HMC948 RF Input

Hi

Regarding HMC948LP3E datasheet, there is C1(5pF) to RF input pin, although there is an capacitor to RF input pin inside IC on Evaluation PCB schematic. I'd like to remove C1. Is it possible ?

Regards,

Hiroyuki 

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  • 0
    •  Analog Employees 
    on Jun 1, 2019 2:11 AM over 1 year ago

    Greetings Hiroyuki.D,

    Please see page 6, and the pin 2 description, showing the ESD circuitry on Pin 2. The external capacitor is necessary for best input dynamic range and accuracy up at the larger signal levels. Because of this, please do plan to use the external coupling capacitor. 

  • Dear Bruce,

    Thank you very much for your support.

    The customer considers replacing HMC1094 by HMC948 due to the long lead time of HMC1094. Actually there is no coupling capacitor for RF input of HMC1094 and he hopes that the same PWB is used for HMC948. According to HMC1094 datasheet, the description of RFIN is as follows. " The dc voltage level of the RF input should be 0 V. If the RF input has a dc level different than 0 V, use a dc block capacitor. " If RF input keeps 0V on the customer side, is it possible not to use coupling capacitor after the replacement ?  

    Regards,

    Hiroyuki

  • +1
    •  Analog Employees 
    on Jun 13, 2019 2:45 AM over 1 year ago in reply to Hiroyuki.D

    Greetings Hiroyuki.D,

    Sorry about the delayed response, as some of us were out at IMS Boston all last week. 

    By now, you may have already tried the HMC948 without external DC block. Omitting the input capacitor will likely work OK, but please understand we cannot condone this level of circuit alteration without at least recommending the following:

    * Check for proper detection accuracy, especially up at the larger signal levels

    * Check the dynamic response (delay, rise, fall time)

    * Check over the expected operating temperature range.

    If all above items test OK, then customer design should be OK, as long as no DC input voltage bias is present at the HMC948 RF input. 

Reply
  • +1
    •  Analog Employees 
    on Jun 13, 2019 2:45 AM over 1 year ago in reply to Hiroyuki.D

    Greetings Hiroyuki.D,

    Sorry about the delayed response, as some of us were out at IMS Boston all last week. 

    By now, you may have already tried the HMC948 without external DC block. Omitting the input capacitor will likely work OK, but please understand we cannot condone this level of circuit alteration without at least recommending the following:

    * Check for proper detection accuracy, especially up at the larger signal levels

    * Check the dynamic response (delay, rise, fall time)

    * Check over the expected operating temperature range.

    If all above items test OK, then customer design should be OK, as long as no DC input voltage bias is present at the HMC948 RF input. 

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