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piezo transducer signal amplification

Discussion in 'Electronic Design' started by desufnoc, Jan 20, 2008.

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  1. desufnoc

    desufnoc Guest

    I wish to use piezo transducer 273-073A to pick up and amplify insect
    activity. What kind of simple circuit would amplify enough for ear
    phones?
     
  2. D from BC

    D from BC Guest

    The gain will depend on how much noise you can tolerate.

    Noise sources can be from induced EMI(ex:hydro lines), intrinsic
    transducer noise and intrinsic op amp noise...
    Possible power supply noise too..

    Most basic would be to use an op amp circuit + head phone driver amp
    module.
    Something more advanced would probably be like a tape head amplifier
    circuit.

    A circuit might pop up with some Goggling..

    I don't know the transducer you're using but that part number reminds
    of Radio Shack numbers.


    D from BC
    British Columbia
    Canada.
     
  3. http://www.thefreedictionary.com/goggling
     
  4. D from BC

    D from BC Guest

    Oopps...
    Maybe I can rescue that..
    How about?
    Goggling at Google. :)

    Got some subs ideas...
    Googlizing...
    Googlization
    Googlyzing
    Googification


    D from BC
    British Columbia
    Canada.
     
  5. Winfield

    Winfield Guest

    To understand piezo microphones, it's useful
    to think of a piece of ceramic, that's going
    to be flexed by an impinging sound wave. The
    first problem is that the acoustic impedance
    of ceramic is so much different than air that
    it'll not interact very well, and only a weak
    signal can be picked up that way. In fact,
    using Google, it appears this transducer is
    meant for use as a contact pickup, e.g. with
    a guitar, piano, etc.

    Second, in case you do want to work with the
    piezo transducer anyway, to analyze its use,
    you only have to realize it appears to be a
    capacitor with its voltage signal in series.
    Resistive loads on capacitive sensors make a
    low-frequency rolloff, so to design your preamp
    you need to know the piezo capacitance and your
    desired low-frequency limit. For example, if
    the capacitance is 150pF (I didn't find the RS
    part's spec), and you wish it to work down to
    50Hz, then the "load" will have to be above
    22 meg-ohms. The answer is to use a JFET-type
    preamp and keep the necessary dc-bias resistor
    at 22M or higher. You can lookup JFET.

    You'll want lots of gain, of course, but we can
    tell you the noise level will be determined by
    a parameter we call voltage noise, e_n, which
    is lowest for JFETs with a large die area.

    There are JFET opamps that are pretty good, but
    discrete JFETs can do much better. If you look,
    you'll find lots written about the subject.
     
  6. MooseFET

    MooseFET Guest


    If you need to go descrete:
    www.interfet.com and look at the IF1801 JFET
    http://www.linearsystems.com and look at the LSK170
    You can also parallel JFETs to get better noise performance. The
    improvement goes as the sqrt() the number of JFETs.

    Depending on the capacitance of the crystal, the current noise of the
    amplifier may also matter. The current noise times Xc gives an
    additional noise.

    As op-amps go, the LT1169 may be about as good as you can do for low
    noise voltage and current.
    http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1009,C1026,P1390,D1297
     
  7. Winfield

    Winfield Guest

    The LT1169 is a nice amplifier, but it's got a
    rather small JFET die area, as evidenced by its
    capacitance, only 2pF. This shows, with its
    moderately-high noise spec, e_n = 6nV.

    As we point out in AoE's lengthy low-noise chapter,
    optimum low-noise performance is had when a JFET's
    Ciss is near to the sensor's capacitance. Sadly,
    it's often hard to reach that goal. For example,
    no opamps are available with anything like 150pF
    of input capacitance, but one of the higher ones
    is Analog Device's AD743, which is 20pF and has
    e_n = 2.9nV, twice as good as the LT1169.

    As for discrete parts, NXP's (Philips) bf862 at
    10pF and 0.8nV is pretty good.

    It's interesting that the bf862 JFET has half the
    capacitance of AD's fine JFET opamp, but instead
    of sqrt-2 more noise, it has 3.6x less noise. My
    suggestion, get a lifetime supply of bf862 JFETs.
     
  8. Joerg

    Joerg Guest


    Lifetime supply? Now please don't tell me that they rang the bell on
    that one ...

    <writing note to self: Get some more BF862>
     
  9. MooseFET

    MooseFET Guest

    There are other JFETs out there:

    The IF1801 is 100pF and 0.5nV/sqrt(Hz)
    The IF3601 is 300pF and 0.3nV/sqrt(Hz)

    The LSK170 is 20pF and 2nV /sqrt(Hz)

    The bf864 has the disadvantage that you can't find it on the NXP web
    site unless you know what to look for.
     
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