Analyzing the Juno-106 DCO circuit

"In the previous posting, we discussed how the core of a typical VCO works, and the main sources of drift and instability in a VCO core circuit. The Digitally Controlled Oscillator (DCO) is a 1980s technology designed to eliminate most or all of these sources of inaccuracy, while still operating as basically an analog VCO. The DCO was a transitional technology that arose as soon as inexpensive microprocessors were available that were fast enough to control the timing of an audio oscillator circuit, but not yet fast enough to compute the oscillating waveform entirely in the digital domain. (A secondary consideration was the fact that fast 16-bit digital-to-analog converters, although available, were still quite expensive at the time.) The distinguishing characteristic of a DCO, as opposed to a purely digital oscillator, is that the DCO does not have a D/A converter in the audio signal path. (It may have a D/A converter in the control path.)"

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