An alternative to the usual sawtooth core portion of a voltage controlled oscillator. The triangle core uses a charging current and an integrating capacitor, like the sawtooth core does, to produce a linear change in voltage until a reset voltage is reached. However, when this occurs, instead of discharging the capacitor abruptly, the triangle core reverses the charging current. The voltage changes linearly, in the opposite direction, until the reset voltage is reached in the opposite direction, and then the charging current reverses again. Triangle cores have the advantage that they do not require high frequency compensation, although careful design is necessary to avoid glitches at the inflection points, or asymmetry of the waveform which would alter the harmonic content. Designing a wave shaping circuit to produce a sine wave is easier when starting with a triangle waveform vs. a sawtooth.
The most commonly used VCO design to employ a triange core was the Curtis 3340. Several modular synth VCO designs have used triangle cores. The ARP 2500 employed an unusual VCO design which used both sawtooth and triangle cores, tied to a common reset mechanism to keep them in phase.