Accurate RC oscillator having peak - to - peak voltage control

A method for generating an oscillatory signal of a predetermined frequency across a series resistor-capacitor (RC) network by ensuring that the oscillatory signal accurately oscillates between first and second voltages generated from a supply voltage source where the frequency of oscillation is determined by both the time constant of the RC network and the difference between the first and second voltages comprising the steps of:

• providing charging-discharging means for discharging a voltage across the capacitor commencing when voltage of the oscillatory signal exceeds a first threshold voltage and for charging said voltage across the capacitor commencing when voltage of the oscillatory signal falls below a second threshold voltage;
• providing first sampling means coupled to said charging-discharging means for obtaining a first sampled voltage of the oscillatory signal upon commencement of discharging of said voltage across the capacitor;
• providing first compensation means coupled to said first sampling means for adjusting said first threshold voltage to be the first voltage modified by a voltage difference between the first voltage and said first sampled voltage;
• providing second sampling means coupled to said charging-discharging means for obtaining a second sampled voltage of the oscillatory signal upon commencement of charging of said voltage across the capacitor;
• providing second compensation means coupled to said second sampling means for adjusting said second threshold voltage to be the second voltage modified by a voltage difference between the second voltage and said second sampled voltage;
• and
• providing differential voltage setting means coupled to said second compensation means for selecting the second voltage from a plurality of different possible voltages and thereby selecting a voltage difference between the first and second voltages.

A circuit for generating an oscillatory signal of a predetermined frequency across a series resistor-capacitor (RC) network by ensuring that the oscillatory signal accurately oscillates between first and second voltages generated from a supply voltage source and where the frequency of oscillation is determined by both the time constant of the RC network and by the difference between the first and second voltages, the circuit including first and second comparators having their outputs respectively coupled to first and second inputs of a flip flop for setting and resetting the flip flop, an output of the flip flop being coupled to the series RC network for controlling the charging and discharging of voltage across the capacitor, the interconnection of the series RC network being coupled to an input of both the first and second comparators, the improvement comprising:

• first voltage modifying means for receiving the first voltage and for applying a modified version of the first voltage to the other input of the first comparator such that the first comparator switches before the oscillatory signal actually reaches the first voltage thereby ensuring that the oscillatory signal precisely reaches the first voltage by the time the flip flop switches;
• second voltage modifying means for receiving the second voltage and for applying a modified version of the second voltage to the other input of the second comparator such that the second comparator switches before the oscillatory signal actually reaches the second voltage thereby ensuring that the oscillatory signal precisely reaches the second voltage by the time the flip flop switches;
• differential voltage setting means coupled to said second voltage modifying means for selecting the second voltage from a plurality of different possible voltages and thereby selecting a voltage difference between the first and second voltages;
• and said circuit being located on a chip with a microcontroller.