amplify the sine wave of a bubba oscillator

[maicael]

i am building a bubba oscillator with C=100n and R= 31k to give a 50HZ sine wave.i tried simulating it on proteus isis but it does not work but i hear simulators are not to be trusted so am going ahead to build it in real life.
My question is this,when reading about bubba oscillator i read that we have to amplify the signal because of attenuation or something.
I want to ask after building the circuit how do i amplify the output signal before feeding it to a comparator for generating a PWM signal.also this simulation softwares are funny atimes.is there anyone with experience on them.any further advice will be appreciated.thanks

 

[MikeMl]

LTSpice sims it just fine... First attachment shows start-up where V(A) comes up to clipping.

Second attachment shows the various nodes in the steady-state (after the start-up period). Output V(E) would have the lowest harmonic distortion, but would have to be buffered if you intend to use it as an output.

 

[maicael]

thanks a lot but how do i buffer the output.

 

[audioguru]

thanks a lot but how do i buffer the output.

A non-inverting opamp has a very high input impedance and a very low output impedance so it makes a perfect buffer.

 

[MikeMl]

thanks a lot but how do i buffer the output.

Here is one way: add a non-inverting amp with a gain of ≈4. V(F) is the buffered output. The amplitude can be adjusted to keep it from being clipped. This whole concept is based on the fact that the OpAmps are modern, CMOS rail-to-rail output (not 741s )

If you dont care about picking the output with the lowest possible harmonic distortion, then use outputs B, C, or D directly (they are already buffered).

 

[Mr RB]

What's the benefit of a "bubba" oscillator?

It looks like a phase shift oscillator, but done in a complex and parts heavy fashion compared to doing it the old way with one transistor and 3 caps?

 

[MikeMl]

What's the benefit of a "bubba" oscillator?

It looks like a phase shift oscillator, but done in a complex and parts heavy fashion compared to doing it the old way with one transistor and 3 caps?

Read page 17 of this TI App Note. Makes sense to me...

 

[Mr RB]

Thanks!