Dramatically increase the frequency range of RC-based voltage-controlled oscillators
A typical voltage-to-frequency converter—also known as a VCO (voltage-controlled oscillator)—IC has a simple linear tuning characteristic relating input voltage to output frequency. It is usually of the form F=kV/RC, where RC is the time constant of the associated timing resistor and capacitor. The output frequency range of these parts varies, but few, if any, tune over the entire range with one set of RC timing components. If you change the timing ratio as the input voltage changes, however, you can magnify the tuning range to take advantage of nearly the entire frequency range in one implementation.