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Abstract

An accurate RC oscillator circuit located within a microcontroller chip for generating a signal of a predetermined frequency that accurately oscillates between two precise voltage levels, i.e., a low voltage (VL) and a high voltage (VH) is disclosed. The oscillator circuit uses first and second comparators having their outputs respectively coupled to set and reset inputs of a flip flop. The output of the flip flop is coupled to a series RC network for controlling the charging and discharging of the voltage across a capacitor of the RC network. The interconnection of the series RC network is coupled to an input of both the first and second comparators. The other input of the first comparator is coupled to a circuit for applying a modified high threshold version (VH') of the high voltage such that the signal generated by the oscillator circuit does not exceed the precise high voltage (VH). Similarly, the other input of the second comparator is coupled to a circuit for applying a modified low threshold version (VL') of the low voltage such that the signal generated by the oscillator circuit does not fall below that precise low voltage (VL). Additionally, means are provided to select different input voltages for the low voltage (VL) such that the desired output frequency of the oscillator may be adjusted to accurately oscillate between the high voltage (VH) and the selected low voltage (VL).

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