Triangular wave generator

Discussion in 'The Projects Forum' started by andy24691, Feb 4, 2012.

  1. andy24691

    Thread Starter Member

    Nov 25, 2010
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    Hi as you may though most likely don't remember from my last plea for help a few months back, I am in the process of designing and building a triangle waveform generator that is capable of producing a waveform at 250 kHz. I'm afraid to say I have progressed very little since then, but I have come up with a circuit and I'm just wanting to know if its any good, I like to be reassured about these things. Also I would be extremely grateful if someone could suggest what high speed op-amps I could use, there are many to choose from and I have difficulty in working out what is appropriate. I foolishly bought some LM6191IN's before which were completely unsuitable for this application. The circuit below uses +/- 10V DC power and the amplitude of the triangle wave should be 5V.

    cheers

    [​IMG]
     
  2. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    I have used this circuit before--it works well.
    The op amp should have a slew rate of at least 10V/us.
    The critical part is the comparator rather than the integrator as its slew rate enters into its propagation delay.
     
  3. DickCappels

    Moderator

    Aug 21, 2008
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    The TL081/2/4 parts should work unless you need really sharp pulses on the pulse output. I am a little concerned that the TL081 family parts will have trouble driving that 400 ohm resistor, so I would suggest using something like 1600 ohms and making the 10 nf capacitor something like 2.7 nf.
     
  4. andy24691

    Thread Starter Member

    Nov 25, 2010
    42
    0
    I'm not sure if that line of op amps are fast enough due to the very high frequency I'm after. The transition time of the square wave will be comparable to that of the triangle wave and ideally it should be negligible to avoid distortion, or so I'm lead to believe.
     
  5. #12

    Expert

    Nov 30, 2010
    16,298
    6,811
    I calculate the slew rate as 2.5 V per microsecond. That is the minimum at the triangle wave. The square portion must go at least 10 time that fast, and faster is better. The TL07x clocks in at 16 V/uS. Time for a parametric search...www.mouser.com

    595-OPA2889ID at Mouser is a dual op-amp that is rated for 250 V/uS for $3.86

    A bit short in the voltage department, but that's how you do it.
     
    Last edited: Feb 4, 2012
  6. andy24691

    Thread Starter Member

    Nov 25, 2010
    42
    0
    It looks good except that I need it to be a DIP IC, I've been looking at the Farnell website because I can order bits and pieces off them through my university. There are a few different OP-AMP's on there but I'm not sure what to go for, some have bandwidths of 500 MHz whilst others are a lot less. I've picked out this one largely because its a bit cheaper, they all seem very expensive I don't know if thats because they're DIP. Do you think it will do the job? The slew rate is 75V/us.

    http://uk.farnell.com/analog-devices/ad744jnz/op-amp-bifet-precision-dip8-744/dp/9604847
     
  7. #12

    Expert

    Nov 30, 2010
    16,298
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    The speed and voltages are right. You might need to increase that 400 ohm resistor to avoid using so much current from the op-amp output. If the output wave form sags, it's the current that's slowing it down, not the slew rate.
     
    Last edited: Feb 4, 2012
  8. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    I think that this will do the job well--if you need a logic level output, some level translation will be required.
    The integrator, operating essentially with unity gain may require feedback compensation to maintain stability--at least this device has provision for compensation.

    Or you may check into using this one for the integrator--it is inexpensive.
    http://www.onsemi.com/pub_link/Collateral/MC33272A-D.PDF
     
  9. DickCappels

    Moderator

    Aug 21, 2008
    2,655
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    Last edited: Feb 5, 2012
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