Digitally controlled oscillator

A digitally controlled oscillator or DCO is a hybrid digital/analogue electronic oscillator used in synthesizers, microcontrollers, and software-defined radios. The name is analogous with "voltage-controlled oscillator." DCOs were designed to overcome the tuning stability limitations of early VCO designs.

The term "digitally controlled oscillator" has been used to describe the combination of a voltage-controlled oscillator driven by a control signal from a digital-to-analog converter, and is also sometimes used to describe numerically controlled oscillators.

This article refers specifically to the DCOs used in many synthesizers of the 1980s. These include the Roland Juno-60, Juno-106, JX-3P, JX-8P, and JX-10, the Korg Poly-61, the Oberheim Matrix-6, some instruments by Akai and Kawai, and the recent Prophet '08 by Dave Smith Instruments.

Many voltage-controlled oscillators for electronic music are based on a capacitor charging linearly in an op-amp integrator configuration. When the capacitor charge reaches a certain level, a comparator generates a reset pulse, which discharges the capacitor and the cycle begins again. This produces a rising ramp (or sawtooth) waveform, and this type of oscillator core is known as a ramp core.

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