Relation To Earlier VCO Designs
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.
A common DCO design uses a programmable counter IC such as the 8253.
This provides stable digital pitch generation but square waves only. Further analog waveshaping is provided afterward. Sawtooth generation is formed by amplifying the integration of the original signal. A control voltage is used to control the sawtooth amplitude since no reset comparator and feedback loop are provided as with an actual analog oscillator core.
This method differs from an analog core (which dictates pitch through oscillatory feedback) to a pitch directly produced by a counter and controlling CPU.
Read more about this topic: Digitally Controlled Oscillator
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