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LMH6552: LMH6552 gain-bandwidth calculation

Hale Tan
Expert 3260 points
Part Number: LMH6552
Other Parts Discussed in Thread: TINA-TI

Hi team,

Does the chip support (2-3V) Vpp 1.25GHz freq Vin to 8V Vpp 1.25GHz freq Vout application scenarios? And could you tell how to calculate it?

  • 0
    TI__Genius 16756 points

    Hello Hale,

    Are you deciding between a 2-3Vpp input signal, or will the input signal vary?  Do you have a target gain for the device?

    Please view page 5 of the LMH6552's electrical characteristics table; there is a specification for Large Signal Bandwidth (LSBW).  This spec shows that operating the LMH6552 in higher gains reduces the available bandwidth; the LMH6552 is a current-feedback amplifier and does not have the same gain-bandwidth dependence as a voltage-feedback amplifier.  For these datasheet values the feedback resistor (Rf) is set to equal the gain-setting resistor (Rg) at 357 Ohms. 

    I would recommend using the LMH6552 SPICE model to simulate your circuit design.  With SPICE simulation you can verify the device's limits and performance in your application.  You can test your preferred supply voltage, gain configuration, and signal bandwidth to examine the part's performance.  On 10V supply set up as +/-5V supplies, the 2-3Vpp input signal does not violate the input common mode range if the device has zero DC bias voltage (that is, the input signal is AC-coupled or has no DC offset).  The output swing limitation is provided as a differential output swing limit at 15.4V.

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    TI__Expert 3260 points

    Thanks Saebeler,

    I didn't find the pspice model, could you share it with me?

  • 0 in reply to Hale Tan
    TI__Genius 16756 points

    Hello Hale,

    Please find the model below.  If you have questions or run into issues using the model, please let me know.  You may also send me your SPICE circuit once you have completed it, so that I can help look it over.

    snom155.zip

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    TI__Expert 3260 points

    Hi Alec,

    I can't open the model with Pspice. Could you show how to open and run it?

  • 0 in reply to Hale Tan
    TI__Genius 16756 points

    Hello Hale,

    I do a quick overview of this process in another thread: https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1272956/lm7372-orcad-capture-pspice-model/

    Please see the attached .olb file, which I retrieved from the .mod file by using the OrCAD AMS Model Editor.  There is a model import wizard, as well as the ability to "Open" -> "Export to Capture Part Library" for .mod files.  This results in a quick translation into PSPICE-usable .olb files.

    LMH6552.OLB

    Please review the files for consistency and let me know if you encounter any errors.

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    TI__Expert 3260 points

    Hi Alec,

    Is this a simulation file? If so, I can't run this file. I just get a file as below:

  • 0 in reply to Hale Tan
    TI__Genius 16756 points

    Hello Hale,

    Please try the files present in this zip folder:

    snom155_edited.zip

    I may have sent the incorrect file previously.

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    TI__Expert 3260 points

    Alec,

    I am sorry that I still find no simulation file.

    How to do the simulation?

  • 0 in reply to Hale Tan
    TI__Genius 16756 points

    Hello Hale,

    I will build a simulation file and send that file; there is an issue with how my generated model attaches to an Isabel symbol for you. 

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    TI__Expert 3260 points

    Hi Alec,

    Thanks. How long does it take you to build this file? The customer is asking the answer to the question.

  • 0 in reply to Hale Tan
    TI__Expert 6050 points

    Hi Hale,

    Attached below is a simulation file with the LMH6552 model.

    Please let me know if you have any issues using this.

    LMH6552.zip

    Thanks,

    Nick

  • 0 in reply to Alec Saebeler
    TI__Expert 3260 points

    Hi Alec,

    I find a TINA model and simulation is as below:

    According to the simulation, it seems that it can't meet the customer requirements. Could you please help to find one device which can meet (2-3V) Vpp 1.25GHz freq Vin to 8V Vpp 1.25GHz freq Vout?

  • 0 in reply to Hale Tan
    TI__Genius 16756 points

    Hello Hale,

    Could you share your input signal(s) used in your simulation?  Also, are you using the updated model we provided in this thread in TINA-TI?  The built-in model in TINA-TI may be outdated.  You can check this by viewing 'Enter Macro' when interacting with the TINA-TI op-amp.  The model date on the website model is present in the file, which states 2008 as the model year.

    Is the input range of 2-3V a single specific voltage, or is the customer sending a varying 2-3V signal into the amplifier?

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    TI__Expert 3260 points

    Alec,

    Hale Tan said:

    According to the simulation, it seems that it can't meet the customer requirements. Could you please help to find one device which can meet (2-3V) Vpp 1.25GHz freq Vin to 8V Vpp 1.25GHz freq Vout?

    As this picture shows, the differential input voltage is the yellow one and the green one. Their respective voltage amplitude both are about 1V. 

    And I tried the new simulation, as below:

    1.25GHz:

    125Mhz:

    It seems that LMH6552 can't amplify the 1.25GHz signal 2Vpp to 8Vpp.

  • 0 in reply to Hale Tan
    TI__Expert 3260 points

    The simulation schematic is as below:

  • 0 in reply to Hale Tan
    TI__Genius 16756 points

    Hello Hale,

    Thank you for the additional data and simulation results.  We are running into the performance limits of the LMH6552.  As the LMH6552 has to drive larger output voltages at higher gains, the bandwidth of the device decreases.  Driving 8Vpk-pk is not going to be possible with the LMH6552 at 1.25GHz; in order to utilize the LMH6552 at such high bandwidths, the device needs to either drive smaller output signals or operate at a lower gain.

    I checked our portfolio of amplifiers; the other high-speed options operating above 1GHz have much lower supply voltages available than the LMH6552.  Could you help me understand what the order of priority is for the following features:

    - Bandwidth/speed

    - Gain/amplification

    - Output voltage drive/swing

    Additionally, you may want to try different RF values as the LMH6552 is a current-feedback amplifier; amplifiers with this architecture are sensitive to optimal RF values.  The datasheet uses RF = 357 Ohms for example in the Electrical Characteristics tables.

    You may need to evaluate what aspects of the design are absolutely required, as it is difficult to swing such a large output signal at 1.25GHz.

    Best,

    Alec