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LMH0002: Can RREF be set to reduce output amplitude to between 300mVpp and 600mVpp SE?

jt
Prodigy 100 points
Part Number: LMH0002
Other Parts Discussed in Thread: LMH0397

Is there an RREF value that would allow reducing the SE output swing to be between 300mVpp and 600mVpp?

Regards,

Josh

  • 0
    TI__Guru* 93670 points
    Hi Josh,

    I think i understand what spec you are trying to meet. Minimum LMH0002 single ended output swing is 665mV.
    1). Perhaps you can have a passive 6dB attenuator. However this means this port would be fixed for 300mV to 600mV output swing. Please take a look at the link below for passive attenuator circuit:
    www.radio-electronics.com/.../attenuator-resistor-values.php
    Or negative output could have this attenuator while positive is normal configuration. But either of the output should terminated while the other output is used. I am not sure how reflection would effect this low data rate.
    2). I have checked LMH0397 and output voltage swing can be changed - through register - to be within 0.5 to 0.6V SE swing.

    Regards,,nasser
    I
  • 0 in reply to Nasser Mohammadi
    Prodigy 100 points

    Thanks Nasser!

    This is for an existing board, with 8 SOIC package part -  so I will give the attenuator a try for now.  Does it make sense to install the attenuator after the inductor || 75 ohm resistor, before the AC coupling cap then?

    Regards,

    Josh

  • 0 in reply to jt
    TI__Guru* 93670 points
    Hi Josh,

    That should be fine. Just make sure your attenuator impedance is 75 ohm in and out. Also, since this is low data rate i suppose parasitics would not play a major role here.

    Regards,,nasser