Electrical – VCO from a rectangular and triangular signal generator


I need to create the simplest rectangular and triangular signal VCO I can using op amps. The output frequency should be changeable between 1k and 15k. I should also be able to change the amplitude of rectangular signal between 2 and 4 V. The triangular has to have the amplitude 5V. I was hoping I could modify this circuit by adding a DC voltage source somewhere to the V- input of the integrator, but I don't know how or if that's the answer to my issue. Can this circuit be modified for what I need or am I wasting my time and should look for something else?


simulate this circuit – Schematic created using CircuitLab

Best Answer


simulate this circuit – Schematic created using CircuitLab

Figure 1. A "get you going" modification.

Your circuit isn't voltage controlled but can be modified to give manual control.

  • Addition of R7 varies the rate that C1 charges (the integral time) and hence the frequency.

  • For single-ended supply you need to bias the op-amps to mid supply. This is done by R8 and R9 and an additional non-inverting, voltage follower, op-amp (OA3) here would help buffer the V+/2 voltage.

  • For 0 - 5 V triangle output with a 5 V supply you need op-amps with rail to rail outputs.

  • To attenuate the squarewave you can add a potential divider or pot, R6, from the output to mid-supply will suffice.