LTC5589 - I/Q Input DC Bias Questions

Question

Hello all, 
 Regarding LTC5589 I/Q input DC bias, 
 There is an internally generated 1.4V DC bias. 
 Q1: The datasheet mentions an option to disable the internal bias. How can this be achieved? 
 
 Q2: I am using an FDA with a common-mode voltage of 1.65V. What would happen if I connect 1.65V-biased I/Q signals to the modulator inputs? My assumption is that it should be fine due to the 1k&Omega; resistors between the input and the internal reference, but I would like to confirm. 
 Thanks 
 Nir

enash · Accepted Answer

Hi Nir, I did not see a reference in the datasheet to disabling the internal bias voltage. It does however state that the external bias voltage should not exceed "2 x Vdc" where Vdc is 1.4 V. So that says that there will be no problem with applying an external dc bias voltage of 1.65V)

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LTC5589 - I/Q Input DC Bias Questions