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high speed full wave rectifier

Discussion in 'Electronic Design' started by Terry Given, Sep 20, 2007.

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  1. Terry Given

    Terry Given Guest

    I've been playing with full wave rectifiers. one of the nicest designs
    is the EDN idea on Jims website. but for 20MHz operation (200kHz
    sawtooths) the opamp is a bit problematic - its response is all about
    how the opamp comes out of saturation, even with the extra diode.

    any thoughts?

    Cheers
    Terry
     
  2. Jim Thompson

    Jim Thompson Guest

    WHAT saturation? Are you tying to run it as single-supply? Don't ;-)

    ...Jim Thompson
     
  3. Terry Given

    Terry Given Guest

    Brain engaged, mouth (OK, fingers) now in neutral - as opposed to the
    other way round.

    1N4148s are not, it seems, infinitely fast :)

    doh.

    Thanks Jim
     
  4. Jim Thompson

    Jim Thompson Guest

    Nope ;-)

    And it takes substantial OpAmp slew-rate at 20MHz to get good
    performance.

    I've only used the design up to around 1MHZ.

    ...Jim Thompson
     
  5. John Larkin

    John Larkin Guest

    Several people are now making RF detector chips, with linear or log
    outputs, and bandwidths into the GHz.

    John
     
  6. Terry Given

    Terry Given Guest


    interestingly enough, the datasheet for a schottky BAT54 has a 5ns Trr ?!

    a BAT81 is pretty good though.
    an LM7171 does a reasonably good job. an LM6152 is terrible. and yeah,
    its the slew rate all right.
    interestingly enough, when I go for a 200kHz bipolar sawtooth, an LM6152
    is almost as good single-supply as with bipolar supplies, and is not
    much worse than the LM7171. But I'll stick in a bipolar supply anyway,
    it'll only cost me $0.20 or so, and this is a proof-of-concept thing

    the application is a crazy smps topology that puts terrible demands on a
    CT (50Hz - 250kHz BW) - so bad I havent made one work well yet. HF or LF
    performance, but not both.

    And the current is bipolar, so a DCCT isnt really feasible - although a
    current-output (eg LEM LAH-xx) DCCT can in theory drive a schottky
    bridge, in practice the phase reversals cause evil R-R glitches -
    probably because when all diodes are off the impedance gets very high.
    no amount of snubbing or (realistic) loading really helps. a shame
    really, cos it was a nice (OK, kinda nasty) idea....

    when we go to an ASIC it'll get a lot easier (it becomes the chip
    designers problem ;). unless we use the same french idiots who've made a
    hash of the other ones. I've suggested we use a guy in Arizona, it'll
    make arguments about politics that little bit more interesting :)

    Cheers
    Terry
     
  7. Tim Williams

    Tim Williams Guest

    Those ratings are kinda weird.. but I suppose it makes practical sense to
    report whatever looks like it. Reverse recovery could be modelled as a big
    capacitance at Vf ~= 0V, after all...

    The thing that doesn't make sense to me is the schottkies that say 100ps
    and some specific test (what was that called..) that doesn't exist except
    perhaps in the annals of the IEEE. What good is a number when you aren't
    told WTF it is!?

    Tim
     
  8. Genome

    Genome Guest

    "unless we use the same french idiots who've made a
    hash of the other ones"

    Suck butt Nigger.

    DNA
     
  9. Fred Bloggs

    Fred Bloggs Guest

    Tektronix has a patent on a technique using feedforward compensation
    specifically for sawtooth rectification at high frequency...
     
  10. Terry Given

    Terry Given Guest

    piss off you whining pommy git
     
  11. Genome

    Genome Guest

    Immigrate to Australia before you call me a pommy git, Kiwi.

    DNA
     
  12. Terry Given

    Terry Given Guest

    its the term we use, too :)

    the first time I referred to myself as a Kiwi, my Murrcan friends were
    bemused - was I a small hairy fruit?

    Cheers
    Terry
     
  13. Genome

    Genome Guest

    Right... That's enough carbon tax. Us French people are not interested
    about how curly the hairs on your bollocks are. You do not have enough
    Atols.

    DNA
     
  14. See bottom of page 19 of the Analog Devices AD8036 datasheet. It does
    what you want within the restriction of 5 volt power supplies. Or do
    you want Jim's circuit at 20MHz?

    http://www.analog.com/UploadedFiles/Data_Sheets/AD8036_8037.pdf

    GG
     
  15. Terry Given

    Terry Given Guest

    How do the french pick their rugby players?

    they simply say "yoplait, yoplait, yoplait"


    I doubt there is much left of mururoa at all.

    Cheers
    Terry
     
  16. Terry Given

    Terry Given Guest

    Hi Glenn,

    thanks, that was one solution I came up with when I went a-googling.
    turns out I just needed to pick better diodes, and I can do it with a
    variety of opamps. I'd have given my left nut for that clamp amp in 1992
    though, when I designed a (not too flash) output stage for a pulse
    generator I built.....

    Cheers
    Terry
     
  17. Genome

    Genome Guest

    Pah! Even without prompting he insults our rugby team. We will come
    along and do carnage.
    Please advise about the creation of the north or south atoll.

    DNA
     
  18. Terry Given

    Terry Given Guest

    it all sounded a bit fishy to me :)

    Cheers
    Terry
     
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