RC oscillator integrated circuit including capacitor
View Patent ↗An RC oscillator integrated circuit includes: an active current mirror connected to an external resistor, for receiving a current signal corresponding to a voltage signal applied to the external resistor, performing 1/N-times division of the received current signal according to an input clock signal, and generating a 1/N-times current signal; an oscillation circuit for generating an output voltage corresponding to a charging- or discharging-operation of a capacitor via a current path formed by the active current mirror; a feedback switching circuit for controlling a charging- or discharging-path of the capacitor by a feedback of an output signal Vo of the oscillation circuit; and a divider for generating not only a first clock signal capable of driving the active current mirror according to the output signal of the oscillation circuit, but also a second output clock signal having a compensated mismatch of the active current mirror.
1. A RC oscillator integrated circuit (IC) comprising:
an active current mirror connected to an external resistor, for receiving a current signal corresponding to a voltage signal applied to the external resistor, performing 1/N-times division of the received current signal according to an input clock signal, and generating a 1/N-times current signal;
an oscillation circuit for generating an output voltage corresponding to a charging- or discharging-operation of a capacitor via a current path formed by the active current mirror;
a feedback switching circuit for controlling a charging- or discharging-path of the capacitor by a feedback of an output signal Vo of the oscillation circuit; and
a divider for generating a first clock signal capable of driving the active current mirror according to the output signal of the oscillation circuit, and a second output clock signal having a compensated mismatch of the active current mirror.
2. The RC oscillator integrated circuit IC according to claim 1 , wherein the oscillation circuit comprises:
a first comparator for receiving a voltage of the capacitor at its positive input terminal, and receiving a threshold voltage at its negative input terminal;
a second comparator for receiving a reference voltage at its positive terminal, and receiving the capacitor voltage at its negative terminal; and
an RS flip-flop for receiving an output signal of the first comparator at its S input terminal, and receiving an output signal of the second comparator at its R input terminal.
3. The RC oscillator integrated circuit (IC) according to claim 1 , wherein the feedback switching circuit comprises:
a first MOS transistor for receiving the output signal of the oscillation circuit at its gate terminal, connecting its drain terminal to the active current mirror, and receiving the capacitor voltage at its source terminal; and
a second MOS transistor for receiving the output signal of the oscillation at its gate terminal, receiving the capacitor voltage at its drain terminal, and connecting its source terminal to the active current mirror.
4. The RC oscillator integrated circuit (IC) according to claim 3 , wherein the active current mirror comprises:
a first active current mirror including: an input terminal for receiving a current signal corresponding to the voltage applied to the external resistor; a first output terminal; and a second output terminal connected to the drain terminal of the first MOS transistor; and
a second active current mirror including: an input terminal connected to the first output terminal of the first active current mirror; and an output terminal connected to the source terminal of the second MOS transistor.
5. The RC oscillator integrated circuit (IC) according to claim 4 , wherein the first active current mirror includes:
a first current mirror; and
a second current mirror for receiving an output current signal of the first current mirror, and generating the received current signal according to the input clock signal.
6. The RC oscillator integrated circuit (IC) according to claim 5 , wherein the second current mirror includes a plurality of second current mirror units arranged in the form of a cascade in which output terminals of front current mirror units are connected to input terminals of rear current mirror units, whereby
if the number of the second current mirror units is N, the second current mirror outputs a ½N-times divided current.
7. The RC oscillator integrated circuit (IC) according to claim 1 , wherein the divider includes:
a first D-flip-flop for receiving the output signal of the oscillation circuit as its clock signal, and receiving a clock signal generated from its Q output terminal via its D input terminal; and
a second D-flip-flop for receiving the clock signal generated from the Q output terminal of the first D-flip-flop as a clock signal, and receiving the clock signal generated from its Q output terminal via its D input terminal, whereby
the clock signal generated from the first D-flip-flop is used as the clock signal for operating the active current mirror.