The SP1648 is an emitter-coupled oscillator, constructed on a single monolithic silicon chip. Output levels are compatible with ECL III logic levels. The oscillator requires an external parallel tank circuit consisting of an inductor (L) and a capacitor (C). A varactor diode may be incorporated into the tank circuit to provide a voltage variable input for the oscillator (VCO). The device may also be used in phase locked loops and many other applications requiring a fixed or variable frequency clock source of high spectral purity.