HMC8038 Isolation Problem ?

Dear,
I observed a problem about the SW HMC8038. When I measure the IL from RF1 to RFC (RF2 terminated with 50 ohm), I measure 1 dB for VCTL = 1 and  41 dB for VCTL = 0 at 1.5 GHz. That means the isolation is about 40 dB but should be higher. 
Could you comment on that?
Parents
  • 0
    •  Analog Employees 
    on Aug 28, 2020 1:45 PM

    Hi

    Did you measure it on the evalboard or did you produce your own board? Could you please share the snapshot of your top layer including vias if its your own PCB?

    Could you please tell the EN state and CTL state? Please make sure they are not floated initially. Also I wonder if you see the same values for different EN states.

    Thanks

  • First of all, thank you for your answer. I just saw your message. I produced own board.
    When, I measure RFC to RF1 (RF2 terminated with 50 ohm) I measure 1dB for VCTL=1 and EN=0 at 1.5GHz.
    When, I measure RFC to RF1 (RF2 terminated with 50 ohm) I measure 40dB for VCTL=0 and EN=0 at 1.5GHz.
    When, I measure RFC to RF1 (RF2 terminated with 50 ohm) I measure 61dB for VCTL=0/1 and EN=1 at 1.5GHz.
    By the way, my network analyzer has an 80 dB noise floor. I can measure signals of 80dB and below.
    I shared the snapshot of top layer my PCB.
  • 0
    •  Analog Employees 
    on Oct 6, 2020 8:54 AM in reply to EgemenMehter

    Hi Egemen,

    It would make sense to increase the power output of the network analyzer and reducing the IF bandwidth for better isolation. I see that you have already achieved 61dB. Achieving higher isolation depends on your measurement environment as well.

    I can measure 70dB around 1.5GHz. It would make sense to use further shielding and absorber if you have any.

    What is the solder paste thickness you use also?

    Thanks

    Sinan

Reply
  • 0
    •  Analog Employees 
    on Oct 6, 2020 8:54 AM in reply to EgemenMehter

    Hi Egemen,

    It would make sense to increase the power output of the network analyzer and reducing the IF bandwidth for better isolation. I see that you have already achieved 61dB. Achieving higher isolation depends on your measurement environment as well.

    I can measure 70dB around 1.5GHz. It would make sense to use further shielding and absorber if you have any.

    What is the solder paste thickness you use also?

    Thanks

    Sinan

Children
  • Hi Sinan,

    Increasing the power and reducing IF BW unfortunately didn’t make any impact on the isolation. 61 dB is achieved for EN is 0 (SW is disabled). Otherwise for EN = 0 (SW is enabled), we continue to have 40 dB isolation.

    By the way, do you measure the isolation with a shielding or absorber on your demoboard? Can the reason be your 4-layer eval-board instead of our 2-layer PCB?

    Thanks.