Ultrasonic amplifier/filter problem

Discussion in 'General Electronics Chat' started by mskh744, Dec 2, 2013.

  1. mskh744

    Thread Starter New Member

    Dec 2, 2013
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    I'm designing an ultrasonic receiver circuit that should deal with a 10 mv signal( may be less !! the limitation here is due to the transducer itself http://www.ram-e-shop.com/ds/general/Ultra_Soinc.pdf ).

    The signal is 40 Khz sinusoidal pulse-modulated signal (pulse duration=1.8 s; pulse width=83 ms) , and I used LM358 for multistage amplification, but I ended up after 4 stages of inverting amplifier configuration (each stage's gain is supposed to be 100; meaning R2/R1=100) with a 1 volt p-p signal and a 0.75v p-p noise !!

    I need to get a 0-5 volt signal when I receive the 83 ms pulse, but I'm starting to think its not possible using commercial amplifiers.

    Any suggestions on the opamp selection itself??

    I also tried to use multistage BJT amplifier (CE configuration) and the signal to noise ratio was much better than the opamps, but the gain was not sufficient!

    I tried to use a band pass filter at 40 khz to eliminate the noise, but no active filter using lm358 could be precise and a passive RC or RLC filter would kill the mv signal I want.

    I used Multisim simulator before I implemented the circuit and it showed some satisfying results. However, when I use the discrete components (whose reliability is not guaranteed) and measure the results on an oscilloscope, its rather depressing results.

    Any help with the amplifier or filter circuit would be much appreciated.
     
  2. sirch2

    Well-Known Member

    Jan 21, 2013
    1,008
    351
    Here's an ultrasonic circuit I adapted from others on the Web. It works differently to what you propose, there are two stages of amplification which then dives a schmitt trigger to get 0 or 5v on the output.

    [​IMG]
     
  3. mskh744

    Thread Starter New Member

    Dec 2, 2013
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    Thanks sirch2 for the help, though the Schmidt trigger won't help in my application.
     
  4. LvW

    Active Member

    Jun 13, 2013
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    100
    What does this mean (...could be precise..)?
    Of course, you can design a bandpass filter around 40 kHz.
    Question: Are you required to use LM358?
    In this case, indeed a pole frequency of 40 kHz is rather problematic.
    However, this should be possible using an opamp with a larger gain-bandwidth-product.
     
  5. sirch2

    Well-Known Member

    Jan 21, 2013
    1,008
    351
    Just interested, why can't you use a Schmitt trigger?
     
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