According to application note the Base Band inputs IAIN, QAIN and detectors VDT1/VDT2 should be biased with Vref (1V). For my reasons I need to bias these pins from other source which is also ~1V, however in this case I have a failure in the AGC loop it became constantly at minimum gain (VAGC = 3V). What could be the cause of this strange behavior. One reason I can thought about, is that the detectors are working with internal Vref (internal band gap reference), and if I apply voltage that is even 50mV larger than Vref it clips the AGC to minimum gain.
Please advice, what could be done to resolve this problem.