Is there an easy way to reduce the gain of HMC788A?

HMC788A has too much gain in my LO signal chain and I believe that it is causing excessive dc offsets in my IQ demodulator. Is there an easy to reduce the gain to around 7 or 8 dB? 

  • 0
    •  Analog Employees 
    on Aug 7, 2018 3:55 PM


    Is there room to put attenuator at output?


    Ivan Soc

  • 0
    •  Analog Employees 
    on Aug 7, 2018 5:10 PM

    I could do this but I would prefer to reduce the amp gain. Let's say that your input power to HMC788A is 0 dBm. So you get an output power of around +14 dBm. If you only need an output power of +10 dBm to drive your LO, you can insert a 4 dB attenuator after the HMC788A. The problem with this is that you now have +14 dBm on the board which has the potential to leak across the board and into the RF input of the IQ Demod and generate a dc offset at the IQ outputs.

    But now you have me thinking. If I put the attenuator before the HMC788 (so Pin to HMC788A is -4 dBm, this ensures that the power level along the signal chain never gets higher than +10 dBm. Noise figure is not a concern at this point in the signal chain so putting the attenuator before the HMC788A is not a problem.