I need a 1KHz 20mVp-p sine wave oscillator?

Discussion in 'General Electronics Chat' started by samy555, Nov 3, 2015.

  1. samy555

    Thread Starter Active Member

    May 24, 2010
    116
    3
    Hello
    I searched in Google and found many circuits but no one of them worked properly especially when the output is lowered to 20mVp-p. I have an oscilloscope of 50 MHz BW. I need that circuit to be used as a function generator to examine some low frequency preamplifiers. I have built many circuits but they all had a defect So I hope that one of the members may provide me a proven circuit.
    Thank you
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Post #2 in this thread. Connect a Pot to V(d), and take the output from the wiper. Alternatively, make a fixed two-resistor voltage divider that drops the natural output voltage of any sine oscillator (which will approach a peak-to-peak voltage just less than the dc supply voltage) to 20mV, and buffer it with another opamp, if buffering is needed.

    Design equations are Fig 9 in this TI app note
     
    Last edited: Nov 3, 2015
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    What was the defect? The circuit you describe is so basic that the defect is the important qualifying parameter.

    ak
     
  4. PeterCoxSmith

    Member

    Feb 23, 2015
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    you could set the frequency with a square wave signal, apply a filter to produce a sine wave, and use an amplifier to set the amplitude. With such a small signal choose a low noise op amp.
     
    Wendy likes this.
  5. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    What is it about them that is 'not working properly'? Can you show links to the ones you've tried?

    Ken
     
  6. samy555

    Thread Starter Active Member

    May 24, 2010
    116
    3
    Thank you Mike
    Can I use LM339 quad comparator?
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    How pure does this signal need to be? If not very exact the project is ridiculously easy, if you need a pure sine wave then it is just easy.
     
  8. ramancini8

    Member

    Jul 18, 2012
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    Build any oscillator mentioned in TI paper; then filter the output heavily, and you will obtain a pretty pure sine wave. The amplitude depends on many things, but it can be divided down with a couple of resistors to obtain your desired amplitude. Use AGC to obtain a fixed amplitude (remember that the AGC BW must be much greater than the signal frequency.
     
  9. Papabravo

    Expert

    Feb 24, 2006
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    Comparators have an open collector (aka digital output). What you want is an operational amplifier with bipolar supplies to give you an analog output.
     
  10. ScottWang

    Moderator

    Aug 23, 2012
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    You may try LF356 or LF357 to do the job:
    Sinewave Vin → VR(Pot) Voltage divider → LF356 inverter amplifier with negative gain
    Sinewave Vin → Fixed Resistor Voltage Divider → LF356 inverter amplifier with negative gain
    If you could choose a good value for the voltage divider then maybe the negative gain is no need.
     
  11. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Again Samy "What is it about them that is 'not working properly'? Can you show links to the ones you've tried?"

    Ken
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    The inexpensive LM324 would be perfect I suspect. Less than a quarter from many sources, will operate at 3VDC.
     
  13. samy555

    Thread Starter Active Member

    May 24, 2010
    116
    3
    I've downloaded these circuits then printed on paper
    I do not recall the links
    Just remember that the last circuit was from the site "handy dandy"
    I finally decided to buy a function generator next month
    thank you all
     
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