Three phase oscillators ( 3 ) :

• Inverters form three-phase VCO - You sometimes need an inexpensive VCO that can produce evenly spaced three-phase outputs over a wide frequency range. This application uses unbuffered U-type inverters for use in ring oscillator setup which generates relatively squarish somewhat sine-like waveforms. The range of frequencies over which the circuit can operate is more than 1000-to-1.   
• Three-Phase Sine-Wave Generator - A circuit generates three-phase sine waves with excellent amplitude and phase symmetry. A variable-frequency, three-phase, sine-wave generator circuit has been designed for use as a source of polyphase excitation in studies of the propagation of traveling waves in plasmas. The circuit internally generates three symmetrical square-wave voltages with precisely 120� phase difference, each square wave containing only odd harmonics. Three switched-capacitor, six-pole Butterworth low-pass filters (U10, U11, and U12) remove the harmonics but pass the fundamental sine-wave component. The operating-frequency range of the circuit, 10 Hz to 10 kHz, is covered in three decade ranges. A Zener-stabilized voltage-controlled oscillator (VCO) functions as a variable-frequency oscillator and covers just over one decade.   
• Waveform generator circuits: Three phase oscillator - This circuit is a simple a phase squarewave oscillator, or tristable. It is like a simple bistable oscillator with 3 stages.   

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