Voltage controlled oscillator capable of linear operation at very low frequencies

摘要

There is disclosed a voltage controlled oscillator (VCO) that receives +V(IN) and -V(IN) control voltages and outputs a VCO output signal having an oscillation frequency determined by the +V(IN) and -V(IN) control voltages. The VCO comprises: 1) a storage capacitor charged linearly by a constant charge current and discharged linearly by a constant discharge current; 2) a comparator for comparing the storage capacitor voltage to an upper threshold voltage and a lower threshold voltage. The comparator output drops to a negative saturation voltage (-V(SAT)) when the storage capacitor voltage rises above the upper threshold voltage and rises to a positive saturation voltage (+V(SAT)) when the storage capacitor voltage drops below the lower threshold voltage. The VCO also comprises: 3) a constant charge current source for injecting the constant charge current into the storage capacitor when the comparator output rises to the positive saturation voltage; and 4) a constant discharge current source for draining the constant discharge current from the storage capacitor when the comparator output drops to the negative saturation voltage.