I am designing an I/Q Zero IF downconverter using an LTC5585 and amplifier LTC6409 to drive an A/D. The datasheet of the Mixer LTC5585 says that an output pull-up resistor should be included to guarantee a DC bias voltage of Vcc-1.5V, in my case Vcc-1.5V = 3.5V as in the following diagram:
I want to use DC coupling between the mixer and the amplifier.
When I add the LTC6409 it loads the LT5585 and changes the Bias point from 3.5V. My question is: Can I change the bias resistor as long as the 3.5V point is conserved and current sink requirements are met?
For example in the following circuit, if I use a 100Ohm pull-up, the LTC6409 will move the bias point to 3.3V, while if I use an 80Ohm resistor, the bias will be 3.5V. Is this acceptable?
Thank you very much!