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Chip like LTC1799

Discussion in 'Electronic Design' started by DaveC, Feb 17, 2005.

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  1. DaveC

    DaveC Guest

    Looking for alternate part like the LTC1799.

    Its a variable 1kHz - 33MHz, square wave oscillator. Uses single resister
    to control frequency. 50% Duty Cycle.

  2. Was it too hard to look up the linear website ?
    Special functions, Silicon Oscillators.
    They have a bunch of these parts.

  3. John Larkin

    John Larkin Guest

    TinyLogic schmitt trigger.

  4. DaveC

    DaveC Guest

    Thanks John and Rene for those two rather flippant replies.

    I have been down the Schmitt road but found that for any variable
    resistor / fixed cap combination the frequency was not selectable.

    I was asking for other manufactures of similar chips to the LTC one. If
    you knew off the tops of your heads that would be quite help full, but I
    can of course do my own research.

  5. James Meyer

    James Meyer Guest

    I saw those earlier replies and calling them "flippant" shows a
    remarkably high degree of restraint on your part. :cool:

    Sometimes I wonder if anyone ever reads more than 5 or 6 percent of the
    words in a post before replying.

    The little LTC1799 is, AFAIK, the only part that does what it does. It
    does it very well too, I might add. I can only surmise that you have a good
    reason for wanting an alternate part. Perhaps the PHB you work for has mandated
    that only second-sourced parts can be used in any design.

    Single-sourced parts can sometimes be a pain, but it's a pain you have
    to learn to live with when you are designing on the "bleeding edge".

  6. Guest

    Guest Guest

  7. John Larkin

    John Larkin Guest

    Why flippant? A cmos schmitt will oscillate with a single resistor,
    and the resistor sets the frequency. It might be useful if you don't
    need high frequency accuracy, it's multi-sourced, and very cheap.

    Oh, don't be idea-phobic.
    What's bleeding-edge about a mediocre-accuracy oscillator?

  8. DaveC

    DaveC Guest

    Sorry John, was having one of those days.

    I did try a schmitt res/cap did not get very good results. I'm clocking a
    DAC & ADC so need mark/space within 40-60% and frequency between 20kHz &

    I dont have a scope where I am, but the ADC conversions became error
    riden. When I get back to school in a week I can use a scope so will
    further investigate the schmitt option.

    I need inverters for this circuit any way so the hex chip is not wasted
    on the board.

  9. For 20kHz-800kHz maybe you could use an 8-pin PIC. Just configure it
    to run RC oscillator mode with Fosc/4 output. You don't even need a
    program. 50% duty cycle is guaranteed. ;-)

    Best regards,
    Spehro Pefhany
  10. DaveC wrote:
    Does this mean that any frequency between 20 kHz and 800 kHz will do
    if the symmetry stays between 40-60%, or must that symmetry hold while
    the frequency is adjusted, continuously between these limits?
  11. DaveC

    DaveC Guest

    Yes it must hold, The frequency is controlled by the user. It's for a
    guitar pedal. A foot controller is used to adjust the frequency at any
    time. If the 40-60% mark/space is lost then you get really awful pops as
    the ADC drops samples.

  12. Then I think you could rig up the VCO in a CD4046 or HC4046 PLL to do
    this. 40 to 1 frequency is a bit large, but if you don't need very
    precise limits, unit t0 unit, I think it would work.
  13. Ken Smith

    Ken Smith Guest

    How about:

    A CD4060 / HC4060

    IIRC the oscillator part of the LT1054 runs at about 30KHz. You can
    combine the oscillator with another useful circuit.

    A TICPAL22V10Z could make the oscillator and divide by two with some extra
    sections to make other glue logic.
  14. I read in that John Larkin <[email protected]
    landPLEASEtechnology.XXX> wrote (in <[email protected]>) about 'Chip like LTC1799', on Sat, 19 Feb 2005:
    It operates at around 30 THz? (;-)
  15. Development without a scope can be rather hard, especially when the
    parts don't behave as expected. To get a 50% dutycycle, a Flipflop
    as divide-by-two could be helpful. But only if the slopes are
    sufficiently fast.

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