VCOTA - straightforward VCO with 13600

7-80 - elektor july/august 1982 This application of the "miracle chip" LM/XR 13600 deals with a voltage controlled triangular oscillator. The OTA is fed back from the output to the input via the voltage divider consisting of R1 and R2. This feed- back from the output to the input is performed via capacitor C, which has a linear charge and discharge rate. The current through C also flows through one of the two diodes; there- fore the trigger points are at ± 0.6 V. The frequency can be calculated as follows: Uc + 15 f 2.4C • Rc [Hz, V, F] The output voltage is: 1.2 • R1 + R2 Vnn R2 straightforward VCO with 13600 Uc It is assumed that the OTA input differential voltage is always so high that the current through C equals the maximum lAgc, which in its turn is identical to: Uc + 15 Rc National/Exar Application R2 15V