Wien-Bridge RC Oscillator using BJT's

Discussion in 'The Projects Forum' started by Bukowskaii, Dec 8, 2011.

  1. Bukowskaii

    Thread Starter New Member

    Dec 8, 2011
    2
    0
    Hello All,

    I am attempting to design a Wien-Bridge RC Oscillator using 2N2222 BJTs from the ground up knowing nothing but the center frequency to begin. I am having trouble biasing my transistors as I am just getting a multitude of ratios between two or three resistors and capacitors but no actual values.

    There are two different designs: Design 1 is using the traditional opamp wienbridge, and Design 2 is a design that he gave us in class that looks like just a two stage common emitter amplifier with a RC Feedback structure.

    I was able to get the R and C for the feedback loop knowing that my center frequency is approx 37.7kHz so 1/(2*pi*R*C) gives 2nF and 2kOhm regardless of the design, but again, this is just arbitrarily pulled values from the ratio, having seen caps from .5n to 5n and resistors from 500 Ohm to 5kOhm. Is there any more precise way to derive these values, as well as the biasing values for the resistors? Once I get the resistor values I'll be able to do low/ frequency analysis knowing that I want the low side cut off to be at least one decade less than the 37.7kHz that I have as my center.

    I am just having issues knowing where to start, and all my research online starts the biasing process by assuming variables without explaining why.

    Thanks in advance
     
  2. Bukowskaii

    Thread Starter New Member

    Dec 8, 2011
    2
    0
    Okay, I am going to use design two, I think it will be a bit more simple. Knowing that I need 3 gain on my first and 1 gain on my second, how do I bias the transistor properly for this gain taking into account the input impudence of the amplifier?
     
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