Triangle to sine wave convertor

Discussion in 'The Projects Forum' started by AetherNZ, Jul 16, 2008.

  1. AetherNZ

    Thread Starter Member

    Mar 23, 2008
    Hi guys, I am designing a function generator (adjustable frequency, triangle, square, sine) for a university project. The design is supposed to be using fundamentals, so no dedicated chips. I have done the triangle and square waves using a couple of current sources, comparators, capacitor (will post up the design later just to check it looks alright). Only have +-6V on the rails and need to output a +-3V signal.

    My current problem is generating the sine wave. I know that you can use a low pass filter so that you just have the fundamental frequency, but how do you set up the filter so that the resonant frequency changes if you change the frequency of the waveform. Ie how do you tune the integrator to work from 20Hz - 20kHz?

    I have looked around and the only fundamental design I could find was this circuit:
    which I dont understand how its produces a sine. Is this just a differential amp? Tried to simulate it but couldnt get it working.

    Thanks in advance :)
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
    The diff amp in the circuit you posted uses the logarithmic relationship between base-emitter voltage and collector current to approximate a sine wave output from a triangle input.
    See this thread, and National's AN-263, for more sine shaping ideas.
  3. AetherNZ

    Thread Starter Member

    Mar 23, 2008
    Thanks for the reply Ron, these look ideal. Don't know why I couldn't find these, seems my search engine skills are quite rubbish.

    Will let you know how I get on
  4. Wendy


    Mar 24, 2008