I'm designing a low power DC/AC sinewave inverter and I have 2 choices for the pulse width modulation :

  1. Generating SPWM using an AVR microcontroller timers/counters.
  2. Generating the waveform using a bubba oscillator with square wave.

I know that the 4-section bubba oscillator has good stability because it has high rate of change of phase with frequency but I don't know if it's suitable for 50 Hz operation I think it's better at lower frequencies(or not?))

  • 1
    \$\begingroup\$ what's a bubba oscillator? What's SPWM (I know what PWM is). What are your other requirements (small size, high accuracy, able to go 0-100%, low cost, purchased parts only?) \$\endgroup\$ – Neil_UK Mar 24 '17 at 6:42
  • \$\begingroup\$ Stability (at 50 hz) and low cost are the most important requirements for now. \$\endgroup\$ – iMohaned Mar 24 '17 at 12:00
  • \$\begingroup\$ @Neil_UK SPWM is simply sine pwm (Sorry i thought it's a common expression :D ) , and here's a good pdf about bubba oscillator : hscott.net/bubba.pdf I acutally got the basic knowledgement from "opamps for every one" from texas instruments. \$\endgroup\$ – iMohaned Mar 24 '17 at 12:06

i don't know if it's suitable for 50 hz operation

A bubba oscillator is just a phase shift oscillator and so can be made to work at any frequency within reason. It uses op-amps to provide low-loading of the phase shift circuits so that the frequency of operation is more mathematically predictable. However it's very wasteful in its use of op-amps.

Like the Wien Bridge oscillator there is no natural amplitude stabilization so you find that the gain has to be dynamically controlled so, when you say: -

I know that the 4-section bubba oscillator has good stability

This isn't exactly true because it trades distortion for amplitude stability.

If you want a decent sine wave oscillator I would consider making one that has a tight bandwidth (high Q) filter and in-built amplitude control like this one from Elliot Sound Products: -

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Stolen from this page.

  • \$\begingroup\$ I got this idea that it has good stability from "opamps for everyone" from texas instruments so i trusted them :/ . Anyway great answer as always and thank you for the page, it's very informative. \$\endgroup\$ – iMohaned Mar 24 '17 at 12:10

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