• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 47 subscribers
  • Views 1649 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Charge Amplifier

Mir
Intellectual 485 points

Other Parts Discussed in Thread: LMC6041

Hi, Require urgent clarification.

I am using a charge to voltage convertor with a piezoelectric sensor. I am modeling the sensor as a ac-voltage source in series with a capacitor (~80pF). My feedback capacitor of the charge amplifier is 220pF//49M ( to get 15Hz lower cutoff). The amplifier works on +/- 15V. Can my charge amplifier saturate in either its output or input?

In this regard, my doubts are: What is the source of charge for the piezo sensor? Can it develop infinite charge? Is the charge developed, in any way, limited by the supply voltage (i.e., C (of sensor) = 80pF, maximum supply voltage is +/-15V, so maximum charge can be Q = CV = 80pF * +/-15V)? In this way, if my input saturates can my output get limited?

Thanks and regards.

  • 0
    TI__Genius 12375 points

    Mir,

    The "source of charge" of a piezoelectric sensor is the electrons in the material of the sensor itself. When these sensors are distorted in some way, electrons are "pushed out" of the material temporarily and flow out into the amplifier where they are converted from a current to a voltage. Strictly speaking the sensor cannot develop infinite charge because the material it is made out of only contains a finite number of electrons, and not all of these electrons are free to be pushed out of the bulk material when it is distorted. However, that is not to say that these sensors can't develop a very large amount of charge which can saturate the amplifier. The charge produced by the sensor is not a function of the supply voltage.

  • 0 in reply to John Caldwell
    Prodigy 10 points

    Hello sir,

    Iam designing an charge amplifier using lmc6041 it working well but the gain in lower frequencies 0 to 100Hz become low how can i increase the gain

  • 0 in reply to Manpreet singh
    Intellectual 485 points

    Hi Manpreet,

    The gain is low in the lower frequencies possibly due to the lower cut-off frequency sitting very high. The laplace transfer function of the charge amplifier configuration tells that I/p RC combination and fd/bk RC combination introduce a pole each. Either pole can be used to fix your lower cutoff by 1/(2piRC) - preferably the fd/bk RC since fd/bk R tends to be large.

    But, cutoff also depends on other factors too. If the above doesn't help, you could post your circuit schematic & test setup as useful information for troubleshooting.

    Mir