A simple version of VCO CMOS using 4049 inverters is shown in the figure. This circuit can be supplied with voltages between 3 and 15 V with the frequency generated depending on the capacitor and resistor. The control voltage must be between 0 and the supply voltage. The signal produced is rectangular and in this case the signal amplitude is constant, equal to the supply voltage. Remember that this circuit does not operate beyond a few megahertz.
