Oscillators and frequency generators find use in a wide variety of applications. They may be realized from simple single op amp topologies or use more elaborate special purpose integrated circuits. Basic op amp oscillators are usually constrained to the frequency range below 1 MHz. Two sine wave oscillators that are based on op amps are the Wien bridge and phase shift types. Both oscillators rely on positive feedback in order to create their outputs. To maintain oscillation, the amplifier/feedback loop must conform to the Barkhausen criterion. This states that in order to maintain oscillation, the loop phase must be 0$$^{\circ}$$, or an integer multiple of 360$$^{\circ}$$. Also, the product of the positive feedback loss and the forward gain must be greater than unity to start oscillations and revert to unity to maintain oscillation. In order to make the gain fall back to unity, some form of gain limiting device, such as a diode or lamp, is included in the amplifier's negative feedback loop. The oscillation frequency is usually set by a simple resistor/capacitor network. As such, the circuits are relatively easy to tune. Their ultimate accuracy will depend on the tolerance of the tuning components and, to a lesser degree, on the characteristics of the op amp used.