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DC to >100MHz Wideband Amp

Discussion in 'Electronic Design' started by Noise Bird, May 30, 2005.

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  1. Noise Bird

    Noise Bird Guest

    Hi!
    I am looking for a DC to >100MHz wideband amp, single supply circuit to
    build to digitaly drive a PIC microcontroller.
    It would be great to have one circuit, but not absolutely necessary.
    Even hints using available ICs would be greatly appreciated.
    Thanks.
     
  2. Mac

    Mac Guest

    I don't exactly know what you mean by "digitally drive a PIC..."
    Maybe the LM6702 would suit your needs?

    --Mac
     
  3. What gain?

    What input impedance?

    What DC offset voltage is acceptable?

    How close does the signal need to get to the rails?

    What do you mean by "digitally drive"?

    What supply voltage?
     
  4. Tim Shoppa

    Tim Shoppa Guest

    am looking for a DC to >100MHz
    The jellybeam solution for small signals is a MMIC. It'll have way
    more bandwidth than you need. But they're pretty much unconditionally
    stable by themselves.

    You said DC, but didn't say anything about gain, voltage ranges, etc.,
    so I feel justified in recommending the MMIC :). Biasing the input
    will be your problem.
    I have no clue what this phrase means. Are you building a frequency
    counter maybe? There are a lot of examples of input-conditioning
    circuits for frequency counters on the web. Some of them even work!

    Tim.
     
  5. Noise Bird

    Noise Bird Guest

    Thanks for your message.
    I'm finally getting back to this.
    Sorry I wasn't clearer before.

    The input will be about 100Mv Hi impeadance, say 100K and the out put
    is to drive a TTL input to a counter.
    So the offset is negligble as long as the output swings from roughly
    ground to 3.5v, TTL levels.
    The available supply is 5 to 6VdDC 100Ma.

    Thank you very much.

    Sincerely,

    Dave
     
  6. Noise Bird

    Noise Bird Guest

    Thanks for your message, Mac.
    I'm finally getting back to this.
    Sorry I wasn't clearer before.

    The input will be about 100Mv Hi impeadance, say 100K and the out put
    is to drive a TTL input to a counter.
    So the offset is negligble as long as the output swings from roughly
    ground to 3.5v, TTL levels.
    The available supply is 5 to 6VdDC 100Ma.

    I'll look into the LM6702

    Thank you very much.

    Sincerely,

    Dave
     
  7. Noise Bird

    Noise Bird Guest

    Thanks for your message, Tim.
    I'm finally getting back to this.
    Sorry I wasn't clearer before.

    The input will be about 100Mv Hi impeadance, say 100K and the out put
    is to drive a TTL input to a counter.
    So the offset is negligble as long as the output swings from roughly
    ground to 3.5v, TTL levels.
    The available supply is 5 to 6VdDC 100Ma.

    I gave the MMIC a look, but need to spend more time researching it.
    Plus search for counter input circuits as you mentioned.

    Thank you very much.

    Sincerely,

    Dave
     
  8. Jim

    Jim Guest


    You might want to investigate the Linear Technology IC
    LT1016 which we use as a squaring circuit for a low level sine wave

    I am not certain as to it's upper frequency limit, but in general it would
    serve as a sine to TTL converter nicely.

    Of course, you might want to make a FET follower to keep the RF input
    high impedance.


    Jim Pennell
     
  9. He said 100 MHz from 100k. With the LT1016's 3.5 pF input capacitance that
    gives a -3dB frequency of 455 kHz. But I doubt that he means that.

    Jonathan
     
  10. colin

    colin Guest

    would a cmos inverter do ?
    maybe a simple level shifter to get the input to about half the supply
    voltage.

    Colin =^.^=
     
  11. Jim

    Jim Guest


    OUCH. Yep, 3.5 pF would be a problem. We are using it at 10 MHz,
    and for our
    purposes, the sensitivity is quite good. Although, we do use an input
    filter network
    and I will analyze it to see if we are absorbing the 3.5 pF into the filter.


    Jim
     
  12. Fred Bartoli

    Fred Bartoli Guest

    Unless some _very_ special case, it can't be 100k @ 100MHz : this is only
    0.016pF

    He'd better refine his specifications.
     
  13. Fred Bloggs

    Fred Bloggs Guest

    Or maybe he is unfamiliar with the concept of a comparator and is using
    the 5th harmonic rule for reproduction of a 20MHz pulse train- but even
    then 100K seems high- and notice that DC makes no sense at all since he
    mentions nothing about level or gain into the PIC- just anything that
    crosses logic thresholds.
     
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