Circuit Project Electronic

Unlike a Wien-bridge oscillator, the phase-shift oscillator in Fig 1 starts up quickly. Also, the circuit does not require that you adjust several trimming resistors just to tune the oscillator to a given frequency. Experiments show that the circuit’s total harmonic distortion (THD) measures approximately 0.5% or less.
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Read more original source:
http://www.edn.com/archives/1994/052694/11di1.htm

A telephone DTMF IC produces, by design, two tones if you connect a single intersection of the IC’s 4[x]4 keypad matrix (Fig 1). (Telephones commonly have 3×4 keypads but, unknown to many people, the applicable standard allows for a fourth row of four keys.) But, if you connect two key inputs at once, the IC [...]

The two circuits below illustrate generating low frequency sinewaves by shifting the phase of the signal through an RC network so that oscillation occurs where the total phase shift is 360 degrees. The transistor circuit on the right produces a reasonable sinewave at the collector of the 3904 which is buffered by the JFET to [...]