AD6676 PIN_0DBFS calculation

Hello,

When one adjusts the IOUTFS current level that defines the PIN_0dBFS, one is changing the input power level that would correspond to digital full-scale of the ADC.   So in your example above where -3.2 dBm represents digital full-scale for setting of 4 mA, an input CW level at IF center of -13.2 dBm would measure to be -10 dBFS on an FFT.   If one kept this input level constant at -13.2 dBm and then reduced IOUTFS to 2 mA (i.e. factor of 2) this will shift the PIN_0dBFS level  to -9.2 dBm (i.e. 6 dB) such that the measured CW tone on FFT will appear as a -4 dBFS on the FFT.  In the time domain, the signal will be 2x the pk-to-pk swing vs the case when IOUTFS is 4 mA.

Note that the AD6676 datasheet excludes the balun loss (which can easily be -0.5 to 1 dB) when stating the PIN_0dBFS level.   The datasheet characterization curves also show that the PIN0_dBFS level also is dependent to the IF setting due to 2nd order effects that are frequency/settings dependent (i.e. IF vs BW vs DAC sample rate).  Note sure what your exact settings are and whether the -3.2 dBm  PIN0_dBFS level
includes balun loss or not.   If one needed to shift the PIN_0dBFS level higher than what can be achieved with IOUTFS=4 mA.........than one can use the ATTEN function that allows one to shift upward in 1 dB increments.

Regards

Thanks for the reply ,In my case i am feeding an input frequency of 261 Mhz and IF frequency of 258 Mhz,Bandwidth is 56Mhz ,considering the  balun loss and cable loss to be  -0.76 dBm,so considering all the losses i am, feeding -2dbm to the ADC which equates to -2.7dBm to the input of the ADC,but after plotting the output samples , I am able to get a fundamental amplitude of -0.356 dBFS which is not excatly 0 dBFS

Hence can I know what value needs to be set to the respective registers to obtain the exact PIN_0dBFS value