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Wideband amp circuit

Discussion in 'Electronic Design' started by Luke Simmons, Jun 21, 2007.

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  1. Luke Simmons

    Luke Simmons Guest

    Can someone please point me to a circuit diagram for a wideband amp
    with the following specs or there about? It will be used with a signal
    generator only (basic and modulated waveforms), not for
    communications, etc.

    100Hz to 2MHz bandwidth
    40Vpp output into 50 ohms

    Thank you for any assistance.

    Luke Simmons
  2. Robert Baer

    Robert Baer Guest

    DC frequencies.
  3. Winfield

    Winfield Guest

    That's +/-20V at +/-400mA = 8W peak, right? And it requires
    a 250V/us slew rate. The APEX PA09 amplifier can do that if
    compensated for high-frequency G = 100 (with a loop-gain
    reducing R + C across the + and - input pins).
  4. tlbs101

    tlbs101 Guest

    One of these with an output current booster will do the trick, plus
    it's much cheaper than anything from Apex (although Apex products are
    great, too):
    or, the app notes in the datasheet show how to parallel 2 of them for
    double the current (which meets your requirement). And 2 OPA552s are
    still cheaper than 1 Apex amplifier.

  5. The Buur-Brown opa552 is a nice part, able to be powered
    from +/-30V supplies. But sadly it's got a slow slew rate
    of only 24V/us. If Luke wants 40Vp-p at 2MHz, then he'll
    need S = 2pi f A = 251V/us slew rate, as I said, which is
    10x faster than the opa552. Sorry.

    One part that might do the trick is Analog Devices' ad815ay.
    This can only be powered from a maximum of +/-15V, but it's
    a dual amplifier and when used in bridge configuration it
    can deliver +/-25V at +/-500mA, with a 900V/us slew rate
    (I was able to pick up a supply of their 15-pin SIP heat-
    sink tab-style power package before they discontinued it).
  6. Fred Bloggs

    Fred Bloggs Guest

    That's just a simple CE with a simple simulated inductor step-down
    load...piece of cake. Take your question to the Basics ng.
  7. Winfield

    Winfield Guest

    Nowadays, with high-performance DC wideband amplifiers
    available, it's tempting to use one of them instead of a
    traditional class-A amplifier. But Luke could consider
    a class-A amp amplifier running with a Vce of roughly
    25V and a current of roughly 500mA, which would have a
    quiescent power dissipation of about 12.5 watts. Then a
    100-to-900mA collector-current excursion would deliver
    +/-20V into a 50 ohm load. The collector-supply inductor
    would have to be greater than 80mH (that's pretty large!)
    for a 100Hz low-freq rolloff. The output-node capacitance
    would have to be under 1600pF for a 2MHz high-frequency
    rolloff. No doubt the large 80mH choke would deliver some
    of that, so a second smaller series inductor would be wise.
    There's more to consider, emitter degeneration, input gain,
    class-A biasing, etc., but it's evening and duty calls.
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