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LMP7711: Buffer Requirements

Lindsey Fike
Intellectual 2170 points
Part Number: LMP7711
Other Parts Discussed in Thread: LMH1983,

Previously when working on a LMH1983 circuit it was recommended that I use Epson's VG-4231CB 27.0000M-GGCZ3 for my VCXO because of its smaller size and better phase noise performance. 

My question is since the VG-4231CB 27.0000M-GGCZ3 has a minimum input impedance of 10M, then do I need the LMP7711 buffer?  I think it was only there because the original VCXO recommended by TI was CTS 357LB3I027M0000 which has an input impedance of 10K.

 

Thanks!

  • 0
    TI__Guru* 93105 points

    Hello Lindsay,

    It seems reasonable that if the VCXO input impedance is being increased from 10 kilohms to 10 Megohms that the LMP7711 buffer would no longer be needed. The loop filter has high capacitance so I don't think that directly driving any VCXO input capacitance is concern either.

    Regards, Thomas

    Precision Amplifiers Applications Engineering