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about the AD9371 ADC out digital code back-off

Question asked by JunHu on May 5, 2017
Latest reply on May 11, 2017 by JunHu

Dear all,

 

recently we are using single tone to check IQ raw data RMS power level after JESD output

(tone frequency is 3.6GHz+3.84MHz)

 

it is a straight-forward thinking that with the digital code RMS level(IQ is with 16 bits signed values), ADC Vpeak (0.707Vp), and applied 9371 gain (say codeword=255, refers to 17dB gain) we can calculate back the equipment power level, and it should align with our equipment output (cable loss is considered)

the basic formula (equipment_out_dBm) = 20*log10( digital_rms/2^15*Vp ) + 10 - 9371_rf_gain + cable_loss

 

but the results are not aligned (>6dB difference)

 

i am double checking the raw data and calculations, 

BTW, i have the following two questions:

1. does the digital/analog filter chain inside 9371 Rx have extra gain ??

2. for 9371 ADC, i guess it is a sigma delta ADC, so does it have output digital code back off  to prevent saturation ?? (meaning, with maximum allowed ADC input power level, the ADC output max digital code can not reached)

 

thanks a lot ~

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