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LMH5401 as an inverter

Timothy Starr
Expert 2445 points
Other Parts Discussed in Thread: LMH5401

Hello-

We'd like to use the LMH5401 to receive a single-ended input from 0 to -1V, with fast negative-going pulses into a 50 Ohm termination resistor. We want to invert the signal so that we can feed into a high speed ADC, with a gain of -1.5V/V.

Figure 60 in the data sheet shows a possible solution, and the gain is described as 4V/V. But isn't it actually -4V/V, since the input is fed to the inverting input of the amplifier?

Thanks and Best Regards,

-Tim Starr on behalf of GG@ES

  • 0
    TI__Genius 15975 points

    Hi Timothy,

    Yes, you are right. When driving the LMH5401 in single-ended configuration like the Figure 60 in the datasheet, the same output will have 180' (-1) phase inversion with respect to the output which is not driven on the input side. As a result, you could say that the gain is -Av or (-4V/V based upon Figure 60) .

    However, the LMH5401 by itself is not stable for noise gain less than 2V/V. As a result, the device needs to be compensated externally using shunt capacitor and resistor by increasing the noise gain for gains below 2V/V. You could refer to the TI design: http://www.ti.com/lit/ug/tiduai1/tiduai1.pdf which walks through stabilizing the LMH5401 for gains less than 2V/V.

    Best Regards,

    Rohit