OSCILLATION CIRCUIT
An oscillation circuit according to an exemplary embodiment of the present invention includes: a power supply voltage terminal applied with a power supply voltage; a feedback loop circuit that outputs an oscillation frequency signal; and a correction circuit that corrects a time constant of the feedback loop circuit in accordance with the power supply voltage applied to the power supply voltage terminal. The configuration facilitates the correction of an oscillation frequency that varies depending on the fluctuation of the power supply voltage.
1 . An oscillation circuit comprising:
a power supply voltage terminal applied with a power supply voltage;
a feedback loop circuit that outputs an oscillation frequency signal; and
a correction circuit that corrects a time constant of the feedback loop circuit in accordance with the power supply voltage applied to the power supply voltage terminal.
2 . The oscillation circuit according to claim 1 , wherein
the correction circuit comprises:
a capacitor element having one terminal connected to a node on the feedback loop circuit; and
a control circuit connected to each of the other terminal of the capacitor element and the power supply voltage terminal, and
the control circuit controls a resistance value between the other terminal of the capacitor element and a ground voltage terminal in accordance with the power supply voltage.
3 . The oscillation circuit according to claim 2 , wherein the control circuit comprises:
a resistor element connected between the power supply voltage terminal arid the ground voltage terminal;
a first transistor connected in series with the resistor element; and
a second transistor that is provided between the capacitor element and the ground voltage terminal, and is current-mirror connected to the first transistor.
4 . An oscillation circuit according to claim 3 , further comprising an additional circuit that is provided between the power supply voltage terminal and one terminal of the resistor element and that changes a correction factor of the time constant with respect to a fluctuation of the power supply voltage.
5 . The oscillation circuit according to claim 4 , wherein the additional circuit comprises a third transistor having a source terminal connected to the power supply voltage terminal, a drain terminal connected to the one terminal of the resistor element, and a gate terminal connected to the one terminal of the resistor element.
6 . The oscillation circuit according to claim 3 , wherein each of the first and second transistors comprises an N-channel MOS transistor
7 . The oscillation circuit according to claim 3 , wherein each of the first and second transistors comprises an NPN bipolar transistor.
8 . The oscillation circuit according to claim 5 wherein the third transistor comprises a P-channel MOS transistor.