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A question To Jim Thompson

Discussion in 'Electronic Design' started by Habib, Jun 24, 2013.

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  1. Habib

    Habib Guest

  2. Guest

    Don't forget to connect power to the OpAmps!!

    TomC
     
  3. Habib

    Habib Guest

    Ok i missed the Vout node, thanks.

    Regards, H.
     
  4. Joerg

    Joerg Guest


    You can just attach your LTSpice file here, or copy it into your post.
    Then people can try to massage it and re-post the corrected version, one
    that (hopefully) runs.
     
  5. Jamie

    Jamie Guest

    What do you need that for? I thought everything was wireless these days?

    Jamie
     
  6. miso

    miso Guest

    In chip design, you minimize the number of "floating" nodes, where in
    this vernacular floating means not being driven by a low impedance
    circuit, i.e. op amp. The parasitics will ruin the circuit response much
    more than the phase effects (say Q enhancement) of the opamps.

    Generally you have one op amp (or more!) per pole in integrated circuit
    designs. And leapfrog design rules!
     
  7. Habib

    Habib Guest

    Ok i'll remember next time.
     
  8. John Smith

    John Smith Guest

    For no reason other than curiosity, what is the maximum frequency that a
    circuit like this could sensibly be used at? Assuming suitable OpAmps and
    layout.
     
  9. Hi Jim, I've never done a notch thing, But I assume it's like a bandpass turned upside down. In which case the GBW requirements are going to be something like
    Fmax * Q ~ GBW/10

    George H.
     
  10. Hi Tim, well I'm not going to try and write down the loop equations. I assume you did them correctly. But my 'simple minded' understanding is that everything to the right of C2 looks like an inductor. (Maybe I have this wrong?) So it's a series RCL. Now if I was to take the output from the otherside of C2, then it would be a bandpass filter... And that's where I got the factor of Q in the max frequency estimate. Hey, if this type of gyratorcircuit can give me a bandpass response without the Q factor that would benice to know.

    George H.
     
  11. Hey that's neat Jim! So with one circuit you change the input 'tap' and get all three outputs from the same point!
    "scratch, scratch".. Scribbling in the back of my notebook.

    So for the figure on page five where you add a series resistor to the C1 branch are the colors for the same GBW of the previous graphs.
    Green = 100kHz
    Red = 200kHz
    Blue = 500kHz.
    (I'm even more amazed if you can make a 100kHz GBW opamp give a BP responsewith a Q of 10 at 20kHz.)

    A recent project had a 80 kHz Q=10 filter (state variable). In the firstgo-round I had 8MHz GBW opamps in it and the Q-enhancement was something over 30% (I can't recall the exact numbers.) They were replaced with AD825's (26MHz.)

    I guess the difference might be that in the SV filter a Q of 10 is also a gain of 10, whereas your filter looks to have a gain of one.

    Thanks again,

    George H.
    (now waiting on the next high Q filter need)
     
  12. Grin... Well for sure I have more faith in you than in me.
    I guess I could do it, and maybe get it right. My big problem is that making sense of the resulting complicated algebra expression would take me even longer.

    It's hard for me to look at it and see where the important bits are.

    George H.
     
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