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LMH6505: Question about inverting gain voltage control

Cameron Wutzke
Intellectual 2801 points
Part Number: LMH6505

I am working on evaluating the LMH6505 (currently on eval board) as a replacement for the ML1350. I had a quick technical question regarding if the LMH6505 has the possibility of inverting the Gain Control voltage scale. Such as in its current configuration, to increase the gain you increase the voltage from 0V to 2V. Is it possible to increase the Gain by going from 2V to 0V. From what I have seen on the data sheet it did not mention it and I just wanted to make sure.

I am trying to use this in a AGC circuit,  at 45 MHz frequency with around 60 dB of gain in an SOIC-8 package, much like the ML1350.

 

If you need any more information just let me know.

thank you for the help!

cameron 

  • 0
    TI__Intellectual 2801 points

    I should add the motivations behind this request, the controller used to control the gain voltage for this chip is also used for other components that follow a similar high to low voltage sweep and we were hoping to get around adding additional op amps to this design to reverse the voltage as space is very limited

  • 0 in reply to Cameron Wutzke
    TI__Expert 6050 points

    Hi Cameron,

    Due to the internal circuitry of the LMH6505, it is only possible to increase the gain as you increase the Vg voltage from 0 to 2V. There is no way to invert the gain control voltage scale. This configuration was chosen to improve the performance of the device, as discussed on page 17 of the datasheet in the "Improving the LMH6505 Large Signal Performance" section.

    Unfortunately, the best solution is adding an inverting amplifier to the driver stage of the gain control voltage as you just mentioned.

    Thanks,

    Nick