Keyboard electronic musical instrument circuitry - uses keyboard reference oscillator into phase comparator VCO feedback circuit for synthesis

摘要

The instrument's keyboard is coupled to a reference oscillator so that a square wave according to the notes played is presented at one input of a phase comparator. The second input is the control loop from the output of the v.c.o. The output of the phase comparator is a voltage which increases or decreases according to frequency deviation on the input and which is fed to an integrator before being applied to the control input of the v.c.o. The latter alters its frequency until it agrees with the phase comparator input frequency and the phase comparator output voltage has disappeared. Frequency division may also be used to provide a 2:1 or 4:1 octave modification of the oscillator frequencies.