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LMH5401EVM: Common mode voltage vs output voltage swing

Part Number: LMH5401EVM
Other Parts Discussed in Thread: DAC38J82

Using the LMH5401EVM in conjunction with the DAC38J82 with Rg=50 ohm, Rf=374 ohm, Ro=23 ohm, Vs(+)=2.5V, Vs(-)=-2.5V, PD=Gnd, Vcm=0.8V.

The nominal baseband input DC common-mode voltage used in the characterization of a wideband quadrature modulator with fractional-N PLL and integrated VCO is 0.45V which should be externally applied.  The nominal baseband input AC voltage is 1.3Vpp differential.  I have some waveforms I can show offline but when the Vcm is set to 0.8V the customer sees 0.45V on the output sinwave?  How can we increase this?

Regards, John Garrett, TI-AFA

  • Hi John,

    Would it be possible for you to attach a circuit diagram of the test setup?  Is the LMH5401EVM driving the quadrature modulator with Vcm = 0.8V? Do you have the part number for the quadrature modulator? Looking at the waveforms would be helpful if you can share it offline.

    Best Regards,