An implementation of an astable oscillator circuit. The circuit output voltage V2 oscillates in an unstable fashion between high and low states.

An implementation of a Colpitts oscillator circuit with a nominal frequency of 9MHz. The frequency of oscillation is given by 1/(2*pi*sqrt(L1*C1*C2/(C1+C2))). LC oscillators have good frequency selectivity due to higher Q levels than are achievable with RC oscillators.

A pulse-width-modulated (PWM) output implemented using a 555 Timer in astable mode. The duty cycle is set by a potentiometer, P1. The potentiometer is controlled during run-time via Duty Cycle Control Knob. The scope shows the resultant output from the 555 Timer. To end the simulation, click on the Stop button.

An implementation of a triangle wave generator circuit using two op-amps. The first stage of the circuit is a comparator constructed from an op-amp. The output of the comparator is limited to about plus or minus 5 volts by the two zener diodes. The limits imposed by the zener diodes result in a square wave.

A voltage-controlled oscillator with feedback control to regulate the output voltage. The oscillation frequency is controlled by the reverse bias voltage applied to the to the varactor diode. The model shows how behavioral and component-level modeling can be mixed when designing a circuit. Provided that the variable trans-conductance device has a fast dynamic response relative to the oscillation frequency, the implementation details are not important. Similarly, the PI controller is in abstracted form, and could either be implemented with op-amps, or in software.