Hero999
Banned
It seems like you don't understand how this circuit works.
In order for an amplifier to oscillate the gain needs to be >1 and have positive feedback and a particular frequency.
The RC ladder network has a total phase shift of 180° at the required frequency.
The amplifier has a phase shift of 180° at broad band ofl frequencies which must include the one your oscilator to work at.
Unfortunately the RC ladder also has a loss of 29 so the smplifier must have a gain of exactly 29 to compensate for this.
More about his can be found on Wikipedia:
https://en.wikipedia.org/wiki/Phase_shift_oscillator
Roff's circuit solves the following problems:
The amplifier has to have a gain of exactly 29.
If it's slightly lower than 29, it won't oscillate, the most likely scenario is it will produce a few oscillations and die away.
If it's higher than 29 you'll get distortion and clipping.
Roff's circuit solves this problems by adding diodes which feed some of the output signal back into the input when the output signal becomes too high, thus introducing more negative feedback and reducing the gain.
In order for an amplifier to oscillate the gain needs to be >1 and have positive feedback and a particular frequency.
The RC ladder network has a total phase shift of 180° at the required frequency.
The amplifier has a phase shift of 180° at broad band ofl frequencies which must include the one your oscilator to work at.
Unfortunately the RC ladder also has a loss of 29 so the smplifier must have a gain of exactly 29 to compensate for this.
More about his can be found on Wikipedia:
https://en.wikipedia.org/wiki/Phase_shift_oscillator
Roff's circuit solves the following problems:
The amplifier has to have a gain of exactly 29.
If it's slightly lower than 29, it won't oscillate, the most likely scenario is it will produce a few oscillations and die away.
If it's higher than 29 you'll get distortion and clipping.
Roff's circuit solves this problems by adding diodes which feed some of the output signal back into the input when the output signal becomes too high, thus introducing more negative feedback and reducing the gain.