-159

 

ACE Setup for the DDC Capture

 

Regards,

Dwijen

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