AD6676 maximum input power (PIN_0dBFS and IDAC1FS) question

Question

In page 28 of datasheet, in the 'Maximum input power (PIN_0dBFS and IDAC1FS) ' section, it shows that a differential voltage swing of &plusmn;240mV peak is obtained for IDAC1FS equals 4mA. This where I feel puzzled. The reason is as following: 
 
 first, Rin=60&Omega;. 
 second, IDAC1FS=4mA. 
 thus, we analysis the input stage of AD6676 in the single ended, the single ended input resistance is RIn_single=30&Omega;, 
 since IDAC1FS=4mA, current swing provided by IDAC1 is &plusmn;2mA peak . 
 so, single-ended voltage swing of &plusmn;2mA &times; 30&Omega;=&plusmn;60mV peak is obtained for IDAC1FS equals 4mA. 
 i.e. a differential voltage swing of &plusmn;120mV peak is obtained for IDAC1FS equals 4mA. 
 
 Why my result is different from the datasheet? Where is wrong?

FormerMember · Accepted Answer

Hello,

Perhaps the best way to analyze is that IDAC1 produces +/-4 mA AC current when DAC code is at max positive and negative settings, This max AC current occurs when differential input of device is swinging +/-240 mV. If one models the DAC output as shown below........it would consist of two DC current sources of 4 mA and a "code-dependent" differential current source of +/4 mA. Seems like the IDAC1FS refers to one leg of the differential DAC.

All that said..............an input in th range of -2 to -3 dBm (IF dependent) results in ADC full-scale (PIN_0dBFS).

Regards

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AD6676 maximum input power (PIN_0dBFS and IDAC1FS) question