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LMH5401: Gain

Ray Vincent Aranzaso
Genius 16345 points
Part Number: LMH5401
Other Parts Discussed in Thread: LMH2110

Hi,

Good Day.

I am trying to understand in LMH5401, what kind of DC gain I am going to get and also what kind of gain I can have if the input is an 8GHz RF signal.

If the input signal is -10dBm 8GHz sine wave with 20mV offset. What should I expect from the output of the LMH5401?

Please advise. Thank you very much.
Best Regards,
Ray Vincent
  • 0
    TI__Expert 3320 points

    Hi Ray,

      Your DC input common mode will be rejected by LMH5401and output common mode is set by VOCM pin. 
    For your 2nd question about AC output for 8GHz -10dBm sin wave, It depends on the gain config you have set on LMH2110. You can refer to Fig 56, Fig 57 and Table 1,Table 2 under sec 7.3 of datasheet depending on your input single ended/ differential ended. Please do remember to see the freq response plot for given gain in Fig 1 and Fig 2 and you could see gain rolls at 8GHz.

    Best Regards,
    Hruday

  • 0 in reply to Hruday Kumar Mudireddy
    TI__Genius 16345 points

    Hi Hruday,

    Good Day.

    Hruday Kumar Mudireddy said:
    Your DC input common mode will be rejected by LMH5401and output common mode is set by VOCM pin.
    For the DC input common mode that will be rejected by the LMH5401, what kind of frequency response should I expect at low frequency?
    For example, if I have a very low-frequency component, say at 1Hz, is that also rejected? or how about 10Hz, 100Hz, 1kHz, 10kHz, 100kHz, 1MHz....?  In Figures 1 and 2, everything is just flat from DC.
    And also what kind of frequency response should I expect from the CM pin? These will determine the distortion of the DC component. Assume I have a 20ns square flat pulse added on top of the 8GHz sin wave as the output of the DAC. Maybe I can use a bias-T or similar LC low pass to extract the DC component and feed the CM pin, what kind of distortion should I expect from the LMH5401?
    Hruday Kumar Mudireddy said:
    For your 2nd question about AC output for 8GHz -10dBm sin wave, It depends on the gain config you have set on LMH2110. You can refer to Fig 56, Fig 57 and Table 1,Table 2 under sec 7.3 of datasheet depending on your input single ended/ differential ended. Please do remember to see the freq response plot for given gain in Fig 1 and Fig 2 and you could see gain rolls at 8GHz.
    Is the LMH2110 in the above line a typo for the LMH5401? The LMH2110 is an RMS power detector?
    Assume I have differential input and have the gain configuration as the evaluation board 4V/V. What kind of gain should I expect? I saw gain rolls at 8GHz in fig 1 and fig2 the red curve is about -12 dB, is that mean I can only see the -22dBm 8GHz component at the output port?
    Best Regards,
    Ray Vincent
  • 0 in reply to Hruday Kumar Mudireddy
    TI__Genius 16345 points

    Hi Hruday,

    Good Day.

    For example, if at the differential input, I have a signal as attached, which contain 


    5mA DC
    20ns pulse between 20ns and 40ns
    7GHz RF amplitude modulated by an envelope
    What should I expect to see at the output of the LMH5401?
    Best Regards,
    Ray Vincent
  • 0 in reply to Hruday Kumar Mudireddy
    TI__Genius 16345 points

    Hi Hruday,

    Good Day. I would like to follow up on the latest customer's query. Thank you very much.

    Best Regards,
    Ray Vincent
  • 0 in reply to Ray Vincent Aranzaso
    TI__Expert 3320 points

    Hi Ray,
       Thank you for your patience. I got a chance to simulate in TINA TI for the input wave form you provided and below is what the output looks like for gain = 4V/V. for 1GHz, 7GHz 

    1GHz:

    7GHz:


    sbom919b (2).TSC
    At 7GHz you could definately see the Gain reduces as expected from datasheet. I am also attaching the TINA sch file. 

    Regards,
    Hruday