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HMC547 ac coupling question

I am wondering if I have a fixed attenuator after the HMC547 switch do I need to have AC coupling caps to the attenuator?  I am trying to minimize my component count and want to make sure a coupling cap is or is not required.


  • Hi Rich,

    The RF ports of the HMC547 are matched to 50-ohm and DC coupled. AC coupling cap can be eliminated if the RF path has line potential of 0Vdc. The HMC547 should be able to connect directly to a fixed 50-ohm attenuator.

    Best Regards,


  • Hi,

    I have a problem with the P1dB of the switch, HMC547MS8E.

    I am using the switch in a receiver operating in the frequency 2-30MHz. According to the datasheets, the switch will operate from dc-3GHz.

    The input power for 1dB compression stated in the data sheets is +33dBm minimum from 0.5-3.0 GHz.

    When I refer to the curve for Input P1dB Vs Vdd, the plot seems to indicate that the P1dB will be lower at lower frequencies, but the minimum should still be above +26dBm.

    Now when I tested the P1dB of the switch, I can only get +16dBm at the 1dB compression point. The control voltages and supply voltages (Vdd) are +5V. The test frequency is 3MHz.

      Please advise why is this so?

  • Hi Andreas,

    The power handling (power compression, IIP3) of the HMC547 are expected to degrade at frequency below 200MHz, of which is a normal behavior of the GaAs FET switches. We have not evaluated the P1dB of the HMC547LP3 below 500MHz, but I believe your measured P1dB of +16dBm at 3MHz is valid based on our experience on other switches of the same process and power handling capability.

    We have a new SPDT switch, HMC1118LP3DE, in the process of product releasing. This switch will be able to handle +35.5dBm from 1MHz up to 13GHz. I've attached the link to the preliminary datasheet of this switch for your review,

    Best Regards,


  • Hi MN,

    Thank you very much for your reply.

    Do you have the release date of the HMC1118? You may email me at

    Thank you once again.