single supply op amp oscillator

Discussion in 'The Projects Forum' started by kahafeez, Dec 8, 2008.

  1. kahafeez

    Thread Starter Active Member

    Dec 2, 2008
    hey people can we make a sine wave oscillator using a single supply op amp??? or will the negative half of the wave clip off???
  2. KL7AJ

    Senior Member

    Nov 4, 2008
    Certainly...but you have to use an output coupling capacitor, at the very least. You will also have to forward bias your non-inverting input....a simple voltage splitter does the trick here.

  3. bertus


    Apr 5, 2008

    Here are two PDF's with tips on how to make single supply designs.

  4. Wendy


    Mar 24, 2008
    Here is an oldy but goody.

    It has the advantage of using a light bulb to serve as an AGC. HP used a design very similar to this to produce one of their first major pieces of test equipment. It produces a very pure sine wave.
  5. gsjaved

    New Member

    May 7, 2009
    Can the schematic of op amp 741 model be used to design a +Vcc/Gnd op amp.

    I tried using it, But the circuit always saturates to the Vcc voltage. The biasing in the circuit, does not come to Vcc/2 (rather I am not able to do it, I started my work by "designing" a single supply op amp).

    Any suggetions.
    I did go through the materials from TI. But somehow was not convinced.

  6. flat5

    Active Member

    Nov 13, 2008
    Use a better op-amp.
    Perhaps the TL071CP.
  7. Wendy


    Mar 24, 2008
    Schematic please? There are ways to use a single supply voltage, but a 741 needs a lot more voltage than most. When you look at the spec sheet they neglect to specify a minimum voltage. I suspect without knowing (because you didn't specify) that you are starving the op amp for power. Figure 12VDC as an absolute minimum, more is better.

    A LM324 is speced for down to 3VDC, as are many newer op amps.

    Have you read this?

    Creating a Virtual Power Supply Ground

    BTW, most of the older op amps, which includes the LM324, have crossover distortions. This will screw with a clean sine wave. How do I know this?

    Something to be aware of.
    Last edited: May 20, 2009
  8. gsjaved

    New Member

    May 7, 2009
    I am actually "designing", rather simulating it on Cadence.

    The flow is like this,
    R2 = R3 = 3600 Q3 area = 3
    R1 = 2.5k voltage at the output = -3.24v
    R13 = 28k voltage at he base of Q1,Q7 = -1.25V
    R8 = 25 cap = 30pF
    R17 = 50
    R81 = 200

    I request you to tell me the mistakes done in this design under these categories:

    1. Blunders
    2. never do it
    3. silly
    4. "foolish"

    In this particular design, I have observed that Q3 saturates and pulls the output to +4.668v when Q30 is changed to "pnp" from "npn"

    The model files used are from the foundry kit.

    My doubts:
    Does this need a start up circuit?
    Does it need a completely different biasing technique , if I were to implement a similar design for +Vcc(+5v)/Gnd supply ?

    Target :
    Design an op amp for +5V/ Gnd , Avol = 80dB, BW = 1Mhz.
    Last edited: May 23, 2009