A typical “Tuning Curve” of a VCO is shown on this slide; frequency versus tuning/control voltage. The Y axis is the output frequency while the X axis is the tuning or control voltage. Users can see from the curve on this slide why these oscillators are called “VCOs”; which stands for Voltage Controlled Oscillators. An input voltage controls the output frequency. Most VCOs have a positive tuning slope as shown (i.e., the frequency increases as the input tuning voltage increases). VCOs can also be designed with a negative tuning slope.