Square traingle VCO - with dual waveform output

This voltage controlled oscillator (VCO) is capable of providing a triangular as well as a squarewave output signal. As with any other VCO, the frequency of the output signal depends on the level of the control voltage (Uc). Remarkably, this design features a wide control voltage range; between 0 V and the positive supply voltage. The power supply voltage can be anywhere in the region of +3 V to +25 V. However, care should be taken when using low voltage supplies that the maximum output level is at least 1.5 V below that of the supply. The circuit is based on the "integrator - comparator" principle. Capacitor Cl is part of the integrator (constructed around opamp Al) and is charged by a constant current level determined by the instantaneous level of the control voltage. Consequently, the output of Al will fall linearly. The output of the comparator (constructed around A2) will change state and transistor T1 will start to conduct when the lower switching threshold of the comparat...