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LM7171: low I/p amplifier circuit design help.

paulrez
Prodigy 40 points
Part Number: LM7171
Other Parts Discussed in Thread: OPA354, THS4031

I am looking to design a circuit to amplify a 10micro volt ac signal @1MHZ, by a gain of 10 then 100 using two lm7171, simulated it works ok but in reality is noise is a problem at a such a low I/p. I can put a 5mv signal in but anything lower and the ic self oscillates. Any advice on controlling the noise problem please? Or is there a better ic for this?

  • 0
    TI__Mastermind 23226 points
    Hi Paulrez,

    Certainly, noise is a problem while detecting such low input amplitude of 10uV. The LMV7171 has an input voltage noise of 14nV/rtHz, which is a bit high for low noise applications. You could instead use the THS4031 which has input voltage noise of 1.6nV/rtHz and should help in detecting low input signal levels. If you are flexible on the IC supply voltage, then the OPA354 should also be a good option. Also, one way to decrease noise at the output is by using the larger gain (x100) in the first stage of the amplifier followed by the x10 gain stage

    Best regards,

    Sean
  • 0 in reply to Sean Cashin
    Prodigy 40 points

    thanks for your reply, very useful information I will look into these options.