CIRCUIT with positive feedback. The FUNCTION of the Schmitt trigger is to convert any regular or irregular shaped input waveform into a square wave output voltage or pulse.The circuit is NAMED a "trigger" because the output retains its value until the input changes sufficiently to trigger a change.Since the output of the Schmitt trigger is a square wave of amplitude ± Vsat, the output if given to a non-inverting integrator, will give a triangular wave.The Triangular wave generator can be converted into a saw-tooth wave generator by injecting variable DC voltage into the non-inverting terminal of the integrator. 1. The Hartley Oscillator is a particularly useful circuit for producing good quality sine wave signals in the RF range (30kHz to 30MHz).2. The Colpitts Oscillator is quite similar to the Hartley Oscillator and produces high-frequency sine waves in the RF range (100 kHz to 300 MHz). 3. The Crystal oscillators can produce either sine wave or square wave outputs over a very wide range of FREQUENCIES, usually from one or two MHz up to several hundred MHz.