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high voltage amplifier with wide frequency range

Discussion in 'Electronic Design' started by Helmut Sennewald, May 13, 2008.

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  1. Hello Steff,

    Apex Microtech makes high voltage amplifiers.
    http://apex.cirrus.com/en/products/apex/index.html
    Distributor in Germany is Hy-Line.
    http://www.hy-line.de/
    I think even the fastest of their amps is too slow for your application.
    Required slewrate:
    150V*2*pi*4e6 = 3800V/us

    Last but not least, if you have a cable at the amp-output,
    it will have at least 0.5pF/cm. The 2pF load you have in mind
    is nothing compared to the capacitance of a possible cable.

    Best regards,
    Helmut from Germany
     
  2. Guest

    Hi,

    I have to design a high voltage amplifier, that should amplifiy a 3Vpp
    sinussodial signal up to 300Vpp. Furthermore the amplifier should work
    with linear phase over the whole frequency range from 100kHz to 4 MHz.
    The load of the amplifier will be a capacitance from 2pF and a
    resistor with changing values higher than 100MOhm. The current, the
    amplifier should provide, is only up to 500mA. I need this amplifier
    for a measurement application.

    I tried in the last days a cascode amplifier which was able to amplify
    the sinussodial up to 300Vpp. The great Problem is, that the sinus
    will be deformed. Additionally the phase isn't linear over the
    interesting frequency range. I also tried a complentary booster, but
    this couldn't provide the high voltage.

    Is there anybody, who can help me?

    Thanks for your help,
    Steff
     
  3. Guest

    Sorry, there was a mistake from me. The maximum current I expect is
    50mA.
     
  4. mike

    mike Guest

    Sinusoids have only two parameters, amplitude and frequency.
    Sometimes it's easier to generate them than to amplify them.
    If your signal is a modulated sinusoid, you may find that you
    need bandwidth in excess of the carrier frequency.

    Look into some of the techniques being proposed for cellular
    base station amplifiers to achieve high linearity with
    efficiencies higher than what's obtainable with Class A.
     

  5. Hello Steffen,
    just one more idea to reduce the high voltage requirement
    for the transistors. Try to use a good transformer.
    Therefore you should look in the RF-handbooks for wide
    bandwidth power amplifiers.

    Best regards,
    Helmut
     
  6. Paul

    Paul Guest

    What do you mean by "linear phase"? Are you specifying a
    maximum phase shift over your frequency range, or are you asking for a
    specific type of filter response and group delay response?
    If you want very little phase shift, you may be asking for
    considerable current drive. For a 5 degree phase shift, your amplifer
    effective output impedance needs to be between 1500 & 2000 ohms.
    That means you need to be able to drive betwwen 150-200 mA at 4 MHz.
    Maybe the 500 mA requirement wasn't as silly as first sounded.
    To be able to keep the amp from slew rate limitation, you need
    about 8-10 mA, but at that limit, your phase shift will be pretty bad.
    The 19Kohm reactance fo the 2pf at 4MHz means that a source impedance
    of 19K will cause a 45 degree phase shift, and a -3db drop in signal
    amplitude. Is that within you requirements?
    Since you are making measurements, you should tell us what the
    accuracy is in terms of amplitude, phase shift, and linearity. If the
    wave form you're measuring is sinusoidal, these are all you might
    need. For complex waveforms, more requirements would have to be
    specified (ie., group delay, overshoot, etc.).

    -Paul
     
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