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LMH6882: What is the actual max output range for output pin?

Alex Lewald
Prodigy 20 points
Part Number: LMH6882

Hello,

I'm using the LMH6882 to amplify input from a piezo (single-ended input) to a differential output. We ran into a clipping issue that was not at the max value of the ADC, and after probing I learned that the output pin on my design only swings ~730mV to ~4.27V or a Vpp of ~3.54V. 

I'm confused because the datasheet (SNOSC84C –AUGUST 2012–REVISED MARCH 2013) page 3 says the maximum voltage output swing is 6Vppd on a 5V supply. Maybe I am not properly understanding the meaning of Vppd but some clarification on this would be appreciated.

Attached is a scope image of the differential output with a 2Vpp input signal on 26dB (max gain) mode. I'm intentionally trying to clip the output to understand the maximum range I can get here. Thanks!

  • +1
    TI__Genius 11455 points

    Hi Alex,

    This is a commonly confused spec and it is does get tricky. The reason we are using this differential output spec is because the outputs are differential outputs for this device. The best way to understand a differential signal is to look at a graph. If you reference the image below, you will see the individual outputs (Vout+ and Vout-) and a differential signal (Vdiff). By definition a differential signal is (Vout+) - (Vout-), where Vout+ and Vout- are complementary signals. If you apply the same math, you will see how Vdiff is equal to this difference in the image below. The major benefit of a differential signal is that it doubles the peak-to-peak signal range compared to the individual output's peak-to-peak range. In this example, the Vpp of each individual output is only 1V but the Vpp of the differential signal is 2V. 

    Best Regards,

    Ignacio