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LMH6629: Minimal voltage sensitivity of an amplifier

xyz xyz
Intellectual 1000 points
Part Number: LMH6629
Other Parts Discussed in Thread: LMH6552, , TLE2037

I have a very small signal within 50uVp  with the frequency range of 10KHz to 10MHz.

I'm gonna amplify it with LMH6629 with a gain of 40 or more. finally I want to sample it with a 14-Bit ADC. the ADC driver is LMH6552.

but I'm thinking of How should I calculate the minimal voltage sensitivity for an amplifier stage? even I could do it another problem is output offset voltage :|

if I want to use an ac coupling using a capacitor I have another problem due to the input stage of ADC driver is 50Ohm :| bcoz fc=1/(2*pi*50*Ccoup)

please guide me is it necessary to use cascade amplifier stages? bcoz the FSR or ADC is 1vpp.

 

Regards

  • 0
    Intellectual 1000 points

    you see I could remove the offset voltage very effectively as follow:

    the output offset voltage is below 20pV! (the input voltage is 100nV!) even I can amplify a smaller signal.

    the step response is excellent

    the noise performance and linearity are excellent

    But there is a problem!!!

    step response:

    the problem is: (the Bandwidth of close loop response)

    at the frequency between 10MHz to 20MHz I see a drop voltage.

    if I zoom in at the above pic:

    the root of this problem is the DC feedback. if I put a resistor in series with 1uF in the negative feedback of LT1037 the problem will be disappear (not completely):

    what should I do?

    Thanks

  • 0 in reply to xyz xyz
    TI__Genius 15975 points
    Hi,

    I think that you might be limited by the GBW product of the LT1037 which is causing a null in the frequency response because its output is no longer low-impedance beyond the 3-dB BW. You might want to replace the LT1037 with TLE2037 and see if the null disappeards.

    Best Regards,
    Rohit