Triangular-Wave Generator (Relaxation Oscillator)
A relaxation oscillator is a popular oscillator circuit type that uses resistor and capacitor phase shift characteristics as well as an amplifier, typically an op-amp, to create a periodic waveform with the controlled frequency. The figure below shows an example of a triangular waveform generator that uses R, C, an integrator, and comparator.
Note that in addition to the triangular wave output, the above circuit also generates a square wave at the output of the comparator. The timing waveform is shown below. The amplitude of the waveform depends on the resistor divider ratio of R2 and R3. As for the frequency, it depends on the values of R1 and the capacitor.