Need resources on non-opamp RC oscillators

Discussion in 'Electronics Resources' started by Eduard Munteanu, Sep 12, 2007.

  1. Eduard Munteanu

    Thread Starter Active Member

    Sep 1, 2007
    I'm looking for free sources of information on designing phase-shift oscillators with custom BJT amplifiers. More specifically, I'd like to read about:
    - how to calculate the phase-shift network's losses, including impedance mismatches.
    - what gain do I need
    - the possibility of having a high input impedance, low output impedance amplifying loop (i.e.: having the loop drive a speaker directly), but without readily-available op-amps involved
    - how do I limit the output peak voltage and current
    - proofs of those relationships

    Shortly, I'd like to design an oscillator loop that can directly drive a speaker and have a predictable power and voltage output.

    As a last resort, you could tell me about easily-obtainable but non-free sources of information if there's nothing else available that you know of.

    Thanks in advance.
  2. Dave

    Retired Moderator

    Nov 17, 2003
    My first instinct would be to have a look in Art of Electronics (Horowitz and Hill), sadly not free but is something they would likely cover (I don't have a copy to hand so can't comment at this moment).

    I'll have a look around the other free-resources I've got to see if there is anything that may be suitable.

  3. Eduard Munteanu

    Thread Starter Active Member

    Sep 1, 2007
    Thanks for your reply, but I have the book and I had already looked through it. It just describes that a opamp-driven Wien bridge oscillator needs a gain of exactly +3 (obtainable with automatic gain control). But this does not give any information about the output voltage amplitude of such an oscillator or how to limit it. I suppose it goes all the way up to the power supply's voltage (the one that drives the opamp). Other than that, there isn't much more information on the subject in "Art of Electronics". And I suppose that +3 gain is calculated for an ~infinite input impedance and ~0 output impedance.
  4. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    you might want to take a look at this attachment.

  5. Eduard Munteanu

    Thread Starter Active Member

    Sep 1, 2007
    Thanks mozikluv, looks quite detailed.

    The 3rd schematic (the one with the zener) looks very similar with one I saw in Horowitz & Hill. Now I'm thinking of using a zener diode to clamp the input in order to limit the output voltage amplitude to less than V_{CC} \over 2.

    I'll post a schematic along with an explanation when I'm done.