ADL5811 connection with ADL5387

Hi Jiwei Sun,

                     From you description of the issue it sounds like you removed  T1,C3 & C4 from the ADL5811 and T1, C11 & C10 from the ADL5387. Are you trying to DC couple these two devices? The ADL5811 has open collector outputs which are pulled up to the 5 V supply. So if the capacitors mentioned above are replaced with jumpers then the ADL5811 output is connected to ground via L1 & L2 on the ADL5387 EVB.

I recommend reviewing the RF INPUT section on page 16, in the ADL5387 datasheet.

These two devices are not compatible for DC coupling and must be AC coupled.

Hi Jim,

Thank you for your suggestions.

In our setup, I did not remove T1, C3 & C4 from the ADL5811 and T1, C11 & C10 from the ADL5387. But the issue is still there. Would you please give us further suggestions?

Are you powering both devices from a single power supply or does each device have its own power supply?

Double check the current limit setting on the power supply. The supply current for the ADL5811 is 185 mA, supply current for the AL5387 is 180 mA. You might be current limited and the voltage is dropping giving the appearance of a short. If the circuit has not been modified, there is no possible way I know of that there could be a short circuit path from the ADL5811 power supply and the ADL5387 ground.

Hi Jim,

Thank you for your help!

Would you please give us options about mixers from Analog Devices that can be compatible for DC coupling with ADL 5387?

Thanks

Hi Jiwei Sun,

                      What is you application? do you require a dc coupled input from the mixer into the ADL5387?

  
While the ADL5387’s RF inputs are DC coupled to the pins, they are not suitable
to be used in DC coupled applications, as you have suggested.  The inputs
require inductor pull-downs to GND level, which are incompatible with any
active mixer outputs that we make, and the inductors will short out any DC info
coming from the mixer anyway.

Hi Jim,

Thank you for your help! I got it.

In our application, we would like to use mixer to convert the measured signal to an intermediate frequency IF signal. And then this IF signal is mixed down to I and Q signal by IQ Demodulator. Would you please give us some suggestions on the selection of IQ demodulator from Analog Device which can be compatible with active mixer?

Thanks.

Hi Jim,

Is IQ Demodulator (ADL5380) compatible with active mixers (such as ADL5811) from Analog Device? I am appreciating that you would give us some suggestions on this question.

As long as you AC couple the mixer outputs to the ADL5380 RF inputs they are compatible.

Hi, Jiwei,

    The demodulators should be selected based on your frequency range and signal dynamic range requirements.  RF/IF demodulators are listed on the following web page:

  RF Modulators | RF Demodulators | Analog Devices

But be careful because some modulators are mistakenly listed on the Demodulator Table also.  All these demodulators can be used with active mixers through ac coupling.  Some have single-ended 50-ohm inputs, while others may have 200-ohm input or differential inputs.  Balun transformers can be used to interface between devices with different impedances, as well as between single-ended and differential products.

Benjamin